/

PRINCIPLES

AND PRACTICES

OF SEED STORAGE

\ - f •

M

UNITED STATES

DEPARTMENT OF

AGRICULTURE

AGRICULTURE

HANDBOOK

NUMBER 506

PREPARED BY

SCIENCE AND

EDUCATION

ADMINISTRATION
PRINCIPLES AND PRACTICES

OF SEED STORAGE

By Oren L. Justice and Louis N. Bass

NAL BIcT^*'''"^' ^S^îcultural Library

10301 Baltimore Blvd

Beltsville, MD 20705-2351

Agriculture Handbook No. 506

On January 24, 1978, four USDA agencies—Agricultural Research

Service (ARS), Cooperative State Research Service (CSRS), Extension

Service (ES), and the National Agricultural Library (NAL)—merged to

become a new organization, the Science and Education Administration

(SEA), U.S. Department of Agriculture.

This publication was prepared by the Science and Education Administration's Federal Research staff, which was formerly the Agricultural

Research Service.

Library of Congress Catalog Card No. 78-600015

Washington, D.C. Issued April 1978

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

STOCK NUMBER 001-000-03653-0
This publication reports research involving pesticides. It does

not contain recommendations for their use, nor does it imply that

the uses discussed here have been registered. All uses of pesticides must be registered by appropriate State and/or Federal

agencies before they can be recommended.

CAUTION: Pesticides can be injurious to humans, domestic

animals, beneficial insects, desirable plants, and fish or other

wildlife—if they are not handled or applied properly. Use all

pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide contain

ers.

¿/4ep44á<s¿ai4^a^

FOLLOW THE LABKL

U.S. DffAXTMENT OF AORICUITUIIE

Trade names are used in this publication solely to provide specific

information. Mention of a trade name does not constitute a

warranty or an endorsement of the product by the U.S. Department of Agriculture to the exclusion of other products not

mentioned.
CONTENTS

Page

Introduction 1

Purpose and significance of safe seed storage 1

The seed, a fragile, living organism 2

From harvest to sowing 4

Decline and death of seeds 5

Scope of publication 6

Seed factors that affect storage life 7

Genetic effects 7

Variation among species 7

Variation among cultivars 8

Generalizations 8

Preharvest effects 9

How seeds are affected 9

Effect of provenance 10

Effect of weather 10

Seed structure and composition 11

Hard seeds 13

Seed maturity 17

Relationship of maturity to storability 17

Grass seeds 17

Other field crop seeds 18

Vegetable seeds 18

Seed size 19

Seed dormancy 20

Relationship of dormancy to storage 20

Dissipation of dormancy 20

Dormancy and lifespan 21

Moisture content 21

Mechanical damage 22

Awareness of seed damage 22

Vulnerability of some seeds to damage 23

Response of seeds to storage conditions 24

Possible involvement of genetics 24

Vigor 25

Effects of storage environment on seed longevity 26

Temperature 26

Temperatures above freezing 26

Temperatures below freezing 30

Seed moisture content and relative humidity 35

Direct effect of moisture on seed deterioration 35

Relationship between relative humidity and seed moisture content 38

Rate of moisture absorption and movement 48

Effect of extreme desiccation on viability and vigor 50

Interrelationship of temperature, seed moisture content, and storage life __ 52

III
Page

Effects of storage environment on seed longevity—Continued

Vacuum and gas storage 57

Barley 57

Corn 57

Flower seeds 62

Grasses 62

Legumes 63

Oilseeds 63

Rice 63

Sorghum 64

Vegetable seeds 64

Wheat 64

Confirmation studies at the National Seed Storage Laboratory 65

Illumination 77

Respiration and heating 78

Depletion of food reserves 78

Respiration products that retard this process 79

Release of heat in respiration 79

Measurement of respiration 79

Some factors affecting respiration 80

Preservatives for reducing respiration . 80

Conclusion 81

Effects of pests and chemicals on seed deterioration in storage 81

Storage fungi 81

Control of fungal deterioration 87

Insects 88

Rodents 89

Fungicides and fumigants 89

Changes associated with seed deterioration 91

Biochemical changes 91

Germination and vigor 92

Yield 93

Cytological changes 94

How seeds are dried 95

Characteristics of water 95

Principles of drying 9g

Methods of drying seeds 96

Natural drying 9g

Sun drying 97

Artificial drying 97

Factors to consider in selecting a dryer system IO9

Drying seeds with desiccants 123

Seed storage structures 123

Basic features of storage structures 124

Protection from water I24

Protection from contamination 124

Protection from rodents 124

Protection from insects 124

Protection from fungi 125

Protection from fire 125

Types of storage structures 126

Farm storage 126

Country elevator storage 126

Seed processor storage 126

IV
Page

Seed storage structures—Continued

Types of storage structures—Continued

Retail storage 127

Research storage 127

Germ plasm storage 127

Constructing controlled atmosphere seed storage facilities 129

Controlling temperature 133

Refrigeration 133

Heat load 134

Refrigeration agent 134

Liquid refrigerants 135

Typical mechanical refrigeration system 135

Condensing units 136

System capacity 136

Compressor capacity 136

Controlling humidity 136

Moisture movement between air and materials 137

Refrigeration-type humidity control systems 138

Desiccant-type humidity control systems 138

Common-sense practices 141

Ventilation 141

Stacking seed bags 141

Removing seeds from controlled storage 141

Warehouse cleanliness 142

Packaging and packaging materials 142

Requirements of different situations 142

Types of packages 142

How packages are filled . 143

How containers are presented to the filler 143

Weighing and measuring devices 144

How containers are closed 144

Packaging field seeds 145

Packaging vegetable and flower seeds 146

Package labeling 147

Porous packaging materials 147

Moistureproof materials 148

Moistureproof storage 148

Response of different crop seeds to moistureproof storage 148

Safe moisture levels for sealed storage 158

Moisture-resistant materials 159

Testing moisture vapor transmission of flexible materials 163

Moisture-barrier storage 164

Use of desiccants in sealed containers 168

Monitoring seed storage environment and seed condition 169

Germination and viability 169

Seed vigor 170

Seed moisture content 170

Fungi and bacteria 171

Relative humidity 171

Temperature 172

Storability of seed lots 172

Detection and identification of fungi and insects 174

Some practical information for storing and transporting seeds at ambient

conditions 174

Examples of storability of different plant species 174

V
Page

Some practical information for storing and transporting seeds at ambient

conditions—Continued

Climatological data pertinent to seed storage 182

Relation of storage conditions to intended storage periods 183

Care of seeds in transit 194

Storage principles applicable to in-transit seeds 194

Historical background 194

Some hazards to be avoided 195

General recommendations 196

Theories regarding seed deterioration 197

Changes in protein structure 197

Depletion of food reserves 197

Development of fat acidity 198

Enzymatic activity 198

Chromosomal changes . 199

Membrane damage 200

Respiration 200

Summary 201

Old and ancient seeds 201

Maximum known survival of crop seeds 202

Maximum known survival of primarily weed and native plant seeds 202

Seeds stored dry 202

Buried seed experiments 209

Circumstantial evidence of long lifespans of seeds 210

Seeds in soil disturbed by digging graves 210

Seeds in soil under forests of known age 211

Seeds frozen in arctic tundra 211

Canna seeds in burial mound 212

Indian lotus seeds buried in former lakebed 212

Life in mummified seeds 213

Glossary 217

Vernacular and botanical-zoological name equivalents 228

Conversion tables for temperatures and measures 240

Temperature conversion 240

Measures of weight 243

Measures of length 243

Measures of area 243

Measures of volume 244

Measures of capacity 244

Literature cited 244

Index 275

VI
PRINCIPLES AND PRACTICES

OF SEED STORAGE

By OREN L. JUSTICE i and Louis N. BASS2

INTRODUCTION

Purpose and Significance of Safe Seed Storage

The principal purpose of storing seeds of economic plants is to

preserve planting stocks from one season until the next. Prehistoric

man learned the necessity of this practice and developed methods of

storing small quantities of seeds for his future use. As agriculture

developed, man expanded his knowledge regarding both the requirements of seed for maintenance of viability and methods of providing

suitable storage conditions. In 1832, Aug. Pyr. de Candolle of France

included a chapter on seed preservation in his book "Physiologie

Végétale." He pointed out that the vitality of seeds would be prolonged

if stored under conditions to protect them from heat, moisture, and

oxygen. About the same time, other authors suggested the use of

tar-coated wooden boxes and iron tanks capable of being sealed with

stopcocks for drawing off the seeds as desired.

Although the storage of seed stocks for planting the following season

remains the most important reason for storing seeds, farmers and

seedsmen have found it advantageous to carry over seeds for 2 or more

years. This practice results in accumulating supplies of desired genetic

stocks for use in years following periods of low production. Many kinds

of seeds—mostly vegetable, flower, and forage seeds—move rather

freely in world commerce. Many of these seed lots are not used the ñrst

year after production.

With increased knowledge and technology of plant genetics and plant

breeding, the necessity for longtime storage of small quantities of the

various cultivars becomes apparent. Facilities for storing genetic stocks

now exist at Fort Collins, Colo., Hiratsuka, Japan, Braunschweig,

Germany, Bari, Italy, Izmir, Turkey, and other locations. Research

workers can obtain genetic stocks considered useful in their breeding

programs from these facilities. The principles to be discussed here

1 Formerly Agricultural Marketing Research Institute, Northeastern Region, Agricultural Research Service. Retired June 1973.

2 National Seed Storage Laboratory, Western Region, Agricultural Research Service.

1
¿ AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

apply equally to all seed storage. Longtime storage of genetic stocks is

not the principal objective of this handbook.

No statistics are available indicating either the actual losses sustained

from substandard storage conditions or the savings effected by optimum storage conditions. However, the importance of suitable storage

becomes apparent when one considers the alternatives. Failure to use

available information about seed storage could greatly handicap the

Nation's agricultural program as follows: (1) Agriculture in the warm,

humid, subtropical, and tropical regions would be less efficient, (2) the

plant breeder would be greatly handicapped by not maintaining genetic

stocks, and (3) international commerce in seeds would be only a small

fraction of its present economic value.

The Seed, a Fragile, Living Organism

In his poem "A Package of Seeds," Edgar A. Guest expressed very

well the theme of this section. When Guest had purchased packages of

seeds, he had thought of them only as seeds. But on one occasion when

he made such a purchase, it flashed through his mind that he had

purchased "a miracle of life," a dime's worth of power that no man can

create and a dime's worth of mystery, destiny, and fate. In working

with seeds, especially in harvesting, cleaning, handling, storage, and

transportation, it is essential to keep in mind at all times that inside the

seed is a dormant miniature plant awaiting the opportunity to continue

its growth.

Basically the seed is made up of the embryo or miniature plant, the

endosperm and other food reserves, and protective coverings consisting

of the seedcoat and, in some cases, accessory structures (ñg. 1). The

embryo is more protected in the resting seed of corn than in bean. In

corn and other grains the major food reserves are stored as endosperm,

whereas in bean they are stored in the two cotyledons or seed leaves,

which also serve as photosynthetic organs for the young plant. Other

structures affecting seed storage are the seedcoat for both corn and

bean and the hilum and micropyle of bean, which may permit the entry

or exit of moisture. Under some conditions the hilum may become soft

or damaged, allowing fungi to enter the seed.

The planting units in several plant families are fruits, botanically

speaking, rather than true seeds. In the grass family the seed or fruit is

called a grain or caryopsis, in the buckwheat and sunflower families an

achene, and in the mint family a nutlet. Some kinds of seeds possess

additional structures, such as glumes, bracts, spines, and hairs, which

aid in protecting the seed from injury, birds, and rodents. In this

publication, all these structures that normally serve as the planting unit

are referred to as seeds.
PRINCIPLES AND PRACTICES OF SEED STORAGE Ó

The orientation of the embryo within the seed and the nature of the

protective coverings are important attributes of any seed that is subSTYLE SCAR

^ FRUIT COAT

ENDOSPERM

COLEOPTILE

PLUMULE

MESOCOTYL

SCUTELLUM

RADICLE

COLEORHIZA

FRUIT SCAR

SEEDCOAT

COTYLEDON SCAR

RADICLE

PLUMULE

^ MICROPYLE

-^ HILUM

LENSCOTYLEDON

B^^^^r-^:^ C

FIGURE 1.—External and internal structures of corn (A) and bean {B and C)
4 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

jected to the numerous mechanical and handling processes from harvest

to planting. For example, a grass seed has its embryonic root tip near

the base of the grain. When the glumes are removed during harvesting,

as in rye, timothy, and wheat, the root tip is only protected by a thin

membrane, which is very vulnerable to physical damage and attack by

storage molds. However, seeds of many grasses, such as barley, oats,

rice, and some cultivars of sorghum, are much better protected since

the enclosing glumes usually remain attached.

The relatively large seeds of bean and soybean have only a moderately thick seedcoat. The plumule, or embryonic stem, is fairly well

developed in the resting seed and Ues between two cotyledons, or seed

leaves. Also, the radicle, or embryonic root, has practically no protection except that provided by the seedcoat. Thus, a bean seed is unusually vulnerable to breakage, especially when dry and roughly treated.

The radicle, plumule, or cotyledons can be damaged. Velvetbean, in the

same plant family as bean and of similar structure, is less vulnerable to

damage from harvesting, handling, and processing because of a slightly

different orientation of the plumule and radicle.

From Harvest to Sowing

Beginning with harvest, seed lots usually pass through a series of

processes necessary for immediate or future use. They include harvesting, drying, cleaning, grading or sizing, transporting, and storing.

Not all commercial seed lots are subjected to all these processes, but the

manner in which seeds are passed through each process can affect their

storage potential.

Each seed faces an uncertain future. It may be harvested too early,

too late, too wet, or too dry. The seed's future can be affected by being

harvested so immature that it cannot germinate, or if it germinates, it

may produce a weak seedling. The moisture content of the seed may be

so high that heating will occur before the seed is dried to a safe moisture

content; it may be damaged during drying, or it may be so dry that it

suffers impaction damage on handling. The potential danger during the

drying process is exposure of very wet seeds to high temperatures or to

temperatures in the critical range for a long time.

In the cleaning and the grading or sizing processes the seed may again

be subjected to impaction damage, which may be caused by low moisture content in the case of bean and many other crops harvested under

arid or semiarid conditions. Radish seed may be damaged severely by

impaction if its moisture content is too high during threshing. High

moisture makes the seeds difficult to remove from their pods.

When transported to market, whether a few miles or across the

ocean, the seed lot is subject to storage under various adverse condi-
PRINCIPLES AND PRACTICES OF SEED STORAGE Ö

tiens—on the truck, in the railway car, on the dock while partially or

entirely exposed to the elements, or in the hold of ships. A seed lot for

use in the following year or years would normally be placed in a

conventional storage facility, which may or may not be conducive to

maintaining vigor and viability. Because of the high capital investment

and cost of maintaining desirable seed storage facilities, many seed lots

are stored under unfavorable conditions.

During processing and shipment, grain for industrial uses is frequently moved through suction-type conveyors at great speed and

force, impacting with metal at curves and bends, and falling great

distances. This results in considerable breakage and other damage. The

amount of this damage can usually be calculated and is tolerated, since

the grain will be processed for food, feed, oil, or other industrial uses.

Grain or other types of seeds to be planted should not be subjected to

such treatments. Damage from impaction and improper drying or

storage may or may not be obvious on casual observation. Seeds may

receive internal fractures from impaction, moisture stress, or heat

stress without corresponding damage to the surface.

Decline and Death of Seeds

This pubUcation is concerned primarily with the various factors

affecting the life and death of seeds in storage. Decline in vigor and

death of seeds can be considered from two aspects: (1) Loss of viability

or death of a seed lot, i.e., a small or large quantity of seed, or (2) death

of an individual seed. Ordinarily people are interested in the viability of

a quantity of seed as this is what they most likely will plant. They want

to know whether the germination capacity of the seed lot is sufficiently

high to produce a satisfactory stand of plants and, if so, the required

rate of planting to produce a stand. The germination percentage of a

seed lot is the proportion of individual seeds capable of producing

normal plants. For this reason the decline in vigor and eventual death of

an individual seed should be considered.

Seeds of most crop species are mature when they attain maximum

dry weight. Most seeds are physiologically mature at this point, but

there are exceptions. When physiologically mature, the seed possesses

its greatest vigor. From this point on, it gradually loses vigor and

eventually dies. The rate of decline is conditioned by several factors,

some of which man can manipulate. Although he can prolong the

deterioration process, he has not been able to stop it.

Since death of a seed is gradual, it is virtually impossible to determine

when life ceases. Not all the life processes proceed at the same rate in

different seeds of a given seed lot. When seeds are stored under various

conditions, these life processes can terminate in individual seeds at
b AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

different times. For example, certain enzymes remain functional for a

time after a seed is dead.

Woodstock (1973)^ expressed biological deterioration of seeds as

follows: "In cellular terms there is no sharp line of demarcation between

life and death in seeds. Rather, seed death is a gradual and cumulative

process as more and more cells die until certain critical parts of the seed

become unable to perform their essential function."

Moore (1955) summarized the transition from seed maturity to death

as follows: "The so-called vigor of life is at its greatest level when the

seed first matures. After maturity, however, that life becomes less and

less vigorous as the never-ceasing aging process moves onward toward

death; but even long before death the seed becomes questionable or

worthless for planting purpose, especially under field conditions that

are not highly favorable for germination and seedling development.

"This transition of life at its fullest, to death with the ever associated

loss of vigor as intermediate steps, may take place slowly or rapidly,

depending upon the kinds of seed, the extent and location of mechanical

injury, the moisture and temperature conditions to which the seeds are

subjected in the field, during harvest, and in storage, and the important

factor of time during which the seeds are subjected to these conditions.

It is this set of conditions that determine the true planting age' of the

seed. Seed may thus be surprisingly old, or dead, at a few days or weeks

of age, or distinctly young many years after maturity."

Scope of Publication

Publications on seed storage began to appear in the second quarter of

the 19th century. At least three or four were in French and German in

the 1830's. From about 1840 to 1875 the publications per decade were

slightly less than in the 1830's but generally greater in depth. From

about 1875 until today the published reports have become so numerous

that it is literally impossible for one person to review the literature on

seed storage. There seems to have been a great proliferation of papers

from about 1890 to 1910, when more and more were published in

English. In addition to gaining practical knowledge on seed storage,

investigators became interested in determining the longevity of seeds.

Some tested the viability of dry seeds taken from (fld herbarium

specimens; others set up longtime experiments by burying seeds in the

soil in such a manner that they could be recovered for future testing.

Owen (1956) and Barton (1961) have described these experiments.

We have assembled information here that we hope will be useful to

those interested in storing seeds of vegetables, flowers, and field crops.

Included is information on the principles of seed storage and their

3The year in italic after an author's name refers to Literature Cited, p. 244.
PRINCIPLES AND PRACTICES OF SEED STORAGE 7

practical application. Seeds of forest trees, fruit trees, and weeds are

not thoroughly discussed. For information on longtime storage of seeds

for retention of germ plasm, see James (1967, 1972) and Ito (1972).

Many changes occur in seeds during storage. The principal changes

considered in this publication are three quality factors—germination

capacity, vigor, and yield potential. Since much information exists on

chromosome aberrations and mutagenic changes in aged seeds as well as

biochemical changes related to enzymes, enzymatic action, and metabolites of these processes, these subjects are treated only briefly.

SEED FACTORS THAT AFFECT STORAGE LIFE

The seed's characteristics, inherent conditions resulting from natural

causes, and man's treatment and handling affect the seed's storage life.

The storage potential of an individual seed is influenced by the following

10 characteristics and conditions and possibly by others.

Genetic Effects

Variation Among Species

Man learned early that seeds of some plant species would survive a

given set of storage conditions longerthan others. This information is so

common today that it may appear unnecessary to mention it here;

however, a few examples are documented.

Essentially all known cases of seeds surviving for a century or more

belong to species with hard impermeable seedcoats. Harrington (1972)

in his list of species with longevity records of 10 or more years included

four genera in this group: Albizia 147 years. Cassia 158 years, Goodia

105 years, and Trifolium 100 years. All belong to the Leguminosae, a

plant family known for producing hard seeds. An exception is a report

by Aufhammer and Simon (1957) that barley, which had been sealed in

glass tubes and placed in the foundation stones of a building in Nuremburg, Germany, showed 12-percent germination after 123 years. Most

species known or estimated to have survived for over 500 years are hard

seeded; for example, species of Canna (Anonymous, 1968)y Lotus

(Ohga, 1923), and Lupinus (Porsild et al., 1967).

In contrast to these leguminous seeds, the seed of peanut, also in the

legume family, is relatively short lived. Seeds of economic species with

a short storage life include lettuce, onion, parsnip, and peanut. Of the

cereals, barley and oats usually have the greatest potential for satisfactory storage, rye probably the least, and corn (maize) and wheat are

intermediate (Haferkamp et al., 1953). Haferkamp et al. (1953) íound

that three lots of 32-year-old barley germinated 96, 80, and 72 percent,

whereas seeds of four lots of oats stored under the same conditions

germinated 84, 66, 55, and 6 percent. MacKay and Tonkin (1967) íound
8 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

barley to have about the same storage capacity as wheat and considerably less than that of oats.

Variation Among Cultivars

Inheritance of seed longevity is not limited to species. Several studies

show that the principles prevailing at the species level are also effective

at the cultivar level, at least for some crop species. Several cultivars of

the same species that were compared for seed longevity differed

significantly. Shands et al. (1967) reported that seeds of the cultivar

Oderbrucker barley had greater resistance to germination loss in

storage than other cultivars. Toole and Toole (1954) found that the

cultivar Black Valentine bean had a longer lifespan in storage than

^Brittle Wax.' James et al. (1967) found significant differences in the

storage of various cultivars of bean, cucumber, peas, sweet corn, and

watermelon. Their review of relevant literature indicates that the work

of Lindstrom (1942), Sahadevan and Rao (1947), and Haber (1950)

consistently supported the probability of dominance of longevity. In a

study of eight soybean cultivars. Burgess (1938) found germination

variations between 21 and 99 percent after 4 years compared with 95 to

99 percent after 5 months' storage. In this study the differences among

cultivars did not show up until the third and fourth years of storage.

Results of studies on inbred lines of corn by Neal and Davis (1956)

suggest that some inbred lines maintain viability better than others

when stored at low temperatures. Lindstrom (1942, 1943) found that

some inbred lines of corn germinated 90 percent after 12 years' storage

at room conditions in Iowa, whereas all seeds of other inbreds were

completely dead. As indicated previously, he also found that increased

longevity in corn inbreds appeared to be dominant; however, he also

pointed out that inheritance of longevity is not simple. He believed it is

possible to introduce genes for longevity into various lines of corn by

backcrossing. Weiss and Wentz (1937) reported short seed longevity

and low vigor of corn to be associated with luteuSg and luteus^ genes

found on chromosome 10. Other luteus genes on the same chromosome

did not decrease storage life of the seeds. The authors were unable to

explain this apparent contradiction.

Generalizations

Not all seed species, cultivars, or individual seeds within a genetic

group are destined to survive for the same period of time under a

specified set of conditions. A lot or sample of seeds does not die at one

time, but the individual seeds making up the lot or sample die over a

period of time. In referring to storage life, lifespan, period of viability,

or storage potential, we mean the length of time required for a certain

percentage of the seeds to die or conversely for a certain percentage to
PRINCIPLES AND PRACTICES OF SEED STORAGE 9

live. Different percentages have been used for different purposes

(Roberts, 1972).

In summary, the seeds of different plant species vary widely in their

lifespan under identical or favorable storage conditions. Only a few

studies have been made to determine the inheritance of long storage life

among cultivars and most of them have pertained to corn (maize). This

might be a worthwhile subject for further study. In planning farm or

commercial storage the expected storage life of the species should be

considered. In experimental studies every effort should be made to use

homozygous cultivars, lines, or strains, and studies should be conducted

under strictly controlled conditions.

Preharvest Effects

Austin (in Roberts, 1972) reviewed the literature on the effects on

viability of the environment during seed development. Included were

such factors as temperature, photoperiod, mineral nutrition, rainfall,

and soil moisture. However, he did not relate these studies to seed

storability. In fact, few, if any, of the studies we have reviewed were

designed to test the relative effects of preharvest factors on seed

storability.

How Seeds Are Affected

Desirable candidates for storage are mature seeds of normal size and

appearance and relatively free of mechanical injuries and storage

micro-organisms. They should not have been subjected to extreme

temperature and moisture conditions during maturation and harvest.

Thus, any preharvest environmental factor that influences these seed

qualities also affects the storability of seed lots. About 95 percent of the

total dry weight of a seed is storage material, which will be used by the

germinating seed and seedling until it can produce its own photosynthetic and nutrient absorbing machinery (Pollock, 1961), It is readily

seen that an immature seed, a seed with an unbalanced chemical

composition, or one mechanically damaged, permitting early entry of

micro-organisms, would be at a disadvantage in storage.

Barton (1941) found that seeds of high initial viability resisted unfavorable storage conditions better than similar seeds of low initial

viability. Working with Austrian winter pea, McKee and Musil (1948)

showed that seed germinating 94 percent did not deteriorate under open

storage at ambient temperatures and humidities at Beltsville, Md., and

four locations in the Southeastern States as rapidly as similar seed that

germinated 75.5 percent at the beginning of the experiment. Brett

(1952a, i9526^ reported that seeds of grasses, legumes, vegetables, and

root crops grown in England with high initial germinations deteriorated

less rapidly than similar seeds of low initial germinations. MacKay and
10 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Tonkin (1967) checked Brett's work by using large numbers of samples

stored under laboratory conditions at Cambridge, England. They confirmed Brett's results for seeds of grasses, root crops, and vegetables

but not for legumes. They concluded that it was unlikely that hard seeds

in legumes accounted for this behavior.

Bunch (1958) adequately summarizes this discussion: "Previous

treatment of the seed, in the field, during harvest, or in previous

storage may have affected the seed in such a way as to lessen its chances

of storing well. In warm and humid climates the seed may deteriorate

on the plant before harvesting. Immature seeds and mechanically

damaged seed are especially liable to lose viability rapidly in storage."

Effect of Provenance

Very little information is available on the effect of provenance, or

location of production, on seed vitality and apparently none relating

provenance directly to storability of seeds. MacKay and Tonkin (1967)

compared the time required for seeds of four forage species grown in

different countries to deteriorate to 80-percent germination. The results

were as follows: Red clover seed grown in Canada required 4 years

compared with 3 years for English- and New Zealand-grown seed;

perennial ryegrass seed grown in Ireland and New Zealand required 4

years; American-grown meadow fescue required nearly 7 years compared with 6 years for Danish-grown seed; and Irish-grown crested

dogtail seed required 6 years compared with 3 years for New Zealandgrown seed. These data may show significant differences among locations of production; however, the seeds were not stored under controlled conditions and sources of seeds were not predetermined; rather,

the data were limited to the seed receipts at the Official Seed Testing

Station at Cambridge, England. Thus, no definite conclusion can be

drawn at this time as to the effect of provenance on storability of seeds.

Effect of Weather

The most obvious preharvest factor affecting seed viability and

storability is weather, especially seasonal changes. Farmers and seedsmen alike know the perils and risks of excessive moisture and freezing

temperatures during the later stages of seed maturation and postmaturation stand in the field. Some documentary evidence follows:

Dillman and Toole (1937) stored seed of four flax cultivars grown

under irrigation in California in 1929 and 1930. The 1930 seed "showed

marked weather injury and a low test weight (36.4 to 45.0 pounds per

bushel)." The germination of four cultivars after 6 years of storage of

the 1930 crop was 1, 4, 0, and 9 percent, whereas the corresponding

germination of the 1929 crop of the same cultivars was 94, 86, 87, and 94

percent.
PRINCIPLES AND PRACTICES OF SEED STORAGE 11

MacKay and Tonkin (1967) showed positive correlations between

weather conditions during ripening and harvesting of barley, oats, and

wheat and the number of years required for the seed to deteriorate to

either below 80-percent or below 50-percent germination. The data

were obtained from large numbers of samples grown in England over a

period of 26 years. Average hours of sunshine and inches of rainfall at

Cambridge were used as indices of weather.

Results obtained on seeds of numerous species stored in an unheated

building up to 33 years at ambient conditions near Lind, Wash., led

Haferkamp et al. (1953) to conclude that healthy matured seed stored

unthreshed and harvested in dry weather is a prerequisite for long

storage life. Riddell and Gries (1956) suggested that variations in

growth of spring wheat from seed of different ages were related to

temperature of maturation rather than to age of seed or storage

conditions. Harrington and Thompson (1952) found that the region

where lettuce seed was grown significantly affected its germination at

between 24° and 30° C. Highly significant positive correlations were

established between germination percentages and the temperature 10

to 30 days preceding harvest.

Moss et al. (1972) found that preharvest rains can cause wheat to

germinate in the ear accompanied by increased activity of a-amylase,

which digests some of the starch. Fortunately there appears to be some

variation among cultivars for activity, suggesting the possibility of

selecting or breeding varieties with resistance to this characteristic.

Early sustained freezes in the Com Belt while seed corn still in the

field has a high moisture content can cause serious damage. The degree

of damage is affected by the temperature reached, duration of low

temperatures, and moisture content of the seed. Effects of the damage

may become obvious soon after a hard, sustained freeze. Some seeds in

such a lot or entire seed lots exposed to less severe freezes may be

damaged only to the extent that the effects are detectable after storage.

Because of the seriousness of the problem and its importance, corn

subjected to freezing has been investigated to a considerable extent.

Some other crop species have been studied also but on a smaller scale.

For additional information, see page 30.

Seed Structure and Composition

The presence or absence of glumes (lemma and palea) in grasses is a

well-known example of a seed structure that influences lifespan. Haferkamp et al. (195S) found that aged seeds of three cultivars of barley

and Red Winter Speltz wheat with hulls retained viability better than

seeds of the same harvests that had been threshed and stored. Other

cultivars of barley and wheat, as well as oats and rye, showed the same

trend but to a less extent. Hulls, chaff, or both had an inhibitory effect
12 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

on the growth of mold, suggesting that the increased lifespan of cereal

seeds was due to suppression of mold growth by the glumes during

storage. Lakon (1954) showed that oat and timothy seeds had a longer

lifespan when stored with the glumes intact compared with similarly

stored machine-hulled caryopses. Seeds of both species behaved similarly. From Lakon's studies the hulled seeds appeared to be damaged

mechanically during removal of the hulls.

Working with seeds from six districts in Sweden, Esbo (1954) reported that the viability of hulled timothy seeds declined 16 percent

during the first year, whereas seeds with the hulls intact showed no

significant loss in viability until the third year. Also, he found that field

emergence of unhulled seed was 6 to 14 percent higher than emergence

of hulled seed. Average germination of six seed lots after approximately 2 years was 78 percent for unhulled and 40 percent for hulled

seed.

Goff (1890) found that hulled timothy seeds, on sale or stored in

Wisconsin, did not germinate as well the first year nor after storage up

to 10 years as did unhulled seeds. The differences were as follows:

Age of seed Percent germination

(years)

1 9

5 18

8 24

10 7

The smaller difference for seed stored 10 years may have been because

the unhulled seed declined in viability after 8 years of storage. Although

Goff used samples from commercial seed lots in his studies, he suggested that the reduced germinability of hulled seeds could not have

been caused by thresher injury "as all seed of either sort that showed

the least indication of injury were rejected from the trials."

Stevens (1935) stored unhulled and hulled timothy seeds under the

same conditions for 11 years. During this period the germination of

unhulled seed declined from 98 to 52 percent, whereas the hulled seed

declined from 97 to 16 percent.

Since the work of Goff and Stevens, several workers have shown that

many kinds of seeds suffer internal damage not always apparent without dissection and special tests (Esbo, 1954), Esbo pointed out that

when the loosely attached palea and lemma are detached from the

caryopsis, the latter is vulnerable to mechanical injury. He definitely

associated the rapid decline in viability of hulled seeds with mechanical

injury.

Roberts ("iPZ?) discussed the protection offered several shapes of seed

to mechanical damage during harvesting, handling, and processing.

Generally small seeds escape injury, whereas large seeds are more
PRINCIPLES AND PRACTICES OF SEED STORAGE 13

likely to be extensively damaged. Size, arrangement of essential seed

structures, and seed composition are contributing factors. Bean and

lima bean are examples of seeds highly susceptible to damage. The large

cotyledons and location of the embryo axis represent a structure that

will tolerate only low level impacts. Although com is a relatively large,

flat seed, its strong pericarp, strong adherence of parts, and location of

embryo offer some protection, yet injuries can be expected to the root

tip, since it is only moderately protected. According to Roberts (1972)y

spherical seeds usually give more protection than flat or irregularly

shaped seeds. Of course, the spherical shape is mediated by other

characteristics, such as relative exposure of vital parts (root and shoot

axes), thickness and strength of seedcoat, and brittleness of all seed

parts at the time of impact.

Justice (1950) referred to the relatively high incidence of abnormal

seedlings in onion, as did Clark (1948). Roberts (79Z29 observed that the

embryonic root tips of onion extend beyond the seed, a condition

conducive to mechanical injury.

Available literature does not relate seed composition or biochemistry

to lifespan. Conceivably some relationships may exist, but more definite

information is needed. Chemical, physical, and nutritive changes during

storage are discussed by Zeleny (in Anderson and Alcock, 1954) and

biochemical indices of deteriorating seeds by Abdul-Baki and Anderson

(in Kozlowski, 1972).

Hard Seeds

Much has been written about hard seeds, or seeds that are impermeable to water within the usual germination period, but little information

is directly related to seed storage.

Most crop species in the legume or pea family (Leguminosae) produce

hard seeds of varying percentages. Harrington ("7916!) indicated that the

important legumes cultivated in the United States probably produce

varying percentages of impermeable seeds except the peanut. Many of

the current crop species can develop hard impermeable seeds when

produced and stored under certain environmental conditions. Although

hard seeds are usually associated with species of the legume family,

they may also be produced by species in other plant families. For

example, hard seeds are frequently found in hollyhock and okra and

infrequently in cotton in the mallow family (Malvaceae), catnip in the

mint family (Labiatae), cranesbill in the geranium fam_ily (Geraniaceae),

canna in the Cannaceae, Ipomoea, Convolvulus^ and Cuscuta in the

morningglory family (Convolvulaceae), and Indian lotus in the Nymphaeaceae.

Possibly impermeable seeds are produced by several species in additional families, especially by the native wild plants. In fact, Passerini
14 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

(1933) explored this possibility, but his data fail to distinguish between

retarded germination caused by impermeable seeds and physiological

dormancy, which may be unrelated to seedcoat effects.

Most of the literature does not state clearly the developmental stage

in which the different legume seeds become hard. According to Lowig,^

fully ripened seeds of white clover contained slightly more hard seeds

than less mature seeds. Lute (1928) found that the percentage of

impermeable seeds of alfalfa increased with maturity. Harrington

("iPiJ^ indicated that 90 percent or more of well-matured seeds of alsike

clover, red clover, white clover, and white sweetclover were hard. It

appears evident that Harrington referred to the condition of seeds

before storage. Martin (1944) found that most lots of red clover seed

obtained from 13 growers in Iowa contained a considerable number of

hard seeds, varying from 0 to 35 percent. Also, Martin (1945) reported

that sweetclover seed lots coming from the harvester contained, on the

average, more than 50 percent of hard seeds. Under certain environmental conditions the hard seed content of some lots increases during

storage.

Helgeson (1932) showed that practically all slightly immature sweetclover seeds were permeable when harvested but were made impermeable by drying them over calcium chloride for 7 days or without the

calcium chloride if kept in dry storage. Impermeability or seed hardness

was prevented by storing the seeds in a moist, cold room. Generally a

warm, dry atmosphere is conducive to hard seed formation and a cool,

moist atmosphere favors a low hard seed population. In many species,

hard impermeable seeds have a longer lifespan than permeable seeds.

This is an obvious advantage to the survival of the species but causes

problems in cultural practices. The current tendency with annual crops

is to plant at a rate that will produce the number of plants desired in a

given area, as uniform germination is necessary to produce uniformity

of crop, permitting "once-over harvesting." Hard impermeable seeds

that germinate at some future date have little planting value under

these circumstances. On the other hand, storage of seed at intermediate

or high relative humidity to minimize the percentage of hard seeds in a

lot contributes to more rapid deterioration of germination capacity,

vigor, or both.

Varying percentages of hard seed of most species become permeable

during overwinter storage in the temperate zone. Softening depends

largely on temperature and relative humidity. Harrington (1916) conducted extensive studies on the hard seed conditions in small-seeded

^LOWIG, K. H. E. A STUDY OF METHODS FOR MAINTAINING THE GERMINATION OF

SEEDS OVER LONG PERIODS OF TIME—JUNE 1, 1965, TO MAY 31, 1970. Final report on

Public Law 480 Project No. ElO-MQ-l(a), Grant No. FG-Ge-106. 180

pp. 1970. [Processed.]
PRINCIPLES AND PRACTICES OF SEED STORAGE 15

legumes. He concluded that nearly all hard seeds of alsike clover, white

clover, and sweetclover in dry storage remained impermeable for at

least 2 or 3 years. Impermeable red clover seeds gradually became

permeable, but 30 to 65 percent of the hard seeds remained impermeable for 4 years or longer. Most alfalfa and hairy vetch seeds became

permeable within 2 years.

Martin (1945) in Iowa found that up to 24 percent of the hard seeds of

sweetclover softened when stored at temperatures around freezing, but

softening was nil at 15°-30° C. This confirmed the observations of

Stevens and Long (1926). Presumably the seeds were stored at ambient

humidities in Iowa. Martin (1944) reported that hard seeds of red clover

from 13 sources softened to a maximum of 33 percent, depending on

source, when stored dry in a laboratory at Ames, Iowa. Two seed lots

changed from a relatively low grade, based on germination percentages,

to a fair grade during a short period of storage. According to Lute

(1928), 50 percent of the hard seeds of alfalfa became permeable within

3y2 years when stored in Colorado.

Researchers have consistently reported great differences in the percentages of hard seeds among species and among seed lots of the same

species (Whitcomb, 19S1\ Esdorn and Stuetz, 1932), Esdorn and Stuetz

(1932) reported that hard seeds of lupines, alfalfa, and red clover

softened rapidly under the suitable temperature-humidity conditions,

whereas softening in hard seeds of alsike clover and white clover

proceeded very slowly.

Much has been written about the structure of leguminous seeds in

relation to water absorption. A few references are cited here. Seedcoat

or testa (Rees, 1911; Watson, 1948), cuticle (White, 1909), hilum

(Hyde, 1954), strophiole (Martin and Watt, 1944), and a general paper

by Coe and Martin (1920). The anatomy of some other crop species that

produce hard seeds is discussed by Simpson et al. (1940) for cotton,

Reeves (1936) for cotton and other malvaceous plants, and Gaertner

(1950) for Cuscuta (Convoivulaceae).

The following genera and number of species (in parentheses) of field

crops, vegetables, herbs, and flowers can be expected to produce hard

seeds. They are included in the "Rules for Testing Seeds" (Association

of Official Seed Analysts, 1970).

Compositae (aster) Leguminosae (legume)

Centaurea—basketflower (1) A/i/sicarpws—alyceclover (1)

Convolvulaceae (morningglory) Coron27/c^-crownvetch (1)

Dzc/iondro^-dichondra (1) Crotoiano^crotalaria (5)

Ipomoeor-mormnggXory (3) Ci/amopsts—guar (1)

^ . , . , Desmodm^rir—beggarweed (1)

Geraniaceae (geranium) Z?ohc/ioi^hyacinth-bean (1)

Geramum^ger^mum (1) Gíj,c¿«^soybean (1)

Labiatae (mint) Indigofera—hairy indigo (1)

Nepeta^csLtnip (1) Lathyrus—roughpea, sweetpea (3)
16 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Leguminosae (legume)—Con. Sesbania—sesbania (1)

Lens—lentil (1) Stizolobium (now

Lespedeza—lespedeza (4) Mucuna)—velvetbean (1)

Lotus—trefoil (2) Trifolium—clover (14)

Lupinus—iupine (6) Vicia—vetch (7)

Afedicagfo—alfalfa, black medic, Fio^wc^—asparagusbean, cowpea (2)

burclover, buttonclover (5) j., ,,.. .

Melilotus—sweetclover (3) .

,,. .^. , , ,-. Asparagus—asparagus (2) Mimosa—sensitive plant (1) f ¡f t- ©

Onobrychis—sainfoin (1) Malvaceae (mallow)

Phaseolus—hesin, lima bean (5) Althaea^-hoWyhock (1)

Pisum—pea ( 1 ) Gossypium—cotton ( 1+)

Puerarior—kudzu (1) Hibiscus—hibiscus, okra (2)

Some snap bean cultivars produce hard seeds, although most do not.

Hard seeds in snap bean are undesirable. Among cultivars containing

hard seeds are Top Notch and Golden Wax (Barton, 1966a)y Decatur

and Blue Lake (Nutile and Nutile, 1947)^ White-Seeded Kentucky

Wonder (Harrington, 1949), and Green Savage (Joubert, 1954),

Lowigs listed 41 cultivars of bean, mostly of German origin, with hard

seeds varying between 0 and 97 percent. Thirteen of these showed hard

seeds occurring at 50 percent or above, and 21 cultivars showed hard

seeds exceeding 25 percent. These figures must be used with caution

since Lowig determined hard seed percentages after storage over

calcium chloride.

Researchers in Puerto Rico (Anonymous, 1942a) found that drying

beans with calcium chloride was unsatisfactory because of the hard

seeds produced. Nutile and Nutile (1947), Harrington (1949), and Barton (1966a) demonstrated the effect of low relative humidity on hard

seed formation in bean. For example, Harrington stored White-Seeded

Kentucky Wonder beans with an initial hard seed content of 33.5-percent and 8.3-percent moisture content. After 60 days of storage at

10-percent relative humidity, 74.4 percent of the seeds were hard,

whereas samples stored at 65-percent relative humidity for the same

time contained no hard seeds.

It is obvious that seed of certain snap bean cultivars can change

readily from permeable to impermeable depending on the relative

humidity of the storage area. Such is not so with seed of other species.

Seed of several small-seeded legume species became hard when stored

at a low relative humidity and remained hard when transferred to a high

relative humidity because the valve-type closure to the hilum permitted

moisture to escape from but not enter the seed. When impermeable

seeds of most species became permeable, they remained so regardless

of the relative humidity where they were subsequently stored.

In some trade practices, hard seeds are regarded as viable. Several

5 See footnote 4, p. 14.
PRINCIPLES AND PRACTICES OF SEED STORAGE 17

scientific papers attest to the fact that not all hard seeds are viable, for

example, Goss (1926) and Toole (1939) for hairy vetch. Crosier and

Patrick (1952) found the viability of hard and nonhard hairy vetch seeds

to be similar during the first 5 years of storage, but after 17 years both

were among the dead ones. Also, dead hard seeds have been reported in

okra.

Nutile and ilutile (1947) and Harrington (1949) made suggestions for

storing bean seed that may have become hard with age. Nutile and

Nutile recommended that such lots not be stored in artificially heated

buildings. Harrington recommended that storing such seeds at about

2F C and a relative humidity of 50 percent or possibly a little higher

should prevent hard seed formation except possibly for very low

percentages in the most susceptible cultivars.

Seed Maturity

Relationship of Maturity to Storability

Several scientists have considered seed maturity as being that stage

when maximum dry weight has been attained (Harrington, 1972; Roberts, 1972). Since many crop species flower, produce, and mature seeds

over a period of several days or even weeks, it is important to know at

what stage of maturity the seeds should be harvested. Much of the

research relating to maturity has been oriented toward production and

harvesting goals without continuing into storage studies. Such studies

have marginal relevance to the relationship of seed maturity and

lifespan in storage. Since healthy, mature, plump seeds generally store

better than immature seeds, any studies that show the relationship

between seeds of different maturity levels and germination, vigor, field

emergence, or yield relate indirectly to storage and lifespan. Many such

studies have been discussed by Harrington (1972) and Austin {in

Roberts, 1972).

Grass Seeds

Several studies on the relationship between seed maturity and storability or longevity have been concerned with grasses. Both the flowering and seed maturity characteristics of the grass plant may extend

over several days depending on crop species. This results in harvesting

seeds of varying stages of maturity from recently fertilized ovules to

mature, plump seeds. Many of the light grass seeds are removed in the

cleaning processes; however, many are not, especially those in the

premilk and milk stages.

McAlister (1943) collected seeds of three species of Agropyroriy three

species of Bromus, Elymus glaucus, and Stipa viridula in the premilk,

milk, dough, and mature stages and stored them at between 15° and 23°
18 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

C at moisture contents of 7-9 percent. Evaluation tests made after 4

and 5 months showed that the seeds harvested in the premilk and milk

stages were generally inferior as to both viability and longevity to seeds

harvested in the dough and mature stages; the only exceptions were

that viability of seeds of Bromus marginatus and B. polyanthus

harvested in the premilk and milk stages was equal to that of seeds

harvested in the dough and mature stages.

Similar results and conclusions have been reported by numerous

workers, including Hermann and Hermann (1939) for Agropyron cristaturriy Griffith and Harrison (1954) for Phalaris arundinaceay Esbo

(1959) for Phleum pratense, Bass (1965) for Poa pratensiSy and Jorgensen (1969) for Festuca pratensis.

Other Field Crop Seeds

Only limited work has been done on seed maturity and storage of

large seeds. However, studies have shown in many instances that

immature or partially filled seeds are inferior to mature seeds in

viability and vigor. These include Dimmock (1947) for com, Blackstone

et al. (1954) for peanut, Inoue and Suzuki (1962) for bean, and Turner

and Ferguson (1972) for cotton. Justice and Whitehead (1942) found

immature velvetbean seed to be inferior in viability to mature seeds.

The germination for nine sublots that could be compared were mature

seeds 73 percent and immature seeds 10 percent. Storage period varied

with sublots from 3 to 7 months depending on the date of harvest.

Vegetable Seeds

Two Japanese workers reported some relevant information on the

effect of maturity on vegetable seed storage. Eguchi and Yamada (1958)

stored seeds of 11 kinds of vegetables (cabbage, carrot, Chinese cabbage, cucumber, edible burdock, eggplant, Japanese radish, pumpkin,

tomato, watermelon, and Welsh onion), which they had harvested at 3-

to 7-day intervals giving 4 to 6 stages of maturity for 2 to 3 years. Their

English summary indicates that eight kinds showed marked losses in

viability of immature seeds compared with mature seeds. However,

Chinese cabbage, pumpkin, and tomato showed little or no difference in

longevity with different maturities.

Pollock (1961) pointed out that maturity studies of carrot are complicated by the fact that at least three orders of ñowers, or umbels, are

produced and each order will flower and produce seeds over a period of

time. Harvesting all umbels at the same time will result in both mature

and immature seeds. He reported that the level of maturity affects both

germination and vigor.

Austin (in Roberts, 1972) harvested carrot seeds in England at four

dates from September 5 through October 5 and classified each harvest
PRINCIPLES AND PRACTICES OF SEED STORAGE 19

into four size groups. As the harvest season progressed, the weight of

seeds declined slightly, but the germination increased by 5 percent,

which probably was not significant. As the size of seed increased, the

mean seed weight increased correspondingly. The germination increased with increased seed size for the first three weight classes (1.00

to 1.75 mm per seed) and for each harvest date, but it decreased by 4

percent for the largest and heaviest seeds (1.75 to 2.00 mm per seed).

These studies suggest that immature carrot seeds do not germinate as

well as mature seeds. Based on studies with seeds of other crop species,

the longevity of immature seeds would be apt to be less than that of

mature seeds when both are stored under identical or similar conditions.

Germination response of seeds removed from mature and immature

squash fruits differed presumably because of seed maturity. Young

(1949) and Holmes (1953) collected mature and immature fruits of

butternut squash and stored them for periods up to about 7 months. At

the beginning of his experiment, Young found seeds from mature and

immature fruits to weigh 7.78 and 5.32 gm per 100 seeds, with average

germination of 90.8 and 19.0 percent, respectively. Four months later,

both mature and immature seed had gained weight by 0.34 and 0.91 gm

and germination had increased to 98.4 and 67.2 percent, respectively.

At the beginning of the experiment, seeds from only 7 out of 25

immature fruits germinated, whereas all immature fruits produced

germinable seeds at the conclusion of the experiment. This indicates

that the seeds of some immature fruits either were too immature to

germinate when harvested or were dormant.

After 7 months of storage of butternut squash. Holmes (1953) found

the weights per 100 seeds to be 10.9 gm for mature and 8.9 gm for

immature seeds. Germination at this time was 97 percent for mature

and 77 for immature seeds. Holmes (1953) also found that the ratio of

fruit weight of typical butternut squashes to seed weight was rather

consistent.

Seed Size

No references have been located relating seed size or weight to

lifespan through storage experiment. On the other hand, numerous

studies have shown the superiority of heavy, mature seeds over light,

immature seeds in germination, vigor, and yield tests. Relatively few

exceptions have been noted. Comprehensive reviews are provided by

Black (1959) Sind Austin (m Roberts, 1972). Austin ^iPZá;) discussed seed

maturity and seed size jointly, possibly because seed size is determined

or mediated to some extent by maturity. His treatment lends credence

to the view that the same or similar vagaries besetting immature seeds

in storage also affect small seeds, at least to some extent.
20 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Seed Dormancy

Relationship of Dormancy to Storage

Some or all seeds of several crop species are dormant at harvest. A

major problem facing seed technologists when testing stored seed for

germination is how to overcome dormancy. Dormancy of freshly harvested seeds may be found in practically all groups or classes of plants,

whether crops or native plants, including grasses, cereals, clovers and

other small-seeded legumes, large-seeded legumes including peanut,

cucurbits, vegetables, flowers, trees, and weeds. In some seeds, dormancy is caused by (1) seed structures, as seedcoats, bracts, glumes,

pericarp, and membranes, which limit the exchange of water and gases,

(2) physiology of the embryo, (3) germination inhibitors or other blocks,

or (4) a combination of these factors.

Storage can affect dormancy in many instances. In most crop species,

dormancy is dissipated within a few to several months when the seed is

stored at ambient temperatures and relative humidities or under controlled atmospheres provided the temperature is held above freezing.

Seed physiologists know that the best method of maintaining dormancy

in seeds is to store them at subfreezing temperatures.

Dissipation of Dormancy

Owen (1956) and Koller (1972) reviewed pertinent literature on the

existence of seed dormancy and its dissipation with time. Only a few

relevant studies are mentioned here. Larson et al. (1986) found that

dormancy in immature seeds of barley, oats, rye, and wheat persisted

longer than in mature seeds when stored at 0° to -35° C, but that

dormancy varied greatly among cultivars of a given crop species. The

duration of dormancy could be increased by lowering the temperature.

In a study of seeds of different cultivars of barley, oats, and sorghum.

Brown et al. (1948)ío\xná that incipient dormancy was overcome in most

cultivars within 1 to 6 months when stored at 40°. At 2.2°, dormancy in

barley and oats persisted for 3 years.

Dore (1955) and Roberts (1972) discussed dormancy in rice. In Dore's

(1955) studies of 21 cultivars, dormancy was lost between the 7th and

11th weeks after harvest except for the cultivar Penifun, which was

dormant for only 5 weeks. Roberts (1972) found the dormancy of rice

cultivars to vary between practically none in the cultivar Tai Chu 65 to

over 100 days (100 days for 50 percent of the seeds to break dormancy)

in Masalaci. Although dormancy among rice cultivars differed markedly, the pattern of viability loss for all cultivars was the same.

The situation with grasses is similar to that for cereals. In many

native American grasses used for range planting, seed dormancy is

much more intense than in cereals. Winchester (1954) found that
PRINCIPLES AND PRACTICES OF SEED STORAGE 21

Panicum maximum var. Trechoglume seed increased in germination

from 11 percent when fresh to 46 percent after storage for 25 months

and seed of Cenchrus ciliaris (buffelgrass) from 3 to 79 percent within

13 months.

Dormancy in Florida runner peanut seed was overcome by Hull (1937)

when he stored it at 20°-25° and 40° C, whereas dormancy in some

samples persisted for 2 years at low temperature storage conditions.

Recently harvested cottonseed can be dormant. Christidis (1955) reported that some cottonseed samples grown in Greece remained dormant up to 5 months. Justice (1956) iownd that the only effective method

of breaking dormancy in seeds of Cyperus rotundus was to place them

on a moist substratum at 40° for 3 to 6 weeks.

Dormancy and Lifespan

In considering the relationship of seed dormancy to storage, a second

area of interest is whether dormancy increases the lifespan of seeds.

Roberts (1972) reviewed pertinent literature on the subject and correctly concluded that available evidence is not sufficient to establish

even a casual relationship. He detailed and analyzed some of his own

experimental work with rice and concluded that his work did not

support the existence of a relationship between dormancy and longevity. This does not exclude the possibility that the lifespan of dormant

seeds of native or wild plants buried in the soil under natural conditions

may be longer than the lifespan of nondormant seeds.

Toole and Toole (1953) found that imbibed dormant seeds of lettuce

did not decay in 105 days, whereas companion samples placed in beakers

with a relative humidity of 85 to 90 percent were dead; the seeds of one

cultivar remained alive for 42 days. This suggested to the authors that

dormancy of the imbibed seeds either held in check or suppressed the

life processes that lead to seed deterioration.

Existing evidence is not sufficient to demonstrate a positive relationship between seed dormancy and lifespan. However, dormant seeds in

storage undergo changes, some of which lead to breaking of dormancy

and others to inducing dormancy. Some of these changes are affected by

storage conditions.

Moisture Content

The moisture content of seeds during storage is no doubt the most

influential factor affecting their longevity. It is important to harvest

mature, relatively dry seeds or to reduce the moisture content of

high-moisture seeds soon after harvest. Bass (1953) found that the loss

of viability of freshly harvested Kentucky bluegrass seed was correlated with the moisture content of the seed and length of time held at a

given temperature. Seed with 54-percent moisture held at 30° C for 45
22 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

hours lost 20-percent germination, but seed with 44-percent moisture

withstood 45° for 36 hours with no apparent loss of viability. Seed with

22- and 11-percent moisture content showed essentially no loss in

viability at 50° for over 45 hours.

McNeal and York (1964) studied the effects of drying sorghum seed

on viability. They concluded that sorghum to be used for seed should be

harvested when the moisture content is about 20 percent or less and

dried promptly to about 11-percent moisture content. The drying temperature should not exceed 43.3° C for very moist seed and not over

54.4° for seed with a relatively low moisture content.

Haferkamp et al. (1953) reported reduced germination of 27-year-old

wheat compared with slightly older wheat. They explained this on the

basis that the June rainfall in 1923 (year of harvest of 23-year-old

wheat) was over five times the average. The authors believed that high

moisture content of the seeds during development greatly reduced seed

viability and longevity. Regarding moisture during seed development,

Mcllrath et al. (1963) made an interesting observation on developing

tomato seeds. Although the moisture content of the placenta and

pericarp of tomato fruits 15 days old or older never dropped below 94

percent, the seeds became dehydrated to approximately 50-percent

moisture content as the organs developed and matured.

Another way in which initial seed moisture content affects storage life

of seeds is through its effect on mediating damage by threshing and

processing machinery and handling. Although it is very important to

reduce seed moisture content to a safe level for storage, it is also

important to be aware of possible adverse effects of low moisture

content. Very dry seeds are susceptible to mechanical breakage and

related injuries. Such damage may result in physical breakage or

fracturing of essential seed parts, make the seed vulnerable to fungal

attack, and reduce storage potential. For more information, see the

section on ''Effects of Storage Environment on Seed Longevity."

Mechanical Damage

Awareness of Seed Damage

As harvesting and threshing machinery and the combine came into

general usage, damage to seeds and grain increased accordingly. Some

of the early work on seed injury related to the mutilation of corn

(Brown, 1922), seedcoat injury of barley and wheat (Hurd, 1921),

broken pericarp of corn (Myers, 1924), and mechanical injury to soybeans (Oathout, 1928). Research on seed injury was expanded greatly

in the 1930's, with the advent and use of the combine thresher. Some

seed species or groups have received greater attention than others

depending on their vulnerability to damage by machinery and handling.
PRINCIPLES AND PRACTICES OF SEED STORAGE 23

Two important characteristics that affect the degree of damage are seed

structure and resistance of the seed to removal from the pod, as in

legumes and crucifers, or from the mother plant, as in the grasses.

Problems arising from these characteristics are affected by moisture

content of seeds and pods, degree of maturity, and possibly other

factors.

Beattie and Boswell (1939) and Moore (in Roberts, Í9Z?)showed that

damaged seeds do not store as well as intact seeds and that fungi enter

the seed through cracks in the seedcoat. In discussing the storage of

seeds of the clovers and medics, Brett (1952a)statedy "From the results

of experiments at Cambridge [England], and elsewhere, it is clear that

scarified seed loses its ability to germinate at a significantly greater rate

than does unscarified seed when stored under the same conditions."

Natural deterioration in spinach seed has demonstrated that the

percentage of abnormal seedlings increases with time and the percentage of normal seedlings decreases. Thus, seedling abnormalities result

not only from mechanical damage but also from natural aging. According to Moore (in Roberts, 1972)^ small and hidden injuries in seeds,

including bruises, may not cause immediate loss in vitality, but they can

become increasingly critical with aging of the seed. Moore (1972)

pointed out that injuries to vital organs, i.e., various parts of the

embryo, become more serious with age than injuries to nonembryonic

tissues.

Vulnerability of Some Seeds to Damage

The amount of fiber in the bean pod, which varies with cultivars,

affects the degree of mechanical damage to the seeds through its effect

on ease of threshing. Apparently this problem was first studied by

Harter (1930) of California, then continued and expanded by his colleagues Borthwick (1932) and Bainer and Borthwick (1934). A comprehensive review of the subject by the Asgrow Seed Co. (Associated

Seed Growers, Inc., 1949) also included results of its own extensive

research studies. This type of research has been continued since the

1950's, especially at the U.S. Department of Agriculture, Beltsville,

Md. (Toole, 1950; Toole et al., 1951; Toóle and Toóle, 1960) and at

Michigan State University (Perry and Hall, I960; Dorrell;^ Dorrell and

Adams, 1969), These studies showed that threshing or combining

produces breaks, cracks, bruises, and abrasions in seeds, which in turn

result in abnormal seedlings of questionable planting value. These

injuries were reproduced by controlled mechanical shock to the seeds

and were greater with reduced seed moisture.

eDORRELL, D. G. SEEDCOAT DAMAGE IN NAVY BEANS (PHASEOLUS VULGARIS), INDUCED BY MECHANICAL ABUSE. 1968. [Unpublished Ph.D. thesis. Copy on file Dept.

of Botany, Mich. State Univ., East Lansing.]
24 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Toole (1950) attempted to compare the germinability of slightly

injured seeds with seeds producing apparently uninjured seedlings of

bean stored for 3, 6, and 9 months. Owing to unpredicted changes

during storage, such as (1) decrease in apparently uninjured seedlings,

(2) corresponding increase in slightly injured seedlings, and (3) increase

in abnormal seedlings, no firm conclusions could be drawn. However,

the author suspected that under unfavorable conditions slight mechanical injuries could predispose the seed to increased deterioration compared with uninjured seed, even though the preliminary study did not

confirm this suspicion.

Response of Seeds to Storage Conditions

There is reliable evidence that damaged seeds of small-seeded legumes do not survive as long as nondamaged seeds. Battle (1948) found

that all alfalfa seeds that had been scarified with sandpaper and stored

for 14 years were dead, whereas unscarified seeds showed 23-percent

germination. Similar results were reported by Graber (1922), Stevens

(1935), and Brett (1952a). In storage experiments, Oathout (1928) and

Mamicpic and Caldwell (1963) demonstrated that damaged soybean

seeds lose their viability earlier than nondamaged seeds. Blackstone et

al. (1954) reported similar results for peanut.

Information on the retention of viability of injured cereals in storage

is extremely limited. In a 17-year experiment Russell (1958) compared

lots of wheat seed having cracked seedcoats with lots of sound seed. At

the beginning of the experiment the damaged seed germinated 4

percent less than the sound seed. This difference gradually increased to

12 percent, where it remained for 9 years of storage. The germination

of the two groups differed slightly during the last 4 years of storage.

Possibly the sound seed declined rapidly in viability after 10 to 12 years.

Hurd (1921), Kuperman (1950), and Wortman and Rinke (1951) showed

that broken cereal seedcoats provide easy access for microflora to enter

the seed. Broken or cracked seedcoats also enhance embryo damage by

chemical treatments, including chemicals used as disinfectants (Bonvicini, 1951). Both fungi and chemical damage reduce the keeping quality

of stored seeds.

Possible Involvement of Genetics

Efforts have been made to determine whether there are genetic

differences among bean cultivars in their tolerance to mechanical injury. Atkin (1958) studied 3 crops of 18 cultivars and concluded that

important fairly constant differences existed. Generally the coloredseeded cultivars had greater resistance to mechanical injury than

white-seeded cultivars. Nevertheless one white-seeded cultivar

(Streamliner) showed some resistance to mechanical injury. This led the

author to believe that a resistant white-seeded cultivar could be devel-
PRINCIPLES AND PRACTICES OF SEED STORAGE 25

oped. On the other hand, DorrelP found that tolerance to seed injury of

navy bean is a complex trait controlled by numerous genes. Population

averages showed no evidence of dominance in the F j and F^ generations

and genetic variance appeared to be primarily additive. Thus, from this

study there is little encouragement that cultivars highly resistant to

mechanical injury can be developed through a breeding program.

It is obvious from available information that mechanical injury to

seeds not only reduces production of normal seedlings but also decreases the storage potential of damaged seeds that apparently would

have produced normal seedlings prior to storage. Many studies have

been made on seed injury resulting from mechanical harvesting,

threshing, combining, and handling, but relatively few of these studies

have been concerned with storage.

Vigor

The vigor of seeds at the time of storage is an important factor that

affects their storage life. Vigor and viability cannot always be differentiated in storage experiments, especially in seed lots that are

rapidly deteriorating. Irrespective of this problem, several workers

have demonstrated that seed lots that were rapidly declining contained

some seeds low in vigor and other seeds that still might be vigorous.

This progressive weakening with age continued until all the seeds

became nonviable.

Obviously new, vigorous seed lots possess a greater storage potential

than older lots that may be approaching rapid deterioration. Generalized curves of the decline in vigor and viability of a seed lot with time

are shown in figure 2. The viability curve gradually decreases, followed

by a sharp decline and finally a gradual loss. The loss in seed vigor

essentially parallels that of viability but at lower levels. The rate at

which seeds will decline in vigor or viability depends on several factors,

including genetic constitution of the species or cultivar, condition of the

seed, storage conditions, uniformity of seed lot, and storage molds if the

relative humidity permits their growth. Among the research workers

who have shown that vigorous seeds reach a point when deterioration

proceeds more rapidly than during the early period of storage are

Patrick (1936) for Chewings fescue seed, Christidis (1954) for cottonseed, and Burns (1957) for blue lupine seed.

The decline in vigor and viability of seeds is sometimes illustrated by

a sigmoid survival curve. The survival curve for dry seeds stored under

favorable environmental conditions can be dissected into three distinct

parts. The first represents the period when the seed is vigorous and

decline in the life functions has proceeded slowly. Eventually this stage

7 See footnote 6, p. 23.
26 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

PERCENT

100 j. ^ ^11^

I

I

VIGOR'^^i

V

VIABILITY

TIME

FIGURE 2.—Decline of viability and vigor with time of a typical seed lot. (Courtesy

of J. F. Harrington.)

ends at a survival level of 90-75 percent, and deterioration then

proceeds very rapidly. After deterioration has proceeded to a survival

level of 25 to 10 percent, it slows again and continues slowly until all

seeds are dead. The curves for vigor and viability are very similar,

except that loss of vigor precedes loss of viability.

EFFECTS OF STORAGE ENVIRONMENT ON SEED

LONGEVITY

Temperature

Temperatures Above Freezing

Storage temperature and seed moisture content are the most important factors affecting seed longevity, with seed moisture content usually

more influential than temperature. Owing to the intricate relationship

between storage temperature and seed moisture content, neither one

can be discussed separately in its entirety. Nevertheless temperature

and seed moisture are discussed here separately to a limited extent to

indicate the relative importance of each, whereas the interaction of the

two is discussed more fully under "Interrelationship of Temperature,

Seed Moisture Content, and Storage Life."

Within limits the storage life of seeds of vegetables, flowers, and field

crops decreases as the temperature increases. Exceptions include certain short-lived seeds. Groves (79i7^ described the relationship between

temperature and lifespan of wheat seeds by a formula. Roberts (1972)

presented formulas that he believed described the relationship of tem-
PRINCIPLES AND PRACTICES OF SEED STORAGE 27

perature and moisture content to the period of seed viability of certain

crop species. He developed nomographs using the formulas for barley,

broadbean, rice, and wheat. The accuracy, limitations, and usefulness

of these formulas and nomographs are still to be determined.

Harrington (1960d) proposed his so-called Thumb Rules, which related seed moisture and temperature to the seed's lifespan. His (1972)

rules stated that the life of the seed is halved (1) for each 5° C increase

in seed storage temperature and (2) for each 1-percent increase in seed

moisture content. Harrington cautioned that, based on current knowledge, the first rule should not be used for storage temperatures below 0°

or above 50°. He also pointed out that the two rules apply independently, and the effects of temperature and moisture are additive. Since

this procedure gives only rough estimates of storage potential under

stipulated conditions, it must be used with caution.

San Pedro (1936) stored seeds of vegetable species in containers with

calcium chloride at four temperatures and determined the percentages

of germination after 7.1, 9.2, 11.3, and 19.5 months. His results for the

11-month storage period (table 1) show that as temperature was increased, even in a dry atmosphere, germination decreased. His averages are mediated by the stage of deterioration of each crop species

during the storage period. For example, cabbage declined in germination by 19 percent between storage at 0° and 28° C, whereas pechay and

sitao declined only 2 and 3 percent, respectively, under the same

storage conditions. The seeds of radish were dead at all storage temperatures after 14.5 months.

Barton (1941) stored seeds of six vegetable species at different

temperatures and relative humidities for 372 days. At 35-percent relaTABLE 1.—Effect of various temperatures on germination of several

crop seeds after storage with calcium chloride for 11 months^

Germination after storage at

Germination indicated temperature (°C)

Crop when stored

Percent

Cabbage 90

Carrot 65

Lettuce 63

Parsley 56

Pechay 99

Radish 85

Sitao 93

Average 79 60 56 55 50

1 Adapted from San Pedro (1936).

0 10-13 20-22 27.5-28

Percent Percent Percent Percent

72 71 63 53

57 51 45 42

61 51 55 50

32 32 31 28

91 89 86 89

23 24 27 9

83 77 81 80
28 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

tive humidity the average germination for lettuce and onion, two

species with short storage lives, was 61, 44, 31, and 9 percent, respectively, at 5°, 10°, 20°, and 30° C, whereas comparative germination

results for tomato and flax were 96, 92, 88, and 85 percent.

Barton (1966b) also stored pyrethrum seeds at various temperatures

in sealed and open containers for up to 15 years. Table 2 ^hows that

temperature markedly affects germination. It also shows that the effect

of temperature is influenced by seed moisture content. In sealed

storage, seed moisture content remains constant, but in open storage it

changes with changes in the relative humidity of the storage area.

Therefore adequately dried seeds in sealed containers usually live

longer at a given temperature than similar seeds in open containers.

The effect of temperature on the storage of soybean seed was

reported by Toole and Toole (1946), They stored seeds of the cultivars

Mammoth Yellow and Otootan at five temperatures and three moisture

contents for 10 years. The months required to lose germination at each

temperature-moisture combination are shown in table 3. Not all seeds

were dead at the favorable storage conditions. In fact, there was no

significant loss in germination at the end of the 10-year storage period at

five storage conditions for Mammoth Yellow and at five conditions for

Otootan. The data for 18.1-percent moisture (Mammoth Yellow) and

17.9 percent (Otootan) show the reduction in seed germination or

lifespan as temperature is increased, or alternatively the increased

germination or lifespan as temperature is decreased. The range in

lifespan is from 3 months at 30° C to 72 months at 2° for Mammoth

Yellow and from 1 month at 30° to 72 months at 2° for Otootan. Similar

data could be compiled for other levels of germination, for example 50

or 80 percent.

TABLE 2.—Effect of different temperatures on germination of

pyrethrum seeds in sealed and open storage after various periods^

Germination in sealed Germination in open

Temperature storage after indicated storage after indicated

(°C) years2 years2

3 13 15 3 13 15

Percent Percent Percent Percent Percent Percent

5 61 53 47 44 U 29

10 53 37 28 38 0

20 46 10 6 47 1

30 1 --. --- 0

1 Data from Barton (1966b). Original germination of seed lot was 57 percent.

2 Dashes indicate no samples were taken.
PRINCIPLES AND PRACTICES OF SEED STORAGE 29

TABLE 3.—Effect of various temperatures on duration of seed germination of 2 soybean cultivars at 3 seed moisture contents^

Cultivar

Moisture

content when

stored

Time required to reach 0-percent

germination at indicated temperature (°C)2

30 20 10 2 -10

Percent Months Months Months Months .Months

Mammoth Yellow _ 18.1 3 9 24 72 120*

13.9 5 24 120 120+ 120+

9.4 24 120 120+ 120+ 120+

Otootan 17.9 1 5 24 72 120**

13.4 5 24 96 120+ 120+

8.1 48 120Í 120+ 120+ 120+

1 Adapted from Toole and Toole (1946).

2Percent germination after 10 years' storage: + = above 90, $ = 44, 17.

Small field plantings were made of 10-year-old seeds that had shown

no loss in germination and of seeds grown the previous year. The

authors found no apparent difference in vigor of growth for either

cultivar when the known genetic variation in Mammoth Yellow was

considered. Many seedling abnormalities were observed in both Mammoth Yellow and Otootan cultivars grown from seeds artificially dried

to 5.4- and 5.2-percent moisture content, respectively. These abnormalities were in seedlings produced from seed stored for only 3 months,

especially from those seeds held at the lower temperatures. Few

abnormal seedlings were produced from seed stored at 30° C, but they

were increasingly numerous at successively lower storage temperatures. The abnormalities of Mammoth Yellow were much more frequent

and more pronounced than those of Otootan. Tests made on seeds

stored for longer periods showed approximately the same proportion of

abnormalities.

Some research has been done to determine the effects of high temperatures on seeds. In general, seed viability and vigor are reduced as

temperature is increased, as time of exposure to high temperatures is

increased, and as moisture content of the seed is increased. Damage is

diminished at a given temperature as the seed moisture content is

decreased. Thus, Waggoner (1917) found the following relationship in

radish seeds:

Nonlethal

Moisture content temperature

(percent) CC)

45 Below 50

4 75

.4 100

Lethal temperature

CC)

55-60

95-100

123-125
30 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Harrington and Crocker (1918)y Smith and Gane (1938)y and Evans

(1957b) showed that low moisture content Kentucky bluegrass, Chewings fescue, and perennial ryegrass seeds can be heated to 100° C or

higher without immediate loss of viability. However, stress tests of

heated seeds showed that vigor decreased before the effects on seed

viability were manifested. White (1909) significantly reduced the percent germination of barley, oats, and wheat by exposing air-dry seeds to

dry heat at 99°-100° for one-half hour. Greater decreases were obtained

by heating for 4V^ hours. Seeds of these three species plus corn (maize)

and rye failed to germinate when the temperature was increased to

122° or higher for 1 hour. The consideration of temperature, time of

temperature exposure, and moisture content of the seeds is essential

when drying seeds for storage. For further information, see the section

on "How Seeds Are Dried."

Temperatures Below Freezing

As background for their experimental results from freezing seeds at

-183°C, Brown and Escombe (1897-98)reviewed at least five papers on

low temperature treatments. They referred to papers by C. de Candolle

and R. Pictet published as early as 1879 and 1885. They froze seeds at

-80° for 2-6 hours, and in 1884 they exposed seeds to -100° for 4 days

without adversely affecting germination. Brown and Escombe (1897-98)

exposed seeds of 12 species with moisture contents of 10-12 percent to

-183° for 110 consecutive hours without damage.

White (1909) observed severe injury to seeds of apple, hemp, lobelia,

parsley, and parsnip after exposure to -200° C for IV2. days, slight

injury to seeds of bean, mustard, pea, radish, sunflower, and turnip,

and no injury to seeds of cress and Ricinus camogdensis. The moisture

content was not given. She subjected seeds of barley, corn (maize), oats,

rye, and wheat to -200° for 2-3 days without any decrease in germination.

Lipman and Lewis (^2954;subjected seeds of 19 species to -250° C for

60 days and evaluated the seeds by greenhouse tests. They found no

significant difference between the frozen seeds and unfrozen controls.

Lipman (1936) exposed seeds of barley, corn, sweetclover, and vetch to

-273.1° just shy of absolute zero, with no impairment of viability,

whereas Becquerel (1953) dried seeds of alfalfa, clover, petunia, and

tobacco and then held them at -272.9° for 2 hours without impairment

of viability.

The superiority of subfreezing temperatures for seed storage compared with higher temperatures has been well established for many

kinds of seeds. Documented experimental evidence dates back to 1928

(Dorph-Petersen, 1928) and possibly earlier. Some of the literature on

seed storage at subfreezing temperatures is summarized in table 4.
TABLE 4.—Sampling of literature on seed storage at subfreezing temperatures

Literature source Seeds

Below 0° C

Storage

Above 0° C

Results (°C)

Dorph-Petersen (1928) Tussilago fárfara -15°

Barton (1932) Annual and perennial delphinium -15°

Beattie and Boxwell (1939)

Kearns and Toole (1939) _

Toole and Toole (1946) .

Onion -6.5°

Chewings fescue -10°

Soybean -10°

4 temps. (0°-20°)

8° and room temp.

4.4° and room

temp.

2°, 10°, 20°, 30°

2°, 10°, 20°, 30°

Above 0°, most seeds were dead

after 4 mo; at -15°, 82 percent of

seeds germinated after 2 yr.

-15° gave slightly better results

than 8°; sealed seed at -15° retained

50-percent viability for 5 yr.

Up to 4 yr, 4.4° was better, but for

longer periods -6.5° was better.

2 yr was too short to test advantage

of -10°; original germination maintained for 2 yr at 10°, 2°, and -10°

for 10-percent moisture and 2° and

-10° for 14-percent moisture.

Nearly full germination maintained

for 6 yr at -10° and 18-percent

moisture; longevity with 18-percent

moisture at higher temperatures

was 1 mo to 3 yr; 13.5-percent

moisture at 2° and -10° maintained

original germination for 10 yr.

2

5

o

r

M

>

Ü

>

O

O

M

CO

O

W

w

Ö

CQH

O

>

O

CO
TABLE 4.—Sampling of literahire on seed storage at suhfreezing temperatures—Continued

Literature source Seeds

Storage

Results (°C)

Below 0° C . Above 0° C

Pack and Owen (1950) Sugar beet -23.3° to -12° None

Barton (1954) 5 species of conifers -4°, -11°, -18° None

Weibull (1952, 1955) 9 vegetable and 16 flower species -20° ±0° and ordinary

storage of 5°-20°.

Seed frozen continuously germinated 83.5 percent in 1928, 81.0 percent in 1949; no reduced vigor during storage.

Deteriorated most rapidly at -4°; to

maintain viability, -18° was best of

3 temperatures used.

Viability of vegetable seeds retained as long or longer at -15° as

at ±0° except parsley; -20° unfavorable for fern asparagus, pansy,

parsley, hybrid petunia, and snapdragon; some flower species stored

better at -20°, others showed no

difference between -20° and ordinary storage; results not consistent

for some other species.

CO

O

2

o

a

r

w

X

>

u

CO

o

o

c!

CO

a

o

>

o

2

o

c:

r

H

a
Sengbusch (1955) Hemp, rye, sugar beet 20°

Hanson and Moore (1959) 6 species of small-seeded legumes and 2 grasses

-7° to -11°

20° -20° superior to 20° for hemp and

rye, which lost viability after 3 yr;

at 20° and -20°, germination was 90

and 98 percent, respectively, after 5

yr; 5 yr too short to evaluate sugar

beet as little change in germination

at 20° or -20° throughout storage.

Laboratory storage Alfalfa, crimson and white clover,

Kobe and Korean lespedeza, Lespedeza sericea, orchardgrass, tall fescue. Germination including hard

seeds after 3, 4, and 18 yr;» -15°

superior to lab. storage; germination after 18 yr (2 seed lots per

species)—crimson clover and 2

grasses: Lab. 0 percent, subfreezing 39 percent; small-seeded legumes other than crimson clover:

Lab. 15.5 percent, subfreezing 79.2

percent.

Barton (1966b) Pyrethrum -4° and -18.5° 5°, 10°, 20°, 30° Complete germination for 13 yr, essentially so for 15 yr when stored

sealed at -4° and -18.5°; latter

better for unsealed seed; lifespan

gradually decreased as temperature

increased from -18.5° to 30°.

2

5

o

>

to

>

o

o

o

tfl

w

a

o

>

Q

118-yr data unpublished but supplied by authors.

00

00
34 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Weibull (1952, 1955) found seeds of a few species that were not

benefited by a subfreezing storage temperature. A "few other examples

have been reported. Roberts (1972) analyzed some of them and concluded that, in some instances, statements were made without considering the moisture content of the seed. He believed that low temperature storage is beneficial to maintaining seed viability, but that there

may be a few exceptions. This position appears to be supported by the

literature.

Early fall freezes while seeds and grain are still in the field have

prompted several studies on the deleterious effects of freezing seed and

grain at high moisture contents. Kiesselbach and Ratcliff (1918, 1920)

studied freezing injury to seed corn because it occurred in the fall with

considerable frequency in Nebraska. They found that death of seed corn

from freezing was directly related to the moisture content of the kernel

and to the duration of exposure to low temperatures. Immature kernels

with a higher moisture content than mature kernels were more susceptible to freezing injury. All seeds were dead when exposed for 24

hours at the following temperatures and moisture contents:

Temperature CO Moisture content (percent)

2.2 to 0 60-65

-4.4 to -6.7 55-60

-6.7 to -8.9 35-40

-13.3 to -15.6 30-35

-17.2 to -20.5 20-25

However, all seeds retained their viability for at least 3 months when

stored at -13.3° to -15.6° C and 12- to 14-percent moisture content.

McRostie (1939) and Rossman (1949) compiled considerable data on

freezing injury of corn seed that essentially confirm the findings of

Kiesselbach and Ratcliff (1918, 1920). All agree fairly well on the factors

causing freeze injury, although their results, when comparable, vary

somewhat in detail as would be expected. According to McRostie (1939),

5-day fluctuating temperatures of -17.8° to -23.3° C, -17.8° to -26.1°,

and 0° to -26.1° caused more damage to corn seed than a constant

exposure to the lowest temperature of any of these regimes. On the

other hand, Rossman ("1949) indicated that repeated freezing and thawing were less injurious than continuous freezing when the total time was

the same. He found similar responses to freezing temperatures by the

two hybrid cultivars he used. Likewise, Kiesselbach and Ratcliff (1918,

1920) found that dent corn and flint corn responded similarly.

In storage experiments with frost-damaged sweet corn seed. Barton

(1960b) found no significant loss of germination in five lots (four cultivars) over 9 years when stored sealed at -5° C with moisture contents

below 13 percent. In open storage at 30° or at -5° in a moisture-saturated atmosphere, the seed decreased in viability by about the same

amounts over 7 years.
PRINCIPLES AND PRACTICES OF SEED STORAGE 35

Apparently seeds of barley, rye, and wheat are nearly as sensitive as

corn to cold injury at high moisture contents. Agena (1961) found a

rapid increase in injury in these species when the grain was stored at

-6° C and moisture contents above 22 percent. Under these conditions,

injury was evident after 1 day of storage and increased with time. He

found that moist grain can be held best for short periods between 0 and

-6° but that fungi soon appear under these conditions. Freezing injury

was greatest at the radicle tip and secreting area of the scutellum.

Wheat was frozen in Uquid nitrogen (bp -195.8° C) for 2 minutes at

moisture contents of approximately 19 to 25 percent by Lockett and

Luyet (1951), Entire seeds with 19.4-percent moisture content dropped

10 percent in germination because of freezing. Corresponding losses in

germination with increase in moisture content of entire seeds were as

follows:

Moisture content Germination loss

(percent) (percent)

21.2 20

23 89

25.1 100

Imbibed decorticated seeds had a considerably lower moisture content

with less germination loss because of freezing than entire seeds imbibed

for the same time. The moisture content of imbibed embryos was much

greater than that of either entire or decorticated seeds.

Freezing injury to sorghum seed is affected by moisture content of

the grain, temperature, and duration of freezing treatment (Robbins

and Porter, 1946; Carlson and Atkins, 1960; Kantor and Webster,

1967), In addition, Carlson and Atkins (1960) showed that the genotype

of the cultivar affects tolerance to freezing injury. Data of Robbins and

Porter (1946) also suggest genetic effects on freezing tolerance; however, a definite statement to this effect cannot be made since the

complete history of each seed lot used is not given. Kantor and Webster

(1967) used two cultivars in their research but were unable to draw a

conclusion with respect to genotype effects. In view of these reports on

sorghum seeds and the reports of Kiesselbach and Ratcliff (1918, 1920)

and of Rossman (1949) on corn, the genetic effect on freeze resistance in

cereals remains unresolved.

Seed Moisture Content and Relative Humidity

Direct Effect of Moisture on Seed Deterioration

Barton (1961) regarded moisture content of utmost importance in

seed deterioration. Seed deterioration increases as moisture content is

increased.

Boswell et al. (1940) illustrated the effects of relative humidity and
36 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

consequently moisture content of the seeds on their storage life. They

stored 10 kinds of vegetable seeds at 2 temperatures, 3 relative humidities per temperature, and under warehouse conditions for 251 days.

Samples were tested on 0 day, every 10 days thereafter for 90 days, and

after 110 and 251 days of storage. Since 10-, 30-, 50-, 70-, and 90-day

tests were not made on peanuts, data were extrapolated to obtain these

results for averages.

The averages for 12 test dates times 10 species, or 120 tests per

storage condition, are as follows: At 26.6° C, with relative humidities of

78, 66, and 44 percent, the respective average germinations were 55.4,

78.9 and 81.3 percent. At 10°, with relative humidities of 81, 66, and 51

percent, the respective average germinations were 80.7, 82.6, and 82.6

percent. In some respects these results do not reveal the true situations

for the following reasons: (1) The storage period was not long enough to

measure deterioration of long-storing species, such as tomato or several

other species at the more favorable storage conditions, e.g., 10° and

51-percent relative humidity. (2) Averaging species such as onion, with

a short storage life, with tomato cancels out the extremes of both

species. For example, the percent germinations of these two species on

the 251st day of storage at 26.6° and relative humidities of 78, 66, and 44

percent were, respectively, onion, 0.1, 37.4, and 72.9 percent and

tomato, 68.1, 85.0, and 91.8 percent.

Since seed deterioration is affected by moisture content, it is important to know what factors affect water absorption and retention as well

as their effects. Obviously the thickness, structure, and chemical composition of the seedcoat affect the rate of water absorption and retention by seeds; in hard seeds the seedcoat restricts total water uptake. Of

the various seed constituents, proteins are most hygroscopic (readily

taking up and holding moisture), carbohydrates are slightly less so, and

the lipids are hydrophobic (lacking an affinity for water). Thus, seeds

containing relatively high percentages of carbohydrates, proteins, or

both, such as rice, other grains, and soybeans, can have moisture

contents of about 13-15 percent at 25° C and 75-percent relative

humidity, whereas cottonseed, flaxseed, and peanuts, which are rich in

oil, would have moisture contents of approximately 9-11 percent at the

same temperature and relative humidity (Barton, 1941). Barton found

that seeds of flax, lettuce, onion, peanut, pine, and tomato showed

differential water absorption and each species retained its same position

relative to other species in all her experiments.

Conceivably a sample of seeds containing both living and dead seeds

might take up a different amount of water than a sample of only live

seeds or, alternatively, all dead seeds. In studies of this phenomenon by

Atkins (1909), Heinrich (1913), Barton (1941), and Simpson and Miller

(1944), all agreed that under storage conditions the total moisture
PRINCIPLES AND PRACTICES OF SEED STORAGE 37

uptake and retention do not differ between living and dead seeds. Seeds

used included bean, cotton, flax, lettuce, onion, peanut, perennial

ryegrass, pine, and sweetpea.

One of Harrington's (1960d) so-called Thumb Rules of drying seed

stated that for each 1-percent reduction in seed moisture content, the

time the seed can be stored without seriously affecting germination is

approximately doubled. Harrington (1972) also indicated that this rule

applies when seed moisture content is between 5 and 14 percent.

Roberts (1972) developed formulas relating temperature and seed

moisture content to the storage life of seeds and indicated that Harrington's (1960, 1972) rule agreed with his formulas. However, Roberts

(1972) pointed out that possibly there are inaccuracies in his own

formulas for both seed moisture content and temperature and suggested that the same may be true for Harrington's (1960, 1972)rule. On

the other hand, both Harrington (1960, 1972) and Roberts (1972) stated

that their procedures give approximate results only.

The doubling of the lifespan of seeds by decreasing the moisture

content by 1 percent shows vividly the effects of slight moisture

changes, especially at the critical point. In sealed storage the expected

life of vegetable seeds with an 8.0-percent moisture content could be

doubled by removing 1.0-percent moisture before sealing. On the other

hand, certain possible pitfalls should be understood and considered

when working near the critical moisture level. Some of these are—

(1) The degree of confidence by which an aliquot of seed tested for

moisture represents the lot or bulk.

(2) The degree of accuracy in grinding, drying, and weighing.

Usually the air-oven methods are accurate to no more than ±0.1

percent.

(3) The possible variation in seed moisture content among different

lots or crops. This can result from differences in chemical composition of

the seed caused by different climatic conditions and cultural practices

during seed development and maturation.

(4) The hysteresis effect, a phenomenon when at a given relative

humidity the equilibrium moisture content of grain and seeds may not

always be the same. When seeds lose water and reach equilibrium at

any stated relative humidity, the equilibrium moisture content of the

seeds may be higher than if dry seeds are allowed to gain moisture to

reach equilibrium at the same relative humidity. This means that seeds

with a moisture equilibrium value of about 12.5 percent at a relative

humidity of 60 percent could possibly have two moisture equilibrium

values depending on whether the original seed moisture content was

greater or less than 12.5 percent. Hlynka and Robinson (1954) showed a

difference of about 4.5 percent at a relative humidity of 40 percent for

wheat but no difference at 90-percent relative humidity. Hubbard et al.
38 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

(1957) found adsorption equilibrium values for corn and wheat to be

approximately 1.6 percent higher than desorption values at 33- and

22-percent relative humidity, respectively.

The most common method of determining the moisture content of

seeds is to heat them in a forced air oven at a given temperature for a

specified time or until constant weight is obtained. The loss of water

represents the moisture content of the seeds. The percentage of moisture can be calculated (1) by the wet weight method—the amount of

water lost is divided by the initial weight of the sample, and (2) by the

dry weight method—the amount of water lost is divided by the dry

weight of the sample after drying. Since the original weight in (2) is

divided by a smaller number than in (1), the answer will be greater for

(2). Thus, in equivalent situations dry weight percentages will be

slightly greater than wet weight percentages.

Percentages of moisture based on dry weight are frequently used in

research and percentages based on wet weight are usually used for

commercial purposes. Seedsmen and seed testing laboratories (Assoc.

Off. Seed Anal., Internatl. Seed Testing Assoc, and Soc. Com. Seed

Tech.) use the wet weight method to determine seed moisture content.

Many U.S. scientists also use this method. However, if the basis for

calculating the percentage of moisture is not stated in the literature, it

is risky to assume that a specific procedure was followed.

Relationship Between Relative Humidity and Seed Moisture

Content

As previously mentioned, the moisture percentages of seeds in equilibrium with a specific relative humidity vary with crop species. At any

temperature air will hold a given amount of water in the form of vapor.

When the air contains all the moisture it will hold, it is said to be

saturated, which is equivalent to the dewpoint or 100-percent relative

humidity. Ordinarily the air is not saturated but contains only a fraction

of the amount of water it would hold if saturated. Relative humidity

reflects the amount of moisture actually in the air as a percentage of the

amount of moisture that the air is capable of holding at the same

temperature. Thus, relative humidity, expressed as a percentage, is

determined as follows: The amount of moisture in the air is divided by

the amount of moisture the air is capable of holding at the same

temperature and multiplied by 100. Warm air can hold more water than

cool air. Thus, if the amount of water in the air is held constant and the

temperature is increased, the relative humidity will be decreased.

Conversely, if the temperature of the air is lowered, the relative

humidity will be increased.

The importance of seed moisture content in retarding seed deterioration cannot be overemphasized. Under all storage conditions the
PRINCIPLES AND PRACTICES OF SEED STORAGE 39

moisture content of the seed will come to equilibrium with the surrounding air if given enough time. In fact, equilibrium is reached

between the seeds and the air in the interstitial spaces among the seeds.

It has been reached when the net movement of moisture from air to

seed, or from seed to air, is zero.

Equilibrium moisture content of seeds is usually determined by the

static method. By this method seeds are placed in containers to hold the

seed sample and acids or dissolved chemicals to provide previously

calculated relative humidities. The containers must be absolutely sealed

from the outside atmosphere and preferably allow entry to measure the

relative humidity of the air. Laboratory desiccators are commonly used

for this purpose. The seeds remain in the container with a known air

relative humidity until equilibrium is reached, after which the seed

moisture content is determined by a reliable method (Hlynka and

Robinson, 1954).

Since the static method may require from a few days to 2-3 months

for seeds to reach equilibrium moisture content with the atmosphere,

another method that reduces this time interval has been developed. By

the dynamic method the air is kept in motion and circulated around the

sample. In one modification of the procedure, the air is passed through

absorption towers, which contain solutions of salts and acids calculated

to control the relative humidity surrounding the seeds. In addition.

Brewer and Butt (1950) found an electric hygrometer to be a useful

instrument for determining equilibrium moisture values within 24 to 72

hours. This is basically a desorption method. Seeds of known moisture

contents are placed in sealed containers with dry air for a specific time.

Thus, moisture moves from the seed to the air in the container. The

relative humidity of the air is determined with the electric hygrometer,

a hair hygrometer, or other means. According to the authors, their

results compared favorably with those obtained by the static method

previously described. The electric hygrometer has the disadvantage of

requiring seed of a wide range of moisture contents, some below the

ambient relative humidities.

Haynes (1961) described a vapor pressure method for determining

seed hygroscopicity. He plotted hygroscopic curves for several seed

species from his data. His curves appear similar to those plotted from

data obtained by the static method. The method has several disadvantages and limitations. For these reasons and because it has not been

widely accepted, it is not described here.

Hygroscopic equilibrium measurements are usually reported as having been made at 25° C, although exceptions are common. The percentage of moisture the seeds attain at a given relative humidity, usually at

25°, is known as the moisture content equilibrium.

The equilibrium moisture content of several crop species at different
40 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

relative humidities is given in tables 5-9. In tables 7-8, only limited data

were available for forage seeds and most were developed for special

conditions. Dexter (1957) used relatively high humidities to study the

effects of mold formation on equilibrium moisture values for seeds of

several forage species, whereas Harrington (1%8) used low humidities

for applications relating to safe sealed storage for at least 3 years.

Unfortunately discrepancies exist between Harrington^s (1968) data at

45-percent relative humidity and Dexter's (1957) data at 55-percent

relative humidity and to some extent at 65-percent relative humidity.

Nevertheless these are the best available tables for forage seeds.

Although the data should not be regarded as exact equilibrium moisture

values, especially for research purposes, they can be used safely as

general guides.

TABLE 5.—Equilibrium moisture content of vegetable seeds at various

relative humidities and approximately 25"" C - wet basis^

Moisture content at indicated relative humidity (percent)

Vegetable

10 20 30 45 60 75 80

Percent Percent Percent Percent Percent Percent Percent

Bean, lima 4.6 Q.Ç, 1.1 9.2 11.0 13.8 15.0

Bean, snap 3.0 4.8 6.8 9.4 12.0 15.0 16.0

Beet, garden 2.1 4.0 5.8 7.6 9.4 11.2 15.0

Broad bean 4.2 5.8 7.2 9.3 11.1 14.5 17.2

Cabbage 3.2 4.6 5.4 6.4 7.6 9.6 10.0

Cabbage, Chinese _ 2.4 3.4 4.6 6.3 7.8 9.4

Carrot 4.5 5.9 6.8 7.9 9.2 11.6 12.5

Celery 5.8 7.0 7.8 9.0 10.4 12.4 13.5

Corn, sweet 3.8 5.8 7.0 9.0 10.6 12.8 14.0

Cucumber 2.6 4.3 5.6 7.1 8.4 10.1 10.2

Eggplant 3.1 4.9 6.3 8.0 9.8 11.9

Lettuce 2.8 4.2 5.1 5.9 7.1 9.6 10.0

Mustard, leaf 1.8 3.2 4.6 6.3 7.8 9.4

Okra 3.8 7.2 8.3 10.0 11.2 13.1 14.5

Onion 4.6 ^.S 8.0 9.5 11.2 13.4 13.6

Onion, Welsh 3.4 5.1 6.9 9.4 11.8 14.0

Parsnip 5.0 6.1 7.0 8.2 9.5 11.2

Pea 5.4 7.3 8.6 10.1 11.9 15.0 15.5

Pepper 2.8 4.5 6.0 7.8 9.2 11.0 12.0

Radish 2.6 3.8 5.1 Q.S 8.3 10.2

Spinach 4.6 6.5 7.8 9.5 11.1 13.2 14.5

Squash, winter 3.0 4.3 5.6 7.4 9.0 10.8

Tomato 3.2 5.0 6.3 7.8 9.2 11.1 12.0

Turnip 2.6 4.0 5.1 6.3 7.4 9.0 10.0

Watermelon 3.0 4.8 6.1 7.6 S.S 10.4 11.0

1 Data from Harrington (1960c) except last column from Toole (1942).
PRINCIPLES AND PRACTICES OF SEED STORAGE 41

TABLE 6.—Adsorbed equilibrium moisture content of grain seeds at

various relative humidities and approximately 25'' C—wet basis^

Moisture content at indicated relative humidity (percent)

Grain

15 30 45 60 75 90 100

Percent Percent Percent Percent Percent Percent Percent

Barley 6.0 8.4 10.0 12.1 14.4 19.5 26.8

Buckwheat 6.7 9.1 10.8 12.7 15.0 19.1 24.5

Corn shelled, white

dent 6.6 8.4 10.4 12.9 14.7 18.9 24.6

Corn shelled, yellow dent 6.4 8.4 10.5 12.9 14.8 19.1 23.8

Oats 5.7 8.0 9.6 11.8 13.8 18.5 24.1

Popcorn, shelled __ 6.8 8.5 9.8 12.2 13.6 18.3 23.0

Rice 5.9 8.6 10.7 12.8 14.6 18.4

Rye 7.0 8.7 10.5 12.2 14.8 20.6 26.7

Sorghum 6.4 8.6 10.5 12.0 15.2 18.8 21.9

Wheat, durum ___ 6.6 8.5 10.0 11.5 14.1 19.3 26.6

Wheat, hard red

spring 6.8 8.5 10.1 11.8 14.8 19.7 25.0

Wheat, hard red

winter 6.4 8.5 10.5 12.5 14.6 19.7 25.0

Wheat, soft red

winter 6.3 8.6 10.6 11.9 14.6 19.7 25.6

Wheat, white 6.7 8.6 9.9 11.8 15.0 19.7 26.3

1 Adapted from Amer. Soc. Agi*. Engin. ASAE ID 245, "Moisture Relations of Grains"

(ASAE Handb., 1972).

The sigmoid shape of a typical curve relating relative humidity to

seed moisture content is shown in figure 3. The curve was derived from

average moisture contents and relative humidities of seeds of 10 vegetable crop species by Nakamura (1958), Because the seeds of each

species have their own moisture-absorbing and moisture-holding potentialities, these curves can be expected to vary to some extent.

Tables 5-9 take into consideration the kinds of seeds and relative

humidity, but they have not been calculated to correct for temperature.

Most research relating to temperature effects has shown that as temperature is increased when seeds are held at a constant relative humidity, the seed moisture content is decreased. Among the researchers who

showed the relationship of temperature to seed moisture equilibrium

were Gane (1941), Gay (1946), Henderson (1952), Thompson and Shedd

(1954), Hogan and Karon (1955), and Hubbard et al. (1957).

Toóle et al. ("i94^^ published the seed moisture content of 15 vegetable

species stored at 3 relative humidities and 3 temperatures. The results

obtained at about 80-percent relative humidity and 11. T, 21.7°, and

26.7° C permit a comparison of temperature effects. In every instance
42 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

TABLE 7.—Equilibrium moisture content of seeds of grasses and

small-seeded legumes at relative humidities below 50 percent and

approximately 25° C—wet basis^

Crop

Moisture content at indicated relative

humidity (percent)

15 30 45

Percent Percent Percent

_ 6.3 8.2 10.2

6.3 8.2 10.2

_ 6.3 8.4 10.5

- 6.8 9.3 11.8

_ 6.2 8.2 10.1

- 7.1 9.1 11.0

_ 6.6 9.0 11.5

. 5.9 7.8 9.7

6.5 8.7

8.7

8.7

8.7

10.9

6.5 10.9

6.5 10.9

_ 6.5 10.9

_ 6.2 8.1 9.9

_ 6.0 8.0 10.0

7.0 8.7

8.6

10.5

_ 6.5 10.7

_ 6.5 8.6

8.3

10.7

_ 6.1 10.6

_ 5.2 7.3 9.4

_ 6.1 8.1

6.5

10.1

4.5 8.6

. 5.9 7.8 9.7

_ 5.9 7.8 9.7

_ 6.1 7.9 9.7

, 5.9 8.0 10.1

_ 5.9 7.8 9.7

_ 5.7 7.6 9.4

_ 5.2 7.2 9.2

_ 6.6 8.4 10.3

. 4.3 5.7 7.0

_ 5.1 6.9 8.7

_ 5.4 7.2 9.0

. 5.9 7.6 9.3

Grasses

Bentgrass, Colonial

Bentgrass, creeping

Bermudagrass, hulled

Bermudagrass, unhulled

Bluegrass, Kentucky

Bluegrass, rough

Bromegrass, smooth

Dallisgrass

Fescue, Chewings

Fescue, creeping red

Fescue, meadow

Fescue, tall

Hardinggrass

Orchardgrass

Redtop

Ryegrass, annual

Ryegrass, perennial

Sorghum, hybrid Ute

Sudangrass, hybrid

Wheatgrass, intermediate

Small-seeded legumes

Alfalfa

Birdsfoot trefoil, broadleaf

Birdsfoot trefoil, narrowleaf

Clover:

Alsike

Crimson

Ladino

Red

Rose

Strawberry cv. Palestine

Strawberry cv. Salina

Subterraneum

White

Sweetclover, yellow-blossom

1 Adapted from Harrington (1968).

the seed moisture content at 21.7° and at 26.7° was lower than at 11.1°.

However, without exception the moisture content at 26.7° was higher

than at 21.7°. The authors indicated that they had no explanation for
PRINCIPLES AND PRACTICES OF SEED STORAGE 43

TABLE 8.—Equilibrium moisture content of seeds of grasses and

small-seeded legumes at relative humidities above 50 percent and

approximately 23"" C—wet basis^

Moisture content at indicated relative

humidity (percent)

Crop

55

Grasses Percent

Bentgrass, Colonial 9.8

Bluegrass, Kentucky 9.7

Bluegrass, rough 9.4

Bromegrass, smooth 11.0

Canarygrass, reed 11.4

Fescue, Chewings 10.0

Fescue, creeping red 10.7

Fescue, tall 10.5

Orchardgrass 9.8

Redtop 10.0

Ryegrass, annual 11.0

Ryegrass, perennial 11.0

Sudangrass, piper 10.8

Timothy 10.9

Small-seeded legumes

Alfalfa

Clover:

Alsike

Ladino

Red

Crownvetch

Sweetclover, yellowblossom

Trefoil, birdsfoot

Vetch, hairy

1 Adapted from Dexter (1957).

65 70 75 80 85

Percent Percent Percent Percent Percent

10.7 11.5 12.5 14.0 14.5

10.8 11.3 12.7 14.3 16.4

11.9 13.9 16.2

12.5 13.1 13.7 16.1 18.4

12.0 12.5 13.5 14.7 15.7

11.2 12.1 14.5 16.9

11.9 12.6 13.8 15.4 18.0

11.9 12.5 13.2 15.0 17.3

10.5 11.0 12.0 13.4 14.9

10.7 11.0 12.5 13.5 15.0

12.1 12.8 14.1 15.7 16.3

12.1 12.8 13.4 14.9 16.6

11.8 14.4 15.6

11.8 12.5 13.6 14.6 16.1

7.8 9.3 12.5 18.3

9.3 15.9 18.9

8.7 10.9 15.4 18.0

9.1 11.2 15.6 18.7

9.4 --- 14.2 18.1

9.3 10.8 12.7 18.3

8.3 10.4 13.9 17.2

11.0 13.0 17.4 18.7

this disparity except possibly "the humidity readings in these chambers

failed to represent the true humidity surrounding the seeds." The

authors pointed out that "the study was not planned to determine the

effect of temperature on moisture content of seed, because the recorded

mean air humidities may not accurately indicate the true conditions

surrounding the seeds." Regardless of the accuracy of the individual

values recorded by Toole et al., the data for 15 vegetable species

strongly indicate that as temperature is increased, equilibrium moisture

content is decreased.

By reducing the results reported by some of these investigators to a

common denominator, the following average values were calculated:

Average decrease in equilibrium moisture content for each 10° C
TABLE 9.—Equilibrium moisture content ofseeds ofseveral crops at various relative humidities and approximately 12° to 25° C^

Moisture content at indicated relative humidity (percent)

Crop —

^Q 20 30 40 50 60 70 80 90 100

Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent

Broadbean 4.7 6.8 8.5 10.1 11.6 13.1 14.8 17 2 22 6 +27 5

Cotton 3.7 5.2 6.3 6.9 7.8 9.1 10.1 12.9 19 6

Flax 3.3 4.9 5.6 6.1 6.8 7.9 9.3 11.4 15 2 214

Lupine 4.2 6.2 7.8 9.1 10.5 11.7 13.4 16.7 +25 0

P^^ 5.3 7.0 8.6 10.3 11.9 13.5 15.0 17.1 22 0 26 0

Peanut 3.0 3.9 4.2 5.1 5.9 7.0 8.5 111 17 2

Rape 3.1 3.9 4.5 5.2 6.0 6.9 8.0 9.3 12^1 +15 5

Soybean --- 5.5 6.5 7.1 8.0 9.3 11.5 14.8 18 8 ---

Sugar beet 4.4 6.3 8.0 9.4 10.7 12.0 13.3 16.6 20.5 22.5

•Compiled from Hall (1957X Karon and Hillery (1949), Kreyger (in Owen, 1956), and Simpson and Miller (1944X

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PRINCIPLES AND PRACTICES OF SEED STORAGE 45

25 r

20 •

o

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LU

^ 15

UÜ

ce

D

i 10

û

LU

LU

00

/

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20 40 60 80

RELATIVE HUMIDITY (PERCENT)

100

FIGURE 3.—Relationship of atmospheric relative humidity and seed moisture content of

vegetable seeds. (Courtesy of Nakamura, 1958.)

increase in temperature—wheat 0.65 (Gane, 1941), 0.43 (Gay, 1946),

wheat and corn 0.72 (Thompson and Shedd, 1954), 0.73 (Hubbard et al.,

1957), blue lupine0.90, comlA,. crimson clover0,62, and sorghumO.S

(Haynes, 1961). Using the data of Toole et al. (1948) tor 15 species of

vegetable seeds stored at approximately 80-percent relative humidity,

the average difference per 10° calculated for storage temperatures of

11.1° and 26.7° amounted to 0.21-percent moisture content. For most of

these crops these relative humidity values do not change greatly as the

temperature is increased or decreased. Although the moisture content

of the seeds increases v/ith an increase in relative humidity, these

values are not greatly affected by temperature.

The slight effect of temperature on seed moisture content is illustrated in figure 4 for sorghum and wheat. Although the curves for these

two species are different, the lines for the different temperatures are

parallel, indicating a continuing relationship as humidity is increased.

These relationships do not hold true in all instances. Curves for corn and

rescuegrass seed (fig. 4) show how the curves can deviate as humidity is

increased. For corn, the equilibrium moisture content decreases 0.96

percent for each 10° C increase at 30-percent relative humidity, but at

70-percent relative humidity it decreases 2.3 percent for each 10°

increase. At a relative humidity of about 56 percent the seed moisture

content of rescuegrass seed is the same at -1° and at 49°. As the
46 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

30

25

20

15

10

Û

UJ

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-1°C

16°C

32° C

49° C

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10 20 30 40 50 60

RELATIVE HUMIDITY (PERCENT)

70 80 90

30

25

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10 20 30 40 50 60

RELATIVE HUMIDITY (PERCENT)

70 80 90

FIGURE 4.—Equilibrium relative humidity curves for sorghum, wheat, corn, and rescuegrass (top to bottom). (Courtesy of Haynes, 1961. )
PRINCIPLES AND PRACTICES OF SEED STORAGE 47

30

25

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ce

: 20

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10 20 30 40 50 60 70

RELATIVE HUMIDITY (PERCENT)

80 90

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10 20 30 40 50 60 7Ö

RELATIVE HUMIDITY (PERCENT)

80 90

FIGURE 4.—Equilibrium relative humidity curves for sorghum, wheat, corn, and rescuegrass (to^ to bottom) (Courtesy of Haynes, IP^i.)—Continued.
48 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

relative humidity is decreased below about 54 percent, the seeds at 49°

hold less water than seeds at -1°. The difference at 25-percent relative

humidity is approximately 0.2-percent moisture for each 10°. On the

other hand, as the relative humidity is increased above 56 percent, the

seeds hold more water at 49° than at -1°. The difference at 80-percent

relative humidity amounts to approximately 0.44-percent moisture for

each 10° change.

Rate of Moisture Absorption and Movement

Studies on moisture absorption and movement in grains and seeds fall

into three categories: (1) Laboratory studies on small samples, (2)

studies on bulk samples of a few pounds to several tons, and (3) studies

on moisture movement of mixed grain with different moisture contents.

For information on moisture movement in grain, see Fisher and Jones

(1939X

Much of the research on equilibrium moisture in small seed samples

has been concerned with ascertaining the time required for the seed to

reach equilibrium. This is regulated by the time required for moisture

(1) to penetrate the seedcoat and (2) to transfer within the seed, based

on the assumption that the relative humidity surrounding the seeds is

uniformly distributed. Since seeds of different species differ as to

seedcoat permeability to moisture, as well as constituents of the endosperm and embryo, it is only logical that the time required to reach

equilibrium moisture will vary with the species.

Dillman (1930) found that dry flaxseeds absorbed hygroscopic moisture more rapidly than wheat seeds, which absorbed moisture more

rapidly than alfalfa seeds. Likewise, Pixton and Warburton (1968)

reported similar results with the soft wheat cultivar Cappelle, which

reached 90-percent equilibrium moisture content in less time than did

the hard wheat cultivar Manitoba.

Temperature also affects the rate of water absorption. Dillman (1930)

found the absorption by dry corn, flax, and wheat seed to be twice as

rapid at 30° C as at 10° but no change from 30° to 40°. Whitehead and

Gastier (1946^7) determined that at 20- to SO-percent relative humidity, sorghum and wheat seeds reached equilibrium moisture content

within 15 days at 20°, whereas nearly 70 days were required at 1°.

The difference between the vapor pressure of the seeds and that of

the surrounding atmosphere is an extremely important factor in determining the rate of moisture movement. For example, if rice of 13-percent moisture content is placed in an atmosphere of 95-percent relative

humidity, it will increase in moisture content faster than at 70-percent

relative humidity. Likewise, the rice will lose moisture more rapidly if

placed at 20- than at 50-percent relative humidity.

Pixton and Warburton (1968) measured the rate of hygroscopic
PRINCIPLES AND PRACTICES OF SEED STORAGE 49

moisture absorption of two cultivars of wheat at relative humidities

from 35 to 90 percent. They found that the time required to reach

equilibrium moisture was neither a gradual progression from 35- to

90-percent relative humidity (absorption) nor a gradual degression from

90 to 35 percent (desorption). Rather, equilibrium was reached in the

following order of relative humidity percentages, with the first number

being the fastest rate:

AbsorptionrSb, 45, 80-90, 60-80

Desorptionr-85-90, 60-80, 35, 45

Moisture uptake is rather rapid for the first 2 to 3 days for many kinds

of seeds, after which it decreases. According to Babbitt (1949)^ wheat,

whole or with pericarp and seedcoat removed, reached near equilibrium

moisture content within 40 hours and the increase thereafter was slow.

Results reported by Pixton and Warburton (1968) for wheat more or

less confirmed Babbitt's report. They found that 90 percent of equilibrium moisture content was reached within 5-14 days by absorption and

2-9 days by desorption. On the other hand, Bréese ("7955^ indicated that

at a relative humidity from 10 to 90 percent, rough rice required at least

60 days to reach equilibrium moisture. Small samples of chaffy grass

seeds appeared to come to equilibrium moisture content within 3-5 days

over a wide range of relative humidity (Dexter, 1957). Harrington and

Aguirre (1963) dried seeds of six vegetable species to near 0-percent

moisture content and placed them in a saturated atmosphere. After 64

hours they had regained moisture to reach the following moisture

percentages (wet weight basis): Onion 9.4, carrot 9.4, cabbage 8.3,

tomato 8.1, lettuce 8.0, and muskmelon 7.5.

Caution should be exercised in placing much confidence in data

obtained at high relative humidity, especially when observed over long

periods of time. Under these conditions, the changes in weight of

samples may be affected not only by changes in water content of the

seeds but also by the growth of micro-organisms and by respiration.

Movement of moisture into or out of bulk grain or seed is very slow.

The time for moisture to enter and be distributed within a seed is only a

small fraction of the time required for it to move through a mass of

seed. Instead of the moisture moving from seed to seed or from grain to

grain, it penetrates the mass through the interstitial airspaces among

the seeds. The movement has been measured. Equilibrium was reached

in wheat at a depth 1 inch below the surface after 400 hours (Babbitt,

1949). Seeds of the six species of vegetables used by Harrington and

Aguirre (1963), previously discussed, had an average moisture content

of 8.5 at the surface of the bulk after 64 hours but only 0.7 percent 3

inches below the surface. Frey (1960) found seeds of wheat and birdsfoot trefoil at the center of 100-kg bags to contain 2-4 percent more

moisture than seeds taken from the surface just inside the walls of the
50 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

jute bags. The seeds had been stored at five temperature-relative

humidity conditions prior to sampling.

These data show how slowly seeds and grain at the center of large

bulks come to equilibrium moisture content. Were this not so, large

bulks of grain within or outside of enclosures could not be stored safely.

Although the relative humidity surrounding a bin of grain may change

gradually or abruptly, the outer layers of the grain insulate the inner

layers to a degree. Each layer forms a temporary barrier, which

mediates the change of relative humidity in the next layer. With

continuing high humidity, the barrier is pushed farther toward the

center of the bulk until equilibrium is reached in the entire lot.

A difference in temperature between two areas or zones of a storage

bin or silo can cause seed or grain to deteriorate. When warm air moves

to a colder zone and becomes chilled to the dewpoint, the moisture in the

air is deposited on the seeds as liquid. This situation can exist when

seeds lie in a zone between a cold outside wall of a storage structure and

the interior core where the temperature is higher. Christensen (1970)

demonstrated this principle by using grain sorghum with a moisture

content of 14.3 percent. A temperature difference of 12°-14° over a

distance of 6--8 inches resulted in rapid transfer of moisture from the

warmer to the cooler part of the grain. The grain where moisture

accumulated became heavily infested with storage fungi and decayed.

Equilibrium moisture content was attained within 12 days.

Effect of Extreme Desiccation on Viability and Vigor

Since increased knowledge and improved technology have promoted

the drying of seeds to very low moisture levels for storage, shipment, or

both in sealed containers, it is important to know whether the drying

process causes losses in viability and vigor. There are essentially no

reports of seed damage caused by drying to approximately 6-percent

moisture content, but several workers have reported damage when

seeds were dried to 5 percent or lower. Toole and Toole (1946) reported

an increase in abnormalities of soybean seedhngs grown from seeds

stored for 3 months at a moisture content slightly above 5 percent.

Abnormalities consisted primarily of deep cracks across the cotyledons

that interfered with using the stored food reserves.

Roberts (1959) found that timothy seed retained its viability better in

storage as its moisture content was decreased to about 7 percent, but

storage at 5 percent decreased viability. Ching et al. (1959) found a

similar trend with perennial ryegrass seeds. At 6-percent moisture

content they did not retain their viability as well as at 8.3 percent.

Apparently caution must be exercised in storing seeds of some

cultivars of cotton, sorghum, and various other crop species at very low

seed moisture contents. Phillis and Mason (1945) reported that as the
PRINCIPLES AND PRACTICES OF SEED STORAGE 51

relative humidity of the storage atmosphere was decreased below 40

percent, germination capacity decreased after storage for 5 years at

24°-27° C. Seeds stored at 40-percent relative humidity germinated 75

percent, whereas seeds at 30-, 20-, and 0-percent relative humidity

germinated 70, 65, and 22 percent, respectively. Seed moisture content

ranged from 6.9, to 5.2, to near 0 at 40-, 20-, and 0-percent relative

humidity, respectively. Phillis and Mason (1945) found that by placing

the low moisture content seeds at a slightly increased relative humidity,

thus gradually increasing seed moisture content, they could overcome

the deleterious effects of desiccation.

Nutile (1964a, 1964b) found that sorghum seeds that had been dried

to 3.0- to 3.5-percent moisture content showed delayed germination and

produced seedlings with damaged radicles, which subsequently developed many secondary roots. However, he was able to overcome the

apparent injury by placing the dry seeds at 55-percent relative humidity

until their moisture content increased to 11 percent. Such preconditioned seeds germinated normally.

McCollum (1953), Pollock et al. (1969), and Pollock and Manalo (1970)

noted that cotyledon cracldng in garden bean seeds can be caused by

stresses during imbibition and germination as well as by mechanical

means. Very dry bean seeds that developed high percentages of cotyledon cracking with rapid imbibition developed less cracking when

allowed to gradually absorb moisture to about 12 percent before imbibition.

Much of the damage previously considered as desiccation and mechanical damage appears really to be stress damage. If so, seeds can be

dried to very low moisture levels for safe sealed storage, but sensitive

kinds may require special handling prior to planting. Seeds dried to a

very low moisture content for sealed storage apparently must be

allowed to equilibrate with normal atmospheric conditions before

planting except in very arid areas, where special slow imbibition techniques will have to be employed.

Seeds of some species that can be dried safely to 2- to 3-percent

moisture content are injured when dried to about 1 percent or lower. At

such low moisture content the first indication of injury is reduced rate of

germination, followed in storage experiments by decreased germination. With severe drying, the symptoms of injury may appear immediately after drying. As the critical point of damage is approached but not

reached, the symptoms will be apparent after storage. These generalizations are based on data by Harrington and Crocker (1918). Seeds of

Kentucky bluegrass reduced to 1.5-percent moisture content suffered

no loss either in germination capacity or in vigor. With 0.2-percent

moisture content no loss in germination was evident, but vigor was

reduced considerably, whereas at 0.1-percent moisture content germi-
52 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

nation capacity had dropped by 5 percent and vigor was seriously

reduced. Further reduction of the seed moisture content reduced the

germination percentage by one-half and all seedlings were very weak.

This trend has been found for seeds of several crop species but not all.

Effect of extreme desiccation on seed viability and vigor is shown in

table 10.

Went and Munz ("iP^ft) subjected seeds of 113 plant species native to

California to extreme desiccation over phosphorus anhydride (P2O5) and

sealed them under vacuum in small glass tubes. No tube was opened

until the appointed time for testing. After 1 year of storage, five species

had lost three-fourths of their germination capacity and some others

had declined to a less extent. It is not known whether this loss was due

to desiccation or to some other factor.

Based on current information, seeds of most crop species can be dried

to 2- to 3-percent moisture content without significant injury provided

injury is not caused by another factor associated with the drying

process, such as high temperature. However, drying below 3- to 4-percent moisture content is not recommended for storage of seeds in

commerce, because extremely dry seeds may be damaged by too rapid

rehydration when planted.

Symptoms of desiccation injury may not be apparent until after

storage. They include cracked cotyledons, damage to food transport

system in the embryo, stunted radicle with unusually heavy development of secondary roots, stubby primary root and shoot, protrusion of

radicle without further development, and decreased germination compared with nondamaged seeds. The last symptom is usually an excellent

indication of reduced vigor.

Another precaution to observe when drying seed is the possibility of

inducing dormancy. Nutile and Woodstock (1967) induced 10- to 25-

percent "low-temperature" dormancy in seeds of six sorghum cultivars

by drying. When placed to germinate at 15° C, dormancy was apparent,

but at 25° the blocks to germination did not exist. Species, and possibly

some cultivars, for which experimental data are not available might well

be treated as suspect.

Interrelationship of Temperature, Seed Moisture

Content, and Storage Life

To some degree both temperature and seed moisture content can be

controlled for practical storage. The nature and degree of control will

depend on the economics applicable to specific situations. These decisions may be affected by local climate and the quantity of seed to be

stored as well as by the length of storage.

Available data on storage of hempseeds demonstrate the effects of
TABLE 10.—Effect of extreme desiccation on seed viability and vigor of several crop species

Source Crop Seed moisture content

Comment

Percent

Harrington and Crocker (1918) Kentucky bluegrass Below 1

Barley- —^ 0.7-0.8

Sudangrass 0.5-0.6

Johnsongrass 0.1-0.2

Wheat About 1.0

Com (maize) Below 2.0

Chewings fescue Approximately

0.5

Perennial ryegrass 0.66

Kentucky bluegrass Below 1

Red fescue Below 1

Highland bentgrass Below 1

Onion Below 1

Cabbage Below 1

Cucumber Below 1

Lettuce Below 1

Green (1961).

Smith and Gane (1938)

Evans (1957b) .

Nutile (1964b) .

Discussed in text.

No injury from drying.

Do.

Slight decrease in germination.

No injury from drying.

Below 2-percent moisture

content, viability reduced in

direct relationship to length

of drying period.

Drying over phosphorus anhydride for 25 days did not

reduce germination significantly.

No immediate loss in viability,

but loss in vigor was apparent.

Severe injury after 5 years of

storage.

Do.

Little or no injury after 5

years of storage.

Do.

Do.

Do.

Do.

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TABLE 10.—Effect of extreme desiccation on seed viability and vigor ofseveral crop species—Con.

Ü1

4^

Source

Nutile (1964b)—Con.

Joseph (1929)

Went and Munz (1949)

QYQJ^ Seed moisture content

Percent

Carrot Below 1

Tomato Below 1

Celery Below 1

Eggplant Below 1

Pepper Below 1

Parsnip 0.4

Native plants of

California.

Comment

Medium injury after 5 years

of storage.

Do.

Severe injury after 5 years of

storage.

Do.

Do.

No indication of injury.

Discussed in text.

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PRINCIPLES AND PRACTICES OF SEED STORAGE 55

temperature and moisture on storage life. In 1950, seed lot 2 was grown

in Kentucky and seed lot 4 in Maryland, and in 1951 they were stored at

Beltsville, Md., until 1960-61, when they were transferred to the

National Seed Storage Laboratory, Fort Collins, Colo. The tests over

the first 5V2 years were made at Beltsville by Toole et al. (1960) and

those from 9 to 12 years of storage by Clark et al. (1963). Lot 2

represented healthy seed of strong vigor, which had a germination

capacity of 98 percent when stored. The viability of lot 4 when stored

was approximately 88 percent. There was no significant loss in germination of lot 2 stored in sealed containers at 6.2-percent moisture.

Unfortunately the data are not available for seed stored at 6.2-percent

moisture and 21° C beyond 5^2 years.

Table 11 shows the effect of seed moisture content, temperature, and

length of storage on seed germination. Seed lot 2 stored at 6.2-percent

moisture content and W C germinated 96 percent after 12 years,

whereas seed stored at 9.5-percent moisture content and 10° lost its

viability completely during the same period. Seed stored at 9.5-percent

moisture content and 10° required 11 years to reach 5-percent germination, but seed stored at the same moisture content and 21° required

only 2 years to reach this germination level. There is greater variation

among germination values for lot 4. This is common in seed lots of

declining viability or of low vigor. Otherwise the trends for moisture

and temperature effects are comparable for the two seed lots.

The effect on an oilseed crop, soybean, of a combination of high

temperature (30° C) and high moisture content (18.1 percent for Mammoth Yellow and 17.9 percent for Otootan) is given in table 12. Only 14

percent of the Mammoth Yellow seeds and none of the Otootan seeds

were viable after 1 month of storage. The high moisture content of both

cultivars stored at -10° caused little or no deterioration until after 72

months of storage. These data show that the viability of soybean is

maintained longer when stored at subfreezing temperatures than at 2°.

No seeds of either cultivar with 9.4- and 8.1-percent moisture content

decreased in viability when stored at -10°, 2°, or 10° for 10 years (cols.

2-4).

The results of an experiment with n}ne species of vegetable seeds and

peanut for storage periods of 110 and 250 days are given in table 13.

This table differs from tables 11 and 12 in that it is based primarily on

vegetable seeds, evaluates storage conditions by crop species and by

their averages, and concentrates on intermediate temperatures. Although the moisture contents at which the seeds were stored are not

shown in table 13, they can be estimated for the different crop species at

each humidity level by referring to tables 5 (veg.) and 9 (peanuts).

The average results for both storage periods show that as storage

temperature or storage relative humidity is increased the germination
56 AGRICULTURE HANDBOOK 506, U.S. DEPT. OFAGRICULTURE

TABLE 11.—Germination of 2 lots of hempseed stored in sealed containers at 8 temperature-moisture conditions for 12 years^

Germination at indicated seed moisture content and temperature (°C)

Storage —

period 6.2 percent 9.5 percent

(years)

-10 0 10 21 -10 0 10 21

Percent Percent Percent Percent Percent Percent Percent Percent

SEED LOT 2

0 98 98 98 98 98 ' 98 98 98

^ 98 96 97 98 99 98 98 97

1 96 99 97 98 98 95 94 64

2 96 96 97 97 98 97 95 5

3 93 97 98 95 98 95 93 0

4 97 98 98 97 98 98 91 0

5 98 96 97 93 98 99 84 0

5^ 93 96 98 98 97 96 65 0

9 --- 96 93 --- --- 97 13

10 92 94 96 --- 95 91 6 ---

11 93 94 96 --- 94 83 5 ---

12 97 98 96 --- 97 95 0 ---

SEED LOT 4

0 87 87 87 87 89 89 89 89

'^ 87 80 87 85 84 87 92 85

1 83 80 92 93 78 87 92 85

2 85 79 90 87 87 82 91 10

3 88 85 85 86 76 83 76 0

4 84 88 93 86 90 89 77 0

5 84 82 86 86 87 78 60 0

5^/^ 80 84 73 76 86 80 42 0

9 --- 82 86 --- --- 77 3

10 53 73 71 --- 58 51 l ._-

11 66 79 68 --- 63 50 1

12 64 69 66 --- 79 62 0 ---

iData from Toole et aL (1960) and Clark et aL (1963).

of the seeds is reduced. After 110 days the averages of seeds stored at

10° C and 81-percent relative humidity differed by only 0.6 percent from

those at 26.7° and 44-percent relative humidity. However, after 250

days the averages differed by 4.1 percent. The data for 44- and

78-percent relative humidity at 26.7° show that seeds of tomato retained

good germination longest and seeds of onion and peanut the shortest

time.

Barton (1939) in experiments with aster seeds over 3 years reported

on seed deterioration under several storage conditions. One of the most

important results in table 14 is the consistently high germination of the

seeds stored under controlled conditions of low temperature and low to

moderate seed moisture content compared to the relatively rapid de-
PRINCIPLES AND PRACTICES OF SEED STORAGE 57

terioration of seeds stored at ambient temperature and the same

moisture content.

Vacuum and Gas Storage

For many years research has been conducted on the effects of a

partial vacuum and such gases as carbon dioxide, oxygen, and nitrogen

on the longevity of various kinds of seeds. The reported results from

these studies are variable and in some instances appear contradictory.

This confusion undoubtedly results from the widely divergent test

methods employed by the various researchers. Because of the lack of

complete information on the test procedures used in numerous studies,

direct comparisons cannot be made between and among the various data

found in the literature. Likewise sealed storage cannot be directly

compared with open storage, because in sealed containers oxygen

concentration in the atmosphere decreases and the carbon dioxide

concentration increases with time (Harrington, 1963), whereas in open

storage the composition of the atmosphere remains constant. Because it

is not feasible to continually adjust the composition of the atmosphere in

sealed containers, most studies have not included gas analyses.

Some workers paid no attention to either seed moisture or storage

temperature, whereas others attempted to control one or the other.

Several used air-dry seeds and room temperature, both of which

provide a minimum of information about the conditions actually used.

Regardless of the kind of seed, the air-dry moisture content in one

geographic area is not necessarily the same as that in another. Likewise

room temperature is not consistent from place to place nor from month

to month, or even from day to day in most localities. To accurately

assess the protective value of either a partial vacuum or a gas, all

environmental conditions have to be considered. Reports on a few kinds

of seeds will illustrate the variable results in the literature.

Barley

The higher the oxygen content of the storage environment, the

shorter the viability period for barley seeds (Roberts and Abdalla,

1968). The deleterious effects of oxygen are produced at relatively low

oxygen concentrations and are most pronounced at the higher seed

moisture levels.

Corn

Since the seedsman wants to store his seeds at the highest practical

moisture level and temperature, Goodsell et al. (1955) stored seed of

two corn hybrids at approximately 8-, 10-, 12- and 14-percent moisture

sealed in air, carbon dioxide, and nitrogen at approximately -18°, 4°,

16°, and 29° C. Generally the average pooled germination of the two
1 ABLE IZ.—6'6ed gemiznatt07I of 2 S oybean «cultivai^s storciiatSnloisture conteriits and i5 temperaturesÎ for 10 years ^ S

Storage Germination at indicated moisture content and temperature (°C)

period

(months)

-10

Reduced moisture 2

2 10 20 30

Natural moisture 3 High moisture 4 >

Q

-10 2 10 20 30 -10 2 10 20 30

2

0

Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent i

MAMMOTH YELL0W5 50

1 ___ --- --- ---... 97 99 98 97 93 14

3 98 98 96 96 97 96 97 96 99 87 98 94 91 96 0 >

0

5 ___ 96 94 93 97 96 96 94 95 98 0 97 98 96 85

9 91 89 89 99 95 93 94 98 97 94 96 94 0 0

12 ___ 93 93 95 99 87 93 95 98 93 96 97 88 W

24 ___ 96 94 98 96 0 96 97 96 0 99 97 1 i

48 ___ 94 96 99 89 98 96 88 95 81

in 72 ___ 99 97 96 70 97 98 39 89 0 ...

96 ___ 95 94 93 47 98 95 19 70 a

120 ___ 92 95 94 0 ___ 98 90 0 17

OTOOTAN 5 3

1 ___ 94 93 92 91 92 0

0

3 ___ 92 93 88 90 88 94 90 95 94 64 94 94 95 79 >

5 ___ 92 90 94 94 89 91 94 92 93 18 94 90 89 0 2

9 93 89 90 96 92 93 91 94 88 0 94 92 89 0

12 ___ 94 94 88 95 91 89 93 92 73 96 92 76 5

24 ___ 90 93 88 92 74 93 95 93 0 92 88 0

48 ___ 89 95 95 88 1 90 93 85 83 30

72 ___ 91 98 93 86 0 94 92 15 93 0

96 ___ 94 96 94 79 98 94 0 27

120 ___ 94 93 95 68 98 91 ... ... ... 44 ... ... ... ...
iData from Toóle and Toóle (1946).

2Mammoth Yellow 9.4 and Otootan 8.1 percent.

3Mammoth Yellow 13.9 and Otootan 13.4 percent.

^Mammoth Yellow 18.1 and Otootan 17.9 percent.

5 Mammoth Yellow 97- and Otootan 93-percent germination before storage.

TABLE 13.—Seed germination of 10 crops after 110 and 250 days of storage at 6 temperature-relative

humidity conditions^

Germination at indicated temperature and relative humidity2

Crop Germination

before

storage

10° C 26.7° C

51 percent 5 percent 81 percent 44 percent

Percent Percent Percent

AFTER 110 DAYS' STORAGE

88 83 80

60 75 59

87 85 93

71 89 90

90 88 89

66 58 66

75 61 79

71 76 60

72 73 76

90 90 92

QQ percent 78 percent

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Bean, kidney 97

Bean, lima 76

Beet 83

Cabbage 93

Carrot 93

Corn, sweet 82

Onion 80

Peanut 83

Spinach 73

Tomato 92

Average 85.0

Percent

68

87

93

90

62

74

375

80

93

Percent

81

65

SS

90

89

67

65

43

69

87

Percent

60

54

78

66

56

13

0

0

23

77

81.0 79.0 77.8 78.4 74.4 42.7

See footnotes at end of table.
TABLE 13.—Seed germination of 10 crops after 110 and 250 days of storage at 6 temperature-relative

humidity conditionsi—Continued

o

Germination at indicated temperature and relative humidity2

Germination

Crop before 10° C 26.7° C

storage

51 percent QQ percent 81 percent 44 percent 66 percent 78 percent

Percent Percent Percent Percent Percent Percent Percent

AFTER 250 DAYS' STORAGE

Bean, kidney 97 78 79 91 92 87 0

Bean, lima 76 58 69 61 47 61 26

Beet 83 85 81 87 88 79 9

Cabbage 93 92 92 88 91 89 1

Carrot 93 91 88 88 90 87 1

Corn, sweet 82 79 60 57 70 66 0

Onion 80 75 76 64 73 37 0

Peanut 83 70 68 49 58 29 0

Spinach 73 73 71 63 75 63 0

Tomato 92 91 91 87 92 85 68

Average 85.0 78.2 77.5 73.5 77.6 68.3 10.5

iData from Boswell et al. (1940).

2Percent germination adjusted to nearest whole number.

3 Correction made in original data based on 77-percent germination after 2^2 months' storage and 70 percent after 8^3 months' storage.

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PRINCIPLES AND PRACTICES OF SEED STORAGE 61

TABLE 14.—Germination of aster seeds after storage at 12 temperature-moisture conditions over 36 months^

Months

12 _

18 _

24 _

30 _

36 _

Germination at indicated seed moisture

Temperature

content (percent)

4.6 6.7 7.9 Ambient

°C Percent Percent Percent Percent

-5 90 88 85 87

5 87 88 80 72

Room 89 84 85 86

-5 87 88 87 86

5 91 90 91 64

Room 90 83 83 83

-5 85 79 87 82

5 83 80 84 46

Room 78 78 60 71

-5 66 71 68 72

5 68 71 56 4

Room 64 35 0 3

-5 84 86 85 82

5 84 87 87 0

Room 75 33 0 15

-5 90 92 91 86

5 91 93 89 0

Room 76 9 0 0

iData from Barton (1939). Seeds stored at room temperatures were sealed in glass

tubes; all others were sealed in tin cans; average germination at start of experiment

assumed to be 90-92 percent.

hybrids in the three storage gases was still 95 percent or better after 5

years for the seeds at 8-, 10-, and 12-percent moisture at -18° and 4°

and those containing 8- and 10-percent moisture at 16°. Seeds containing

12- or 14-percent moisture at 16° and those with 8- and 10-percent

moisture at 29° deteriorated rapidly after 1 year. Corn seeds containing

12- to 14-percent moisture were practically all dead after one-half to 1

year, regardless of the surrounding gas.

Sayre (1940) stored corn seeds with 18-percent moisture in oxygen,

carbon dioxide, and nitrogen at 30° C. The seeds in oxygen died within 3

years and the germination of the seeds in carbon dioxide and nitrogen

dropped noticeably. At low temperatures corn seeds with 18-percent

moisture sealed in carbon dioxide and nitrogen had good germination

for 5 years.

Struve« dried corn seeds to near 0-percent moisture, sealed them in

oxygen and in nitrogen, and stored them at -30° to 50° C. Seeds at -30°

«STRUVE, W. M. DRYING AND GERMINABILITY OF MAIZE. 1958. [Unpublished Ph.D.

thesis. Copy on file Dept. of Botany, Iowa State Univ., Ames.]
62 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

remained unchanged through 31 months, those at 50° in nitrogen

showed a progressive reduction in vigor, and seeds in oxygen died

within 7 months. He also stored corn seeds with 1-percent moisture

content in atmospheres containing 0-, 20-, 60-, and 100-percent oxygen

at 0°, 5°, 10°, 15°, 25°, 35°, and 50°. He concluded that oxygen concentration may become an important factor in the deterioration of corn

seeds in sealed storage.

Flower Seeds

Primula sinensis sealed in carbon dioxide declined only 30 percent in

viability over a 7-year period, whereas unsealed seeds lost all viability

(Lewis, 1953), Seeds of Salvia splendens deteriorated seriously when

sealed under a vacuum (Chopinet, 1952), Aster seeds kept equally well

when sealed in air or a partial vacuum (Barton, 1939). Sealing under a

partial vacuum had no advantage over sealing in air for maintaining the

viability of verbena seeds (Barton, 1939),

Barton (1960a) stored seeds of Lobelia cardinalis with 6.9- and

4.7-percent moisture in sealed glass vials in air, oxygen, carbon dioxide,

nitrogen, and vacuum and in open containers for up to 25 years at

laboratory temperature, 5°, and -5° C. In all cases, viability was lost

more rapidly at laboratory temperature than at 5° and -5° and at

6.9-percent than at 4.7-percent moisture. At laboratory temperature,

6.9-percent moisture seeds in air, open or sealed, lost viability rather

rapidly. Seeds sealed in oxygen lost viability even more rapidly,

whereas carbon dioxide, nitrogen, and a partial vacuum extended the

life of the seeds for 6 to 8 years. When seed moisture was reduced to 4.7

percent, seed longevity was increased at laboratory temperature. Carbon dioxide, nitrogen, and vacuum were superior to air and oxygen,

with oxygen causing the most rapid deterioration. There were no

significant differences in the response of seeds to atmospheres of carbon

dioxide, nitrogen, or under vacuum at room temperature or to air,

oxygen, carbon dioxide, nitrogen, or vacuum at 5° and -5° except those

resulting from increased time in storage.

Grasses

The effect of nitrogen was negligible on the longevity of Chewings

fescue (Gane, 1948a) and meadow fescue (Evans et al., 1958), There

was no advantage in using either nitrogen or a partial vacuum rather

than air for sealed storage of seeds of Kentucky bluegrass and creeping

red fescue (Isely and Bass, 1960). In fact, when the seeds were

subjected to an unfavorable temperature, loss of viability was more

rapid for seeds packaged with nitrogen or under vacuum than with air.
PRINCIPLES AND PRACTICES OF SEED STORAGE 63

Legumes

Seeds of both red and white clover stored under vacuum and in

nitrogen were shorter lived than those stored unsealed (Davies, 1956),

Red clover seeds containing 10.3-percent moisture when sealed with

carbon dioxide lost all viability in 23 years, but when calcium chloride

was used with the carbon dioxide, only about one-third of the initial

viability was lost (Evans, 1957a),

No atmosphere tested, including air, vacuum, carbon dioxide, nitrogen, helium, and argon, was consistently or significantly better than all

others for 2 years of sealed storage of crimson clover seeds (Bass et al.,

1963a),

Oilseeds

Soybeans in open storage for nearly 6 years lost viability (Guillaumin,

1928X whereas seeds sealed in an atmosphere free of oxygen germinated 92 percent and those under a vacuum had 100-percent viability.

Low moisture (7 percent) cottonseeds retained their initial viability

when sealed in air, oxygen, carbon dioxide, or nitrogen and stored at 21°

and 32° C (Simpson, 1953). Seeds with 13-percent moisture dropped to

one-half to two-thirds of the original germination under all storage

conditions. The loss of germination with oxygen was no greater than

with carbon dioxide or nitrogen; however, the loss in air was greater

than in the pure gases.

Bass et al. (1963b) found that air, vacuum, carbon dioxide, nitrogen,

helium, or argon was neither consistently nor significantly better than

the others for sealed storage of safflower and sesame seeds for 2 years.

Rice

Much of the literature pertains to the storage of rice seeds for both

food and seed. In areas where rice is grown, seed moisture content

tends to remain high even when the seeds are air-dry. Deterioration of

high moisture (20.8 percent) seeds at 30° C can be delayed for a few

weeks by sealing them in an atmosphere of carbon dioxide mixed with

1,000 p/m of ethylene oxide (Kaloyereas, 1955).

Kondo and Okamura (1927, 1929, 1930, 1934) and Kondo et al. (1929)

found that both rough and hulled rice can be stored sealed with carbon

dioxide or air for up to 4 years with little loss of viability provided the

seed moisture content is less than 13 percent. They reported that

carbon dioxide had a slight advantage over air. Rice dried to 5-percent

moisture and sealed in an atmosphere of nitrogen germinated 99 percent after 8 years, but with 13-percent moisture all viability was lost

(Sampietro, 1931). Seeds with either 5- or 13-percent moisture lost all

viability when sealed in carbon dioxide, air, or under a partial vacuum.
64 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Sorghum

Sorghum seeds during the second year of storage retained significantly higher germination when sealed under a partial vacuum than

when sealed in air, carbon dioxide, nitrogen, argon, or helium (Bass et

al., 1963a).

Vegetable Seeds

For pea seeds the period of safe storage decreased as the oxygen

concentration in the storage atmosphere increased from 0 to 21 percent

(Roberts and Abdalla, 1968), The deleterious effects of oxygen were

more pronounced at the higher seed moisture contents. There was no

advantage in using sealed storage under nitrogen or a partial vacuum

rather than air for onion seeds (Gane, 1948b; Isely and Bass, 1960),

However, seeds sealed in carbon dioxide retained their viability better

than did similar seeds sealed in air (Lewis, 1953; Harrison and McLeish,

1954; Harrison, 1956), Vacuum, carbon dioxide, nitrogen, helium, and

argon storage had no advantage over sealed-in-air storage for lettuce

seeds during 2 years (Bass et al., 1962), Although lettuce seeds sealed

in carbon dioxide retained their viability better at room temperature

than did similar seeds sealed in air, storage in carbon dioxide revealed

differences in longevity between cultivars (Harrison and McLeish,

1954; Harrison, 1956).

Cabbage seeds stored equally well when sealed in air, nitrogen, or a

partial vacuum (Isely and Bass, 1960). Parsnip seeds retained their

viability better when sealed in carbon dioxide than in air (Lewis, 1953;

Harrison, 1956). Dandelion seeds retained their viability about equally

well when sealed in a partial vacuum or in air, except seeds containing

7.9-percent moisture seemed to deteriorate more rapidly in a partial

vacuum (Barton, 1939).

Wheat

Wheat, like rice, is an important food crop, which has received much

attention because the condition of storage greatly affects its milling and

processing qualities as well as its seed germination. To improve the

storage of wheat seeds for both planting and food purposes, studies

have been made on the effects of nitrogen and carbon dioxide on seed

viability. Loss of viability of high moisture wheat seeds can be delayed

for several days by sealing under either 50 or 75 percent of carbon

dioxide (Peterson et al., 1956) or nitrogen (Glass et al., 1959). However,

once deterioration starts, it proceeds rapidly. It can be delayed for

several additional weeks by combining nitrogen storage with a lower

temperature (20° C); however, even this combination is unsatisfactory

for extended storage.
PRINCIPLES AND PRACTICES OF SEED STORAGE 65

Confirmation Studies at the National Seed Storage Laboratory

Obviously some kinds of seeds under certain circumstances are benefited by vacuum or gas storage. The question then is "Under what

conditions is vacuum or gas storage practical and desirable?" To more

fully understand the interrelationship involved, a comprehensive study

was undertaken at the National Seed Storage Laboratory, Fort Collins,

Colo. One lot each of the following kinds of seeds was adjusted to 4-, 7-,

and 10-percent moisture and sealed in air, under vacuum, and in carbon

dioxide, nitrogen, helium, and argon and stored at -12°, -1°, 10°, 21°,

and 32° C: 'Dixie' crimson clover, 'Great Lakes' lettuce, 'Pacific No. 1'

safilower, 'Margo' sesame, and 'RS 610' hybrid sorghum. No gas analyses were made after storage. Germination tests were made at the time

of storage and at intervals thereafter. Because commercially available

equipment was very expensive, Bass and James (1961) developed a

simple, inexpensive device for vacuum and gas sealing of tin cans. The

complete sealer (fig. 5) consists of a vacuum chamber, soldering gun,

three-way valve, vacuum gage, several lengths of air hose, hose clamps,

a brass tee fitting, and a source for both vacuum and gas.

Germination tests were made in electronically controlled water-curtain germinators operated at 20° C for crimson clover and lettuce and a

20° to 30° night-to-day alternation for safilower, sesame, and sorghum.

Each test consisted of two 100-seed replicates planted according to

ofiicial procedures (Association of Official Seed Analysts, 1954) except

safilower, for which official procedures had not been developed at that

time. Safflower was planted the same as sorghum. In all tests only

normal seedlings—those capable of producing plants—were recorded.

For crimson clover, which has hard seeds, the percentage of hard seeds

was added to the percentage of normal seedlings to give total germination.

^^&:m

PN-5396

FIGURE 5.—Device for sealing tin cans from which air has been extracted by vacuum or

gas has been added.
66 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

The data (table 15) show that regardless of the kind of seed, no

storage atmosphere consistently gave the highest germination percentage at all temperatures for seeds of all moisture levels tested. The data

also show that there are distinct differences between kinds of seed in

their response to temperature and seed moisture content.

Of the five kinds of seeds, sorghum showed the least sensitivity to the

interaction between seed moisture content, storage temperature, and

storage atmosphere (table 15). Only the 10-percent moisture seed

showed really drastic germination reductions when stored at 32° C. At

that temperature seeds in all atmospheres except those under a partial

vacuum (3 percent) and in argon (5 percent) were completely dead. At

21°, seeds with 10-percent moisture in a partial vacuum, helium, and

argon did not show a significant reduction in germination, but seeds in

all other atmospheres did. Significant reductions in germination were

recorded for 4-percent moisture seeds under vacuum at 21° and in air,

nitrogen, and helium at 32°. Significant reductions in germination occurred for 7-percent moisture seeds in all atmospheres at 32°. No

significant reductions were recorded for seeds of any moisture content

in any atmosphere at 10°, -1°, and -12°.

Crimson clover seeds (table 15) stored in paper envelopes (check)

showed a significant decrease in germination after 8 years of storage at

each temperature for each initial moisture level except 4- and 10-percent moisture seeds held at -12° C. Except for 7- and 10-percent

moisture seeds at 10°, 21° and 32°, only an occasional sample of sealed

seeds showed a significant decline in germination. Such declines were

not consistent for storage temperature, seed moisture, or surrounding

atmosphere. A significant decline in germination of sealed seeds stored

at -12° was recorded for 7-percent moisture seeds in a partial vacuum

and for 10-percent moisture seeds in air. At -1°, significant germination

losses occurred with 7-percent moisture seeds held in nitrogen and with

10-percent moisture seeds held in air, vacuum, carbon dioxide, nitrogen, and helium. The significant germination declines recorded at 10°

occurred for 7-percent moisture seeds in air, carbon dioxide, and

nitrogen and for 10-percent moisture seeds in air, vacuum, carbon

dioxide, nitrogen, and helium. At 21°, significant decreases occurred for

7-percent moisture seeds in air, carbon dioxide, nitrogen, and helium

and for all 10-percent moisture seeds.

The only significant decrease in germination of 4-percent moisture

seeds held at 32° C was for those in nitrogen. All 7-percent moisture

seeds showed a significant decline, with the highest germination maintained in an atmosphere of argon. Argon also gave the highest germination of 4-percent moisture seeds at 32°.

The sealed 10-percent moisture seeds at 32° C showed a significant

decline in germination the first year of storage and germinated 12
TABLE 15.—Gennination of 5 kinds of seeds stored ivith approximately 4-, 7-, and 10-percent moisture content at 5

temperatures in various atmospheres in sealed viietal cans; check samples were in paper envelopes

Germination' after 8 years of storage in indicated atmosphere

Temperature Seed Initial

rc) moisture germination Carbon

Air Vacuum dioxide Nitrogen Helium Argon Check 2

Percent Percent Percent Percent Percent Percent Percent Percent Percent

5

CRIMSON CLOVER ^

r

-12 4 82 84 86 87 86 89 86 78

7 92 87 80 89 89 83 85 78 >

10 91 80 89 86 82 85 84 83

-1 _ 4 82 85 88 84 91 80 86 m

7 92 83 83 84 81 85 83 71 >

10 91 70 69 81 81 74 85 75 H

10 4 82 82 78 82 78 83 88 44 o

7 92 76 86 78 79 85 86 41 Q

10 91 42 77 74 80 81 85 45 ^

21 4 82 80 85 82 76 88 75 33

7 92 81 89 80 81 82 87 34

10 91 5 11 15 11 7 5 34 £^

32 4 82 80 77 77 72 80 80 71 o

7 92 69 74 70 76 76 79 69

10 91 0 0 0 0 0 0 73

LETTUCE

-12 4 97 96 96 94 94 96 94 92

7 97 98 97 94 95 97 96 96

10 95 94 95 93 93 92 95 95

-1 4 97 90 95 89 90 93 93 84

7 97 76 62 96 96 95 95 90 <^

10 95 91 91 92 96 93 94 96 -^

See footnote at end of table.
TABLE 15,—Germination of 5 kinds of seeds stored with approximately 4-, 7-, and lO-percent moisture content at 5 ^

temperatures in various atmospheres in sealed metal cans; check samples were in paper envelopes^Con. ^

Temperature Seed Initial

Germination 1 after 8 years of storage in indicated atmosphere

(°C) moisture germination Carbon ^

Air Vacuum dioxide Nitrogen Helium Argon Check SS

o

Percent Percent Percent Percent Percent Percent Percent Percent Percent ^

LETTUCE—con. 5d

10 4 97 90 5 93 95 89 95 0 s

7 97 1 91 93 94 90 92 0 §

21

10

4 97

95

90

OOOOOOOO

90 92 89 90 93 0 §

10

7 97

95

OOOOOOOW

OOOOOOOg

32 4 97 36 90 92 85 92 88 2 ^

10

7

95

97

0

0000000

0 0 0 0 0

SAFFLOWER

-12 4 95 87 89 92 92 90 89

7 94 83 87 82 89 86 83

10 95 79 75 79 85 72 81

-1 4 95 91 92 89 93 86 95

7 "94 90 87 89 84 87 84

10 95 72 78 79 70 79 69

10 4 95 89 84 91 88 89 89

7 94 85 75 75 80 81 81

10 95 0 0 0 0 0 0

21 4 95 90 67 90 87 90 93

10

7 94

95

000000

0 0 0 0 0 0

0 Ü

C«3

3

86 o

88 ^

88 >

o

90 w

86 o

88 Í

81 50

'^ t?d

86

64

61

54
32

47

10

-1247

10

-147

10

1047

10

2147

10

3247

10

-1247

10

-1_47

10

1047

10

See footnote at end of table.

95

94

95

94

92

88

94

92

88

94

92

88

94

92

88

94

92

92

95

91

92

95

91

92

95

91

8900

92

890

92

870

9000

9100

8700

90

94

94

92

94

87

90

90

92

88 90 0 0 0 0

SESAME

90 94

90 91 0 0

89 91

85 87 0 0

92 92 0 0 0 0

91 93 0 0 0 0

84 89 0 0 0 0

SORGHUM

92 89

93 91

92 93

92 92

91 93

95 92

92 92

87 87

83 85

00

94

870

96

840

9200

8900

8600

92

92

95

89

89

90

93

89

83

8600

93

880

89

870

8920

8900

8700

95

93

92

93

93

91

88

85

00

89

870

93

840

9410

9400

8700

92

86

92

90

91

86

91

90

90

53

60

53

92

93

89

94

90

90

88

95

70

94

95

92

95

89

93

71

76

76

2Sr

CO

84

>

88

Ö

88

S

83

>o

86

wOwMaO>O

CO
TABLE 15.-Germination of 5 kinds of seeds stored with approximately 4-, 7-, and 10-percent moisture content at 5

temperatures in various atmospheres in sealed metal cans; check samples were in paper envelopes—Con.

Temperature Seed

moisture

Initial

germination

Germination '' after 8 years of storage in indicated atmosphere

(°C)

Carbon

Air Vacuum

Percent

dioxide

Percent

Nitrogen

Percent

Helium

Percent

Argon

Percent

Check

Percent Percent Percent Percent

21 SORGHUM—con.

4 92 83 82 93 84 90 87 55 7 95 86 87 88 87 87 85 84

32

10

4

91

92

72

65

82

89

70

82

75

69

82

81

87

90

80

50 7 95 65 77 70 71 72 74 46

, T i • ' n . ,. ^

10 91 0 3 0 0 0 5 40

1 Least significant difference at 5-percent level of probability is 10 percent.

O

>

Q

2

o

c;

M

>

O

Od

o

o

?^

GO

O

O

2

o

c¡

H

c;
PRINCIPLES AND PRACTICES OF SEED STORAGE 71

percent or less at the end of the second year. By the end of the eighth

year, even the few hard seeds initially present were dead.

Maximum germinations were distributed among atmospheres as follows:

Atmosphere Seed moisture Temperature

and (percent) CO

combinations

(number)

Air(l) 4 32

Vacuum (3) 7 10

21

10 -12

Carbon dioxide (2) 7 -12

10 21

Nitrogen (2) 4 -1

7 -12

Helium (4) 4 -12

21

32

7 -1

Argon (6) 4 10

32

7 10

32

10 -1

10

In some tests the same germination was recorded for seeds in two or

more atmospheres. This finding applies to the tabular data for lettuce,

safflower, sesame, and sorghum (pp. 72-74).

The data for lettuce (table 15) show that seed moisture and storage

temperature had more effect on germination than did the composition of

the surrounding atmosphere. Drying to 4-percent moisture before

sealing made possible the storing of lettuce seeds at as high as 32° C

with significant differences between atmospheres evident only at 32°.

The apparent significant decline to 5-percent germination for 4-percent

moisture seeds in a partial vacuum at 10° resulted from a defective seal

after evacuation. The 1-percent germination for 7-percent moisture

seeds in air at 10° also resulted from a defective seal. In both tests a fine

hole in the solder allowed the seeds to absorb moisture from the

atmosphere until an unsafe level was reached. These data emphasize

the need for extreme care in sealing seed containers. Highest germination of lettuce seeds in sealed cans occurred as follows:
72 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Atmosphere Seed moisture Temperature

and (percent) (°C)

combinations

(number)

Air (2) 4 -12

7 -12

Vacuum (3) 4 -12

-1

10 -12

Carbon dioxide (2) 4 32

7 -1

Nitrogen (4) 4 10

7 -1

10

10 -1

Helium (2) 4 -12

32

Argon (3) 4 10

21

10 -12

Safflower seeds must be dried to 4-percent moisture (table 15) for

safe, sealed storage at ordinary temperatures regardless of the surrounding atmosphere. Seeds containing 7-percent moisture cannot be

stored safely above 10° C, and 10-percent moisture seeds cannot be

stored above -1°. All sealed 10-percent moisture safflower seeds

showed a significant loss in germination during 8 years of storage. The

array of highest germinations for safflower seeds sealed in various

atmospheres was as follows:

A fmosphere Seed moisture Temperature

and (percent) rc)

combinations

(number)

Air (2) 7 -1

10

Vacuum (0) - ---

Carbon dioxide (4) 4 -12

10

32

10 -1

Nitrogen (3) _ , 4 -12

7 -12

10 -12
PRINCIPLES AND PRACTICES OF SEED STORAGE 73

Atmosphere Seed moisture Temperature

and (percent) CC)

combinations

(number)

Helium (1) 10 -1

Argon (2) 4 -1

21

The data for sesame seeds (table 15) show that this oilseed does not

store well when sealed in any atmosphere at moisture levels above 7

percent unless the temperature is kept at -1° C or lower. For sealed

storage in any atmosphere at higher temperatures seed moisture content must be reduced to 4 percent. The distribution among atmospheres

of the highest germination percentages for sesame seeds was as follows:

Atmosphere Seed moisture Temperature

and (percent) (°C)

combinations

(number)

Air(l) 7 -1

Vacuum (0)

Carbon dioxide (4) 4 -12

32

7 -12

-1

Nitrogen (2) 4 -12

-1

Helium (2) 7 -1

10

Argon (2) 4 10

21

No atmosphere was consistently better than all others for preserving

the germination of sealed sorghum seeds. Therefore it is interesting to

note that among seed moistures and storage temperatures the following

combinations, with atmospheres that gave the highest germinations

after 8 years of sealed storage, were about equally divided:

Atmosphere Seed moisture Temperature

and (percent) (°C)

combinations

(number)

Air(4) 4 -1

7 -1

10

10 10
74 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Atmosphere Seed moisture Temperature

and (percent) (°C)

combinations

(number)

Vacuum (4) 4 -12

-1

7 32

10 -1

Carbon dioxide (3) 4 -1

21

7 21

Nitrogen (3) 4 -12

10

10 -12

Helium (2) 4 -1

7 -12

Argon (5) 4 -12

32

7 10

10 21

32

The distribution of highest germinations for all five kinds of seeds

among the various atmospheres in sealed metal cans is summarized as

follows:

Atmosphere, Seed moisture Temperature

combinations (percent) (°C)

(number), and

kind of seed

Air (10):

Crimson clover 4 32

Lettuce 4 -12

7 -12

Safflower 7 -1

10

Sesame 7 -1

Sorghum „ 4 -1

7 -1

10

10 10

Vacuum (10):

Crimson clover 7 10

21

10 -12
PRINCIPLES AND PRACTICES OF SEED STORAGE 75

Atmosphere, Seed moisture Temperature

combinations (percent) CC)

(number), and

kind of seed

Vacuum (10)—Continued

Lettuce 4 -12

-1

10 -12

Sorghum 4 -12

-1

7 32

10 -1

Carbon dioxide (11):

Safflower 4 -12

10

32

10 -1

Sesame 4 -12

32

7 -12

-1

Sorghum 4 -1

21

7 21

Nitrogen (14):

Crimson clover 4 -1

7 -12

Lettuce 4 10

7 -1

10

10 -1

Safflower 4 -12

7 -12

10 -12

Sesame 4 -12

-1

Sorghum 4 -12

10

10 -12

Helium (11):

Crimson clover 4 -12

21

32

7 -1
76 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Atmosphere, Seed moisture Temperature

combinations (percent) CC)

(number), and

kind of seed

Helium (11)—Continued

Lettuce 4 -12

32

Safflower 10 -1

Sesame 7 -1

10

Sorghum 4 -1

7 -12

Argon (18):

Crimson clover 4 10

32

7 10

32

10 -1

10

Lettuce 4 10

21

10 -12

Safflower 4 -1

21

Sesame 4 10

21

Sorghum 4 -12

32

7 10

10 21

32

It is obvious from this distribution of highest germinations that no one

atmosphere is decidedly better than the others for safe, sealed storage

of seeds.

The data in table 15 show that regardless of the kind of seeds or the

atmosphere in the sealed container, only adequately dried seeds (4-

percent moisture) retained their germination reasonably well during 8

years of storage at 32° C. Some kinds did not keep well at 21°, and

sesame seeds with 7- and 10-percent moisture lost all viability at 10°

except for 1 or 2 percent when sealed in helium or argon.

It is obvious from the data that seed moisture content at the time of

sealing has a far greater effect on seed longevity than does the surrounding atmosphere. For most situations the added expense of using

an atmosphere other than air appears unnecessary. However, even for
PRINCIPLES AND PRACTICES OF SEED STORAGE 77

sealing in air, most kinds of seeds require additional drying before

sealing if the sealed seeds are to be subjected to a temperature above

iO° C. In general, the added advantage, if any, of an atmosphere other

than air is not realized except during very long-term storage.

Illumination

Only limited studies have been made on the possible effects of light on

stored seeds. At least four investigators, who have studied the potential

effects of white light on the storage life of seeds, have found no positive

effect of illumination that could not be explained by the reduction in

seed moisture content caused by the light treatment (Tammes, 1900;

Bacchi, 1955; Wyttenbach, 1955; Litynski and Urbaniak, 1958). Harrington (1972) indicated that ultraviolet rays from the sun can reduce

longevity of seeds before harvest and hasten deterioration of stored

seeds. Since Harrington (1972) did not indicate the source of his

information, these statements are assumed to be extrapolations from

the effects of ultraviolet radiation on other biological materials.

Barton (1947) claimed that when Cinchona ledgeriana seeds with a

moisture content as high as 9.4 percent were exposed to light during

storage in a laboratory, there was some evidence of harmful effects.

However, the author indicated that the moisture content of the control

samples stored in darkness may have been reduced during storage and

thus provided a more suitable storage environment. Also, seeds stored

in sealed glass tubes and not resealed for future use after opening did

not confirm the initial conclusion.

Perhaps the most comprehensive study of this type was made by

Litynski and Urbaniak (1958). For 4 years they studied light effects on

the storage life of seeds of eight vegetable species and seven field crop

species that had been exposed to white light, orange-yellow light,

blue-violet light, diffused light of reduced intensity, and darkness. In

studying possible benefits of spectral characteristics of the filters used

and light intensity, they found no consistent benefit. Any apparent

benefit might be explained by the possible drying of the seeds by the

orange-yellow rays as opposed to the lack of drying by the blue-violet

rays. DiflFused Kght was not beneficial to the retention of seed viability.

Jensen (1941, 1942) claimed that the storage life of cabbage and

cauliflower seeds was increased significantly by illumination simultaneously with a mercury-quartz lamp and a heat lamp. Principal irradiation by the mercury-quartz lamp was from 300|JL to 450(ji with a maximum energy peak at about 325|x, whereas the heat lamp emitted

radiation from about 350|JL to 550|x with a peak at 485-550fjL. In Jensen's

work (1941, 1942) the seeds were exposed to light in the open, either on

a canvas with constant stirring or on a moving belt provided with
78 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

ventilation. Although we cannot disagree with the claims that light

affects the storage life of seeds, we believe that the author's findings did

not exclude the possibility of seed dehydration, which resulted from the

treatment procedure responsible for the increased storage life.

Harrington (1972) explained the relationship of a macromolecular

water layer, which insulates a macromolecule against oxidation and

subsequent deterioration of molecules, cells, and embryonic tissue. The

removal of this macromolecular layer renders the molecule vulnerable

to oxidation by several agents including ultraviolet light. Maes and

Bauwen (1951) studied the effect of infrared rays on preserving wheat

seeds and some oilseeds. They found that infrared rays inhibited the

lipolytic degradation of wheat germ and some oilseeds. The phenomenon was not caused by a change in the moisture content of the germ, as

the moisture content remained unchanged during radiation and storage.

The published information on the effects of illumination on the

storage life of seeds is controversial. Until these controversies are

resolved, no general recommendation can be made that would apply to

field, vegetable, and flower seeds.

Respiration and Heating

Respiration has been defined as an oxidative-reduction process occurring in all living cells, whereby chemical action occurs, producing

compounds and releasing energy that are partly used in various life

processes. Respiration is discussed here only as it relates to practical

seed storage. The following phases of respiration may be considered: (1)

Depletion of food reserves, (2) formation of intermediate or end products that may affect seed storage, and (3) release of energy, much of

which is in the form of heat. Of these three phases, perhaps the release

of heat has the greatest application to seed storage.

Depletion of Food Reserves

Since respiration is an oxidation process, there must be a substrate

(the seed) with which the oxygen can combine. Also, respiration is

possible only in the presence of enzymes, some of which are very

specific and some more general in their functions. As respiration proceeds, more and more of the seed food reserves are used up. There is

some evidence that the carbohydrate reserves in the endosperm of

wheat, on which much research of this nature has been conducted, are

used before the reserves in the embryo. Ordinarily the sugars and

starches are digested before the lipids and proteins. When stored seeds

are protected from insects and vermin and the environment is unfavorable for the development of molds and bacteria, the respiration process

continues under some conditions to the state or condition wherein the

seed appears as charcoal, for example, carbonized barley seeds taken
PRINCIPLES AND PRACTICES OF SEED STORAGE 79

from the Anatolian excavations of Alishar, dating to about 1000 to 3000

B.C. It is doubtful that seeds stored under reasonably favorable conditions of temperature and humidity would lose enough dry weight over 5

to 10 years to significantly weaken them.

Respiration Products That Retard This Process

One product of respiration is carbon dioxide. Most relevant research

has shown that in a closed system the accumulation of carbon dioxide

inhibits respiration (Crocker and Barton, 1953). In bag and bulk storage

the carbon dioxide is usually dissipated and thus has little effect on

respiration. Milner and Geddes (in Anderson and Alcock, 1954, pp,

152-220) indicated that renewal of oxygen in open storage can occur

with normal changes in barometric pressure. The inhibition of respiration by carbon dioxide in a closed system can be used advantageously by

storing seeds in sealed containers in which the carbon dioxide replaces

the air. Inhibitory concentrations of carbon dioxide in respiring soybeans were found to be from 12 to 14 percent. Milner and Geddes (m

Anderson and Alcock, 1954, pp, 152-220) reported that a carbon dioxide

concentration of 7 percent affected respiration in wheat and at 12

percent inhibition was marked.

Release of Heat in Respiration

The typical textbook equation for respiration is

CgHjgOg + 6CO2 = 6CO2 4- 6H2O + 673 kg calories.

This equation shows that for oxidation of 1 mole of a hexose, 6 moles of

oxygen are required; that 6 moles each of carbon dioxide and water

result from this oxidation; and that 673 kg calories of energy are

released. The complete combustion of a gram of glucose yields 3.76

calories. Not all glucose or other sugars proceed to complete combustion. Moreover the amount of heat released per unit of substrate varies

with the kind of material involved. The important point here is that heat

is evolved from respiration.

Under favorable storage conditions the heat of respiration is of little

or no concern for practical seed storage. However, at higher moisture

levels the heat of respiration can produce much damage to stored seed.

This would probably occur with freshly harvested seed having a high

moisture content (De Witt et al., 1962), with seed in storage areas not

well protected from the weather, with seed in the holds of ships where

the temperatures are high, or where it is not adequately protected from

the elements.

Measurement of Respiration

Because respiration in the resting seed proceeds very slowly, equipment and methods to measure the amount and rate must be precise.
80 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Methods commonly used to study respiration in seeds include measuring

oxygen absorption and carbon dioxide evolution. Because each method

has weaknesses (see Bartholomew and Loomis, 1967)^ many researchers measure both oxygen absorption and carbon dioxide evolution, which also provide data for computing the respiration quotient.

This quotient is the ratio of carbon dioxide produced to the amount of

oxygen consumed, usually written as CO/Og. Attempts have been made

to measure water production in respiration, decrease in dry matter

(substrate), evolution of heat, and loss of energy as a measure of

respiration. These methods have not been as successful for measuring

small bulk samples as measurement of oxygen absorption and carbon

dioxide evolution.

Some Factors Affecting Respiration

The apparent respiration of seed lots and the associated heat may

arise not only from the seeds but also from the fungi and bacteria on the

seeds, especially at seed moisture contents in equilibrium with approximately 75-percent relative humidity and higher. According to Milner

and Geddes {in Anderson and Alcock, 1954, pp. 152-220)^ critical

moisture percentages that increase respiration are wheat 14.6, barley

14.5, corn 14.2, and flaxseed 11.0. Other examples of equilibrium

moisture content of seeds are in tables 5-9. Since mold spores do not

germinate at relative humidity levels much below 75 percent, the

relative humidity of the storage area should be considerably less than 75

percent for safe storage for more than 1 year. Molds grow readily at

humidities above 75 percent. Bacteria are of minor importance in seed

storage as their relative humidity requirement is above 90 percent. If

held at optimum temperature (usually 25° to 30° C), fungus spores may

germinate at a lower relative humidity than at a nonoptimum temperature.

Respiration increases as temperature is increased until limited or

terminated by inactivation of enzymes or enzyme systems, by increase

in temperature, exhaustion of the substrate or oxygen, and accumulation of carbon dioxide to inhibitory levels. Ching (1961) found that

increased moisture accelerated respiration of perennial ryegrass and

crimson clover seeds more than did increased temperature.

Preservatives for Reducing Respiration

Considerable research has been conducted to find a chemical that will

inhibit the development of micro-organisms on seeds, grain, and oilseeds without adversely affecting their quality. Much of this work was

done at the Department's Southern Regional Research Laboratory,

New Orleans, La., by Altschul et al. (1946) ^ná Lambou et al. (1948),

Preserving seed viability for propagation poses quite a different prob-
PRINCIPLES AND PRACTICES OF SEED STORAGE 81

lern than controlling the growth of molds on grain and oilseeds to be

used for milling and industrial purposes. Unfortunately no successful

chemical or application has been found to control storage micro-organisms or respiration without damaging the seed embryo.

Conclusion

The most effective method of keeping the respiration of stored seed

to a minimum is to keep the seed dry. It should be dried to a moisture

content safe for storage and held at a relative humidity that will

maintain a safe moisture content throughout storage. Most of the

research on seed respiration has been on cereal seeds, oilseeds, and tree

seeds. Nevertheless seeds of other plant groups or species have been

the subject of interesting studies. For more information, see Miller

(1938), Crocker and Barton (1953), and Milner and Geddes (m Anderson

and Alcock, 1954).

EFFECTS OF PESTS AND CHEMICALS ON SEED

DETERIORATION IN STORAGE»

At harvest, seed lots contain much extraneous material, most of

which is removed by cleaning. However, certain fungi, bacteria,

viruses, and insects are not removed, and they cause or hasten seed

deterioration. In addition, chemical treatments to control fungi, insects,

and rodents may affect germination and longevity.

Seedborne viruses are rather uncommon. When present they usually

remain dormant in stored seeds and infect the seedling subsequent to

germination. Bacteria and actinomycetes, although capable of damaging

stored seeds, usually remain quiescent because the relatively high

moisture content necessary for their growth seldom occurs in commercial seed storage.

Storage Fungi

Saprophytic and parasitic seedborne fungi include Alternaría, Chaetomium, Cladosporium, Fusarium, Helminthosporium, and Rhizopus

spp. They remain dormant during seed storage unless seed moisture

content increases greatly, e.g., to over 14 percent in cereals. However,

these fungi may prevent infection of grass seeds by storage fungi

during the first part of the storage period (Kulik and Justice, 1967).

Certain molds (fungi), not usually present in or on seeds at harvest, can

carry out their life cycle on stored seeds (fig. 6).

These fungi, termed "storage fungi" by Christensen and Kaufmann

(1965) to differentiate them from the "field fungi," which are present in

»Prepared by M. M. Kulik, research plant pathologist, Agricultural Marketing Research Institute, Northeastern Region, Agricultural Research Service.
82 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

• ;%,«•

* !;' .

1^'

PN-5397, PN-5398

FIGURE 6.—Above, an enlarged cottonseed completely overgrown by the storage fungus

Aspergillus ochraceus; below, its spore head greatly enlarged.
PRINCIPLES AND PRACTICES OF SEED STORAGE 83

or on seeds prior to storage, can destroy stored seeds (table 16), because

they can grow under limited moisture conditions where field fungi and

other micro-organisms cannot grow. In fact, many of the storage fungi

are actually osmophilic and grow best under relatively dry conditions

(table 17). Some can invade seeds with moisture contents in equilibrium

with an ambient relative humidity of 65 percent. Typical moisture

contents are corn 13.8, oats 13.2, rye 14.3, and wheat 14.1 percent

(Kreyger, 1954). (All moisture contents in this section are on a wet

weight basis.)

Storage fungi have been reported to invade and destroy cereal grains

(Christensen and Kaufmann, 1969), cocoa beans (Bunting, 1930), cottonseeds (Arndt, 1946), grass seeds (Kulik and Justice, 1967), locustbeans and Scotch beans (Snow et al., 1944), peas (Fields and King,

1962), peanuts (Diener, 1958), and soybeans (Milner and Geddes, 1946).

They can attack almost any kind of seed under favorable environmental

conditions, since these molds can grow on most organic materials.

Invasion of seeds by storage fungi may result in loss of viability,

increase in free fatty acids, decrease in nonreducing sugars, development of musty odors, and discoloration. Deterioration can occur in a few

days when seeds are stored under unfavorable conditions.

Storage fungi are principally Aspergillus and Pénicillium spp., which

commonly occur throughout the world. They are usually present in

large numbers in the air and on surfaces in seed storage areas; they may

be on a few seeds in a lot. They will invade and destroy seeds at 4°-45° C

and 65- to 100-percent relative humidity. Their activity is largely

determined by the physical condition, vitality, and moisture content of

the seed and the ambient temperature and relative humidity of the

storage area. Consequently, the fungal population reflects the kind and

efficiency of the postharvesting handling, conditioning, and storage

environment of a seed lot.

Much of our knowledge of storage fungi has come from studies of

their activity in stored cereal seeds. Of the many Aspergillus spp., only

a few have been reported to attack stored cereal seeds. A. amstelodami, A. chevalieri, A. repens, A. restrictus, and A. ruber grow in

seeds with a moisture content of 13.2 to 15 percent. The major fungi

found in cereal seeds above 15-percent moisture content are A. candidus. A, flavus, A, ochraceus, A. tamarii, and A. versicolor (Christensen, 1957). Pénicillium spp., though not as common as Aspergillus

spp., are often found in cereal seeds, particularly in lots with a moisture

content above 16 percent and stored at relatively low temperatures

(Christensen and Kaufmann, 1965).

A rapid growth of fungi in stored seeds can produce so-called hot

spots caused by heating. Using seeds with 18-percent moisture content.

Oilman and Barron (1930) found in laboratory tests that A. flavus, A.
TABLE 16. -Frequency o/Aspergillus glaucus in stored grass seed and germination after 2 to 12 months'storage under

16 temperature-relative humidity (RH) conditions'^

Storage

temperature

(°C)

10

20

30

35

10

20

30

35

10

20

30

35

10

20

30

35

35-percent RH 55-percent RH 75-percent RH 95-percent RH

Fungus

frequency Germination

Fungus

frequency Germination

Fungus

frequency

Percent

16

3

27

48

5

3

50

77

1

2

26

7

1

0

5

1

Percent

93

94

94

94

91

88

92

92

94

94

97

93

90

94

93

Percent

6

2

8

31

1

5

29

20

1

2

9

2

0

1

1

1

Percent Percent

2 MONTHS' STORAGE

91 5

92 1

93 47

91 84

4 MONTHS' STORAGE

91 2

92 50

89 100

85

8 MONTHS' STORAGE

94 0

95 95

91

49

12 MONTHS' STORAGE

90 1

94 66

73

19

Germination

Fungus

frequency

Percent

92

91

11

16

88

88

16

93

64

Percent

1

99

96

93

3

100

95

7

45

92

27

Germination

Percent

92

90

53

1

92

83

0

94

4

92

lEach value is average for Festuca arundinacea, F. rubra, Lolium multiflorum, and Poa pratensis; 100 seeds per sample cultured on 10-percent

sodium chloride-malt agar after sodium hypochlorite treatment; 200 seeds per sample used to determine germination.

2 Data from Kulik and Justice (1967). (With permission of Microform Internatl. Mktg. Corp. exclusive copyright license of Pergamon Press Journal

Back Files.)

00

4^

>

O

2

o

a

H

a

?ow

a

>

o

o

?^

C/2

O

>

o

2

o

c:
PRINCIPLES AND PRACTICES OF SEED STORAGE 85

TABLE 17.—Colony diameter of mass isolates of ö Aspergillus species

grown for 24 days at 22^-24'' C on malt agar substrate^ 2

Colony diameter on malt agar with indicated sodium chloride

Aspergillus species (percent)

and isolate (No.) ———^——

Control 5 10 15 20

Mm Mm Mm Mm Mm

amstelodami

1 31 82 85 86 74

2 56 79 84 88 72

3 49 81 86 89 74

Average 45 81 84 88 73

flavus

1 86 84 76 30 6

2 85 83 58 0 0

3 - 90 90 90 40 0

Average _^ 87 86 75 23 2

niger

1 87 87 73 31 9

2 87 88 76 11 0

3 90 90 90 63 2

Average 88 88 80 35 4

ochraceus

1 90 90 80 65 0

2 83 90 85 62 9

3 88 88 88 82 42

Average 87 89 84 70 17

parasiticus

1 82 83 54 24 0

2 83 84 67 34 0

3 83 86 6S 27 1

Average 83 84 63 28 0

terreus

1 34 80 77 48 2

2 35 80 71 44 2

3 51 83 75 44 3

Average 40 81 74 45 2

iMalt extract 30 gm, agar 15 gm, water 1 1; 6 replications per isolate per treatment.

2 Data from Kulik and Hanlin (1968).
86 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

fumigatus, and A. niger raised the temperature of barley, oats, and

wheat from 17° to 43° C. These results were confirmed and extended by

Christensen and Gordon (1948). Mead et al. (1942) showed that the rise

in temperature can be even higher if the seed contains a high proportion

of broken kernels and cracked seedcoats. Similar hot spots can occur in

bulk seed, which contains pockets of moist seeds, as the natural insulating properties of the surrounding dry seeds prevent rapid dissipation of the heat generated by respiration of the moist seeds and the

associated fungi.

Pockets of moist seeds can arise in low moisture content seeds

through roof leaks, insect activity, and moisture translocation when

temperature gradients within the seed mass are allowed to occur. The

fungi associated with hot spots in seeds stored on the farm were studied

by Wallace and Sinha (1962), They observed that hot spots may occur at

any location in a bin and that temperatures can increase to 53° C in

winter. Field fungi such as Altemaria spp. were not common in the

heated seeds, although they were present in many of the viable seeds.

The heated seeds were infected chiefly by storage fungi, mainly Pénicillium and Aspergillusspp.y especially A, flavus^ A, fumigatuSy and A,

versicolor, Absidia spp. were also frequently observed. Christensen

(1957) stated that "heating is likely to be the final and violent effect of

mold invasion of the seed, not an indication of beginning deterioration."

Sinha and Wallace (1965) investigated the succession of fungi and

actinomycetes populations associated with progressive stages in the

heating process of an artificially caused fungus hot spot in stored wheat.

The growth of Pénicillium cyclopium and P, funiculosum in a moist

pocket of grain stored at -5° to 8° C for 4 months began the heating

process. A maximum temperature of 64° was reached in this hot spot.

Since these two fungi cannot live above 55°, bacterial and biochemical

activity was deemed responsible for the increase to 64°. The following

ecological succession of micro-organisms, which often overlapped, was

observed: Pénicillium cyclopium, P, funiculosum, Aspergillus flavus,

A, versicolor, Absidia spp,, and Streptomyces spp.

Several investigators have studied the mycoflora of freshly harvested

and stored peanuts. Hanlin (1966) observed the internally borne mycoflora of Georgia peanuts. Fusarium spp. were found in 20.7 percent.

Pénicillium spp, in 18.5 percent, and Aspergillus spp. in 7.5 percent of

the seed at harvest. Jackson (1965) used dilution methods to investigate

the mycoflora of soil that adhered to dry peanut pods. Relatively small

numbers of Aspergillusflavus, A. niger, A, terreus, Rhizopus spp., and

Sclerotium bataticola were found. Pénicillium citrinum, P, funiculosum, P, rubrum, and Fusarium spp. were found in large numbers.

Aspergillus flavus, A, niger, Rhizopus spp., and S, bataticola extensively penetrated pods and kernels when dry; the infested pods were
PRINCIPLES AND PRACTICES OF SEED STORAGE 87

hydrated for 6 days at 26°, 32°, or 38° C. As the temperature increased,

infection by A. flavus and A, niger increased.

Garen (1966)studied the endogeocarpic floras of Virginia peanuts and

reported that ''Trichoderma viride seems a dominant and Pénicillium

spp. seem sub-dominants in the climax endogeocarpic community of

sound and rotting peanut pods; and Aspergillus flavus and A, niger,

which have a potential for causing trouble, are quantitatively minor but

persistent species in this flora/'

Diener ("iPöO) investigated Georgia farmers' stock peanuts (uncleaned

and unshelled) that had been stored for 8 to 56 months. He found that

the predominant fungi consisted of certain species of the Aspergillus

glaucus group (amstelodami, chevalieri, repens, and ruber), A. restrictus, A. tamarii, Cladosporium spp., Pénicillium citrinum, Torula

sacchari, and members of the Mucorales. Large numbers of fungi were

directly associated with kernel moistures of 12.5 percent or greater at

the time the seeds were stored. Kernel moisture content decreased to

about 7 percent, which is considered safe, in 3 to 4 weeks after the bins

were filled, regardless of the initial moisture content of the kernels.

During the 5-year storage period the moisture content of no sample

ever exceeded 6.8 percent. There was no relationship between percentage of initial kernel damage, final damage, or increased damage

during storage.

Control of Fungal Deterioration

Deterioration of stored seeds by fungi is controlled principally by

drying the seeds to a safe moisture content prior to storage in a dry

place. Most storage fungi cannot invade seeds that are in moisture

equilibrium with 65-percent relative humidity or lower. However, some

fungi are xerophytic and can invade seeds that contain only sUghtly too

much moisture.

Because the moisture content of a seed lot represents the average of

many seeds, some individual seeds may possibly contain an unsafe

amount of moisture even though the moisture content of the lot is at a

safe level. Seeds containing too much moisture are susceptible to

invasion by storage fungi, which may then spread throughout the lot.

Therefore it is extremely important to accurately measure seed moisture content. For best results, seeds should be dried as soon as possible

after harvest, then thoroughly cleaned prior to storage in an environment where they will not absorb moisture.

Fumigation to control insects ordinarily has no detectable effect on

storage fungi (Christensen and Hodson, 1960).

For the effects of micro-organisms on stored cereal seeds, see Semeniuk (1954), Christensen and Kaufmann (1969, 1974), and Wallace

(1973).
88 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Do not assume that the effects of storage fungi on seeds of other field

crops, flowers, or vegetables will necessarily be the same as those on

stored cereal seeds. For example, Kulik (1973) found that seeds of

cabbage, cucumber, pepper, radish, and turnip inoculated with spores

of either of two common storage fungi and stored at 85-percent relative

humidity and 22°--25° C for 30 days remained largely free of invasion.

Qasem and Christensen (1958) found that 84 percent of the corn seeds

they inoculated with a storage fungus and stored at 85-percent relative

humidity and 20° were invaded by the fungus after 1 month. Also, Tuite

and Christensen (1957) found that 100 percent of the wheat seeds they

inoculated with a storage fungus and stored at 80-percent relative

humidity and 25° were infested after 1 month.

Insects

As with storage fungi, much of our knowledge of insects that attack

stored seeds comes from studies of stored grain and grain products.

According to Henderson and Christensen (1961), stored seeds are

attacked primarily by those insects that destroy stored grain and grain

products. Of the several hundred insect species associated with stored

grains and seeds, only about 50 cause problems. Of that 50 only about a

dozen cause serious damage, including the rice weevil, granary weevil,

lesser grain borer, Angoumois grain moth, cadelle, sawtoothed grain

beetle, khapra beetle, and flat grain beetle. The weevils puncture the

seedcoat and destroy the endosperm, but other stored-product insects

attack the embryo. In either case the germination potential is reduced

or totally destroyed.

Stored-product insects that fly migrate to previously noninfested

seed storage areas. Seeds may also become infested from contaminated

storage bins or sacks or in the field prior to harvest. One species of

chalcid lays its eggs individually in seeds of alfalfa, certain clovers, and

trefoils. The larva gradually consumes the contents of the seed and

becomes an adult wasp. It then chews its way out of the seed, mates,

and the female lays her eggs in host seeds, whether on the plant or in a

seed warehouse.

Control measures recommended by Lieberman et al. (1961) are

designed to destroy as many as possible of the larva-infested seeds:

"One should clean all seed carefully and destroy or use the cleanings,

prevent seed from forming on volunteer plants, clear the field after

harvest, work all chaff into the soil, and, if necessary, provide moisture

to encourage the growth of fungi present in the soil that will kill the

overwintering larvae in the seeds."

Additional insect control measures include thorough cleaning and

fumigation of all seed-handling equipment, seed containers, and storage

areas, and when required an insecticide application.
PRINCIPLES AND PRACTICES OF SEED STORAGE 89

For some types of insects, fumigating the seeds before or during

storage is also essential to good control. Seed fumigation must be very

carefully done, as some fumigants under certain conditions are very

harmful to seed germination. Methyl bromide is especially harmful to

seed germination when improperly applied.

Cotton (1954, 1960) reported on the role of insects in deterioration of

stored seeds.

Rodents

Rats, mice, and squirrels destroy thousands of pounds of seed each

year. Much of the loss is not what these rodents eat, but what they

scatter and mix. They have been reported to destroy as much as 200

million bushels of grain each year in the United States (Cotton, 1960).

Even greater losses occur in other parts of the world. The best control

for rodents is to keep them out of seed storage areas. This can be

accomplished by rodentproof construction and by eliminating such

entryways as cracks and holes in walls and floors and unscreened

ventilators. Cleanliness inside and outside storage areas also helps to

keep rodents away.

Rodent infestations can be eliminated by using traps, poison baits, or

fumigation. Generally toxic gases are handled by an expert. Spencer

(1954) 3Lnd Cotton (1960) published detailed accounts of rodents in grain

and their control.

Fungicides and Fumigants

Seed treatments have long been recognized as injuring seeds in

storage. Clayton (1931) reported that the recommended treatment for

many kinds of seeds with mercuric chloride, liquid organic mercurials,

or hot water greatly reduced seed longevity. However, seeds treated

with fungicide dusts usually suffered no injury from the treatment.

Crosier (1988) found abnormal germination in wheat seeds that had

been treated with Ceresan and held in cool, dry storage for 1 year prior

to being tested for viability. Corn seed of 12-percent moisture or less

was treated by Koehler (1938) with several mercurials and stored up to

1 year. When treated seed was stored near the roof of an open shed, it

was definitely injured every time. In general, in this study, freshly

treated seeds performed better by a small margin.

Miles (1939) showed that storage of cottonseed treated with Ceresan

or New Improved Ceresan in a dry laboratory up to 17 months caused

no injury to the seed. In another study. Miles (1941) stored mechanically delinted cottonseed treated with New Improved Ceresan in 100-

pound bags (storage conditions not given). Germination tests showed no

injurious effects after 17 months in cotton bags.
90 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Seeds of alfalfa, ladino clover, red clover, and sudangrass were

treated with New Improved Ceresan, Arasan, Spergon, Semesan, or

yellow cuprocide by Kreitlow and Garber (1946) and were stored in

closed or open containers at 10° or 25° C for 30 months. At 25°, only the

germination of sudangrass treated with New Improved Ceresan was

greatly reduced. At 10°, germination of treated seeds and controls

stored in closed containers was much better than that of seeds stored in

open containers. Jute seeds treated with a mercuric acetate or ethyl

mercuric chloride dust were stored by Ghosh et al. (1951) for more than

14 months in airtight, moisture-free, nonporous containers without any

reduction in viability.

Koehler and Bever (1954) reported reduced germination of oats and

wheat caused by volatile mercury compounds. The reduction increased

as dosage, length of storage, and moisture content of the seed increased. Compounds differed in the amount of injury they caused.

Reduced viability was not always related to volatility of the compound.

In another study, wheat seeds of two cultivars of about 10-percent

moisture content were treated by Koehler and Bever (1956) with 11

organic mercury fungicides and stored for 10 months in stoppered

bottles at 4.5° or 21° C. Germination tests in sand showed that most of

the treatments caused significantly lower stands than in the nontreated

controls. Also, there were striking differences among the compounds in

the amount of injury they caused. In general, however, they found that

seed storage at low temperature resulted in less seed injury.

Nakamura et al. (1972) treated seeds of beet, cabbage, carrot, eggplant, pea, pepper, and tomato with four organic mercury and four

organic sulfur fungicide dusts. The seeds were then stored for up to 3

years. Organic mercury compounds greatly reduced the viability of

eggplant seeds and caused some injury to seeds of beet and cabbage.

Seeds of carrot, pea, pepper, and tomato were not injured by these

compounds. Seeds of these vegetables treated with organic sulfur dusts

and stored for 1 year did not undergo reduced germination. Properly

applied fungicides usually do not impair germination during favorable

storage conditions.

Young (1929) investigated the effect of several fumigants on seed

viability for controlling rice weevils. He found that seeds of alfalfa,

barley, beans, buckwheat, clover, corn, cowpeas, lima beans, oats, rye,

sunflower, timothy, and wheat could be treated with up to twice the

minimum lethal concentration of ethylene dichloride, isopropyl formate,

tertiary butyl chloride, and trichloroethylene without seriously reducing their viability. Ethylene oxide and methyl chloroacetate seriously

reduced germination.

Cobb (1958) fumigated seeds of 14 field crops and 15 vegetable crops

at 3 moisture contents with methyl bromide. Germination tests were
PRINCIPLES AND PRACTICES OF SEED STORAGE 91

made immediately after fumigation and after storage for up to 90 days.

Some seeds were stored for up to 2 years. He found that injury

occurred while seeds were in contact with the methyl bromide, that

fumigant injury was not reversible, that seeds uninjured by fumigation

did not exhibit subsequent injury, and that some seeds injured by

fumigation declined in viability more than the nontreated control seeds.

Based on his study, Cobb recommended that "the fumigation of dry

seed at low temperatures and gas concentrations offers the greatest

opportunity for the safe use of methyl bromide." He also recommended

"that for fumigation when seed viability is important, test fumigation

and germination should be done before large-scale fumigation is attempted with methyl bromide."

King et al. (1960) evaluated hydrogen cyanide, methyl bromide, and

carbon tetrachloride alone and in mixtures with several other fumigants

for their effect on germination of barley, corn, cotton, oats, rice,

sorghum, and wheat at three seed moisture levels and three treatment

temperatures immediately after fumigation and after storage in polyethylene bags for 12 months at room temperature. They found that

either a high seed moisture content or a high temperature during

fumigation caused a reduction in viability. A high seed moisture content

combined with a high temperature usually resulted in extensive injury.

Fumigated seeds of all seven crops produced less vigorous seedlings

than did the nonfumigated controls, although in some cases differences

in germination percentages between the fumigated and nonfumigated

seeds were minor. The rate of germination of stored seeds was decreased by fumigation. The authors recommended that "germination

tests should be performed immediately before sale if fumigated seed

have been in storage for a prolonged period."

Potgieter and de Beer (1972) treated white corn, yellow corn, and

grain sorghum with methyl bromide gas or phosphine gas, then planted

the seed in a sandy loam soil after about 1% inches of rainfall. Methyl

bromide fumigation was rather injurious and repeated fumigation with

phosphine decreased field performance.

CHANGES ASSOCIATED

WITH SEED DETERIORATION

Biochemical Changes

Seed storage begins immediately after maturity regardless of where

or how seeds are held. During seed development anabolic processes

predominate and bring about a gradual increase in dry matter, including

development of an embryo and food reserves. Following maturation

biochemical changes continue and eventually catabolic processes pre-
92 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

dominate and deterioration becomes apparent. Catabolic changes occur

more slowly under low temperature and low relative humidity than

under high temperature and high relative humidity.

Although much has been written about chemical changes associated

with seed deterioration (Crocker and Barton, 1953; Zeleny in Anderson

and Alcock, 1954; Abdul-Baki and Anderson in Kozlowski, 1972; Roberts, 1972), our knowledge of biochemical deterioration of seeds is still

inconclusive. Attempts have been made to correlate such factors as

depleted food reserves, increased enzyme activity, increased fat acidity, membrane permeability, and similar changes with deterioration.

Biochemical changes in the aging process take place in both the embryo

and endosperm. By embryo transplant technique Kikuchi (1954) and

Floris (1970) found that embryos from new seeds grew slower when

transplanted to old ("decrepit") endosperm than when transplanted to

the endosperm of new seeds. Kikuchi (1954) reported that the embryo

deteriorated more rapidly than the endosperm, and he theorized this

was because of fundamental differences in their nature. Floris (1970)

concluded that aging is a progressive process accompanied by accumulation of toxic metabolites, which progressively depress germination

and growth of seedlings with increased age. Obviously important biochemical changes take place in the embryo and endosperm during

storage, but the significance of these changes in relation to deterioration

is not fully understood.

Villers (in Heydecker, 1973) proposed that deterioration in dry stored

seed results from the lack of operable systems to repair and replace

organelles, whereas in moist stored seeds repair systems are fully

operable. He pointed out that the full consequences of damage accumulating during storage are not evident until imbibition.

Germination and Vigor

From prehistoric times man has known that the germination capacity

of seeds declined with age (James, 1967). Even today most studies of

physiological and biochemical changes in seeds, oilseeds, and grain

include plans for determining the percent germination as a criterion of

deterioration or change.

Vigor is considered here in relation to the seed's strength or power of

germination, its ability to send out a strong root and shoot even under

conditions of stress, and its freedom from attack by micro-organisms.

Loss in vigor can be thought of as an intermediate stage in the life of

the seed, occurring between the onset and termination of decline

(death). Decline in vigor is extremely difficult to measure. No generally

accepted method has yet been found to measure vigor, but the most

useful available methods are based on measurements relating to ger-
PRINCIPLES AND PRACTICES OF SEED STORAGE 93

mination capacity. For example, Abdalla and Roberts (196%), working

on seed deterioration of barley, broadbeans, and peas, reported that the

percentage of seed viability is an excellent indicator of growth potential

of the surviving seeds, irrespective of the factors responsible for the

loss of viability. Gill and Delouche (1973) found rate of germination and

seedling growth of corn to be the most consistent and sensitive measures of the progress of deterioration. A similar conclusion was drawn

by Christidis (1954), who found that the rate of germination of stored

cottonseed increased for the first 5 years of storage and then gradually

decreased throughout the following 6 years.

As the catabolic changes continue with increasing age, the ability of

the seed to germinate is reduced. The curve in figure 2 shows that

measurable decline in viability or germination capacity does not begin

immediately after maturity. Under favorable storage conditions the

initiation of decline may be a few months to many years depending on

storage conditions, kind of seed, and previous storage conditions. When

making germination tests on stored seed, one of the first indications of

deterioration is reduced vigor, which is shown by reduced rate of

germination and production of weak or watery seedlings and seedlings

with stunted radicles. Seeds with reduced vigor would appear to produce low yields compared with fresh vigorous seeds; however, this is

not always true.

Yield

Old seed can be vigorous and alternatively new seed can be deteriorated depending on the storage conditions to which they have been

subjected. Therefore seed of a given chronological age may or may not

be deteriorated. Some of the pertinent literature does not make this

distinction. If a maximum yield of a given crop is to be obtained, a

minimum number of plants per acre (or hectare) is necessary. If the rate

of planting low germinating seed is increased to satisfy this minimum

requirement, yield is not decreased compared with the yield from new,

vigorous seed. The problem is whether plants from seeds of low vigor

can compete in the field with plants from vigorous seeds.

Abdalla and Roberts (1969a) plsLuted seeds of barley, broadbeans, and

peas in a culture medium and in the field. Plants from some seeds

associated with decreased viability exhibited retarded growth of roots

and shoots and increased variability in growth during early life. The

early inhibition of growth rate did not persist, and there was evidence

that under normal cultural conditions the low growth rate during early

plant development might be compensated for in later growth stages.

They concluded that unless the germination of deteriorated seed of

barley, broadbeans, and peas is less than 50 percent, the final yields are

not significantly affected.
94 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Christidis (1954) found that plants from cottonseed up to 10 years old

yielded about the same weight of seed cotton as plants from fresh seed.

Others who have reached similar conclusions from work with seeds of

different crop species are Rodrigo (1939) with mung beans, Barton and

Garman (1946) with aster, lettuce, pepper, and tomato, Fulutowicz and

Bejnar (1954) with sugar beet, and Ghosh and Basak (1958) with jute.

Barton and Garman (1946) found yields of crops from seeds of the four

species, which had been stored at -5° C up to 13 years, were equal to

those of fresh seeds. Thirteen-year-old lettuce seed produced larger

heads than did fresh seeds. Likewise plants from the 11-year-old mung

bean seed used by Rodrigo ("i95ft) produced significantly higher yields of

pods and beans than plants grown from fresh seed.

Not all the evidence is in favor of normal yields of crops produced

from deteriorating seed. Newhall and Hoff (1960)stored onion seeds for

22 years over calcium chloride in a closed desiccator. Field tests

revealed a 30-percent loss in yield by the 22-year-old seed compared

with yield of fresh seed. Bulbing vigor was reduced by 15 percent,

although this was hardly detectable by casual observation.

Chirkovskiy (1953) reported that longtime storage of tobacco seed

resulted in loss of germination and lower yields of leaves per plant

compared with yields of plants from fresh seeds. He (1956) indicated

that aging of seeds had a depressing effect on plant development,

especially during early growth and that unfavorable storage conditions

increased the depressing effect.

Corn that germinated only 38 percent in the field yielded only 50

percent as much grain as seed that germinated 80 percent in the field

(Heit and Munn, 1947), It is not clear whether the reduced yield was due

to reduced field stand, weakened vigor, or both. They also claimed

reduced yields from aging seeds of cucumber and soybean. Presumably

they credited the reduced yields to low seed vigor, as seeds of both

crops produced seedlings with stubby roots insufficient to properly

anchor the plant or to provide an adequate supply of soil nutrients.

Because information is limited on plant yield from seeds of low or

weakened vigor, future research should segregate the principal factors

so the contribution of each can be ascertained. Among these factors are

use of uniform genetic stocks, isolation of low vigor effects, and effects

of competition versus noncompetition with other plants under normal

field conditions.

Cytological Changes

One of the changes associated with seed aging is aberration of

chromosomes, sometimes referred to as mutagenic effects, de Vries is

credited with discovering mutations in aging seeds in 1901 (Kostoff,
PRINCIPLES AND PRACTICES OF SEED STORAGE 95

1935), Some of the chromosome alterations in aged seed include fragmentation, bridges, fusion, ring formation of chromosomes, and variation in nuclei size. These changes have been found in a relatively large

number of crop and native plant species, including Antirrhinum^

Crépis, Datura, Nicotiana, barley, broadbean, com, onion, pea, rye,

sugar beet, and wheat.

According to James (1967), there is no evidence that these cytological

aberrations develop in seeds stored under favorable conditions. The

seeds used in most experimental work so far have been subjected to

high storage temperatures or humidities or both. Possibly James'

statement can be questioned depending on what is considered favorable

or unfavorable storage conditions. For example, Blakeslee (1954) found

mutations in Datura seeds stored at room temperature. He did not

indicate that either the temperature or the relative humidity was

unfavorable during storage. He also found a very low frequency of

mutations in Datura seeds that had been buried in the soil for 39 years.

HOW SEEDS ARE DRIED

Characteristics of Water

Because drying involves removing water from the seed, let us first

consider some of the characteristics of water. In nature, water exists

simultaneously as a solid, liquid, and gas. Water freezes at 0° and boils

at 100° C. It contracts as it cools to near the freezing point but expands

on freezing. The quantity of solid or liquid water is expressed by weight

or volume, whereas the quantity of gaseous water is given as percent

humidity, either relative or absolute. The amount of water in a seed is

its moisture content, which is measured on a wet or dry weight basis

with respect to the seed weight. When seed moisture content is given on

the wet weight basis, the amount of water in the seed is a percentage of

the seed weight before the water is removed. When seed moisture

content is expressed on the dry weight basis, it is a percentage of the

seed weight after the water is removed.

During development, maturation, and ripening, the water content of

seeds gradually decreases until harvested seeds finally dry to the point

where there is no further reduction in moisture because their water

content reaches equilibrium with the ambient relative humidity. Any

further change in seed moisture content will be the result of a change in

either the relative humidity or the temperature of the air or both.

Because of chemical differences in their composition, not all kinds of

seeds will equilibrate at the same moisture content at a given relative

humidity. In fact, not all cultivars of a given kind of seed nor even all

lots of a cultivar have exactly the same equilibrium moisture content for

any given relative humidity.
96 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Water in seeds is present in liquid form in cell walls and cell contents

and in gaseous form in intercellular spaces. Since water is removed

from seeds by evaporation, it is removed only in its gaseous form.

Principles of Drying

Seed drying requires the transfer of heat, because a seed can be dried

only by evaporating moisture from its surface, and the heat content of

moisture vapor is greater than that of liquid water. Heat transfer may

be accomplished by contact, convection, or radiation. Most seed-drying

equipment transfers heat by convection. Drying of a seed requires that

evaporation of moisture from its surface be accompanied by the

transfer of moisture from its interior to its surface. When water

evaporates from the seed surface into the atmosphere, a moisture

gradient is set up inside the seed that causes internal moisture to move

toward the surface. If evaporation from the seed's surface occurs too

rapidly, the extreme moisture stress that develops can, and usually

does, damage the embryo and cause loss of viability. It is therefore

essential that seed drying be carefully controlled to prevent stress

damage. It is also important that the vapor pressure of the surrounding

atmosphere not be allowed to increase. If the vapor pressure of the

atmosphere becomes greater than that of the seed surface, the seed will

gain rather than lose moisture. Additional information on principles of

drying seeds can be found in Anderson and Alcock (1954X Hall (1957),

Brandenburg et al. (1961), Kreyger (1963a)y Harrington and Douglas

(1970), and Philpot (1976).

Methods of Drying Seeds

Methods of drying seeds include natural drying, sun drying, unheated, heated, and dehumidified air-drying, drying in storage and

before storage, drying with desiccants, vacuum drying, and freeze

drying. These methods may be used alone or in various combinations.

Natural Drying

Natural drying occurs in the field during ripening and in the bin after

harvest. It is the process by which seeds lose water naturally without

help from man. The extent of natural drying is regulated by such

factors as air temperature, relative humidity, and wind velocity. Shatter resistance, harvesting procedures, and workload of the producer

also affect the amount of natural drying permitted before harvest. A

hot, dry wind prior to full maturity can seriously damage a seed crop by

causing too rapid drying, but a moderate temperature and relative

humidity can produce top-quality seed. Some but not all seed crops are

harvested or partially harvested before the seeds dry to moisture
PRINCIPLES AND PRACTICES OF SEED STORAGE 97

equilibrium with the atmosphere. Such seeds must receive additional

drying. Sometimes the plants are cut and placed in windrows and this

speeds up natural drying.

Sun Drying

Where sun drying is possible, seeds may be spread in screen-bottom

trays placed on low racks in the sun or on flat-roofed houses, or they

may be spread on the ground or on concrete. Seeds dried in the sun are

stirred from time to time to facilitate rapid, uniform drying. Sun drying

is used for such seeds as cantaloup, cucumber, pumpkin, tomato,

watermelon, and others that are threshed wet. Because these seeds do

not separate readily from the surrounding pulp, fermentation, chemical

treatment, or mechanical action is used to help free them. Once freed,

they are washed thoroughly and placed in screen-bottom trays to be

cured in the sun. Although these and other kinds of seed are frequently

dried naturally, they may also be dried artificially. Most seeds harvested at a moisture content too high for safe storage are dried

artificially. Solar heat can be used in the bin drying process (fig. 7).

Artificial Drying

Three basic types of seed dryers are layer, batch, and continuous

flow. There are sound engineering and economic reasons why each type

is better suited for certain kinds of drying than the others. No one type

of dryer is best suited for all drying needs. The user must choose the

best one for his specific needs. One should not attempt to select a seed

dryer without first obtaining sufficient information on the advantages,

disadvantages, and Umitations of all available dryer systems. One must

also have sufficient information on the specific drying requirements of

the kind or kinds of seeds to be dried. Table 18 presents data for several

crops. Although not complete, the data provide a reference for related

kinds of seeds.

Layer Drying.—Layer drying is usually in-storage drying, which

may be done with or without supplemental heat. For layer drying, the

storage area is equipped with a network of air ducts attached to a large

fan. The air ducts (fig. 8) should be placed on the floor of flat storage

structures so they provide reasonably uniform airflow, cooUng, and

drying in the entire mass of seeds. The manifold should be as close to

the wall as possible, and in round buildings it should be opposite the

door so as not to interfere with unloading. The method of unloading

must always be considered when locating the aeration tubing. Other

factors such as depth of seeds, accumulation of fine particles, and

uneven loading have a direct bearing on operation efficiency of the

drying system. The size and speed of the fan are determined by the size

of the storage area, the kind and depth of seed to be dried, the
98 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE
PRINCIPLES AND PRACTICES OF SEED STORAGE 99

TABLE 18.—Static pressures and estimated quantities of various seeds

and grains that can be dried per batch per fan horsepower for

different airflows and seed depths^

Seed and Maximum quantity

airflow per Seed Static that can be dried

bushel

(ft3/min) depth pressure2 per fan horsepower^

Ft Water gage in Bu

Alfalfa:

5 _ 1 0.66 960

2 1.93 330

10 1 1.09 290

2 3.75 80

Blue lupine:

5 _ 2 .32 1,990

3 .41 1,550

4 .56 1,140

6 1.15 550

8 2.25 275

10 ___ 1 .29 1,100

2 .42 760

3 .74 430

4 1.10 270

6 2.83 110

8 3.65 85

20 1 .35 470

2 .75 210

3 1.60 100

4 3.05 50

Crimson clover:

5 _ 1 .52 1,225

2 1.39 460

3 2.95 220

10 1 .82 390

2 2.65 120

Fescue, Ky. 31:

5 _ 1 .37 1,720

2 .77 830

3 1.51 420

4 2.45 260

10 1 .51 625

2 1.35 240

3 3.04 100

20 1 .80 200

2 3.05 50

Kobe lespedleza:

5 _ 1 .33 1,930

2 .59 1,080

3 1.06 600

See footnotes at end of table.
100 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

TABLE 18.—Static pressures and estimated quantities of various seeds

and grains that can be dried per batch per fan horsepower for

different airflows and seed depths^—Continued

Seed and

airflow per Seed Static Maximum quantity

that can be dried

bushel

(ft^/min)

depth pressure»

per fan horsepower^

Ft Water gage in Bu

Kobe lespedeza—Continued

4 1.81 350

6 4.03 160

10 _ ___ 1 .42 760

2 1.00 320

3 2.14 150

4 3.93 80

20 _ .__ 1 .62 260

2 2.09 75

Lespedeza sericea:

5 __ .__ 1 .66 960

2 1.93 330

10 _ .__ 1 1.09 290

2 3.75 80

20 _ ___ 1 2.00 80

Oats:

5 __ .__ 2 .47 1,350

3 .82 780

4 1.29 490

6 3.01 210

10 _ .__ 1 .36 880

2 .77 410

3 1.63 200

4 3.05 100

20 _ .__ 1 .51 310

2 1.65 100

Rescuegrass:

5 __ .__ 2 .33 1,930

3 .46 1,380

4 .65 980

6 1.21 525

8 2.25 280

10 _ .__ 1 .29 1,100

2 .44 720

3 .73 430

4 1.25 250

6 3.01 100

20 _ .__ 1 .34 470

2 .75 200

3 1.63 100

4 3.05 50

See footnotes at end of table.
PRINCIPLES AND PRACTICES OF SEED STORAGE 101

TABLE 18.—Static pressures and estimated quantities of various seeds

and grains that can be dried per batch per fan horsepower for

different airflows and seed depths^—Continued

Seed and

airflow per

bushel

(ft3/min)

Seed

depth

Static

pressure2

Maximum quantity

that can be dried

per fan horsepowers

Ft Water gage in Bu

Soybean:

5 __- 2 .33 1,930

3 .43 1,480

4 .62 1,025

6 1.25 510

8 2.33 270

10 _. 1 .29 1,100

2 .44 720

3 .70 450

4 1.29 250

6 3.19 100

20 _- 1 .35 470

2 .77 200

3 1.72 90

4 3.25 50

Wheat:

5 __. 1 .33 1,930

2 .59 1,080

3 1.06 600

4 1.85 340

10 _- 1 .42 760

2 1.05 300

3 2.11 150

20 _- 1 .65 240

2 2.25 70

iData from Wheeler and Hill (1957).

2 Includes 0.25-in allowance for loss from duct friction.

3 Airflow (ft3/min) per horsepower based on formula

ft^ min

cent.

static efficiency

0.000157 X static pressure

-, with static efficiency assumed here at 50 pertemperature of the air, and the amount of air movement desired. Each

layer of seed is partially dried before the next is added. The rate at

which the dryer can be filled depends on the amount of moisture to be

removed and how rapidly it is removed. The entire depth, of seed is

finally dried in place. Because the dried seeds remain in the dryer, this

type of dryer is not satisfactory for large operations or for those that

require a variety of drying conditions.
102 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

I I

FIGURE 8.—Diagram of air duct arrangement for square, round, and rectangular

in-storage seed and grain dryers.

Harvesting for storage in layer dryers can be accelerated by using

several bins, supplemental heat, or both (fig. 9). However, the amount

of heat used must not overdry the lower layers of seed before the top

layers are dried. One cannot simply turn up the heat to dry faster

because this may seriously overdry the lower layers. According to

McKenzie (1966), layer drying, contrary to popular belief, requires

superior management. Layer drying is suitable for on-the-farm drying

of corn, soybean, and cereal grain seeds.

Batch Dryers.—Batch dryers may be either portable or stationary.

Portable batch dryers may or may not have a burner attached. Some

batch dryers are specially designed wagons with porous beds that

permit heated or unheated air to be forced upward through the seeds,

whereas others are simply drying chambers. The wagon-type dryer can

be taken to the field for filling, whereas the other types cannot. In any

case, the batch-type dryer can dry only a fixed amount of seed at a time.

After drying, the seed has to be cooled before it can be transferred to

storage. Because of the time involved in drying and cooling, it is

necessary to have several drying chambers for efficient harvesting and

drying of seed crops. Since stationary batch dryers usually have a
PRINCIPLES AND PRACTICES OF SEED STORAGE 103

FIGURE 9.—In-bin layer drying with supplemental heat. Bins are filled in rotation, one

layer at a time. As each layer partially dries, successive layers are added until

storage is full and the grain is dried in place. (Courtesy of Bruce McKenzie, Purdue

Univ.)

greater capacity than portable dryers, they are preferable for commercial installations.

Stationary batch dryers may be a bin, column, or rotary drum. In

bin dryers the seeds are spread over a perforated floor, and in a column

dryer they stand in a vertical column. Depth of seeds over the floor or in

the column varies with the type of seed being dried. In the rotary

dryers a revolving, perforated drum slowly tumbles the seeds as heated

air passes through them.

Batch-type dryer installations vary from a single drying chamber to

many such chambers. Batch-type drying plants generally utilize one of

five drying systems: (1) Double or two pass, (2) single-pass reversing,

(3) single pass, (4) suction, or (5) tunnel. Batch dryers are suitable for

both on and off the farm drying of many kinds of seeds, including cereal

grains, corn, millet, sorghum, and soybean.

In the double- or two-pass drying system (fig. 10), the heated drying

air is first directed through a bin containing nearly dry seeds, where the

air picks up a small amount of moisture and loses a little of its heat. The

air is then transferred and exhausted through a bin of high moisture

content seeds, which need warming up. The double pass makes a more
104 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

FILLING AND EXHAUST

y AIR DOORS \

DRIER EAR CORN

UNLOADING

DOORS

, UPPER AIR

DOORS

HOT AIR

TUNNEL

-

TRANSFER

AIR TUNNEL

LOWER AIR

" DOORS '

WETTER EAR CORN

UNLOADING

DOORS

5 22+<

12

FIGURE 10.—Double- or two-pass drying system. (Courtesy of Corn States Hybrid Serv.

Des Moines, Iowa.)

complicated drying system; however, it adds about 25 percent to the

drying capacity of a drying plant and reduces fuel costs substantially,

although power costs are increased some. The two-pass system provides added protection to the viability of the seeds by using cooler air

(27°- 32° C) on the higher moisture seeds. Only the relatively dry seeds

are subjected to a possible 43°.

For the single-pass reversing drying system (fig. 11), the seed drying

plant is designed to allow a single pass of air with provisions for

reversing the direction of airflow through the various bins to facilitate

uniform drying. In the single-pass system the air goes through the seed

and is exhausted. During the early stages of drying, a great deal of heat

is transferred from the air to the seeds and considerable water is taken

up by the air; however, toward the end of the drying cycle, little heat or

moisture is transferred, resulting in considerable drying potential being

wasted. This method has approximately 80 percent of the drying

efficiency of the two-pass system.

The single-pass system (fig. 11) has no provision for reversing airflow; consequently, it has only about 75 percent of the efficiency of the

two-pass system. With this system the seeds on the bottom of the bin

will be overdried and those on the top underdried. A uniform moisture

content is obtained by blending after the seeds are removed from the

dryer.

In the suction drying system (fig. 12) the blower is placed at the

exhaust side of the drying bins. This system can be used with either the
PRINCIPLES AND PRACTICES OF SEED STORAGE 105

FILLING AND EXHAUST AIR

y" ROOF DOORS N^

EAR CORN:

Lower Exhaust Air Doors Used

on Single-Pass Reversing

ONLY. Typical Both Sides

^Top Air DoorS'

Used on SinglePass Reversing

ONLY

HOT AIR

TUNNEL

BOTTOM AIR

DOORS

FIGURE 11.—Single-pass and single-pass reversing drying system. (Courtesy of Corn

States Hybrid Serv., Des Moines, Iowa.)

Louvers to Cool Bins Prior

to Shelling-Open Fill Door

and Exhaust Air Door-Close

All Others

TRANSFER

AIR TUNNEL

EAR CORN

EXHAUST

AIR TUNNEL

-Top Transfer Air Doors

Typical

^.är- Unload Doors

Typical

FIGURE 12.—Suction two-pass drying system. (Courtesy of Corn States Hybrid Serv.,

Des Moines, Iowa.)

one-pass or two-pass design and is worthy of careful consideration when

a new installation is planned.

The tunnel dryer is another form of the heated air batch dryer. It is

used for certain vegetable seeds, such as cucumber, muskmelon, and

tomato, and for drying seeds in bags. Because vine crop and tomato
106 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

seeds have to be washed to remove adhering fruit pulp, they require

rapid drying immediately after washing. Rapid drying is accomplished

by spreading the seeds in thin layers in screen-bottom trays, which are

either placed in a tunnel dryer or dried in the sun, as explained

previously. Tunnel dryers consist of open trenches through which

heated air is circulated up through the seeds in the trays. Seeds in bags

can be dried in a tunnel dryer by building the tunnel with a cover having

special holes over which the bags of seeds are placed. This is the most

inefficient system of drying seeds. A tunnel dryer can be constructed

with a capacity to meet a specific need.

Continuous Flow Dryers.—The continuous now dryer may be horizontal or vertical (fig. 13). It is called continuous flow because the seeds

move slowly from the point of entry to the point of exit and are dried as

they move through the unit. A continuous flow dryer is not suited for

drying small quantities. For best efficiency, the system must be full of

seeds at all times. Consequently, the continuous flow dryer is not at all

suited to an operation requiring frequent changes from one kind or

cultivar of seed to another. Its greatest value is for grain drying where

thousands of bushels of a single cultivar can be dried without interruption.

Modification of Basic Dryer System,—The dryeration (fig. 14) represents a new grain drying process developed at Purdue University. It is

a combination of high-speed and high-temperature drying and slow

cooling (McKenzie et al., 1968). With the dryeration process, no cooling

is done in the dryer. Grain is discharged at 50° to 60° C from the dryer,

still carrying 1- to 3-percent excess moisture into a separate cooling bin.

The hot grain is held without mechanical cooling for a tempering period.

It is then cooled slowly to remove the excess moisture before being

transferred, dry and cool, to storage or load out. The dryeration

process, because of the high drying temperature and the tempering

period, may not be as satisfactory for seed drying as it is for grain

drying.

Dehumidified Air Systems.—In dehumidified air systems, a dehumidifier dries the air before it is heated and passed through the seeds. The

air dryer converts the latent heat in the moisture to sensible heat in the

drying airstream, which lowers the relative humidity of the air by

decreasing the total moisture in the air. The rise in temperature

associated with dehydration reduces the amount of heat needed from

the main heat source, which reduces fuel costs while drying efficiency is

increased. Dehumidified air can be used with either a batch-type or a

continuous flow dryer. All that is required is to install a dehumidifier in

the air delivery system.

Dehumidification, although generally used with a closed system, can

be incorporated into any drying system. The air passes through the
PRINCIPLES AND PRACTICES OF SEED STORAGE 107

FIGURE 13.—Vertical continuous flow dryer. (Courtesy of Ferrell-Ross, Oklahoma City,

Okla.)

dehumidification medium, usually silica gel, and then is circulated

through the rest of the system back to the dehumidifier (fig. 15). Since

the drying medium has to be recharged or dried out, either a two-tower

or a rotary system is used. With the two-tower system (fig. 16), one

tower dehydrates the air while the drying medium in the other tower is

being dried. The switch from one tower to the other is automatic. With

a rotary dehumidifier (figs. 17, 18) the drying agent is held in a circular

unit, which continuously rotates so that one section is drying the air

while the desiccant in another section is being dried.
108 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

WET CORN IN

20-30%

DRYER

BATCH OR

CONTINUOUS

(93° C)

-T-rTO STORAGE

OR MARKET

FIGURE 14.—Schematic flow diagram of dryeration process. (Courtesy of Coop. Ext.

Serv., Purdue Univ.)

In general, seed drying plants are custom engineered for specific

purposes (figs. 19, 20). For example, a dryer plant designed to dry ear

corn cannot be used to dry Kentucky bluegrass strippings. Dryers, as

well as drying plants, are sometimes designed for special purposes. A

special-purpose dryer (fig. 21) was developed by the National Seed

Storage Laboratory for conditioning small quantities of seed for storage

research projects. The trays used in the dryer were designed for loose

seed; however, by means of a system of cross wires to allow air

movement between packets, the trays can be used for either bulk or

packet drying, especially if the wire grid is removable.

A special walk-in seed-drying room was constructed at the New York

Agricultural Experiment Station to handle relatively large samples of

plant materials in bags (fig. 22) (Dolan et al., 1973).

Miscellaneous Dryers.—Seeds can also be dried under a partial

vacuum, by the freeze-drying process, or by infrared radiation

(Schroeder and Rosberg, 1959), all of which are used extensively in the

food industry. Each of these drying methods has certain advantages

and disadvantages. In general, they are more costly than conventional

drying methods, and in some cases they are suitable only for drying

small quantities of seed. In vacuum and freeze-drying, seed moisture

content can be reduced to very low levels without using excessively high

temperatures. Seed dried to moisture levels below air dryness must be

stored in either moisture-barrier containers or dehumidified rooms;

otherwise the advantage of such drying will soon be lost through

rehydration.

Much of this information was reported by Anderson and Alcock

(1954), Hall (1957), Wheeler and Hill (1957), Brandenburg et al. (1961),

Kreyger (1963a, 1963b, 1972), Barre (1963), McKenzie (1966), McKenzie
PRINCIPLES AND PRACTICES OF SEED STORAGE 109

et al. (1968), Harrington and Douglas (1970), Peterson (1971), and

Philpot (1976),

Factors To Consider in Selecting a Dryer System

Drying Capacity,—The drying capacity should be sufficiently large to

permit continuous, efficient harvest of the seed crop, regardless of

WARM

DRY á^

AIR

WARM

DRY á ^ AIR

WARM

DRY

AIR

HYDRYER PLANT

FRESH AIR WASTE AIR

^'

BURNERS

H FAN OO *\

\r/^ •^ >

MAIN

FAN pxO)

V FAN %/

./, ty>

BURNERS 0 K. "^ 4<

^ DRY AIR

^ FRESH AIR

FRESH AIR

PLAN VIEW

/ \

iOOl ^ FRESH AIR

FRESH AIR

SIDE VIEW

BURNERS

FRESH AIR

I MIXED

' AIR

FRESH AIR

^DRY

AIR

AIR

DRYER

UNIT

^ FRESH AIR

FLOW DIAGRAM

FIGURE 15.—Flow dia^ams of air movement through a combination dehumidified-air

heated-air dryer system. (Courtesy of Corn States Hybrid Serv., Des Moines, Iowa.)
no AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

whether only one or several cultivars are to be dried. Daily capacity of

the drying system should efficiently handle one day's harvest.

Investment Necessary To Get Capacity.—If the investment in drying

capacity is excessively high, costs of drying are bound to be high. Since

ownership costs are often about half the cost of drying, the initial cost

as well as the maintenance costs should be carefully considered when

selecting a dryer.

Fuel and Power Costs.—The cost of fuel to heat the drying air and

PN-5399

FIGURE 16.—Two-tower dehumidifler for use in storehouses. (Courtesy of Seedburo

Equipment Co., Chicago, 111.)
PRINCIPLES AND PRACTICES OF SEED STORAGE 111

power to operate the fan may not vary much among dryers; however,

such costs must be included when total cost of drying is calculated.

Since high-speed systems tend to increase costs more than capacity,

they cost more to operate.

Airflow.—Efficiency of a dryer is directly related to airflow, which is

determined by the output of the fan. Generally the airflow per horsepower does not vary greatly among fans of comparable size. However,

some industry rating practices are confusing. For example, fan motors

sometimes deliver more horsepower than their nameplate rating.

Nameplates on fan motors sometimes carry a dual rating, showing a

range of horsepower. Such practices tend to make one fan seem more

efficient than another with the same horsepower rating when the

difference is actually the result of one motor delivering a higher

horsepower.

FIGURE 17.—Cutaway view of a rotary dehumidifier. (Courtesy of Com States Hybrid

Serv., Des Moines, Iowa.)
112 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

HN-5400

FIGURE 18.—High capacity rotary dehumidifler with 50,000 cubic-foot-per-minute airflow. Equipment includes a 150,000 cubic-foot-per-minute capacity main blower and

air-heater unit. (Courtesy of Corn States Hybrid Serv., Des Moines, Iowa.)

'-^

FIGURE 19.—This com drying plant utilizes the most recent advancements in drying and

handling equipment. (Courtesy of Equipment Specialists, Inc., Taylorville, 111.)
PRINCIPLES AND PRACTICES OF SEED STORAGE 113

PN-5402

FIGURE 20.—^The dried ear com from figure 19 passes from the bins along the permanent

discharge conveyor directly into the sheller. (Courtesy of Equipment Specialists,

Inc., Taylorville, 111.)

Heat Input and Drying Temperature.—Assuming the airflow is sufficient for the drying method used, failure of a system is usually the

result of heat management. Systems fail because of too much or too

little heat. Too much heat reduces seed quality, and too little heat slows

drying. There are desirable and workable air-heat ratios for each dryer

system. These ratios vary with the dryer and the kind of seed. For best

quality, seed temperature should not exceed 43° C for grain and 32° for

vegetable seeds. Higher temperatures will increase drying rate but will

also reduce seed quality. Air temperature can exceed seed temperature

if the seed is not exposed long enough to reach air temperature or pass

critical limits. Table 19 gives effects of heating time, temperature, and

seed moistui-e content on loss of viability for several kinds of seed.

Laboratory studies by Bass (1953) and Grabe (1957) showed that the

higher the moisture content of Kentucky bluegrass and smooth bromegrass seeds, the lower the temperature and the shorter the time at that

temperature required to bring about viability or germination loss (fig.

23) (table 20). Grabe (1957) also showed the effects of various temperatures and drying periods on the germination of smooth bromegrass

seeds (table 21). He noted that none of the temperature-time treatments used adversely affected the germination of smooth bromegrass

seeds, even after 29 months of storage.
114 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

J

I'N-540:i, PN-54Ü4

FIGURE 21.—Seed dryer developed by National Seed Storage Laboratory, Fort Collins,

Colo. Above, assembled; below, disassembled, showing twin-blower air diffuser (A),

top ventilation holes (B), and screen-bottom seed tray (C).
PRINCIPLES AND PRACTICES OF SEED STORAGE 115

- i-A

t

«a

2/

LS

PN-5405

FIGURE 22.—Interior of a seed-drying room, showing slotted floor, plywood covers, exit

duets, and inlet hot air duct near ceiling. (Courtesy of N.Y. Agr. Expt. Sta.,

Geneva.)

Williams (1938) reported that it is advisable to remove excess moisture from perennial ryegrass, timothy, and orchardgrass (cocksfoot)

seeds as quickly as possible after harvest. He referred to excess

moisture as being that above the norms he set. They were about 14

percent for ryegrass, 13.6 percent for timothy, and 13 percent for

orchardgrass. Because of their greater rate of absorption and slower

rate of drying, seeds of perennial ryegrass require more careful atten-
116 AGRICULTURE HANDBOOK 506. U.S. DEPT. OF AGRICULTURE

TABLE 19.—Effect of different heating times on viability of various

seeds at different seed temperatures and moisture contents (static

conditions)^

Effect of heating time on seed viability^ at

Seed Moisture indicated seed temperature (°C)

content

30 40 50 60 70

Percent Hours Hours Hours Hours Hours

Broadbean 12 4- 4- 2- Vk- 1/4*

16 4- 4- 2- 1/4* '/«*

24 3- 3- 1* ^/«* '/«*

Lupine 10 4- 4- 2- 11/2* 1-

14 4- 4- 2- IV2* 1/2*

19 3- 3- 2- 1/2* '/«*

Maize 12 4- 4- 2- 1/4* v^*

15 4- 4- 1/2* 1/4* '/«*

21 3- 3- 1/2* 1/4* '/«*

Oats 12 4- 4- 2- 1^2- 1/4*

14 4- 4- 2- 1/4* ,/^*

19 3- 3- 1/2* 1/4* '//

Pea 12 4- 4- 2- 11/2* 1/4*

15 4- 4- 2- IV2* 1/4*

21 3- 3- 1/2* ^/«* v^*

Rape 6 4- 4- 2- iy2- 1-

9 4- 4- 2- IV2- 1/4*

13 3- 3- 2* 1/2* '//

Rye 13 4- 4- 2- 1/4* ^/e*

16 4- 4- 1/2* 1/4* '/«*

21 3- 3- 1/2* 1/4* '/«*

Ryegrass 12 4- 4- 2- Vh- 1-

15 4- 4- 2- 11/2* 1/4*

22 3- 3- 2* 1/4* v^*

Sugar beet 11 4- 4- 2- 1/2* 1/4*

15 4- 4- 2- 1/4* 1/4*

20 3- 3- 2- 1/4* 14*

iData from Kreyger (196S).

2Asterisk (*) indicates decrease and dash (-) no decrease in viability.

tion during drying than those of orchardgrass and timothy. A current of

warm air at not more than 43° C alternating with a cool (15°-18°) one (20

min warm, 10 min cool) is particularly beneficial for drying ryegrass and

orchardgrass seeds. Drying with a continuous warm air current adversely affected viability, even when the temperature did not exceed

35°.

Wileman and Ullstrup (1945) found that germination of ear corn with

an initial moisture content of 35 percent or more dropped rapidly when

dried at 49° C; however, corn with 25 percent or less initial moisture

suffered no appreciable germination loss when dried at 49°, whereas
PRINCIPLES AND PRACTICES OF SEED STORAGE 117

corn with 20 percent or less initial moisture showed no germination loss

when dried at 54°.

Drying at too high a temperature or too rapidly can drastically reduce

seed viability (Toole and Toole, 1946; Griffith and Harrison, 1954; Raun

100

HAND HARVESTED 20 C

^^--j^,^^:^^^-^

z

LU

U

z

o

I-<

z

cc

60

40

20

54% MOISTURE

40% MOISTURE

22% MOISTURE

11% MOISTURE

4 8 16 24 32 40 48

HOURS AFTER HARVEST

100

HAND HARVESTED 30 C

<

Z

CC

4 8 16 24 32 40 48 56

HOURS AFTER HARVEST

100

^ 60

z

o

I-<

z

cc

HAND HARVESTED 40 C

100

HAND HARVESTED 50 C

I 16 24 32 40 48 56

HOURS AFTER HARVEST

cc

LU

4 8 16 24 32 40 48

HOURS AFTER HARVEST

HAND HARVESTED 60 C HAND HARVESTED 70" C

1ÜÜ

>/^^ \

100

h- -; ~~A 1-

?» 80 f \ \ z 80

Ill \

LU

Ü I O

cc ( \

\

OC

LU

60 \

UJ

Q. 60

z \ Z

o \ o

h- 40 [\ \ 1- 40 < \

<

Z - z

^ \ ^

CC 70 \ cc 70

UJ LU

C5 ^ \ ü

0

I \ _^

0

4 8 16 24 32 40 48 56

HOURS AFTER HARVEST

4 8 16 24 32 40 48 56

HOURS AFTER HARVEST

Fi(;URE 23.—Germination of Kentucky bluegrass seeds with four moisture contents after

4-48 hours at various temperatures without drying.
TABLE 20.—Viability of bromegrass seed as affected by interactions of temperature, moisture content, and duration of

treatment in 1953 and 1954 laboratory studies

Year, temperature,

and moisture

content

(percent)

1953

Viability after indicated hours of heat treatment

12

Percent

40° C:

56.6 88

51.4 93

39.3 83

32.4 89

20.0 95

13.2 93

50° C:

56.6 88

51.4 93

39.3 83

32.4 89

20.0 95

13.2 93

60° C:

56.6 88

51.4 93

39.3 83

32.4 89

Percent

91

94

99

93

96

40

79

90

93

91

94

1

4

41

69

84

90

90

97

94

94

5

30

72

89

92

95

1

0

2

27

87

92

92

94

92

90

0

12

67

90

93

0

0

2

29

20 28

91

94

89

93

97

90

0

3

34

75

91

94

0

0

0

0

89

90

89

96

95

96

0

0

6

49

92

99

0

0

0

0

36

Percent Percent Percent Percent Percent

93

85

94

95

96

0

0

3

32

89

95

0

0

0

0

44

Percent

90

91

88

91

93

86

0

0

1

11

73

87

0

0

0

0

52

Percent

87

88

86

92

95

91

0

0

1

5

89

93

0

0

0

0

00

>

o

2

o

a

r

c!

?d

M

K

>

o

o

o

>

o

2

o

(^

H

a

w
20.0

13.2

1954

40'

50'

C:

38.1

28.4

15.0

C:

e38.1

28.4 .

15.0

60° C:

38.1

28.4

15.0

95

93

91

89

91

91

89

91

91

89

91

84

91

85

95

84

93

85

93

1

94

O

97

63

90

96

20O

91

84

89

91OO

85

82

90OO

73

38

77

90OO

72

19

79

93OO

70

21

12

92OO

63

O

94

12O

90OO

34

85

90

93O

90OOO

S25orw>>oHOw

COO

C/2 MWO

C/2 O>O^
TABLE 21.—Summary of results of artificial drying experiments on germination of 13 lots of

smooth bromegrass seed in 1953 and 1954^

to

o

Year and Moisture content Germination

lot size Drying Temperature Drying

(lb) temperature of seeds time Before After Before After

°C

1953

Unknown

Do

Do

Do

Do

Do ^

Do ^

Do

917

900

2,100 .

2,400

5,600 ^

1954

49

52

- 55

60

^3,,52

^9,. 60

^9, 66, 71

60

_„ 66

_ 77

99

Hours Percent Percent Percent Percent

83

90

93

90

91

91

91

89

90

90

96

92

96

40 4V4 20.0 13.0 81

30 4 20.2 14.9 91

41 31/4 17.0 11.4 94

55 3% 21.0 12.0 86

65 1^4 21.3 12.3 92

48 2, 2 20.8 13.3 84

50 2, 21/2 28.8 17.0 90

56 2, 1, 21/4 27.2 16.0 90

64 1 14.5 6.7 89

62 2 23.9 5.9 91

76 2 19.4 7.7 93

84 2 12.1 5.0 93

85 4 14.3 95

iData from Grabe (1957),

-'Maximum temperatures in bottom 6 inches; temperatures in remainder of load were lower than these data.

^Seed dried 2 hours at lower temperature, then completed at higher temperatures.

>

o

2

o

c:

r

c:

?o

m

>

o

00

o

o

o

o

>

o

2

o

r
PRINCIPLES AND PRACTICES OF SEED STORAGE 121

and Frey, 1957), Excessive drying can also result in loss of viability and

the development of seedling abnormalities, especially under certain

storage conditions (Evans, 1957b; Nutile, 1964a, 1964b), Heated airdrying may induce a dormant condition, which can seriously affect field

stand establishment unless it is overcome before planting (Wright and

Kinch, 1962; Nutile and Woodstock, 1967).

Handling and Labor Requirements,—The various drying methods

obviously differ in the amount of handling equipment and labor needed.

In-storage layer drying involves two seed handling operations—filling

and unloading the bin. Batch and continuous flow drying require four

operations, namely, loading and unloading the dryer and filling and

unloading the bin. The volume of seed to be dried determines handling

equipment cost rather than the type of dryer. A large volume of seed

requires a more elaborate and expensive seed handling system.

Weather.—Weather is a major factor in seed drying operations. It

determines the amount of time available for harvesting and drying a

seed crop. Extended periods of cool, damp weather can markedly

increase harvesting and drying costs, whereas hot, dry winds can

reduce such costs. During periods of wet weather, extra heat and air

movement are required for efficient drying. During periods of hot, dry

weather, the amount of supplemental heat needed for rapid drying is

much less than that required during warm, humid weather.

Drying Rate,—The rate at which moisture leaves a seed depends on

how much the seed lacks moisture equilibrium with the air surrounding

it, the air temperature, and the composition, size, and shape of the seed.

When the initial seed moisture content is high, the rate is faster if the

temperature is high or if relative humidity is low. A change from very

slow to rapid air movement will increase the rate of drying. The rate of

drying drops off as the moisture content of the seed decreases. This

means that as the moisture content of seed decreases, longer exposure

to heat is required for each percentage of moisture removed.

In bulk drying the rate of moisture loss is not uniform throughout the

depth of seeds in a dryer. As the seeds dry, the interface between dry

and wet seeds gradually moves through the seed layer. Since the seeds

nearest the heated air source dry fastest and those farthest away dry

slowest, there is always a range in seed moisture levels through the

layer of seeds in a dryer.

The drying rate for individual kinds of seeds depends on their

individual properties as to release of moisture. However, various kinds

can be grouped with regard to their tendency to release moisture

(Kreyger, 1963a). There are fast drying seeds such as grasses, rape,

and sugar beet; normal drying seeds such as barley, oats, rice, rye, and

wheat; and slow drying seeds such as bean, corn, lupine, and pea (table

22).
122 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

TABLE 22.—Comparison of approximate rates of drying and releasing

moisture at 5 moisture contents for various seeds^

Seed and Rates at indicated moisture content (percent)- wet basis

drying group

22 20 18 16 14

DRYING PER °C PER HOUR

Percent Percent Percent Percent Percent

Broadbean 0.14 0.08 0.05 0.03 0.016

Garden pea (green) .19 .11 .07 .045 .03

Lupine .33 .19 .11 .07 .04

Maize - .27 .18 .10 .06 .03

Oats .9 .5 .3 .2 .12

Rape 3 2.3 1.6 1.0

Rye .45 .35 .23 .14 .07

Ryegrass 1.5 .8 .5 .32 .2

Sugar beet 3.3 2.4 1.6 1.0 .6

Wheat .42 .3 2 .13 .07

RELEASING MOISTURE (TENDENCY)^

Slow drying Number Number Number Num,ber Number

Broadbean 70 40 25 15 8

Garden pea (green) 95 55 35 23 15

Lupine 165 95 55 35 20

Maize 135 90 50 30 15

Normal dryivg

Oats 450 250 150 100 60

Rye 225 175 115 70 35

Wheat 210 150 100 65 35

Qin'ck drying

Rape 1,500 1,150 800 500

Ryegrass 750 400 250 160 100

Sugar beet 1,650 1,200 800 500 300

1 Data from Kreyger (1963a).

^^ Wheat at 18-percent moisture content is taken as 100; all values are relative to this

Williams (1938) found that by using a 20-minute warm air (43° C) and

10-minute cool air (15°-18°) alternation, moisture content of ryegrass,

timothy, and orchardgrass seeds can be reduced about 4.5 percent in

11/2-2 hours. Drying time for 25 percent or lower moisture ear corn can

be reduced about 20 percent by using 49° rather than 43° (Wileman and

Ullstrup, 1945).

The average time required to dry six lots of 21- to 25-percent

moisture ear corn to 12- to 13-percent moisture was reduced from 811/2

to 641/2 hours by raising the drying air from 43° to 49° C and thereby

decreasing its relative humidity. Drying rates for specific kinds of seed

are largely unavailable because such factors as the initial moisture

content, the temperature, relative humidity, and velocity of the air, and

the depth of the seed layer must all be considered simultaneously.
PRINCIPLES AND PRACTICES OF SEED STORAGE 123

A preliminary estimate of drying rate can be obtained by recording

the moisture loss from a known weight of seed held under known drying

conditions for a specified length of time. Knowledge of whether the

kinds of seeds are slow, normal, or fast drying is very helpful in

determining the type of dryer system to install. For example, a continuous flow dryer is generally suitable for quick and normal drying seeds

but not for slow drying seeds, nor is it suitable for nonfree-flowing

seeds. Batch dryers are better for slow drying and nonfree-flowing

seeds. A low temperature is used at the start and gradually increased as

drying progresses. This practice is fairly common in the field corn

seed-producing areas where double-pass dryers are used.

Drying Seeds With Desiccants

Barrow (1915) reported that 5-percent calcium chloride by weight

minimized heating and deterioration of cottonseeds during storage.

Kondo and Isshiki (1936) reported that either calcium oxide or calcium

chloride could be used to desiccate rice seeds. They found that calcium

oxide absorbs only about one-third as much moisture as calcium chloride

but absorbs it faster. One kg of calcium chloride or 3 kg of calcium oxide

will absorb 1-percent moisture from 5.1 bushels of rice. According to

Kondo and Terasaka (1936), both calcium chloride and calcium oxide

desiccate rice for safe, sealed storage for food but not for seeds. Dexter

and Creighton (1948) found that wood blocks impregnated with calcium

chloride, magnesium chloride, magnesium sulfate, or sodium chloride

effectively removed moisture from stored grain; however, they did not

determine what effect, if any, storage with the impregnated wooden

blocks had on germination.

Although seeds can be dried safely with desiccants, drying large

quantities of high moisture seeds with desiccants is neither practical nor

economically feasible because of the large amount of desiccant needed

to remove 1 percent of water from each pound of seed. Use of desiccants with small quantities of seed in sealed containers is discussed

under "Packaging and Packaging Materials."

SEED STORAGE STRUCTURES

A considerable amount of seed becomes useless each year from

improper storage. Seeds must be stored dry and kept dry. As previously indicated, longevity of seeds is controlled primarily by seed

moisture content and storage temperature. For maximum storage life,

these two conditions must be carefully controlled. However, much of

the seed produced each year needs to be stored only from harvest until

the next planting season. Such seed may or may not require storage

under conditions other than normal air temperature and relative humidity depending on the kind of seed and the local climate. A seed
124 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

storage facility must have certain basic features, regardless of any

adaptations for special purposes (Barre, 1954; Wheeler and Hill, 1957).

Basic Features of Storage Structures

Protection From Water

Rain, snow, ground moisture, or any source of water should never be

allowed to come in contact with seeds, as it increases seed moisture

content. High seed moisture content increases respiration, heating, and

mold growth and sometimes promotes sprouting in storage, all of which

decrease seed quality. The roof and sidewalls of seed storage structures

must be free of holes and cracks that permit the entry of rain or snow.

Cracks and knotholes in wood walls and roofs should be filled. All bolts

and screws in metal buildings should have rubber washers, especially

those in the roof. Since soil moisture can be absorbed readily on contact

by seeds, all seed storage structures must have a waterproof ñoor. A

wood floor should be elevated and a concrete floor should have a

moisture barrier under it. A metal floor is naturally impermeable to

water but will soon rust out if kept moist continually.

Protection From Contamination

Because individual seeds of different cultivars of various crops are

indistinguishable from each other and because the kinds of seeds are

often difficult to separate, each seed lot must be kept free of seeds from

other lots. Storage facilities should be constructed to provide maximum

protection from chance contamination. For bulk storage, a separate bin

must be provided for each cultivar. For bag storage, seeds of each

cultivar must be stacked separately. Seeds may also be stored in

toteboxes. Toteboxes and stacks of bags on pallets can be moved readily

by a forklift. All bags, toteboxes, and bins must be carefully and

conspicuously labeled.

Protection From Rodents

Since large quantities of seeds may be lost because of inadequate

protection from rodents, precautions must be taken to prevent their

entry into storage buildings. Metal and concrete buildings normally

provide good protection from rodents. With care, wood buildings can

also be constructed to keep them out. Metal bins with tight covers

provide rodent protection, and cloth bags can be treated to repel

rodents. For further information, see the section on "Effects of Pests

and Chemicals on Seed Deterioration in Storage."

Protection From Insects

Although insects do not constitute a major problem with some kinds

of seeds, a good storage facility should be so constructed that any part.
PRINCIPLES AND PRACTICES OF SEED STORAGE 125

or all of it, can be fumigated to control insects at any time. Insect

problems can be kept to a minimum by thoroughly cleaning and fumigating each time a bin is emptied. Areas where bags and toteboxes are

stored should be kept free of loose seeds and trash at all times.

Cleanliness eliminates insect breeding places and facilitates insect control. For further information, see "Effects of Pests and Chemicals on

Seed Deterioration in Storage.''

Protection From Fungi

Under certain circumstances, storage fungi can cause considerable

damage to stored seeds. Since fungi grow best under warm, humid

conditions, storage structures should provide cool, dry conditions.

Damage from storage fungi can be kept to a minimum by carefully

drying seeds to a safe moisture content, usually less than 12 percent,

and holding them under dry conditions. Sometimes ventilation of

storage structures, especially steel buildings, is necessary to prevent

the accumulation of translocated moisture. Temperature differentials

can cause water vapor to move from warmer to cooler areas of a bin,

usually to the upper surface. Such moisture movement can provide

conditions favorable for fungus growth unless adequate precautions are

taken to prevent its accumulation. Seeds can be treated with various

chemicals to control fungi. Fungicides are applied routinely to many

kinds of seeds as part of their normal processing. However, fungicides

to control soil fungi may not control storage fungi. For further information, refer to "Effects of Pests and Chemicals on Seed Deterioration

in Storage."

Protection From Fire

Danger from fire loss is greatest with wood buildings; however, wood

can be chemically treated to retard burning. The hazard of a fire in wood

buildings can be reduced by cleanliness, both inside and around the

building. All seed storage buildings, especially processing areas, should

be equipped with special dustproof and sparkproof electrical outlets and

switches, which greatly reduce the chances of an electrical fire. All

wiring should be rodentproof. Although metal and concrete buildings

are fireproof, the same electrical wiring precautions should be practiced

in them as in wood buildings because dust explosions and fires can be

caused by electric sparks. Structures with these general characteristics

should provide safe storage for most kinds of seeds from harvest to the

next planting season, except in areas with extremely high temperatures

and relative humidity. In such areas, additional protective measures,

namely temperature and humidity control, are required to maintain

seed quality during storage.
126 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Types of Storage Structures

Farm Storage

Farm storage is usually for a few days or weeks during the harvest

season. Seeds are seldom held on the farm longer than from harvest to

the next planting season. They may be stored in bins, bags, or in some

cases on the ground. Ground storage is generally temporary and used

only in an emergency. Bulk lots may be stored in wood or metal bins,

granaries, and barns. Seeds, unless very dry, keep better in wood than

in metal buildings because heat buildup is greater and moisture loss is

slower in metal than in wood buildings. Heat accumulation in metal

buildings can seriously reduce the viability of seed stored with high

moisture. Heat buildup can be reduced by painting the outside of the

building white, by ventilation, or both. Seeds in bags may be stored in

any farm building where space is available. This practice frequently

causes large losses through insect and rodent damage. When bagged

with a high moisture content, seed will heat and soon become worthless.

(Barre, 1954; Wheeler and Hill, 1957; Harrington and Douglas, 1970)

Country Elevator Storage

Many country elevators accumulate seeds during and immediately

after harvest. Storage, which is usually for a limited time, may be

either in bulk, in wood or metal bins, in concrete silos, or in bags or

toteboxes in wood, brick, concrete, or metal buildings. Country elevators frequently have a fanning mill to remove trash before storing

seeds. Fanning also helps reduce seed moisture content. Country elevators frequently have facilities for insect and rodent control and may

have drying equipment (Barre, 1954).

Seed Processor Storage

Seed processors as a group store a major part of the seeds held for

future use in the United States. Their storage facilities vary widely in

size and construction, ranging from small wood or metal buildings to

large multistoried wood, brick, or concrete warehouses. Some processors use well-insulated rooms, in which the temperature and relative

humidity are controlled for maximum viability protection, especially for

high-cost items. Seed processors store both processed and unprocessed

seeds. Uncleaned seeds may be put in bags, pallet boxes, or bulk bins.

Each container has certain advantages and disadvantages for specific

kinds of seeds. Uncleaned seeds are usually stored in an area well

separated from where the cleaned seeds are stored. Completely processed seeds are generally stored in the container in which they will be

shipped. Some processed seeds are stored by the processor in retail

packages, but other seeds are repackaged by the retailer. Storage

facilities operated by seed processors usually have the basic require-
PRINCIPLES AND PRACTICES OF SEED STORAGE 127

ments previously discussed and may also provide for special needs of

individual kinds of seeds and for protection from unfavorable climatic

conditions.

Retail Storage

Seed retailers must hold their stock for varying lengths of time,

usually under normal atmospheric conditions for their individual locations. Retail storage is usually far from ideal; however, except in very

hot, humid areas, the shelf life of seeds in cloth, paper, or thin plastic

containers is usually sufficiently long to permit marketing with little loss

of viability. In hot, humid areas, shelf life of seeds is limited unless they

are dried to a safe level of 5- to 8-percent moisture and put in moisture-barrier packages. At the retail level little or no attempt is made to

provide protective storage.

Research Storage

Scientists must store varying quantities of specific seed stocks in

order to have viable seeds available for their research. Although

refrigerated, dehumidified storage is best suited for long-term holding

of seeds, such conditions are not uniformly available to research scientists. They frequently must use less than ideal conditions, although

ordinarily they use the best facilities available.

In some geographic areas, numerous kinds of seeds can be stored

without loss of viability for several years under normal atmospheric

conditions. In tropical and subtropical areas, controlled atmospheric

storage conditions are essential to preserve research seed stocks for

periods longer than a few days. The only alternative method is sealed

storage. For safe, sealed storage for up to 3 to 5 years at ambient

temperatures, seeds must be dried to 5- to 8-percent moisture content

before they are sealed in moistureproof containers. For longer storage,

the moisture content must be reduced to 2.5 to 5 percent before

packaging.

Germ Plasm Storage

Germ plasm preservation centers, such as the U.S. National Seed

Storage Laboratory (fig. 24) (James, 1972), the U.S. Regional Plant

Introduction Stations, the Japanese National Seed Storage Laboratory

(Ito, 1972), and similar facilities throughout the world, must have the

best possible storage conditions to minimize regrowing of seed stocks.

Many kinds of seeds held under the conditions used in the U.S. National

Seed Storage Laboratory do not have to be regrown more frequently

than every 20 or 30 years.

This laboratory is a three-level building. The machine room (fig. 25),

control room, biochemistry laboratory, growth chamber room, custo-
FIGURE 24.—U.S. National Seed Storage Laboratory, Fort Collins, Colo.

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00

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a

a

a

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to

a

X

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D

BO

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PRINCIPLES AND PRACTICES OF SEED STORAGE 129

PN-5407

FIGURE 25.—Machine room of the U.S. National Seed Storage Laboratory, showing some

of the equipment required for a refrigerated storage facility.

dian's supply room, workshop, garage, and a supply storage room are on

the first level. The second level houses the administrative offices. The

seed storage rooms (fig. 26) and germination laboratory (fig. 27) occupy

the third level.

The seed storage rooms, accessible from a common corridor, have a

total capacity of approximately 180,000 pint cans for samples. Seed

sample capacity can be increased manyfold by using containers tailored

to fit the sample. Storage conditions are maintained at about 4° C, with

an average relative humidity of approximately 35 percent. This combination was selected as suitable for storing most kinds of seeds for a

relatively long time. Three of the rooms are equipped to maintain a

temperature as low as -12° if desired. For research purposes a variety

of temperatures and relative humidities are available in smaller rooms

not used for routine storage of germ plasm.

Constructing Controlled Atmosphere Seed Storage

Facilities

Safe storage of seeds requires careful control of both the temperature

and the relative humidity of the storage area. They cannot be controlled

except in specially constructed rooms or buildings. Because of the need
130 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

PN-5408

FIGURE 26.—Sample storage room of the U.S. National Seed Storage Laboratory, where

a scientist is checking samples stored in tin cans.

for effective barriers from outside sources of heat and moisture, the

walls, ceiling, and floor of a seed storage room must have satisfactory

heat insulation and a moisture vapor seal. Figures 28-30 illustrate

construction techniques that will provide the necessary heat and moisture barriers.

Floor insulation is frequently installed in a bed of hot asphalt, which

provides a good vapor seal. The amount of insulation used depends on

the temperature to be maintained and the type of material used, such as

ñber glass, spray on foam, Styrofoam, and cork. Insulating materials
PRINCIPLES AND PRACTICES OF SEED STORAGE 131

PN-5409

FIGURE 27.—Laboratory workers in the U.S. National Seed Storage Laboratory testing

seeds for germination or decline in viability as storage time is increased.

must be kept dry for maximum efficiency. If the material does not have

a characteristic for dryness built into it, moisture protection must be

provided outside the insulation.

Board-type insulation should be applied in two or more layers, with

the joints lapped or staggered to minimize heat and moisture penetration through the joints. To cope with the problem of building movement

with changing temperature, an accordianfold is used in the corner

flashing vapor seal material. Ceiling insulation can be of many kinds.

Ceiling and wall finishes usually consist of one-half inch or more of

cement plaster applied as two coats. Where the wall is subject to shock,

the finish coats are reinforced with galvanized metal lath. Wood, metal,

or concrete bumpers are installed on walls where trucks might accidentally hit them.

Cold storage rooms must have no windows and their doors must be

well insulated and well sealed. For large openings, roller hung doors

may be better than swinging doors. Roller doors not only fit tighter but

can be operated electrically. A relatively new idea is the use of a high

velocity stream of cool air across the face of the door, usually from top

to bottom. This may not be the complete solution to the entrance of heat

and moisture, but it does provide some protection. Double-door air locks
132 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

WEARING

FLOOR

FIGURE 28.—Floor construction of a refrigerated seed or grain storehouse, emphasizing

importance of tight seals and insulation. (Courtesy of Amspec, Inc.)

and small anterooms also help reduce heat and moisture entering cold

storage rooms.

The biggest problems in refrigerated dehumidified storage are heat

and moisture leakage through the walls, roof, floor, and around the

doors; heat generated by the lights; and heat and moisture generated by

people working in the room. These, of course, can best be reduced by

incorporating adequate preventative measures into actual construction

of the storage room or warehouse. It is usually desirable to construct

several controlled temperature rooms rather than a single large warehouse. By having several individually controlled rooms, annual operating costs can be lowered significantly. During periods when only small

quantities of seeds are stored, one or two rooms rather than an entire

warehouse can be refrigerated.

Most refrigerated seed storage facilities use forced air circulated

through a cooling coil, then throughout the room. For large areas, a

duct system distributes the cold air uniformly throughout the room. The

final decision as to the structural design of the building or room and the

size and type of refrigeration system must be left to a competent

refrigeration engineer. It is far better and more economical to install

initially adequate insulation, moisture protection, and refrigeration
PRINCIPLES AND PRACTICES OF SEED STORAGE 133

VENT

CORNER

FLASHING

ASPHALT

EMULSION

MASTIC

SEALER

CHANNEL

SUPPORT

SLIPSHEET

METAL PAN

(FLANGES DOWN)

—^^^^

FIGURE 29.—Metal pan ceiling for blast freezer, emphasizing supporting structure, close

fitting seals, and insulation. (Courtesy of Amspec, Inc.)

capacity than to remodel an unsatisfactory system. For further information, see May (1964), Dryomatic Division, LogEtronics (1965), Munford (1965), Cooke (1966), and Harrington and Douglas (1970),

Controlling Temperature

Refrigeration

Since refrigeration in broad terms is any process by which heat is

removed, it is the only way to obtain and maintain the low temperature

required for long-term storage of seeds. Ventilation can be considered

to be refrigeration; however, ventilation is suitable for only minor

downward adjustments of temperature. To obtain very low temperatures, mechanical refrigeration must be used in addition to air circulation. Refrigeration is accomplished by transferring heat from the body

being refrigerated to another body where the temperature is below that

of the body being refrigerated. Because heat moves readily from an
134 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

VENT

FLEXIBLE

INSULATION

CORNER

FLASHING

MASTIC

SEALER

ADHESIVE

DOW FOAM

PLASTIC

INSULATION

PORTLAND

CEMENT

MORTAR

ADHESIVE

T-BAR

DOW FOAM

PLASTIC

INSULATION

FIGURE 30.—Construction utilizing suspended T-bar ceiling and foam plastic insulation

for seed storage facility. (Courtesy of Amspec, Inc.)

area of high temperature to one of lower temperature, thermal insulation is always necessary around an area to be refrigerated.

Heat Load

The heat load is the rate at which heat must be removed in order to

produce and maintain the desired temperature. Heat load is affected by

such factors as temperature of the space or material to be refrigerated;

heat leakage through the walls, floor, ceiling, and door opening of the

chamber; heat from lights, motors, and other electrical equipment; and

people working inside the refrigerated chamber. Total heat from these

sources determines the heat load for a particular refrigeration system.

Refrigeration Agent

The body employed to absorb heat is the refrigeration agent or

refrigerant. Cooling systems are classiñed as either sensible or latent,

according to the effect the absorbed heat has on the refrigerant. The

cooling process is said to be sensible when the absorbed heat increases

the temperature of the refrigerant and latent when the physical state of

the refrigerant is changed. With either process the temperature of the

refrigerant must always be lower than that of the area or material being

refrigerated. Continuous refrigeration can be achieved by either a
PRINCIPLES AND PRACTICES OF SEED STORAGE 135

sensible or a latent cooling system. With a sensible cooling system, the

refrigerant is chilled and recirculated. Latent cooling may be accomplished with either a solid refrigerant, such as ice or solid carbon dioxide

(dry ice), or a liquid. Ice and dry ice are not recommended as refrigerants for seed storage rooms.

Liquid Refrigerants

Mechanical refrigeration systems are based on the ability of liquids to

absorb enormous quantities of heat as they vaporize. Vaporizing liquids

provide a refrigeration system that can be easily controlled. Such

systems can be started and stopped at will and the rate of cooling can be

predetermined within narrow limits. The vaporizing temperature of the

liquid can be regulated by controlling the pressure at which the liquid

vaporizes. By using a closed system, the vapor can be readily condensed

back into a liquid so that it can be used over and over again to provide a

continuous flow of liquid for vaporization.

Since no one liquid refrigerant is best suited to all applications and

operating conditions, the refrigerant selected should be the one best

suited to meet the specific needs of each storage facility. Of all the fluids

currently used as refrigerants, the one nearest the ideal general purpose refrigerant is dichlorodifluoromethane (CClgFg). It is one of a

group of refrigerants introduced under the trade name "Freon," but it

is now manufactured under several other proprietary names. To avoid

any confusion among trade names, this compound is now referred to as

Refrigerant-12 or R-12.

Refrigerant-12 has a saturation temperature of -29.8° C, which

means it can be stored as a liquid at ordinary temperatures only under

pressure in heavy steel cylinders. Although an insulated space can be

refrigerated by allowing liquid R-12 to vaporize in a container vented to

the outside, this is not a practical method of refrigerating a seed storage

room. The container in which the refrigerant vaporizes during refrigeration is called the evaporator and is an essential component of any

mechanical refrigerating system.

Typical Mechanical Refrigeration System

A typical mechanical refrigeration or vapor-compression system consists of the following essential parts: (1) An evaporator to provide a heat

transfer surface through which heat moves from the space being

refrigerated into the vaporizing refrigerant; (2) a suction line to convey

the refrigerant vapor from the evaporator to the compressor; (3) a

compressor to heat and compress the vapor; (4) a hot gas or discharge

line to carry the high-temperature, high-pressure vapor from the compressor to a condenser; (5) a condenser to provide a heat transfer

surface through which heat passes from the hot gas to the condensing
136 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

medium; (6) a receiving tank to hold the hquid refrigerant for future

use; (7) a liquid line to carry the liquid refrigerant from the receiving

tank to the refrigerant metering device; and (8) a refrigerant metering

device to control the flow of liquid to the evaporator. The typical

vapor-compression system is divided into a low and a high pressure

side. The refrigerant metering device, evaporator, and suction line

constitute the low part of the system; the compressor, discharge line,

condenser, receiving tank, and liquid line constitute the high pressure

side of the system.

Condensing Units

A condensing unit may be either air or water cooled. Condensing

units of small horsepower are frequently equipped with hermetically

sealed motor compressor assemblies. Large condensing units are

usually water cooled.

System Capacity

The capacity of a refrigeration system is the rate at which it removes

heat from the refrigerated space. Capacity is usually expressed in

terms of units of heat removed per hour or its ice-melting equivalent. In

other words, a mechanical refrigeration system that will cool at a rate

equivalent to the melting of 1 ton of ice in 24 hours is said to have a

capacity of 1 ton. The capacity of a mechanical refrigeration system

depends on the weight of refrigerant circulated per unit of time and

refrigerating effect of each pound circulated.

Compressor Capacity

The capacity of a compressor must be such that the vapor is drawn

from the evaporator at the same rate at which it is produced. If the

vapor is produced faster than the compressor can remove it, the

accumulation of excess vapor will increase the pressure in the evaporator; this will, in turn, increase the boiling temperature of the refrigerant. If the capacity of the compressor is such that the vapor is removed

too rapidly from the evaporator, the pressure in the evaporator will

decrease and lower the boiling temperature of the refrigerant. In either

case, the refrigeration systems will not function properly. For any good

refrigeration system, the rate of vaporization must balance the rate of

condensation of the vapor back to a liquid. Such a balanced system will

function properly and refrigerate exceptionally well. For further information, see Dossat (1961).

Controlling Humidity

Air is a mixture of gases, consisting primarily of nitrogen, oxygen,

carbon dioxide, water vapor, and small percentages of rare gases. Each
PRINCIPLES AND PRACTICES OF SEED STORAGE 137

gas, including water vapor, exerts its own partial pressure in the

mixture just as though the other gases were not present. The sum of

these partial pressures equals the total pressure of the mixture. The

amount of water vapor that can be contained in the air mixture is a

constant value depending only on the temperature and pressure of the

mixture. Thinking of humidity in terms of partial pressure makes it

easier to understand the movement of moisture from one area to

another, for moisture moves from a high to a low pressure area. It is

therefore possible for moisture to move against the flow of air. Pressurizing a room will not prevent moisture from moving in, although it

could slow down its entry.

Relative humidity is normally measured by taking dry-bulb and

wet-bulb temperature readings and finding the intersection of those

readings as plotted on a psychrometric chart. The point of intersection

will correspond to a particular relative humidity. Relative humidity can

be changed by raising the air temperature without changing absolute

humidity. For further information, see Dryomatic Division, LogEtronics (1965).

Moisture Movement Between Air and Materials

Structural materials, such as wood and cement, contain moisture

throughout, whereas such materials as steel and glass hold moisture on

their surface. The rate of moisture vapor movement between such

materials and air is determined by the difference in moisture vapor

pressure between them. If their moisture vapor pressures are equal,

moisture will not move from one to the other.

When moist seeds are placed in a dry atmosphere, moisture will flow

from the seeds into the atmosphere. Because the air cannot hold nearly

all the moisture held in the seeds, the air will soon become saturated

with the moisture given off by the seeds, and unless new dry air is

provided, drying of the seeds will stop. Because construction materials

contain moisture, that moisture as well as the moisture in the seeds has

to be removed. Once the room and the seeds reach moisture equilibrium

with the desired relative humidity, the drying system has only to

remove the moisture that enters the controlled atmosphere room

through door openings, leakage through seams and cracks, and penetration of the barrier material. The storage area is kept at a designated

relative humidity, which, in turn, prevents any change in the moisture

content of stored seeds once they have reached moisture equilibrium

with the maintained relative humidity. For additional information, see

Hass (1961, 1965), Sijbring (1963), Dryomatic Division, LogEtronics

(1965), and Munford (1965),
138 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Refrigeration-Type Humidity Control Systems

The refrigeration-type dehumidifier draws warm, moist air over a

metal coil with fins spaced far enough apart to permit partial frosting

and still allow for sufficient passage of air. The frost can be removed by

electrical heater, hot gas, or water defrosting at regular intervals

regulated by a timeclock. To be effective at low temperatures, a

refrigeration-type dehumidification system must cool the air below the

desired temperature and reheat it to the desired temperature. Airhandling units are available with built-in refrigeration coils, electric

defrosters, and reheat coils. An engineered unit such as described may

be better than a piecemeal assembly because the correct wattage is

provided in the unit.

The simplest method of regulating the reheat in a room is to wire the

reheat coils through a relay to a humidistat. Although the refrigeration-reheat system can effectively control relative humidity as well as

temperature, it is not the only system available and in some cases may

not be the best. When very low relative humidity is to be maintained,

operation of the refrigeration-reheat system becomes very expensive.

Desiccant-Type Humidity Control Systems

Dehumidifiers using Hquid or solid desiccants in conjunction with

refrigeration can frequently reduce the cost of maintaining very low

relative humidities. These desiccants absorb moisture vapor from the

airstream and later eject it outside the room. Desiccant dehumidifiers

generally use dry chemicals for small systems and salt solutions for

systems with extremely large volumes of air. For seed storage facilities, dry desiccant systems are almost invariably used. The dehumidifier incorporates one or two beds of granulated silica gel or activated

alumina, which can absorb much water vapor. For example, silica gel

can absorb as much as 40 percent of its weight in water vapor at

100-percent relative humidity and proportionally less at lower relative

humidity.

With the two-bed system most frequently used for seed storage

facilities, the air is circulated through one bed at a time. One bed is

recharged, or dried out, while the other is taking up moisture. The

switch from one bed to the other is usually programed by a timeclock for

maximum efficiency.

Recent developments receiving wide application are the rotary drum

or cylinder (fig. 31) and rotary disc (fig. 32) dehumidifiers. The rotary

dehumidifiers have one or more beds divided into two airstreams by

sealing strips. The bed or beds rotate slowly, and while part of each bed

is absorbing water vapor from the airstream, the remainder is being

recharged. The end result is much the same as for the two separate bed

systems except that the rotary systems seem to have a higher drying
PRINCIPLES AND PRACTICES OF SEED STORAGE 139

PN—5410. PN—Ó4I1

FIGURE 31.—Above, rotary cylinder dehumidifier used to control relative humidity in

seed storage rooms; below, arrangement of cylinder, reactivation heaters, and seals

in this dehumidifier. (Courtesy of Dryomatic Div.)
140 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

capacity for a given volume of air passing through the dehumidifier. In

contrast to the refrigeration type, desiccant dehumidifers are not

affected by the freezing of moisture and can handle air at -40° to +80°

C as long as the appropriate desiccant is used.

PN-5412, PN-5413

FIGURE 32.—Above, rotary disc dehumidifier used to control relative humidity in seed

storage rooms; below, arrangement of discs and seals in this dehumidifier. (Courtesy

of Dryomatic Div.)
PRINCIPLES AND PRACTICES OF SEED STORAGE 141

For seed storage facilities where both a low temperature and a low

relative humidity are needed, a combination refrigeration-desiccant

dehumidifier system will probably provide the most reliable temperature and relative humidity control at the least cost. Maintenance cost of

dehumidification systems is usually small. For desiccant systems, the

desiccant material should be changed every 3 to 5 years. For additional

information, see Hass (1961, 1965), James (1962), Cooke (1966), Beck

(1966, 1972), and Welch (1967),

Common-Sense Practices

Ventilation

Seeds stored wet tend to get hot whether stored in bulk or in bags

unless heat is rapidly dissipated as it is generated. Both heat and excess

moisture can be dissipated through ventilation. A steady stream of air

moving through a bin of loose seeds or a warehouse full of bags of seeds

will collect the heat as it is generated and transport it away. Preventing

heat buildup is essential to maintaining good germination. A good

ventilating system will soon pay for itself through improved seed

quality.

Stacking Seed Bags

Most processed seeds are handled in bags, which are stored in stacks.

Bags of seeds of each genus, species, and cultivar are stored in separate

stacks. To allow for proper ventilation, stacks of seed bags should be

well spaced, both between the bags and between the stacks. Bags of

seeds must be stacked carefully to prevent slippage and falling. Falling

bags are hazardous to employees as well as subject to breakage on

impact. Stacks that are excessively high often cause the bottom bags to

burst. It is especially important that bags moved by forklift be stacked

securely on pallets.

Removing Seeds From Controlled Storage

Dry seeds removed from cold storage and exposed to a warm, humid

atmosphere will absorb moisture readily. Unless preventive steps are

taken, bags of cold seeds will become moist from the condensing

atmospheric moisture. Moisture condensation can be prevented by

warming the seeds in a dry atmosphere or by warming in a room

ventilated with rapidly moving air. Use of moisture-barrier containers

can prevent condensed moisture from coming into contact with the

seeds. Proper aeration can bring cold bulk seeds up to normal atmospheric temperature without surface accumulation of condensed atmospheric moisture. Unless seeds held under controlled atmosphere

storage are kept dry after removal from storage, the protective effects

of controlled storage will soon be lost.
142 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Warehouse Cleanliness

Warehouse cleanliness, or lack of it, can markedly affect seed quality.

A clean warehouse has fewer rodents and insects and they are more

easily controlled. A clean warehouse reduces the chances of accidental

mixtures and personnel accidents. It also presents a better company

image to visitors.

PACKAGING AND PACKAGING MATERIALS

Requirements of Different Situations

Seed-packaging methods are many and varied (Bass et al., 1961), The

equipment for filling packages ranges from a simple spoon or seed

scoop, to the manually controlled gravity flow from a bin, to the

high-speed automatically controlled small packet filler. Package-filling

equipment has no effect on the genetic or physiological quality of seeds;

however, it may affect the physical quality of seeds through impact or

undue pressure. Heavy seeds, especially bean, corn, pea, and soybean,

can be fractured by impact on the individual seed by either striking or

being struck by a hard object or firm surface. Seeds containing too much

or too little moisture damage easily on impact. Damage from repeated

impact is accumulative. Seeds may also be injured by force feeding

through a restricted opening or between pressure rolls. Physical damage can occur during any handling operation from harvest to planting.

Types of Packages

Packages for processed seeds may be burlap, cotton, paper, or film

(plastic, foil) bags, metal or fiberboard cans or drums, glass jars,

fiberboard boxes, or containers made of various combinations of materials. The types and sizes of containers used for wholesale distribution

of field seeds are usually the same as those used for retail sales. For

vegetable and flower seeds, wholesale containers may be large fabric or

multiwall paper bags, large fiberboard or metal cans or drums, or

fiberboard boxes, whereas retail containers are usually small paper,

film, or film-laminated envelopes, small fiberboard boxes, or small metal

cans.

The packaging materials, methods, and equipment used are dictated

by the kinds and amounts of seeds to be packaged, the type of package,

duration of storage, storage temperature, relative humidity of the

storage area, whether packaging is for wholesale, retail, or local use,

and geographical area where the packaged seeds will be stored, exhibited, or sold. Packages that will contain seeds and protect most

physical qualities of seed lots are made of materials with sufficient

tensile strength, bursting strength, and tearing resistance to withstand

normal handling. However, such materials do not protect seeds against
PRINCIPLES AND PRACTICES OF SEED STORAGE 143

either insects and rodents or changes in moisture content unless special

protective qualities are built into them. Researchers frequently use

whatever container happens to be convenient without regard to the

moisture protection it may or may not afford. However, there is an

increasing awareness of the savings in time and expense that are

realized by using suitable moisture-barrier containers for storing valuable breeding stocks.

Seeds stored for a short time or under cold, dry conditions will retain

good viability in porous paper or fabric containers, whereas seeds

stored or marketed under tropical conditions (Ching, 1959) will lose

viability rapidly without maximum moisture protection. Except in

tropical and subtropical climates, many kinds of seeds do not require

special moisture protection during the first winter after harvest when

held in the area where produced. However, seeds carried over to the

second planting season often require drying and packaging in moisture-barrier containers to prevent loss of viability and vigor.

How Packages Are Filled

Except in very limited operations that employ hand-filling, seeds to

be packaged are delivered to hopper bins above automatic or semiautomatic filling machines. Seeds may come to the hopper from bulk storage

bins by gravity flow through pipes and by airlift, belt conveyors,

forklifts, or the human shoulder. Since practically all seeds are sold by

weight, it is necessary to put a predetermined amount into the individual packages. Even seeds that appear to be sold by volume are associated with weight; namely, a bushel of corn equals 56 pounds, a bushel

of wrinkled peas 56 pounds, and a bushel of smooth seeded peas 60

pounds. Most package-filling equipment has built into it a seed-measuring device, or it is manually or automatically controlled by a signal from

a weighing device.

How Containers Are Presented to the Filler

Large nonrigid containers of burlap, cotton, lined bags, multiwall and

7- and 10-mil polyethylene bags are usually presented to the filler

manually. They are held in place by hooks, clamps, or by hand during

filling. Polyethylene and similar materials may be formed into bags

from sheets or rolls, filled, and sealed in a continuous operation. Large

rigid containers, other than metal or glass, are usually formed into an

open box by hand and presented to the filling equipment either manually

or by a conveyor that automatically positions each container. Small,

semirigid, preformed containers may be opened with a jet of air and

automatically positioned for filling. Rigid containers come from the

manufacturer ready for filling. They are positioned for filling either

manually or by conveyor.

Placing seeds in rolls of tape may be considered a form of packaging.
144 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

During the midtwenties, equipment was developed for forming the

tape, placing the seeds, and making the roll. Although this form of

packaging did not become popular at that time, there currently appears

to be a revival of interest in this method.

Weighing and Measuring Devices

Scales for weighing seeds range from the large truck scale, which

weighs an entire load at a time, to the common beam scale or an

elaborate scale that activates either a pneumatic or electric device that

shuts off the flow of seeds when a predetermined weight or volume is

reached. In retail stores many types of scales are used, some of which

automatically compute the cost to the customer based on the price per

pound. Some scales are so delicate they can weigh a few small seeds,

such as petunia. Measuring devices range from a simple spoon or scoop,

to a calibrated cylinder or cup, to the measuring device associated with

the automatic scales.

How Containers Are Closed

Hand-tying of cotton and burlap bags has been largely replaced by

sewing. Although there is still some sewing by hand, most of it is done

by machine. Polyethylene and other thermoplastic materials are usually

sealed by applying heat at 93.3° to 204.4° C to the ñlm for a given time

while the film is under pressure. Within limits each kind and thickness

of material has specific temperature, time, and pressure requirements

(table 23) for proper sealing.

TABLE 23.—Approximate heat-sealing requirements for selected

thermoplastic materials^

Material Heat sealing Time Pressure

Film °C Seconds Lh/in2

Polyethylene (PE) density:

Low 2 120-205

Medium _ 150-205

High 120-220

Polyester, 0.25 mil 150-205 0.2-2 20-60

Metalized polyester, 0.2 mil ^ - 135-205 .2-2 20-60

Lamiyiate

Scrim/PE/Foil/PE 275 ±3 40-60

Paper/Saran/PE 150 1 40

50-lb kraft/PE/ 0.05 mil foil/PE 190 ±7 40-60

1 Specific temperature, time, and pressure vary with kind and thickness of each film and

kinds of films in each laminate.

-Heat sealing varies with thickness of material.
PRINCIPLES AND PRACTICES OF SEED STORAGE 145

Heat sealers range from small hand-operated rollers or bars, to

foot-operated bars, jaws, and clamps, to elaborate automatic bag- or

pouch-forming, filling, and sealing machines. Some sealers use thermostatically controlled bars, bands, or rollers, and others use high-intensity thermal impulses of short duration. Most are readily adjustable

for use with many kinds and thicknesses of material. However, the

quality of the seal produced by hand- and foot-operated equipment

depends on the skill of the operator. Properly adjusted automatic

sealers seldom produce a poor seal. Considerable experience is required

before an operator can consistently apply the appropriate pressure for

the precise dwell time required to produce a good seal. It is especially

important that seed packages of proper moisture-barrier materials be

well sealed as a leak in the seal will soon negate the moisture protection

provided by the material.

Semirigid or rigid containers, other than metal or glass, are usually

sealed with cold or hot glue appHed either by hand or automatically by

machine. Most machines that apply glue also form and fold the open

ends of the containers and place them under pressure until the glue has

set. Rigid containers, such as fiber drums, may have slip-on caps or lids

that clamp into position. These lids are applied manually, whereas lids

for metal cans are applied mechanically. Can sealers are manually

operated, semiautomatic, or fully automatic. Usually the equipment is

the same as that used by food processors for hermetically sealed cans. A

partial vacuum or a gas can be introduced into the can when semiautomatic and fully automatic equipment is used for sealing. Some cans are

sealed with pressure lids similar to those used on paint cans.

Packaging Field Seeds

Field seeds are generally packaged in burlap, osnaburg, or seamless

and multiwall paper bags containing 50 or 100 pounds or one-half to 3

bushels of seeds. A few companies use moisture-barrier packages, such

as elastic multiwall paper bags with either an asphalt or a polyethylene

ply in the multiwall, burlap or cotton bags with polyethylene liners, and

burlap/asphalt/paper-laminated bags for cereal, soybean, and hybrid

sorghum seeds. Many hybrid corn seed producers either package all or

part of their crop each year in moisture-resistant packages or hold their

seed in controlled storage. Moisture-resistant bags used for seed corn

are made of multiwall/asphalt/paper, elastic multiwall/asphalt/paper,

multiwall and elastic multiwall/paper with a polyethylene-barrier ply,

or 7- or 10-mil polyethylene.

A valve-type polyethylene bag has been developed that prevents any

loss of material while filling and that seals easier than the conventional

bag. The valve-type bag also permits easy introduction of fumigants or

gases into the filled bag prior to sealing.
146 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Some companies are packaging hybrid corn in acre units, each package containing the exact quantity of seed required to plant a specified

number of acres.

Turf grass seed for the wholesale market is usually put in fabric bags

of 25- to 100-pound capacity. Sometimes a 4- or 5-mil polyethylene liner

is used for moisture protection. At retail, turf grasses are sold as single

species or combinations of species packaged in paper, cloth, or polyethylene bags, metal cans, or cardboard boxes. The cardboard boxes may

be plain, polyethylene, or wax paper lined, foil or wax coated, or wax

paper or foil overwrapped.

Tobacco seeds are packaged in paper packets, cardboard boxes or

cylinders, or metal cans of V2- or 1-ounce capacity.

Moisture-resistant containers, such as wax- or polyethylene-coated

cardboard boxes or drums and polyethylene, cotton, ov paper combinations, are being used for various forage grasses and legumes. Cottonseeds previously dried to 6- to 8-percent moisture content are packaged

in burlap/asphalt/paper bags or wax- or polyethylene-coated boxes.

Large wood or steel pallet boxes with covers are being used extensively

in the seed industry for bulk storage of both uncleaned and cleaned

seeds. Such bulk storage reduces handling costs and increases the

efficiency of cleaning plant operations by permitting a greater amount of

mechanization. There is no handwork involved in handling pallet boxes,

but with bags or small boxes, a great deal of handwork is required.

Packaging Vegetable and Flower Seeds

In the vegetable seed industry, the packaging method is determined

primarily by the type of customer for which the seeds are packaged.

Seeds for wholesale distribution are usually packaged in fabric bags of

25- to 100-pound capacity. The bags may or may not have polyethylene

liners. Beans, peas, and sweet corn are usually packaged in multiwall/asphalt/paper bags containing 25 to 100 pounds of seed. For retail

sales, most vegetable seeds are packaged in paper packets, sometimes

with foil inserts, containing a fraction of an ounce to several ounces;

cardboard boxes holding a few ounces; and 2- to 4-mil polyethylene,

cellophane, acetate, paper, and foil-laminated bags with capacities of 1

to 5 pounds. Various kinds of vegetable seeds are also packaged in

hermetically sealed metal cans of various sizes. These containers are

especially beneficial for shipments overseas and into tropical areas.

Flower seeds at the wholesale level are packaged in paint-type cans,

glass jars, and fabric bags with polyethylene liners. For retail sales,

paper, paper/polyethylene, acetate, cellophane, and foil-laminated

packets are the predominate types. Wholesale packages of flower seeds

usually contain several pounds, whereas retail packets contain a given

number of seeds or a fraction of an ounce.
PRINCIPLES AND PRACTICES OF SEED STORAGE 147

Package Labeling

Researchers and seedsmen alike need to identify the contents of each

container, both as to species and cultivar. Frequently other information, such as percentage of Uve seeds, purity, noxious weed seed

content, and seed treatment, if any, must also be recorded as required

by law. This may be done by printirig the required information on a tag

attached to flexible cotton or fiber bags, by printing on a label glued to

tin cans, cardboard boxes, or cardboard or metal drums, or by printing

or stamping the information directly on the container, such as lithographing cans or embossing metal lids.

Porous Packaging Materials

Burlap or hessian bags are made of good quality jute yarn in a variety

of fabric constructions. Since burlap is exceptionally strong, burlap

bags lend themselves to stacking high in storage and to rough handling,

and they can be reused many times. Seed bags of cotton are made of

sheeting, printcloth, drill, and oànaburg fabrics as well as a special

seamless material. Osnaburg and seamless fabrics have the greatest

strength and tear resistance of the cotton materials. Bags made of these

materials are reused many times, whereas bags of other cotton materials are used only once. Reuse of fabric bags is largely confined to

storage of unprocessed seed as certification standards require new bags

for shipment of processed seeds.

Paper products are extensively used for seed packaging. Small seed

packets are mostly made of bleached sulfite or bleached kraft paper and

surface coated with a very white clay to facilitate printing. Basically

paper packets are designed to contain, without loss, a given quantity of

seeds, not to protect seed viability.

Many paper seed bags are of multiwall construction consisting of

several layers of smooth or crinkled paper. Multiwall paper bags are

produced in a variety of constructions, each designed for a specific

purpose. Ordinary multiwall bags have poor bursting strength and

consequently when piled high, the bottom bags burst. The top bags in

high piles often slip. Under very dry conditions, multiwall bags dry out

and become brittle along folds and at wear points. Elastic multiwall

bags consist of several layers of crinkled paper. Elastic materials cannot

be evaluated by the usual physical test data for tensile and tear strength

because the entire principle of the elastic multiwall bag depends on

built-in stretchability.

Cardboard, in the form of boxes and cans, is used extensively in seed

packaging. Cardboard containers protect most physical qualities of seed

and are well adapted for automatic filling and sealing equipment. Porous

packaging materials adequately contain or hold the seeds and protect
148 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

them from mechanical mixtures, but they do not provide moisture

protection.

Moistureproof Materials

Metal containers when properly sealed provide an absolute moisture

and gas barrier and completely shield the products from any effects of

light. Metal containers provide complete protection against rodents,

insects, changing humidity, flood, and harmful fumes. Metal cans are

well adapted to high-speed automatic filHng and sealing.

Glass containers are not widely used in seed packaging. Although

glass provides essentially the same protection as metal, its fragility

makes it less desirable for commercial packaging. Glass containers are

frequently used in research and as display receptacles in seed and

hardware stores, where bulk sales of seed are made. Glass containers

are often used by home gardeners for carryover of small quantities of

seed from one season to the next.

Adequate drying before sealing is absolutely essential for safe

storage of seeds in airtight, moistureproof containers, especially for

seed stored at warm temperatures or shipped to tropical areas. Much

research has been done on the effects of sealed moistureproof storage

on seed longevity. Some workers used air-dried seeds, whereas others

carefully dried the seeds before sealing.

Moistureproof Storage

Response of Différent Crop Seeds to Moistureproof Storage

Cereal Seeds.—Numerous studies have shown that rice seeds held in

airtight storage outlive seeds held in open storage provided they are

adequately dried before they are placed in airtight storage (Vibar and

Rodrigo, 1929; Kondo and Okamura, 1930, 1932-33, 1938; Rodrigo,

1935, 1953; Kondo and Terasaka, 1936). Rice seeds dried by high heat

before sealing were dead after 26 to 28 years, but seeds dried by the sun

to 11- to 13-percent moisture were stored safely for 30 years (Kondo and

Okamura, 1932-33). Cultivar differences in storability were demonstrated by Vibar and Rodrigo (1929)^ who reported that the germination

of seeds of the rice cultivar Hambas declined 18 percent in 51 months,

whereas seeds of the Inintew cultivar declined only 5 percent.

Because corn seed is usually planted the year after harvest, people in

the Corn Belt usually have no problem with storage. However, corn is

now grown in areas where temperature and humidity conditions frequently cause rapid loss of viability during storage. Research has shown

that sealed storage prevents rapid loss of viability of corn seeds

provided their moisture content is sufficiently low when the seeds are
PRINCIPLES AND PRACTICES OF SEED STORAGE 149

sealed (Vibar and Rodrigo, 1929; Rodrigo, 1935, 1953; Kaihara, 1951;

Barton, 1960b). Sealed seeds with 11-percent moisture content maintained full viability for 9 years at -5° C but showed reduced viability

after 1 year at 30° (Barton, 1960b). Although sealed glass jars were

used in this study, similar results could be expected with any type of

sealed moistureproof container, such as a metal can or drum or a

multiwall bag with a foil layer.

Sorghum seeds in commerce usually are not stored longer than over

winter. However, plant breeders frequently need to hold seeds for

many years. Sorghum seeds dried and sealed in glass bottles retained

their viability longer than did similar seeds stored in gunny sacks

(Krishnaswamy, 1952). We found that cultivar RS619 sorghum seeds

retained their germination up to 8 years at -12° and -1° C, whether in

paper envelopes or sealed metal cans (table 24). Sealed seeds at 10°

retained viability significantly better than did unsealed seeds. At higher

temperatures the results were variable. Some of the variability can be

attributed to differences in seed moisture content. The seeds in sealed

metal cans had an initial moisture content that did not change with time.

The moisture content of the seeds in paper envelopes adjusted with

time to moisture equilibrium with the relative humidity in the storage

chamber. The low relative humidity at the higher temperatures allowed

the seeds to attain a low moisture content and partly offset the effects of

temperature on longevity.

TABLE 24.—Germination of 5 kinds of seeds at 3 initial moisture

contents after storage in paper envelopes or sealed metal cans

under 5 temperature and relative humidity conditions for 4 and 8

years

Storage temperature (C),

relative humidity (RH)

(percent), and initial seed

moisture content (percent)

-12° and 70 RH:

4

7

10

-rand 60 RH:

4

7

10_ „

See footnote at end of table.

Germination 1 after storage for indicated container

and years

Paper envelope Sealed metal can

0 4 8 4 8

Percenit Percent Percent Percent Percent

CRIMSON CLOVER

, 82 79 78 84 84

92 84 78 87 87

91 83 83 87 80

. 82 80 66 80 85

92 78 71 89 83

91 85 75 86 70
150 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

TABLE 24.—Germination of 5 kinds of seeds at 3 initial moisture

contents after storage in paper envelopes or sealed metal cans

under 5 temperature and relative humidity conditions for 4 and 8

years—Continued

Storage temperature (C),

relative humidity (RH)

(percent), and initial seed

moisture content (percent)

Germination i after storage for indicated container

and years

Paper envelope Sealed metal can

Percent Percent Percent Percent

CRIMSON CLOVER—COn.

Percent

10° and 60 RH:

4 82

7 92

10 91

21° and 30 RH:

4 82

7 92

10 91

32° and 15 RH:

4 82

7 92

10 91

-12° and 70 RH:

4 97

7 : 97

10 95

-l°and 60 RH:

4 97

7 97

10 95

10° and 60 RH:

4 97

7 97

10 95

21° and 30 RH:

4 97

7 97

10 95

32° and 15 RH:

4 97

7 97

10 95

-12° and 70 RH:

4 95

7 94

10 95

See footnote at end of table.

74 44 82 82

71 41 80 76

77 45 75 42

67 33 83 80

71 34 83 81

76 34 43 5

83 71 75 80

76 69 76 69

78 73

LETTUCE

3 0

95 92 96 96

95 96 95 98

95 95 93 94

91 84 94 90

95 90 97 76

96 96 94 91

94 0 93 90

94 0 94 1

92 0 21 0

11 0 89 90

6 0 4 0

14 0 0 0

89 2 90 36

84 2 0 0

93 0

SAFFLOWER

0 0

95 86 94 87

94 88 94 83

95 88 91 79
PRINCIPLES AND PRACTICES OF SEED STORAGE 151

TABLE 24.—Germination of 5 kinds of seeds at 3 initial moisture

contents after storage in paper envelopes or sealed metal cans

under 5 temperature and relative humidity conditions for 4 and 8

years—Continued

Storage temperature (C),

relative humidity (RH)

(percent), and initial seed

moisture content (percent)

Germination! after storage for indicated container

and years

Paper envelope Sealed metal can

Percent Percent Percent Percent

SAFFLOWER—con.

Percent

-rand 60 RH:

4 95

7 94

10 95

10° and 60 RH:

4 95

7 94

10 95

21° and 30 RH:

4 95

7 94

10 95

32° and 15 RH:

4 95

7 94

10 95

-12° and 70 RH:

4 94

7 92

10 88

-Fand 60 RH:

4 94

7 92

10 88

10° and 60 RH:

4 94

7 92

10 88

21° and 30 RH:

4 94

7 92

10 88

32° and 15 RH:

4 94

7 92

10 88

See footnote at end of table.

93 90 97 91

95 86 90 90

94 88 92 72

96 81 95 89

96 88 91 85

92 86 0 0

90 64 94 90

89 61 0 0

89 54 0 0

63 53 93 89

63 60 0 0

65 53

SESAME

0 0

95 92 94 92

92 93 90 89

93 89 0 0

93 94 91 92

92 90 89 87

90 90 6 0

96 88 92 90

92 95 68 0

88 84 0 0

91 88 93 91

90 88 0 0

91 83 0 0

94 86 95 87

95 88 0 0

95 70 0 0
152 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

TABLE 24.—Germination of 5 kinds of seeds at 3 initial moisture

contents after storage in paper envelopes or sealed metal cans

under 5 temperature and relative humidity conditions for 4 and 8

years—Continued

Germination i after storage for indicated container

Storage temperature (C), and years

relative humidity (RH)

(percent), and initial seed Paper envelope Sealed metal can

moisture content (percent)

0 4 8 4 8

Percent Percent Percent Percent Percent

SORGHUM

-12° and 70 RH:

4 _^ 92 96 94 93 90

7 __ 95 93 95 94 94

10 ^ 91 93 92 97 94

-rand 60 RH:

4 ^ 92 93 95 91 92

7 _ 95 94 89 94 94

10 _ 91 92 92 92 87

10° and 60 RH:

A _^ 92 90 71 90 90

7 _ 95 91 76 93 90

10 . 91 91 76 93 92

21° and 30 RH:

A ____ , 92 85 55 94 83

7 ^ 95 84 84 92 86

10 91 80 80 84 72

32° and 15 RH:

4 . 92 77 50 90 65

7 - . 95 76 46 85 64

10 ^ 91 73 40 69 0

' Least significant difference at 5-percent level of probability is 10 percent.

Forage Grasses.—Seeds of Echinochloa, Eleusine, Panicum, Pennisetum, Paspalum, and Setaria retained their viability longer when

dried and stored in sealed bottles than when stored in gunny sacks.

Sealed Echinochloa, Panicum, and Setaria seeds retained approximately 70-percent germination for 38 months (Krishnaswamy, 1952).

Crested wheatgrass, intermediate wheatgrass, and smooth bromegrass

seeds retained high viability best at -18° C whether sealed or open

(Knowles, 1967). At 1°, seeds stored in sealed glass jars held their

germination better than those in open storage. At 21°, seeds in sealed

containers retained a higher percent viability than did seeds in paper

envelopes; however, the viability of sealed seeds sharply declined

during 4 years of storage.
PRINCIPLES AND PRACTICES OF SEED STORAGE 153

Turf Grasses.—Perennial ryegrass seeds containing 6-, 8-, 12-, 16-,

and 20-percent moisture were stored in sealed metal cans at 3°, 22°, and

38° C in a warehouse in Oregon (Ching et al., 1959), After 3 years of

storage, the 6-percent moisture seeds showed some decline in germination at 38°, seeds with 8-percent moisture retained good germination at

all temperatures except 38°, but seeds with 12- and 16-percent moisture

remained viable only at 3°. Seeds with 16- and 20-percent moisture

deteriorated within 3 months when stored at 22° and 38°. Ching and

Calhoun (1968) reported that after 10 years of sealed storage, 6-percent

moisture ryegrass seeds stored at 22° and 38° gave significantly lower

laboratory germination percentages than new seeds and similar seeds

held at other temperatures; however, field emergence was not significantly different from that of all other seed lots.

Kentucky bluegrass seeds with 8.7-, 6.2-, and 4.9-percent moisture

packaged in sealed tin cans and stored at 1°, 10°, and 21° C germinated

at approximately their original level after 30 months in storage regardless of the seed moisture level (Bass, 1960). Creeping red fescue

containing 11.4-percent moisture in sealed metal cans dropped sharply

in viability during the first 3 months of storage at all temperatures;

seeds sealed with lower moisture levels retained good viability longer,

especially at the lower temperatures.

Forage Legumes.—Crimson clover seeds containing 6-, 8-, 12-, 16-,

and 20-percent moisture were stored in sealed metal cans at 3°, 22°, and

38° C in a warehouse. Seeds with 16- and 20-percent moisture at 22° and

38° deteriorated within 3 months, those with 8-percent moisture were

preserved well except at 38°, and those with 12- and 16-percent moisture remained viable only at 3°. The 6-percent moisture crimson clover

seeds remained highly viable after 3 years of storage under all temperature conditions. (Ching et al., 1959) Ching and Calhoun (1968) reported that after 10 years of sealed storage only 16-percent moisture

crimson clover seeds held at 3° germinated significantly lower than

fresh seeds in laboratory tests. In the field there were no significant

differences in emergence between fresh and 10-year-old seeds regardless of the temperature under which the sealed seeds had been stored.

In our studies, crimson clover seeds with 4- and 7-percent moisture

retained higher viability or germination in sealed metal cans than in

paper envelopes at all storage conditions (table 24). However, the

10-percent moisture seeds lost viability more rapidly in the cans than in

the paper envelopes when stored at 21° and 32° C. This was, of course,

because the seeds in paper envelopes lost moisture during the early

weeks of storage, whereas those in the cans did not. The 10-percent

moisture seeds in metal cans actually declined 50 percent in viability

during the first year of storage at 32°, whereas the seeds in paper

envelopes declined only 11 percent.
154 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

These data show that seeds in hermetically sealed containers may lose

viability more rapidly than those in open storage if seed moisture

content, storage temperature, or both is too high.

Alfalfa seeds with 6.8-percent moisture germinated 78 percent after

24 years in sealed glass bottles, and red clover seeds with 6.9- and

6.7-percent moisture germinated 74 and 71 percent, respectively (Nutile, 1958).

Fiber and Oil Crops.—Flaxseeds containing 7- to 8-percent moisture

when stored in metal containers retained good germination for 13 to 16

years at temperatures prevailing in Mandan, N. Dak. (Dillman and

Toole, 1937). Cottonseeds with 6- to 8-percent moisture in sealed glass

jars kept for 7 to 10 years at 21° C without loss of viability (Simpson,

1942, 1953). Good quality cottonseeds with 7- to 11-percent moisture

content retained high viability for over 25 years in sealed metal cans at

1° (Pate and Duncan, 1964).

Hempseeds with 8.6-percent moisture or less retained good germination for 3y2 years at 2° C (Crocioni, 1950). Seeds with 5.7-percent

moisture still retained their initial viability after 15 years of sealed

storage at -10° and 10° (Toole et al, I960] Clark et al., 1963). Two lots

of seeds with 6.2-percent moisture in sealed cans retained full viability

for 12 years at -10°, 0°, and 10°, whereas a third lot of lower initial

germination decreased 23 percent in germination during 12 years of

storage. The two high germinating lots of hempseeds when stored with

9.5-percent moisture retained good viability at -10° and 0° but deteriorated rapidly at 10°. Seeds of the poorer germinating lot declined

10 percent at -10°, 27 percent at 0°, and lost all viability at 10° during 12

years of storage.

Kenaf seeds with 8-percent moisture retained their initial viability for

12 years when stored sealed at -10°, 0°, and 10° C. Seeds with

12-percent moisture, which had retained full viability for bVz years at

-10° and 0° and showed a significant loss of viability after ÍV2 years at

10° (Toole et al., 1960), were nonviable after 12 years at 10° and had

declined sharply at 0° (Clark et al., 1963).

For both safflower and sesame seeds, careful control of seed moisture

is absolutely essential for sealed storage. Safflower seeds containing 4-

and 7-percent moisture retained their germination about equally well in

paper envelopes and in sealed metal cans when stored for 8 years at

-12°, -1°, and 10° C (table 24). The 4-percent moisture seeds in sealed

cans retained better viability than did the envelope-stored seeds at 21°

and 32°. However, 7-percent moisture seeds in sealed metal cans lost all

viability in less than 4 years at 21° and in less than 1 year at 32°.

Ten-percent moisture seeds in sealed metal cans retained fair viability

for 8 years at -12° and -1°; however, all were dead in less than 3 years

at 10° and in less than 1 year at 21° and 32°. The seeds in paper
PRINCIPLES AND PRACTICES OF SEED STORAGE 155

envelopes at 21° and 32° markedly decreased in viability, but no sample

was completely dead regardless of the initial moisture content or

storage temperature. For safe, sealed storage of safflower seeds at a

temperature greater than 10°, seed moisture content must be reduced

to 4 percent or less before sealing.

Sesame seeds in sealed metal cans did not retain satisfactory germination when seed moisture content exceeded 7 percent for storage at

-12° and -1° C (table 24). At 10° and higher, seed moisture content

must not exceed 4 percent. Ten-percent moisture seeds in sealed metal

cans do not store well at any temperature. The 10-percent moisture

seeds at 10° germinated 73 percent after 1 year but were nearly all dead

at the end of the second year. Seeds at 21° and 32° lost all viability in less

than a year. As with safflower, sesame seeds are very sensitive to both

seed moisture content and storage temperature and must be carefully

dried to 4-percent moisture before sealing unless the seeds are to be

held continuously at -12° or -1°.

Under Philippine conditions the germination of air-dry soybean seeds

stored in sealed containers lost viability after 23 months. (Vibar and

Rodrigo, 1929) and 54 months (Rodrigo, 1953). In Illinois the germination of air-dry soybeans in sealed containers dropped only 2 percent

during the first year but declined sharply thereafter, and nearly all

seeds were dead within 8 years (Burlison et al., 1940), The germination

of 'Illsoy' at 7 years was comparable to 'Manchu' at 4 years and

'Lexington' at 5 years, indicating cultivar differences in keeping quality

(Burlison et al., 1940).

Soybean seeds conditioned to various moisture contents, then sealed

in pint jars, and stored at various temperatures lost viability at a

different rate at each storage condition (Toole and Toole, 1946). Cultivars of Mammoth Yellow and Otootan gave essentially the same

results. Seeds with 18-percent moisture at 30° C were nonviable in less

than 3 months, and similar seeds at 10° died within 2 years. Seeds stored

at subfreezing temperatures retained good germination for 6 years but

were unsatisfactory for planting after 10 years. Air-dry seeds of

13.5-percent moisture, however, retained essentially their full initial

viability for 10 years at 2° and -10°. Soybean seeds dried to 9-percent

moisture or less before sealing retained full viability for 10 years at 10°,

2°, and -10° (Toole and Toole, 1946).

Peanuts in sealed storage retained satisfactory germination up to 37

months (Vibar and Rodrigo, 1929; Rodrigo, 1953).

Vegetable Seeds.—Onion seeds kept very well in sealed storage

(Brison, 1941, 1942). Seeds dried to 6.4-percent moisture before sealing

germinated 90 percent after 13 years at room temperature (Brown,

1939). However, in another study (Asgrow Seed Co., 1954), 6.3-percent

moisture content seeds retained good viability for only 3 years at 32° C.
156 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Although onion seeds dried to below 8-percent moisture before sealing

kept well for 4 years at 5° (Beattie and Boswell, 1939), 6.7-percent

moisture is recommended for longer storage. Dry seeds in sealed

containers in a laboratory lost viability in 38 months (Rodrigo, 1953).

Sealed onion seeds held in cold storage at 5° to 10° without deterioration

for 2 years did not deteriorate when held 3 months at natural conditions

after removal from storage (Myers, 1942). This indicates that adequately dried onion seeds held sealed in cold storage can be safely

marketed after removal from cold storage.

Rodrigo (1935, 1953) reported that under Philippine conditions the

viability of air-dried mung beans stored in sealed containers in a

laboratory was maintained up to 201 months. Cowpeas similarly stored

remained viable for 123 months. White-seeded tapilan beans lost viability gradually over 10 years, whereas black-seeded tapilan beans

maintained their original viability (Vibar and Rodrigo, 1929; Rodrigo,

1935). Yellow tapilan seeds lost viability in 138 months, whereas black

tapilan seeds maintained viability up to 201 months (Rodrigo, 1953).

Seeds of 'Buff Cross,' 'Mahogany Brown,' and WilFs Red Kidney'

beans germinated 20 percent, whereas 'Improved Michigan Robust'

seeds germinated 50 percent after 38 years of storage in sealed canning

jars in a laboratory at Geneva, N.Y. (Waters, 1962). For Top Notch

Golden Wax' and 'Bountiful' bean seeds stored open and sealed at -18°,

-2°, 5°, 10°, 20°, and 30° C and ambient temperature in a laboratory at

Yonkers, N.Y., sealing extended longevity when storage was in a

humid room, even as low as 5° (Barton, 1966a). Sealing was without

effect at -18° and -2° for up to 15 years. Storage at 30° caused rapid

deterioration in both open and sealed containers.

The germination and vigor of canned cucumber seeds did not change

significantly in 36 months when seed moisture was 5.3 percent or less at

32° C or lower (Asgrow Seed Co., 1954). With higher seed moistures,

temperature becomes more critical. Seeds with 9.4-percent moisture

became worthless in 3 months at 32° but held viability and vigor well for

30 months at 15.6°. Tin cans were superior to chlorinated rubber, waxed

cellophane, and paper bags inside linen ones (Coleman and Peel, 1952).

Dry seeds in sealed containers in a laboratory lost viability in 38 months

(Rodrigo, 1953).

For safe sealed storage at room temperature, parsnip seeds must be

dried to less than 1.7-percent moisture before being sealed (Joseph,

1929). For safe storage at 5° to 7° C, the critical moisture level was 6.13

percent. When ovendry, 4-, 6-, and 8-percent moisture content parsnip

seeds were stored for 6 years in sealed and unsealed containers at room

temperature, 5°, and 6.7°, the best keeping was obtained with 4-percent

moisture seeds at 6.7°, followed by ovendry at 5° (Beattie and Tatman,

1950). Sealed storage also was effective in prolonging the life of carrot
PRINCIPLES AND PRACTICES OF SEED STORAGE 157

seeds (Coleman and Peel, 1952; Dutt and Thakurta, 1956). In open

storage viability was lost in 9 months, but in sealed storage the seeds

retained their viability.

Sealed storage prolonged the life of seeds of brussels sprouts, cabbage, cauliflower, knolkol or kohlrabi, radish, and rutabaga or swede

(Coleman and Peel, 1952; Rodrigo, 1953; Dutt and Thakurta, 1956;

Madsen, 1957). Loss of viability of dry seeds in sealed containers in a

laboratory occurred in 37, 39, and 46 months for cabbage, radish, and

cauliflower in that order (Rodrigo, 1953). In open storage, seeds of

cabbage, cauliflower, and kohlrabi lost viability in 9 months, but seeds

sealed in a desiccator retained their viability for 8 years (Dutt and

Thakurta, 1956). Four lots of swede seeds retained their original

germination for 10 years when stored at 4-percent moisture in sealed

glass bottles (Madsen, 1957). Cauliflower seeds stored similarly retained good viability for 8 years, whereas brussels sprouts seeds sealed

at 4 percent retained their viability well for 16 years. Radish seeds with

4-percent moisture in sealed glass bottles retained their viability well

for more than 8 years. Two lots declined slightly by the end of the 15th

year.

For dry eggplant seeds in a sealed container in a laboratory, loss of

viability occurred in 53 months (Rodrigo, 1953). Tomato seeds with

5.9-percent moisture did not change significantly in viability and vigor

during 36 months of sealed storage at 32° C. With increased seed

moisture, temperature became more critical and tomato seeds lost

viability rapidly above 21° (Asgrow Seed Co., 1954). Potato seeds

stored in sealed containers at temperatures from 0° to that of a

basement room near Greeley, Colo., retained good germination for up

to 13 years (Clark, 1940; Wollenweber, 1942; Stevenson and Edmundson, 1950). Germination of seeds at room temperature dropped to 26

percent after 18 years and 17 percent after 20 years (Wollenweber,

1942).

Use of sealed containers can extend the storage life of lettuce seeds

(Coleman and Peel, 1952; Bass et al., 1962). Air-dry seeds in sealed

containers in a laboratory lost viability in 27 months (Rodrigo, 1953),

but 4-percent moisture seeds retained good viability for 8 years at 21° C

or colder (table 24). Seeds with 7-percent moisture lost all viabiHty in

less than 1 year at 32° and germinated only 4 percent after 4 years at 21°

and 1 percent after 8 years at 10°. Seeds sealed with 10-percent

moisture retained good germination for 8 years when stored at -12 and

-1°. Seeds at 10° kept well for 3 years but deteriorated rapidly

thereafter.

For dry asparagus seeds stored in sealed containers in a laboratory,

loss of viability occurred at 50 months (Rodrigo, 1953). Beet seeds

placed in sealed bottles at 4-percent moisture and stored at room
158 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

temperature did not lose viability in 10 years (Madsen, 1957), and

storage in tin cans was superior to storage in waxed cellophane,

chlorinated rubber, or paper bags in linen ones (Coleman and Peel,

1952). Pepper seeds canned with 4-percent moisture or less stored well

for 36 months at 32° C or lower. As seed moisture content was

increased, the maximum safe storage temperature decreased (Asgrow

Seed Co., 1954). Dry pepper seeds in sealed containers in a laboratory

lost viability at 65 months (Rodrigo, 1953). Okra seeds with 8- to

25-percent moisture content were stored for 10 years in sealed containers at room temperature of 2r-38° and at 2°-5° in cold storage. The

upper moisture limit for 10 years in cold storage was 12 percent, and a

moisture content as low as 8 percent was required for 7 years of safe

storage at room temperature (Martin et al., 1960).

Safe Moisture Levels for Sealed Storage

It is apparent from this discussion that simply sealing seeds in

airproof and moistureproof containers is not necessarily a satisfactory

packaging procedure for safe long-term storage. The research reviewed

points up the need for careful drying to a moisture level that is safe for

the highest temperature under which the seeds may be stored.

The results of Oregon experiments indicated that the following seed

moisture level percentages can be considered safe for 3 years of sealed

moistureproof storage under moderate temperatures for the following

crops: Alfalfa 6, trefoil 7, clover, perennial ryegrass, soybean, and

sweet corn 8, bentgrass, bluegrass, fescue, timothy, and vetch 9, and

barley, bromegrass, common ryegrass, field corn, oats, rye, and wheat

10 (Ching, 1959).

Moisture content percentages of the following are considered safe for

up to 3 years of sealed storage: Cabbage, cauliflower, pepper, and

tomato 5, celery and lettuce 5.5, cantaloup, cucumber, eggplant, onion,

and watermelon 6, parsley 6.5, carrot and pea 7, beet 7.5, and bean,

lawn grasses, spinach, and sweet corn 8 (Bass et al., 1961).

Koopman (1963) listed the following percentages of moisture as safe

for moistureproof packaging of flower seeds: Ageratum 6.7, Alyssum

6.3, Antirrhinum 5.9y Aster 6.5, Bellis 7.0, Campanula 6.3, Lupinus

8.0, Myosotisl.l, Nemesia5.1, Penstemon6.5, Petunia6.2, and Phlox

7.8.

The Federal Seed Act and all State seed laws require that all seed lots

offered for sale be retested for germination at specified intervals.

California took the lead in extending the germination test interval for

adequately dried seeds marketed in hermetically sealed containers

(Calif. Dept. Agr., 1973). Federal regulations soon followed California's

lead. The rules and regulations under the Federal Seed Act (U.S. Dept.

Agr., 1968, pp. 17-83) currently provide that the seeds in hermetically
PRINCIPLES AND PRACTICES OF SEED STORAGE 159

sealed containers shall not exceed the following percentages of moisture

on a wet weight basis:

Beet, field

Beet, sugar

Bluegrass, Kentucky

Clover, crimson

Agricultural Seeds

Percent

._^ 7.5

^^__ 7.5

„„_ 6.0

^ 8.0

Percent

Fescue, red 8.0

Ryegrass, annual 8.0

Ryegrass, perennial 8.0

All others 6.0

Vegetable Seeds

Percent

Bean, garden 7.0

Bean, lima 7.0

Beet 7.5

Broccoli 5.0

Brussels sprouts 5.0

Cabbage 5.0

Cabbage, Chinese 5.0

Carrot 7.0

Cauliflower 5.0

Celeriac 7.0

Celery 7.0

Chard, Swiss 7.5

Chives 6.5

Collards 5.0

Corn, sweet 8.0

Cucumber 6.0

Eggplant 6.0

Kale 5.0

Kohlrabi 5.0

Percent

Leek 6.5

Lettuce 5.5

Muskmelon 6.0

Mustard, India 5.0

Onion 6.5

Onion, Welsh 6.5

Parsley 6.5

Parsnip 6.0

Pea 7.0

Pepper 4.5

Pumpkin 6.0

Radish 5.0

Rutabaga 5.0

Spinach 8.0

Squash 6.0

Tomato 5.5

Turnip 5.0

Watermelon 6.5

All others 6.0

Moisture-Resistant Materials

Polyethylene Films.—The most extensively used thermoplastic film

is made from an entire family of aliphatic hydrocarbon resins. Commercially available polyethylene resins fall into three groups: (1) Conventional low density types with specific gravity of 0.914 to 0.925 gm

per cubic centimeter, (2) medium density types with specific gravity of

0.93 to 0.94, and (3) high density types with specific gravity of 0.95 to

0.96. Density differences are due to differences in molecular structure.

Molecular structure determines the physical structure of the resins.

Resin properties and extrusion variables determine film properties,

which in turn determine the utility of the film. Physical properties

determine the usefulness of a given film. They include tensile, tearing,

and bursting strength, moisture vapor, carbon dioxide, and oxygen

transmission rates, sealability, elongation, and folding endurance.

Conventional low density films have always been considered more
160 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

satisfactory for seed packages than medium and high density films

because of differences in bursting and tearing strength and film elongation or stretch. However, a special medium density film shows

considerable promise. Resin manufacturers and film processors are

continually working to improve bursting and tearing strength and

elongation of medium and high density films.

Medium and high density films tend to show progressively less

permeability to moisture vapor and gases than conventional low density

films. Medium density films show one-half to one-third and high density

films one-fourth to one-fifth the permeability of low density films. A

1-mil low density film tested at 37.8° C and 100-percent relative humidity will permit passage of 1.4 gm of moisture vapor through 100 square

inches of film during 24 hours, a medium density film will transmit 0.7

gm, and a high density film 0.3 gm under the same conditions. A 10-mil

low density film at 37.8° and 100-percent relative humidity will transmit

0.13 gm of moisture vapor per 100 square inches per 24 hours, approximately one-tenth the amount transmitted by the 1-mil film.

A medium density (specific gravity 0.938) polyethylene film has been

developed that surpasses the performance of conventional polyethylene.

A 7-mil film of this special material has a moisture vapor transmission

rate of 0.10 gm per 24 hours per 100 square inches, which is less than

that of 10-mil conventional polyethylene. This special medium density

film has better tensile properties and greater elongation than conventional polyethylene. Because of its high percentage of stretch, this

medium density film has very good puncture resistance.

Both clear conventional polyethylene and the special translucent,

white, medium density polyethylene films are subject to slow deterioration on direct exposure to strong sunlight or ultraviolet radiation. However, deterioration can be retarded by incorporating into the

film carbon black or other pigments, which will absorb the ultraviolet

rays. The special medium density film has a very high resistance to

stress cracking, which has been reported in a few instances with

conventional polyethylene.

Rats and mice sometimes present a problem with conventional polyethylene, but no rodent attack on bags made of the special medium

density material has been reported. Perhaps this material is a solution

to rodent problems.

With a tight closure, such as is produced with a heat seal, both the

10-mil conventional polyethylene and 7-mil medium density polyethylene bags are almost completely insectproof. Thin films may be penetrated by some insects.

Polyethylene films can be laminated to themselves, to other films,

paper, textile fabrics, and fiberboard. Moisture barrier and other

physical properties are improved by laminations. The various proper-
PRINCIPLES AND PRACTICES OF SEED STORAGE 161

ties of each film included in a laminate are more or less additive. Some

laminated films are completely impervious to various gases and practically impervious to moisture vapor. Some laminated materials handle

well on automatic packaging machinery and others handle best by hand

depending on the nature of the materials used in the lamination.

Polyester Films,—These films are heat sealable, transparent, flexible

plastic materials, with low moisture vapor, carbon dioxide, and oxygen

transmission rates and great tensile strength. They will not dry out or

become brittle with age because they contain no plasticizer. Polyester

film can be laminated to itself and practically any other material, and its

flexible laminates can be used with most flexible packaging equipment.

A new construction that utilizes a base of light cotton fabric and

metalized polyester film offers easier fabrication, stronger seals, resistance to flex damage, rough handling, and pinholes.

Polyvinyl Films,—These films are heat sealable, deteriorate slowly

in sunlight, and have outstanding tensile strength and tear resistance,

but they provide only moderate protection unless they are laminated to

an effective moisture-barrier material. They heat-seal over a wide

range of temperatures, are ideal for automatic packaging machinery,

and laminate well to paper, foil, or other films. PolyvinyFs resistance to

sunlight and aging indicates that packages will not dry out or become

brittle.

Cellophane,—This family of films is made of regenerated cellulose

and is produced in more than 100 varieties, each designed for a specific

purpose. Moistureproof types, which have very low moisture vapor

transmission rates, are used for small seed packages. Cellophane alone

does not make a very satisfactory seed package because it becomes

brittle with age or under arid conditions and it breaks easily. Several

firms dealing in flexible packaging materials, however, do produce

combinations of cellophane and polyethylene, which do not become

brittle like cellophane alone and offer fairly good moisture protection.

Polyethylene-cellophane laminates are rather extensively used in seed

packaging as they heat-seal easily and perform well on automatic

packaging machines.

Pliofilm,—Pliofilm is a thermoplastic, rubber, hydrochloride, plastic

film, resistant to ripping, tearing, and splitting. It seals well at low

temperatures, has good moisture-barrier properties, and can be laminated to itself, paper, foils, or other films. Pliofilm can be used on any

package machine designed for flexible film packaging.

Aluminum Foil,—Annealed aluminum foil has a tensile strength of

8.5 pounds per inch of width per mil thickness. It increases in strength

as the gage, or thickness, is increased and as the temperature is

lowered. Tensile strength and resistance to tearing and bursting are
162 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

greater for strain hardened foil than for annealed foil of the same

thickness.

Aluminum foil has a low moisture vapor transmission rate, even for

less than 1.5-mil thicknesses, which have tiny perforations called pinholes. These seem to be an inevitable result of rolling metal to very thin

gages. Microscopic measurements of all the pinholes in 100 square

inches of 0.4-mil foil gave an estimated area of 0.00004 square inch. A

single hole of this area would transmit about 0.19 gm of water vapor per

24 hours at 37.8° C and 100-percent relative humidity. The number and

size of pinholes decrease with increasing foil thickness. Moisture vapor

transmission decreases also with increasing foil thickness. A 0.35-mil

foil will transmit approximately 0.29 gm of water vapor per 100 square

inches of foil per 24 hours at 37.8° and 100-percent relative humidity, a

0.5-mil foil will transmit 0.12 gm of water vapor under the same

conditions, and thicker films transmit almost no water vapor at all.

Aluminum foil is commonly used in laminations and separately as a

coating and overwrap material for cardboard boxes. Aluminum foil

alone does not make good seed packages, but it can be bonded to other

materials to produce combinations having almost any desired characteristics. Even though thin gages of aluminum foil have some pinholes,

combinations with various supporting materials, such as paper or plastic

films, offer effective barriers to moisture vapor and gas transfer. With

the proper selection of materials, combinations can be produced that

will completely restrict moisture vapor transfer.

Laminations.—Laminations of aluminum foil with other materials

have been satisfactorily used for all sizes of seed packages. Examples of

such laminations include (1) aluminum foil/glassine paper/aluminum

foil/heat-sealing lacquer, (2) aluminum foil/tissue paper/polyethylene,

and (3) kraft paper/polyethylene/aluminum foil/polyethylene.

Burlap and cotton can be laminated to paper with asphalt or a

compound latex adhesive to produce a material that will provide good

protection from liquid water but only limited protection from water

vapor. Other constructions utilize such barrier materials as vegetable

parchment, pliofilm, polyethylene, rubber coatings, and foil. Moistureresistant multiwall bags usually have a barrier material, such as asphalt

or polyethylene, between the two outer layers of paper. A good asphalt

laminate at 26.7° C and 75-percent relative humidity has a moisture

vapor transmission rate of 0.17 gm per 100 square inches per 24 hours.

Some seed bags are constructed of paper/polyethylene/aluminum foil

laminates. These combinations afford better moisture protection than

either foil or polyethylene used along with paper. Films of cellophane,

pliofilm, polyester, polyvinyl, aluminum foil, and polyethylene are used

alone or in various combinations for seed packages.
PRINCIPLES AND PRACTICES OF SEED STORAGE 163

Testing Moisture Vapor Transmission of Flexible

Materials

There are several methods of measuring the rate of moisture vapor

transmission through a material. Two methods used in Norway are the

dish method and the method according to Bange (Fornerod, 1963). In

the dish method a strong desiccant is sealed in a special dish by a piece of

the material to be tested. The dish is placed at a controlled temperature

and relative humidity. At periodic intervals the dish is weighed and the

weight change is used to calculate the rate of passage of moisture vapor

through the test material.

The method according to Bange is similar but more accurate for very

slow moisture vapor transmission. The Bange method uses a salt

solution rather than a desiccant in the dish, which is placed in a

measuring apparatus. A strong desiccant is placed in the left pan of the

balance and its weight gain is measured from time to time. From these

measurements the moisture vapor transmission is calculated.

An easy method for an individual to use is to fill a container of the

material to be tested with water, seal it, and place it in a desiccator over

calcium chloride. Moisture penetration is measured by the weight loss

of the package. Conversely, the package can be sealed full of calcium

chloride, then placed in a desiccator over water. In this case weight gain

is used to measure the rate of moisture vapor penetration. No elaborate

special equipment is required for this method of testing moisture vapor

transmission, only a reliable balance for weighing.

From the test data available, not all manufacturers appear to use the

same temperature and relative humidity when testing moisture vapor

transmission of their materials. Some give grams of water per 100

square inches of test material per 24 hours at 37.8° C, with 100-percent

relative humidity on one side and 0 percent on the other side of the

material being tested. Others use the U.S. Bureau of Standards

method, which measures water vapor penetration as grams of water per

100 square inches of test material per 24 hours at 37.8°, with 90-percent

relative humidity on one side and 0 percent on the other. For law

enforcement purposes the Federal Seed Act specifies use of the Bureau

of Standards method.

In the National Seed Storage Laboratory at Fort Collins the moisture

protection of test materials is measured by the change in seed moisture

content over time. Seeds in packages made of good moisture-barrier

materials show little change in seed moisture, whereas seeds in poor

moisture-barrier materials gain or lose moisture rapidly. A simple

method, which does not destroy the seeds, as when making a seed

moisture test, is to weigh the test package when filled and at intervals

thereafter. However, the outside of the package must be free of liquid

water. Also, paper on the outside can hold extra water and give
164 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

erroneous results. The moisture vapor transmission rate can be calculated using the amount of weight change, the time between weighings, and the surface area of the package. The moisture vapor transmission rate measured by either of the last two methods will be less

than the rate for the same material measured by the U.S. Bureau of

Standards method unless the test package is subjected to the specified

temperature and relative humidity.

Moisture-Barrier Storage

The development of polyethylene and other flexible moisture-barrier

packaging materials prompted studies to determine the value of these

materials as protective packages for seeds. Thin gages of polyethylene,

polyester, and similar materials do not provide very much moisture

protection (Barton, 1949, 1953; Isely and Bass, 1960; Miyagi, 1966).

Storage life was increased by storage in containers made of 5- or 10-mil

polyethylene for the following seeds: Alta tall fescue, Chewings fescue,

corn, creeping red fescue, cucumber, hemp. Highland bentgrass, kenaf,

Kentucky bluegrass, onion, peanut, ryegrass, sudangrass, and wheat

(Anonymous, 1959; Cooper, 1959; Bass, I960, 1968; Chinget al., 1960;

Toole et al., I960, 1961; Milligan and Hayes, 1962; and Grabe and Isely,

1969),

Kraft multiwall bags with laminated paper/foil/polyethylene liners

were as effective as tin cans in maintaining a moisture barrier during

storage and shipment of cabbage, soybean, and wheat seeds (Caldwell,

1962), The water vapor transmission rates of polyethylene materials

are inversely proportional to their protective value for seed storage

under tropical, temperate, and warehouse conditions (Ching and AbuShakra, 1965), Packaging materials containing aluminum foil provide

good moisture protection (Harrington, 1960a, 1960b, 1963; Lowig, 1963;

Bass and Clark, 1974; and Clark and Bass, 1975),

The need for moisture protection is determined by the storage

conditions and so is the protective value of a barrier material to a

certain extent. A good barrier material, such as a heavy foil laminate,

will provide adequate moisture protection regardless of the storage

conditions; a mediocre material will not give satisfactory moisture

protection when relative humidity is high (table 25).

To provide a rigorous test, we stored crimson clover seeds in a

variety of materials (table 26) in a 20° C night (15 hours) - 30° day (9

hours), water-curtain germination chamber, in which the relative

humidity was 95 to 100 percent constantly. The data (table 25) show

which materials provided satisfactory moisture and germination pro^

tection. Seeds in the same materials stored at 10° and 50-percent

relative humidity showed a different moisture and germination picture.
TABLE 25.—Moisture content and germination of crimson clover seeds packaged in various

flexible materials and stored for2 years in walk-in germinator held at20°-30° Cand 95- to

100-percent relative humidity (RH) or at 10° and 50-percent relative humidity

Moisture Germination

Moisture

after 2 years at—

Germiafter 2 years at—

Material

No.i

when 20°-30° and 10° and nation 20°-30° and 10° and

stored 95- to 100- 50-per- when 95 - to 100- 50-perpercent RH cent RH stored percent RH cent RH

Percent Percent Percent Percent Percent Percent

1 3.4 227.9

13.0

8.9

4.6

74

74

20

42

72

2 3.4 73

3 3.3 20.0 6.4 74 0 76

4 3.3 18.7 6.7 74 0 85

5 3.4 29.0 6.9 74 0 79

6 _:__ 3.4 22.5 8.5 74 0 77

7 3.4 18.5 5.8 74 1 70

8 3.3 16.2

10.3

5.8

5.8

74

74

0

72

84

9 3.3 80

10 3.4 3.4 3.3 74 75 81

11 3.3 6.6 3.3 74 72 74

12 3.3 19.8 7.0 74 0 79

13 3.4 13.1 5.7 74 27 79

14 3.2 3.3 3.4 74 73 70

See footnotes at end of table.

2

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TABLE 25.—Moisture content and germination of crimson clover seeds packaged in various

flexible materials and stored for2 years in walk-in germinator held at 20''-30° Cand 95- to

100-percent relative humidity (RH) or at 10° and 50-percent relative humidity—Con,

Moisture Germination

Material

No.i

Moisture

when

stored

after 2 ,years at—

Germination

after 2 years at—

20°-30° and 10° and 20°-30° and 10° and

95- to 100- 50-per- when 95- to 100- 50-perpercent RH cent RH stored percent RH cent RH

Percent Percent Percent Percent Percent Percent

15 __ 3.4 3.5 3.5 74 78 11

16 __ 3.3 3.4 3.3 74 73 78

17 __ 3.3 230.9 8.8 74 20 80

18 __ 3.4 4.0 3.3 74 70 81

1 See table 26 for identification of materials.

2 Seed dead by 6-mo test.

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PRINCIPLES AND PRACTICES OF SEED STORAGE 167

Results of our studies suggest that a foil laminate such as material 10,

11, 14, 15, 16, or 18 (tables 25 and 26), properly sealed, provides as much

moisture protection as a sealed metal can. The data (table 25) also show

that for long-term storage the container must provide adequate moisture protection for the most humid condition to which the seeds could be

subjected, not just the intended storage relative humidity. When

preserving germ plasm, care must be taken to guard against any

eventuality.

TABLE 26.—Construction and source of 18flexible packaging materials

tested for suitability as moisture-barrier seed packages^

Material

No.

Construction Source

1 20-lb brown kraft coin envelopes Cupples-Hess Co.,

Div. of St. Regis

Paper Co.

2 _. 30# paper/17# Saran/0.5-mil polyethylene Chase Bag Co.

3 0.5-mil mylar/Saran coating/2-mil polyethylene Continental Can Co.

4 0.5-mil bioriented polypropolene/adhesive/

250K204F cellophane/28.8-lb (2-mil)

polyethylene extrusion coating.

Milprint, Inc.

5 250K204F cellophane/adhesive/30- to 39-lb

Saran-coated opaque glassine.

Do.

6 0.5-mil A mylar/29.2-lb medium density

polyethylene extrusion coating.

Do.

7 . _ _ __. 1.25-mil oriented polypropylene, 1-side

coated with 2-mil branched

polyethylene.

North American

Packaging^Co.

8 _ _ 4-mil cast polypropylene Avisun Corp.

9 Heat-seal coated 2-mil foil Aluminum Co. of

America.

10 _ Paper/foil/polyethylene designated FX12530 __ Reynolds Metals Co.,

Packaging Research

Div.

11 Polypropylene/foil/polyethylene designated

FX12529.

Do.

12 0.5-mil oriented polypropylene/Saran

coating/2-mil polyethylene.

Continental Can Co.

13 Marlex-' Tr 101 6-mil high density polyethylene Mehl Manufacturing

Co.

See footnotes at end of table.
168 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

TABLE 26.—Construction and sources of 18 flexible packaging materials tested for suitablility as moisture-barrier seed packages^—Con.

Construction Source No.

14 45-lb polyethylene/0.5-mil foil/10-lb Union Bag Camp Co.

polyethylene/50-lb extensible multiwall kraft.

15 2.5-oz sq yd scrim/1-mil polyethylene/0.35-mil Chase Bag Co.

foil/3.0-mil polyethylene.

16 0.5-mil A mylar/7-lb polyethylene/0.35-mil Rap Industries.

foil/15-lb polyethylene.

17 5-mil ethyl-vinyl-acetate film Union Carbide Corp.,

Plastics Div.

18 140 RSO cellophane/10-lb polyethylene/0.35- Rap Industries.

mil foil/17-lb polyethylene.

1 These packaging materials were contributed through the courtesy of the individual

firms.

2A trademark name for Phillips family of olefin polymers.

Use of Desiccants in Sealed Containers

Although the use of desiccants has received some attention from seed

researchers, it has not received much attention from the seed industry.

The longevity of rice seeds in sealed containers has been increased by

including in the container a drying agent, such as calcium oxide

(quicklime) or calcium chloride (Nakajima, 1927; Kondo and Kasahara,

1941; Ito and Hayashi, 1960), Rice seeds in a closed container with

calcium chloride retained good viability for 9 and 10 years (Nakajima,

1927; Kondo and Kasahara, 1940). Germination of rice seeds having

10-percent moisture when sealed was maintained for 1 year at 40° C

when calcium chloride was enclosed with the seeds. Seed with 16-percent initial moisture was preserved at room temperature with calcium

chloride, and without it all viability was lost (Kondo and Okamura,

1931).

Tobacco seeds sealed with calcium chloride germinated 88 percent

after 11 years and 81 percent after 25 years (Kincaid, 1943, 1958), and

seeds sealed with calcium oxide germinated 87 to 92 percent after

nearly 21 years (Schloesing and Leroux, 1943). Storage with silica gel

improved longevity of timothy seeds (Roberts, 1962), quicklime preserved Viola tricolorseeds (Lowig, 1953), but seeds of Zoysia japónica

sealed with calcium chloride lost germination rapidly after 2y2 years

along with seeds sealed without a desiccant (Radko, 1955). Temperature had little effect on the longevity of bean, eggplant, lettuce, and

tomato seeds stored over calcium chloride (San Pedro, 1936). Germina-
PRINCIPLES AND PRACTICES OF SEED STORAGE 169

tion percentages of several crops after 10 years over calcium chloride

were Avena sativa 89, Capsicum annuum 70, Cucumis sativus 80,

Cucúrbita pepo 55, Oryza sativa 62, Raphanus sativus 81-89, Solanum

melongena 37, and Zea mays 79 (Kondo and Kasahara, 1940),

Most desiccants do not injure seeds; however, quicklime did have an

injurious effect on seeds of several species, such as Oryza sativa,

Phaseolus radiata var. pendulus (= Vigna radiata), and Vicia sativa

(Nakajima, 1927). Calcium oxide did not improve the longevity of

^Golden Cross Bantam' sweet corn (Edmond, 1959),

Although most of the studies showed that seeds sealed with desiccants lived somewhat longer than those sealed without them, their use

has not received wide application in the seed industry because of several

factors. Probably the most important are the added cost of the desiccant

and the larger container required for it. Also, when a package is

opened, the desiccant is soon useless. Because most seeds are stored

commercially only from harvest to the next planting season, the added

expense is not easily justified except possibly in very humid areas

where seeds deteriorate rapidly under normal storage conditions.

Use of desiccants may offer some economic advantage for long-term

storage. However, without the results of a comprehensive study, one

cannot be certain of their value in preserving seed viability and vigor

during long-term storage in sealed moistureproof containers, because

for adequately dried seeds a desiccant may be of no benefit. Such a

study should include several kinds of seeds with a wide range of

moisture levels, stored with different amounts of each kind of desiccant,

and at temperatures from below freezing to 32° C or higher. Desiccants

could be very beneficial when used in conjunction with some of the

flexible packaging materials that have limited moisture-barrier qualities.

MONITORING SEED STORAGE ENVIRONMENT

AND SEED CONDITION

Germination and Viability

Ordinarily seeds are tested for germination and viability by laboratories equipped and staffed to determine the quality of seeds. Inexperienced individuals planning to conduct germination and viability research should receive some training in a reputable laboratory. In the

germination test a seed to be considered as having germinated must

produce a seedling with normal or approximately normal features.

Some kinds of plants produce hard seeds that are considered to be

viable although they do not germinate when tested according to officially accepted procedures. Sometimes dormant seeds require special
170 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

germination test procedures. A viability test aims to quickly detect all

live seeds whether dormant or not. The tetrazolium and the embryo

excision tests are used for this purpose.

The procedures for testing seed germination and viability are found

in the "Rules for Testing Seeds" by the Association of Official Seed

Analysts (1970), special handbooks published by the Association of

Official Seed Analysts, the "International Rules for Seed Testing"

published by the International Seed Testing Association (1966), the

"Rules and Regulations of the Secretary of Agriculture," U.S. Department of Agriculture, published in the Federal Seed Act of August 9,

1939, with revisions, and in certain supplementary publications (Grabe,

1970] Justice, 1972), Information concerning the availability of these

rules for seed testing and the special handbooks can be obtained from

the Seed Branch, Grain Division, Agricultural Marketing Service, U.S.

Department of Agriculture, Washington, D.C. 20250.

Seed Vigor

Vigor as applied to seeds is an indefinite term. No definition for seed

vigor has been accepted generally. The methods used to test seed vigor

are just as vague. Neither the Association of Official Seed Analysts nor

the International Seed Testing Association has included methods of

testing seeds for vigor in their procedures. The best known and commonly used vigor test is the so-called cold test developed for corn and

subsequently adapted for a few other crop species. One problem with

this test has been the difficulty of standardizing the fungi and soil used

in making the test. Additional information on this test can be obtained

from the Iowa State University Seed Laboratory, Ames 50010, where

the test was developed.

Other procedures used in research include the respiration test, which

measures oxygen consumption and carbon dioxide release, the GADA

(glutamic acid decarboxylase activity) test, various types of stress

tests, rate of seedling growth test, and the tetrazolium test. Each of

these tests has been useful for specific kinds of seeds but has not proved

reliable for a wide range of various kinds of seeds. Woodstock (1973)h^^

reviewed the literature on vigor tests.

Seed Moisture Content

Practical methods of testing seeds for moisture include oven methods

and electric moisture meters. Basically the oven methods operate on the

principle that the seed moisture is driven oif by heating. The difference

in weight of the seeds caused by heating represents the moisture

content. The temperature and time of heating have been reported for
PRINCIPLES AND PRACTICES OF SEED STORAGE 171

many kinds of seeds. The heating regimes have been developed to

minimize weight changes not produced by moisture.

Large seeds are frequently ground to decrease drying time. Many

seeds are heated to 130° C, whereas others should not be heated above

100° and a few at lower temperatures. A common method is to dry seeds

for 24 hours at 100° to 105°. At the higher temperatures, volatile

materials can be driven off and oils and fats oxidized, both resulting in

weight changes. As the drying temperature is decreased, the drying

time must be increased proportionately. Drying schedules have been

published in the "International Rules for Seed Testing'' (1966). These

rules were developed for air ovens that operate at normal atmospheric

pressure. Vacuum ovens with the advantage of reducing drying time

are available. All oven methods have the disadvantage of requiring

much equipment, weighing of materials, and considerable time for

testing. However, they are the more accurate of the practical methods.

Electric moisture meters have an advantage in speed over all other

practical methods. Most electric moisture meters are based on measurements of either conductivity or the dielectric properties of the seed.

Although these measurements vary with the moisture content of the

seeds, they are affected to some extent by other factors. Calibration

charts have been developed for many kinds of seeds. Calibrations

should be based on the testing of relatively large numbers of samples,

covering a wide range of moisture contents, sources of samples, and

years of harvest.

With most moisture meters, the test can be completed within 1 or 2

minutes. Disadvantages are relatively high cost of equipment, need for

careful, painstaking calibration for each kind of seed, and in some cases,

especially for very wet and very dry seeds, failure of the equipment to

be highly accurate. For more information on methods of testing seeds

for moisture content, see Hlynka and Robinson {in Anderson and

Alcock, 1954), Hart et al. (1959), and Zeleny (1961).

Fungi and Bacteria

Methods of testing seeds for the presence of seedborne micro-organisms are given in the "International Rules for Seed Testing" (1966).

For additional information, see Muskett (1948), de Tempe (1961),

Naumova (1970), Baker (1972), and Neergaard (1973).

Relative Humidity

A psychrometer is commonly used to measure relative humidity.

Sling psychrometers are inexpensive, reasonably accurate, and easy to

use. This instrument consists of a dry-bulb thermometer, which

measures the ambient temperature, and a wet-bulb thermometer,
172 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

which measures the reduced temperature caused by the cooling effect of

the evaporating liquid. This cooling effect is in proportion to the relative

saturation of the air being tested. Recording psychrometers have the

advantage of providing a record at any time over the interval covered

by the clock and chart. Both temperature and relative humidity are

recorded by the hygrothermograph. This instrument requires special

attention when changing the charts. The directions for its use should be

followed very closely. Recording units are available that use electrical

resistors to measure humidity and thermistors to measure temperature.

Although expensive, they are very accurate. Major changes in relative

humidity can be detected with cobalt chloride cards. At different

positions on the card, the color changes as the relative humidity

progressively increases.

Temperature

Thermometers, like psychrometers, are made in several forms. When

a high degree of accuracy is not required, simple, inexpensive stemtype thermometers can be used to measure the temperature of the air

or the mass of seeds. Although some or most of the thermometers of

this type may be accurate, they must be removed from the seed mass

before taking the reading. By the time the reading is taken, the

mercury column may have changed, and thus it gives an erroneous

reading. Recording thermometers, with or without a sensing element,

are available. Of course, these instruments provide a continuing record,

which can be cited for future reference if desired. Multipoint recorders

provide essentially the same information, but each instrument can be

equipped with several sensing units, or thermocouples, allowing the

monitoring of several locations simultaneously. Thus, hot spots in a

mass of seed or grain may be detected with a thermocouple that

conceivably could go undetected if the other temperature sensing and

recording instruments were used. Thermographs, recording thermometers, and multipoint recording units are rather expensive. Their use

may or may not be justified depending on the degree of accuracy

desired, chance of product heating in storage, extent of business

operation, and frequency of use.

Storability of Seed Lots

Considerable research, mostly at the Mississippi State University

Seed Technology Laboratory, has been conducted to develop a practical

method for predicting relative storability of seed lots, especially those

to be stored for future use. Although several potential tests were

devised and evaluated in this research, two were more successful than

others—the accelerated aging test and the modified aging test.
PRINCIPLES AND PRACTICES OF SEED STORAGE 173

The following information has been taken from reports by Delouche

et al. {1967, 1968), Delouche and Baskin (1971), and Goff (1972). "In the

accelerated aging test, the germinative responses of representative

samples of seed lots are determined after exposure to conditions of

temperatures of 40° to 45° C and 100-percent relative humidity for

varying periods of time up to 204 hours. The modified aging test

measures the germinative responses of samples after they have been

held at 30° and 75-percent relative humidity for various periods of

time."

Optimum accelerated aging conditions and treatment times in the 2

tests are given for 16 kinds of seeds in table 27.

TABLE 27.—Optimum accelerated aging conditions and treatment

times in 2 tests for predicting seed storability of 16 crops^

Accelerated aging test Modified aging test

Crop Temperature Treatment time at 30° C

at 100-percent Treatment time and 75-percent

relative humidity relative humidity

°C Hours Weeks

Alfalfa 42 84 6

Bean 42 84 20

Bromegrass 45 72 9

Corn 42 84 24

45 60

Crimson clover 40 72 9

Fescue 42 84 15

Lespedeza 40 72 6

Lettuce 40 72 9

Onion 42 72 6

Radish 45 48 24

Red clover 40 72 9

Sorghum 45 72 12

Soybean 40 72 9

Timothy 42 60 6

Watermelon 45 144 21

Wheat 45 48 18

1 Data from Delouche and Baskin (1971).

We do not claim that these tests will accurately predict the storability

of all seed lots of a given crop species. The principles involved do offer

the seedsman a means of detecting some seed lots that should not be

stored for extended periods of time. More accurate predictions could be

made if the seed lots were stored under controlled temperature and

relative humidity rather than under ambient conditions.
174 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

The researchers who developed the accelerated aging test of predicting seed storability are confident that the method or modifications

will ultimately be perfected so that storability of seed lots can be

predicted with considerable accuracy. Additional information on these

test procedures can be obtained from the Seed Technology Laboratory,

Mississippi State University, State College 39762.

Detection and Identification of Fungi and Insects

Ordinarily the manager or superintendent of the storage warehouse

must monitor his seed stocks. It is his responsibility to check for

evidence of fungi and insects. Their presence may be detected either by

observing their growth on or in the seed mass or by development of hot

spots. If hot spots are detected, the cause should be ascertained

immediately. The cause may be traced to molds, insects, or both.

Specialists may be required to identify molds or insects. The State

agricultural colleges and universities and State departments of agriculture frequently will make simple identifications of occasional specimens

for residents. Depending on their background, some county agricultural

agents may perform this service. Seed companies often employ a plant

pathologist. Some official and commercial seed testing laboratories

routinely conduct seed health tests.

SOME PRACTICAL INFORMATION FOR STORING

AND TRANSPORTING SEEDS AT AMBIENT

CONDITIONS

Examples of Storability of Different Plant Species

There is much variability in the lifespan or storage life of seeds of

different plant species. The lifespan of seeds of certain aquatic and

woody plants is very short, whereas seeds of some leguminous species

and a few other kinds retain viability for over a hundred years. Only the

practical storage life of cultivated species of field, vegetable, herb, and

flower seeds is discussed here, not species with extremely short or

extremely long storage lives. Seed longevity per se is not included. The

information here relates to the retention of viability of most individual

seeds in a lot, not the elapsed time before the last viable seed in a lot or

sample is dead.

Species for which information is available have been listed. The data

can be used as guidelines for closely related species not given. The

information is rather scanty, some of it is outdated, and most of it has

been obtained under nonuniform storage and test conditions. This

obviates accurate comparisons.
PRINCIPLES AND PRACTICES OF SEED STORAGE 175

As indicated by the column heading, "Relative Storability Index," in

the tabulation, the data do not refer to specific years of storage. In

general, the authors classified in category 1 those plant species of which

50 percent or more of the seeds can be expected to germinate after 1 to

2 years of storage under favorable ambient conditions at latitudes of

approximately 35° to 48° N., in category 2 after 3 to 5 years, and in

category 3 after 5 or more years.

Examples of relative storability of field, vegetable, herb, and flower

seeds of high viability and vigor are as follows:

Relative storability

Seed FIELD CROP SEEDS index

Alfalfa 3

Alyceclover 3

Bahiagrass 2

Barley 2

Bean, field 2

Beet, field and sugar 3

Bentgrass:

Colonial (including Astoria and Highland) 3

Creeping 3

Velvet 3

Bermudagrass 1

Bluegrass:

Bulbous 2

Canada 2

Kentucky 2

Nevada 2

Rough 2

Texas 2

Wood 2

Bluestem:

Big 2

Little 2

Sand 2

Brome:

Mountain 2

Smooth 2

Buckwheat 2

Buifalograss 3

Burclover:

California 3

Spotted 3

Buttonclover 3

Canarygrass 1

Canarygrass, reed 1

Carpetgrass 3

Clover:

Alsike 3

Berseem 2

Crimson 2
176 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Relative storability

Seed FIELD CROP SEEDS—con. index

Clover—Con.

Ladino 3

Lappa 3

Large hop 3

Persian 3

Red 3

Strawberry 3

Subterraneum 2

Suckling (small hop) 3

White 3

Corn:

Field 1

Pop 2

Cotton 1

Cowpea 1

Crested dogtail 2

Crotalaria 3

Dallisgrass 1

Dropseed, sand 2

Fescue:

Chewings 2

Hair 2

Meadow 2

Red 2

Sheep 2

Tall 2

Flax 2

Grama:

Blue 2

Side-oats 2

Hardinggrass 1

Hemp 2

Indiangrass, yellow 1

Japanese lawngrass 2

Johnsongrass 2

Kudzu 2

Lespedeza:

Korean 1

Sericea or Chinese 2

Siberian 2

Striate 1

Lovegrass, weeping 2

Lupine:

Blue 1

White 1

Yellow 1

Manilagrass 2

Meadow foxtail 2

Medic, black 3

Millet:

Foxtail (common, German, golden, Hungarian, Siberian) 1
PRINCIPLES AND PRACTICES OF SEED STORAGE 177

Relative storability

Seed FIELD CROP SEEDS—con. index

Millet—Con.

Japanese 2

Pearl 1

Proso 1

Oatgrass, tall ._ 1

Oats 2

Orchardgrass 1

Panicgrass, blue 2

Pea, field 2

Peanut 1

Poppy 2

Rape 2

Redtop 1

Rescuegrass : 2

Rhodesgrass 2

Rice 2

Ricegrass, Indian 2

Roughpea 2

Rye 1

Ryegrass:

Italian 2

Perennial 2

Sainfoin 1

Smilo 3

Sorghum: Grain and sweet _^ 1

Soybean 1

Sudangrass 1

Sunflower 1

Sweetclover:

White 3

Yellow 3

Switchgrass 2

Timothy 2

Tobacco 1

Trefoil:

Big 2

Birdsfoot 2

Vaseygrass 1

Velvetbean 1

Vetch:

Common 2

Hairy 3

Hungarian 2

Monantha 2

Narrowleaf 3

Purple 2

Woollypod 3

Wheat, common 2

Wheatgrass:

Fairway crested 2

Intermediate 2
178 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Relative storability

Seed FIELD CROP SEEDS—con. index

Wheatgrass—Con.

Pubescent 2

Slender 2

Standard crested 2

Tall 2

Western 2

Wild rye:

Canada 2

Russian 2

Zoysia (see Japanese lawngrass and manilagrass)

VEGETABLE SEEDS

Artichoke 1

Asparagus 1

Bean:

Garden 1

Lima 1

Beet 3

Broadbean or horsebean 2

Broccoli 2

Brussels sprouts . 2

Cabbage 2

Cardoon 1

Carrot 2

Cauliflower 2

Celeriac 2

Celery 2

Chicory 2

Collards 2

Corn, sweet 2

Cowpea 1

Cress:

Garden 2

Water 2

Cucumber 2

Dandelion 1

Eggplant 2

Endive 2

Kale 2

Kohlrabi 2

Leek 1

Lentil 1

Lettuce 1

Muskmelon (cantaloup) 2

Mustard, India 2

Okra 2

Onion 1

Pakchoi 1

Parsley 1

Parsnip 1

Pea, garden 2

Pepper 1
PRINCIPLES AND PRACTICES OF SEED STORAGE 179

Seed VEGETABLE SEEDS—COn.

Relative storability

index

Pe-tsai (Chinese cabbage) 2

Pumpkin 2

Radish 2

Rhubarb 1

Rutabaga 2

Salsify. 1

Soybean 1

Spinach:

Common 2

New Zealand 2

Squash 2

Tomato 3

Turnip 2

Watermelon 2

HERB SEEDS

Anise

Balm

Basil, sweet

Borage

Caraway __

Chervil

Coriander _ _

Dill

Fennel

Hyssop

Marjoram _

Rosemary _

Sage

Savory

Thyme

FLOWER SEEDS

Achillea, the pearl 2

Ageratum 2

Alyssum 2

Amaranthus 3

Anemone 1

Angel-trumpet 2

Arabis 1

Armería 1

Asparagus, fern ^ 1

Aster, China 1

Babysbreath 2

Bachelor's button, cornflower 2

Balloonflower 1

Balsam 2

Begonia 1

Bellflower, peach 2

Browallia 1
180 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Relative storability

Seed FLOWER SEEDS—con. index

Bugloss 2

Butterflyflower 2

Calceolaria 1

Calendula 2

Calliopsis, dwarf and tall 2

Candytuft:

Annual 1

Perennial 1

Canna 2

Canterbury-bells 2

Carnation 2

Cathedral bells 1

Centaurea:

Royal 3

Velvet 3

Chrysanthemum, annual 3

Cineraria, common 2

Cleome, spiderflower 1

Cockscomb 2

Cockvine 1

Coleus, common 2

Columbine 1

Coneflower 1

Coralbells 1

Coreopsis, perennial 1

Cosmos 2

Cyclamen 2

Cypressvine 3

Dahlia 2

Daisy:

African 1

African lilac 2

English 1

Painted 1

Shasta 3

Swan river 2

Dames rocket, sweet rocket 2

Dusty-miller 2

Firebush, Mexican 1

Flax:

Flowering 3

Perennial 3

Foxglove 1

Gaillardia 2

Geum 1

Gilia 2

Globe amaranth 2

Gloxinia, common 1

Godetia 2

Gourds 3
PRINCIPLES AND PRACTICES OF SEED STORAGE 181

Relative storability

Seed FLOWER SEEDS—con. index

Heliopsis 1

Heliotrope 1

Hibiscus 2

Hollyhock 3

Hyacinth-bean 2

Iris, Japanese 2

Jerusalem or Maltese cross 2

Jobs-tears 2

Lantana 1

Larkspur:

Annual 1

Hybrids 2

Linaria 2

Lobelia 2

Lunaria, honesty 2

Lupine:

Annual types 2

Russell hybrids 2

Marigold:

African 2

French 2

Marvel of Peru, four-o'clock 2

Matricaria 1

Mignonette 1

Morningglory 3

Myosotis 1

Nasturtium 2

Nemesia 1

Nicotiana 2

Nigella 2

Pansy 1

Penstemon 1

Petunia 2

Phacelia 2

Phlox 1

Physalis 2

Pinks, China 2

Poppy:

California 2

Corn, Shirley 3

Iceland 2

Mexican tulip 1

Oriental 2

Portulaca 2

Primrose 1

Rose campion 2

Sage:

Mealycup 2

Scarlet 1

Salpiglossis 3
182 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Relative storability

Seed FLOWER SEEDS—con. index

Saponaria 2

Scabiosa 2

Snapdragon 2

Sneezeweed, helenium 2

Snow-on-the-mountain 2

Solanum 2

Statice 1

Stocks 3

Strawflower 1

Sunflower 2

Sweetpea:

Annual 3

Perennial 2

Sweet-william 2

Verbena 2

Vinca, periwinkle 1

Viola 1

Wallflower 2

Zinnia 3

The following references were used in compiling the Hst: Bodger

Seeds Ltd. (1932), Filter (1932-33), Goss (1937), Harrington (1972),

James et al. (1964),_ Madsen (1962), Owen (1956), Pritchard (1933),

Sifton (1920), Ullmann (1949), Welton (1921), and Wheeler and Hill

(1957).

Climatological Data Pertinent to Seed Storage

Although the relative humidity and temperature of the storage

environment can be controlled artificially, the cost of providing such

control in large storage areas is usually not economically feasible. Thus,

most seeds stored in North America are kept at ambient temperatures

and relative humidities. Storage as used here includes holding of seeds

for processing, shipment, or sale, as well as the period of shipping.

Because of the wide range of climatic conditions in the United States,

its territories, Puerto Rico, Canada, and Mexico, climatological data

useful to seedsmen, seed merchants, and farmers could be provided in

maps; however, weather maps give less specific information than tabular data and may be difficult to interpret.

The data in table 28 are relatively longtime averages and should

provide reliable guidelines for persons planning to store seeds at

ambient conditions at the indicated locations. Data are given for January, April, July, and October, the first month of each season, as well as

annual averages. Locations have been selected to give a fairly representative cross section of the area covered. For locations not shown,

data from the nearest station should be used or adapted, based on
PRINCIPLES AND PRACTICES OF SEED STORAGE 183

known facts about the local climate. For example, if one is going to store

seeds at ambient conditions in Dayton, Ohio, from July to January, he

would probably check the conditions at Cincinnati and Columbus, Ohio,

as well as at Indianapolis, Ind. Six-month averages for these three

locations for July and October are temperature 19° C and relative

humidity 70.1 percent. For practical purposes, these values would be

close enough for Dayton. If the seed is to be stored for a year, the

annual averages for the three locations should be used, as 12° and

71.7-percent relative humidity. Other adaptations may be necessary for

other locations, especially where relatively great climatological differences occur within short distances, as in mountainous areas or near

large bodies of water. Annual averages should be used with great care

because of extreme seasonal differences that can be masked in them.

These data provide a guide for drying carryover seed and storing it in

moisture-barrier containers. It should be remembered that basement

rooms, unless well ventilated, always have a higher relative humidity

than aboveground rooms and can be potentially dangerous as seed

storage areas.

Another possibility is to obtain original and up-to-date information

from the National Weather Records Center, U.S. Department of Commerce, NOAA, Asheville, N.C. 28801. This Center can provide current,

more complete, and longtime averages of temperatures, relative humidities, and several other weather and climatological data for many

stations not shown in table 28.

Relation of Storage Conditions to Intended Storage

Periods

The first question asked of seed storage specialists is "How should I

store my seed?" For an adequate answer the speciahst must know

where and what kinds are to be stored for how long. In arid areas many

kinds of seeds can be stored for 5 years or longer under ambient

conditions provided the temperature is not too high. In temperate

regions the same kinds of seeds may keep only 2 or 3 years, whereas in

the humid subtropical and tropical regions viability may be lost in a few

months or even weeks at ambient conditions.

A useful guide for commercial seed storage for up to 5 years is

Harrington's (1960d) thumb rule that states "the sum of the temperature in °F and the percent relative humidity should not exceed 100." For

example, various kinds of seed stored at 50° F (10° C) and 50-percent

relative humidity showed no loss in viability during 5 years of storage

(James et al., 1967), Comparable results can be obtained by drying seed

to 5-percent or lower moisture content and storing it in sealed moisture-barrier containers at ambient temperatures up to 32° C. At higher

ambient temperatures some refrigeration is desirable.
TABLE 28.—Climatological data for 188 weather stations in the United States, its territories, Puerto Rico, Canada, 00

and Mexico^ hi^

Average temperature and relative humidity (RH)2 for-- >

o

Location of ?o

weather station January April July October Annual o

c:

Temp. RH Temp. RH Temp. RH Temp. RH Temp. RH

°C Percent °C Percent °C Percent °C Percent °C Percent

United States: >

Alabama:

Birmingham 8 72 17 65 27 74 18 70 17 70 to

o

Mobile 11 74 19 73 28 78 21 72 20 73 o

Montgomery 9 74 18 67 28 75 19 70 19 74

Alaska:

Anchorage -11 74 2 m 14 73 2 77 2 72

c;

C/2

Fairbanks -24 69 2 61 16 70 -3 79 3 69 O

Juneau -4 70 3 75 13 78 6 84 4 78

Nome -16 78 -6 81 10 87 1

.3 81 3 81

Arizona: o

Phoenix 11 49 19 36 32 37 21 43 21 42 >

Tucson 10 47 18 26 30 41 21 38 19 38 2

Yuma 13 43 22 33 34 40 26 40 23 39 o

Arkansas: ci

Fort Smith _^^ 4 68 17 63 28 Q^ 17 QS 7 67

Little Rock _ 5 73 17 66 28 71 18 69 7 70

California:

Fresno 8 80 16 57 27 41 18 54 17 61

Los Angeles _ __ 12 59 15 64 21 QQ 18 64 17 62

Red Bluff 7 72 15 51 27 32 18 47 17 51

Sacramento „ _ 7 82 14 m 23 54 17 60 16 m
San Diego 12 68 15 66 20 75 18 72 17 71

San Francisco_

9 79 13 77 17 79 16 76 13 77

Colorado:

Alamosa -8 68

5 46 18 57

7 56

5 57

Denver -2 53

8 52 23 48 11 47 10 50

Grand Junction -3 69 11 43 26 34 13 46 12 48

Connecticut:

Bridgeport -2 64

9 63 23 72 13 70 11 70

^w

Hartford -2 69

8 66 23 73 12 73 10 71

2

Delaware,

o

Wilmington

1 70 11 65 24 71 14 73 12 70

D.C., Washington_

3 66 13 59 26 71 15 71 14 67

Florida:

>

Jacksonville __ 13 76 21 70 28 77 22 79 20 75

o

Miami 19 75 23 72 28 78 26 79 24 76

Orlando 16 75 22 69 28 77 24 75 22 74

>

Tallahassee 12 77 20 72 27 80 21 75 20 75

Owo

Tampa 16 77 22 71 28 78 24 71 22 76

Georgia:

Atlanta

7 72 16 64 26 73 17 68 17 69

Macon9 71 18 66 27 76 18 74 18 71

Savannah 11 72 19 68 27 78 20 76 19 73

Hawaii:

i

Hilo 22 80 22 81 24 80 24 81 23 81

O

Honolulu 73 74 23 69 26 67 26 69 24 70

>

Kahului 22 79 23 75 26 71 25 73 24 74 t?d

Lihue 21 80 22 73 24 75 24 77 23 77

Idaho:

Boise -2 78 10 56 24 38 11 55 11 58

Lewiston -1 75 10 52 23 35 11 61 11 57

Pocatello -3 78

8 54 21 37

9 55

8 53

00

See footnotes at end of table. en
TABLE 28.—Climatological data for 183 weather stations in the United States, its territories, Puerto Rico, Canada,

and Mexico^—Continued

Average temperature and relative humidity (RH)2 for—

Location of

weather station

January April July October

Temp. RH Temp. RH Temp. RH Temp. RH

Annual

Temp. RH

>

o

2

o

a

r

a

X

>

a

00

United States—Con.

Illinois:

Chicago

Peoria

Springfield _

Indiana:

Evansville _

Fort Wayne

Indianapolis

Iowa:

Des Moines _^

Dubuque __

Sioux City _

Kansas:

Concordia _ _

Dodge City __

Topeka

Wichita

Kentucky:

Lexington _

Louisville __

Percent

76

73

80

76

81

74

73

77

73

71

68

71

71

72

73

Percent

9 68

11 66

12 70

13 65

9 69

11 69

10 65

9 64

9 64

12 61

12 60

12 64

14 62

12 63

13 64

24

24

25

26

23

24

26

23

23

26

26

26

27

24

26

Percent

68

72

69

68

67

71

69

67

66

60

57

65

62

72

67

°C

13

13

13

16

12

13

12

11

11

13

13

13

16

14

15

Percent

69

71

70

69

73

71

65

70

65

62

61

64

60

69

68

9

11

12

14

10

12

10

9

9

12

13

13

14

13

14

Percent

76 S

72 P^

73 S

a,

70 GO

73

73

71

72

69

65

62

68

65

69

69

o

>

o

2

o

a
Louisiana:

Lake Charles 11 81 21 78 28 80 21 78 20 78

New Orleans 13 77 20 73 28 76 21 72 21 75

Shreveport

9 75 18 69 28 72 19 70 19 71

Maine:

Caribou -12 73

2 71 18 75

6 724 74

Portland -6 72

6 70 20 76 10 788 74

Maryland,

^2

Baltimore

1 65 12 62 25 70 14 71 13 67

5

Massachusetts:

o

Boston -1 69

9 63 23 69 13 68 10 67

Worcester -4 68

7 60 21 68 11 70

8 68

Michigan:

>

Alpena -7 76

4 71 19 728 77

6 75

a

Detroit -3 76

9 65 23 65 12 71

9 70

Grand Rapids -4 82

8 67 21m 14 74

9 73

>o

Lansing -6 79

7 66 22 70 11 778 74

O

Marquette -7 74

4 69 19 718 716 74

Sault Sainte

O

Marie -9 77

3 72 18 778 814 77

Minnesota:

Duluth -13 75

3 69 18 757 76

4 75

Ü

International

Falls -16 72

3 65 19 726 77

3 72

Minneapolis-

>Q

St. Paul -11 73

7 63 23 669 67

7 69

M

Mississippi:

Jackson9 76 18 74 28 78 19 77 19 76

Meridian8 76 18 70 27 76 19 76 18 74

See footnotes at end of table.

^.1.^

CX)

-q
TABLE 28.—Climatological data for 188 weather stations in the United States, its territories, Puerto Rico, Canada,

and Mexico^—Continued

00

00

Average temperature and relative humidity (RH)2 forLocation of

weather station

January April July October

Temp. RH Temp. RH Temp. RH Temp RH

Annual

Temp. RH

>

O

2

o

a

c:

w

>

o

United States—Con.

Missouri:

Columbia -1

Kansas City „ _ -1

St. Louis 3

Springfield 1

Montana:

Billings -6

Havre -10

Helena -7

Kalispell -6

Nebraska:

Lincoln -4

North Platte ^_ -4

Scottsbluff -3

Valentine -6

Nevada:

Ely -4

Las Vegas 6

Reno -1

Winnemucca __ -2

Percent

71

68

72

76

62

77

67

78

74

72

67

73

66

47

69

74

Percent

13 61

13 62

13 64

13 66

7 56

6 59

7 56

6 64

11 66

9 63

8 58

8 63

6 47

18 23

9 49

8 49

Percent

26 67

26 63

26 63

24 70

23 46

21 51

19 48

18 53

27 65

24 64

23 60

23 62

19 33

32 22

20 38

22 29

°c Percent

14 71

14 62

15 65

14 69

10 53

8 60

7 61

7 72

14 63

11 64

10 59

10 58

8 45

19 25

9 53

9 41

13

13

13

13

6

7

6

11

9

9

8

7

19

10

9

Percent

69 o

o

66 t^

67 E>

71 c!

Ç«

56

64 :?

59 O

67 ^

>

o

69 2

o

67 c:

t-*

61 H

a

66 ?d

M

48

28

53

41
New Hampshire,

Concord -6 72

6 65 21 72

9 75 10 71

New Jersey,

Atlantic City

1 699 67 22 77 14 77 12 73

New Mexico:

Albuquerque

2 57 13 36 26 43 14 45 13 45

Roswell4 54 14 38 26 51 16 54 15 44

New York:

2

Albany -4 71

8 64 22 70 11 74

9 70

Binghamton -4 77

7 69 21 75 10 76

8 75

o

Buffalo -4 77

7 80 21 69 11 73

8 73

r

Canton -9 78

6 69 19 70

8 758 74

New York

1 67 11 64 25 68 15 68 12 67

>

Syracuse -4 75

7 67 21 69 11 73

9 74

a

North Carolina: id

Asheville

2 77 13 70 23 84 13 83 13 78

>

Charlotte

6 67 16 62 26 75 17 72 16 69

H

Raleigh

6 72 15 64 26 76 16 76 16 72

o

North Dakota:

Bismarck -12 72

7 64 22 64

8 66

5 68

^

Devils Lake -16 75

4 67 19 69

6 70

3 71

Fargo -14 74

6 69 22 68

8 70

4 71

a

Williston -12 71

6 60 22 58

8 64

4 65

^

Ohio:

o

Cincinnati2 77 13 67 26 70 16 71 13 71

>

Cleveland -3 78

8 67 22 67 12 69 10 71

W

Columbus -1 78 11 67 24 68 12 70 11 71

Toledo -3 73

9 68 23 72 12 72 10 72

Oklahoma:

Oklahoma City

3 70 15 62 27 64 17 66 16 66

Tulsa

See footnotes at end

3

of table.

67 16 62 28 65 17 67 16 66

00

CD
1 ABLE Zö.—enmato^Logical üiata jor 100 weamer sicliions Vn lite uniiea. oiaies, I LS LernLOI'tf^s, i-u^nlu nicu, Lyiirtuvia^ CO

and Mexico^--Continued 0

Average temperature and relative humidity (RH)2 for-- >

0

Location of

weather station January April July October Annual 2

Temp. RH Temp. RH Temp. RH Temp. RH Temp. RH H

°C Percent °C Percent °C 1Percent °C Percent °C Percent

United States—Con. >

Oregon: 0

Baker -3 78 7 61 19 54 8 65 7 67 00

Burns -3 77 7 54 21 37 8 56 8 58 p=^

Eugene 4 88 10 75 19 63 12 83 11 77 ß

Portland 3 83 11 71 19 67 12 81 11 75 a

Roseburg 5 87 11 68 19 60 7 79 12 74

Ö

Pennsylvania:

Harrisburg -1 68 11 63 22 67 12 70 12 67 H

Philadelphia - 0 70 11 65 24 70 13 72 13 69 0

Pittsburgh -2 73 9 65 22 68 12 68 12 68 >

Rhode Island, 0

W

Providence -2 QS 8 m 23 74 12 74 11 71 0

South Carolina: c!

Charleston 10 76 18 72 27 82 19 71 19 70

Columbia 9 71 17 64 28 73 18 71 18 70

South Dakota:

Huron -12 75 8 65 22 65 9 66 7 70

Rapid City 6 67 7 56 23 54 10 53 8 60

Sioux Falls 9 73 8 66 23 67 11 68 8 70

Tennessee:
Knoxville

4

Memphis6

Nashville4

Texas:

Abilene7

Amarillo3

Brownsville_ 16

Del Rio 11

El Paso6

Fort Worth_8

Houston 12

Midland7

San Antonio ^^ 11

Utah:

Milford -3

Salt Lake City -3

Vermont,

Burlington-8

Virginia:

Norfolk5

Richmond3

Roanoke3

Washington:

Seattle3

Spokane4

WallaWalla___1

Yakima -2

West Virginia:

Charleston3

Elkins -1

Huntington2

Parkersburg _„1

See footnotes at end of table.

74 14 62 25 72 15 71 15 75

74 17 66 28 71 18 69 17 70

76 16 64 27 69 17 69 16 70

62 18 56 28 54 18 61 18 59

62 14 53 27 56 16 60 14 58

79 23 77 29 76 24 75 23 77

66 21 56 29 57 21 65 21 61

44 17 27 28 43 18 45 18 39

5

68 18 63 29 59 20 62 19 63

o

83 21 81 28 77 22 75 20 79

r

52 18 44 28 47 18 58 17 53

69 20 66 29 64 22 66 21 67

>Ö

639 31 24 22 10 32

9 38

76 10 53 24 38 12 54 11 56

>o

766 65 22 70

9 74

7 73

O

¡72

72 14 68 26 77 17 75 16 70

O

73 14 64 25 75 15 77 14 72

C/3

69 14 59 24 71 14 68 13 66

Ö

in

809 69 18 66 11 81 11 74

O

818 58 21 44

9 68

9 64

>

79 12 54 24 39 12 61 12 60

w

80 11 51 22 47 11 67 11 62

69 13 60 24 77 14 73 13 70

77

9 69 21 82 12 78 10 77

71 13 61 24 77 14 72 13 71 hi

74 12 62 24 72 13 72 12 71

^
TABLE 28.—Climatologicaí' data for 183 weather stations in the United States, its territories, Puerto Rico, Canada, 1—4

and Mexico^—Continued

Average temperature and relatif^e humidity (RH)2 for-- >

Q

Location of ?d

weather station January April July October Annual

Temp. RH Temp. RH Temp. RH Temp. RH Temp. RH

r

"C Percent °C Percent °C Percent °C Percent °C Percent

?0

United States—Con. >

Wisconsin: O

CO

Green Bay 17 73 6 67 22 m 9 72 7 71

LaCrosse 16 72 8 67 23 74 11 74 8 73 i^

Madison 17 76 8 62 22 67 10 71 8 72 i

Milwaukee -7 74 6 71 21 70 11 72 8 72 c;

Wyoming: Ç/2

Casper -5 63 6 59 22 46 8 56 7 57

Cheyenne -3 55 5 59 19 53 8 54 7 56 Í

Lander -7 62 6 53 21 41 7 53 7 53 O

Sheridan -7 67 6 60 19 52 7 57 7 61 "^

American Samoa, >

Q

Pago Pago 27 84 27 86 26 82 27 84 27 83 2

Guam 25 83 26 81 26 87 26 87 26 84 c:

Puerto Rico, San Juan 23 78 25 78 27 81 27 82 27 80

Canada:

Alberta: M

Edmonton -14 76 4 58 17 63 5 61 3 67

Lethbridge -8 71 6 55 19 50 7 53 6 59

British Columbia,

Penticton -3 81 9 57 20 49 9 69 9 65
Manitoba, Winnipeg -18 78 3 68 20 64 6 69 3 70

Nova Scotia,

Halifax -5 83 4 75 19 80 9 82 7 79

Ontario:

London -5 84 6 73 21 69 10 78 8 77

Ottawa -11 75 6 60 21 66 8 71 6 69

Quebec:

Montreal -9 75 6 63 21 67 9 70 7

Quebec -12 76 3 64 19 70 7 74 4

Saskatchewan:

Regina -17 81 3 63 19 59 5 65 2

Saskatoon -17 76 4 62 19 59 5 63 2

Mexico:

Chihuahua 11 50 19 36 26 52 18 51 18

Ensenada 13 79 15 81 20 82 18 82 17

Guaymas 19 52 24 48 32 63 31 67 15

Mexico City 11 53 18 45 18 67 16 65 16

Monterrey 14 58 23 59 27 62 22 69 22

Soto la Marina _^_ 18 78 25 75 28 76 24 79 24 77 o

Tampico 19 78 24 78 28 79 27 77 24 78 ^

Torreón 16 57 23 47 27 51 22 58 22 53 w

Ö

iData from (1) "Local Climatological Data, Annual Summary With Comparative Data," 1972, and (2) "Climatic Atlas of the United States," 1968, ^

both published by National Oceanic and Atmospheric Administration, U.S. Department of Commerce; (3) "Atlas of American Agriculture," U.S. g

Department of Commerce, 1928; (4) "U.S. Naval Weather Service World-Wide Airfield Summaries," v. VII (Central America), February 1968; and >

(5) Meteorological Branch, Canada Department of Transport. w

2Each average relative humidity, except one, represents the average of 4 readings taken at approximately 12 p.m., 6 a.m., 12 m., and 6 p.m. For

Milford, Utah, the average represents readings taken at 11 a.m. and 5 p.m., the only data available. Each fraction resulting from averaging

temperatures and relative humidities is rounded to the nearest whole number; 0.5 is raised to the next number.

CO

70 ^

w

71 ^

n

69 r

67 C/2

>

"Z

46 o

80 ^

ÍO

78 >

58 H

O

68 W
194 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Using the correct seed moisture content for sealed storage is very

critical as seed sealed with too high a moisture content may lose

viability more rapidly than air-dry seed in open storage at the same

temperature. For very long-term storage, seed should be dried to

5-percent or lower moisture content, sealed in moisture-barrier containers, and held at -17.8° C, whereas storage at 4° and 50-percent

relative humidity in open containers is satisfactory for many kinds of

seed for 10 years or longer.

There are, of course, exceptions, as some kinds of seeds cannot

endure freezing and others cannot tolerate dehydration without losing

viability. The cost of storing a given quantity of seed increases rapidly

as the storage conditions become more exacting. Thus, the storage

facility should be related to storage time, commensurate with the needs

for maintaining satisfactory levels of seed viability and vigor. All

storage structures must be designed to protect the seeds from insect

and rodent infestations.

It should be emphasized that the intended storage period is only one

of several items to be considered when deciding on storage conditions

for a particular lot of seed. The more significant of these are seed

factors, storage environment, effect of pests, and storage structures.

Care of Seeds in Transit

Storage Principles Applicable to In-Transit Seeds

As pointed out by Harrington (1972) and others, seeds are in storage

from the date of their physiological maturity until they are planted.

Thus, seeds in transit are, in fact, in storage. As used here, the

expression "in transit" includes not only the time the seeds are being

moved from one location to another but also the time they are awaiting

shipment, whether in a warehouse, railroad car, truck, airplane, boat,

or on a dock awaiting further consignment. While in transit the seeds

are subject to the same storage principles as seeds in warehouses. The

principal differences between warehouse storage and in-transit storage

are the relatively fast changes in the seed environment that can result

from modern transportation and the failure of personnel to foresee or

predict all the hazardous conditions to which the shipment may be

subjected. The two principal envionmental factors that determine

whether a seed shipment will arrive safely at its destination are the

temperatures to which the seeds are exposed and the seed moisture

content, which is controlled by the relative humidity of the air or

protective packaging.

Historical Background

Moodie (1925) reported on the effect of temperature on seeds shipped

from Australia to England and from England to Australia. Since the
PRINCIPLES AND PRACTICES OF SEED STORAGE 195

temperatures used aboard ship were not precise and moisture content

of the seeds was not controlled, his results are not completely convincing. From his experiments Moodie concluded that seeds stored under

cool conditions with little variation are likely to retain viability better

than when stored under warm conditions with extensive variations in

temperature, von Degen and Puttemans (1981) shipped predried and

nondried seeds of several species of field crops and vegetables between

Hungary and Brazil. Their results proved conclusively the beneficial

effect on germination of predrying the seeds before shipment and

maintaining low moisture content during transit.

Foy (1934), working at Palmerston North, New Zealand, and Kearns

and Toole (1939), working at Washington, D.C., proved conclusively

through cooperative studies that Chewings fescue seed could be shipped

between New Zealand and the United States and between New Zealand

and England without serious loss of viability by predrying the seed

before shipment and avoiding exposure to high temperatures and

humidities. Their carefully conducted studies, which included seeds

exchanged between the three countries and seed stored at Washington,

Palmerston North, and Cambridge, England, were carried out on only

one kind of seed, Chewings fescue. However, the basic principles

relating to seed moisture content as well as relative humidity and

temperature during shipment govern the maintenance of viability of

transoceanic shipment of various kinds of seeds. The results are so

convincing that very little research of this nature has been reported

since.

The deleterious effects of high temperature, high relative humidity,

or both are mitigated by the length of time the seed will be under a

particular set of conditions. For example, a shipment of seed from Cape

Town, South Africa, direct to New York by modern freighter may

arrive at its destination without any loss in germination. On the other

hand, a similar shipment by tramp freighter, which would spend up to 6

weeks stopping at Belem and Hanaus, Brazil, might arrive at New York

with significantly reduced germination. Both cargoes in this hypothetical example passed through tropical waters; however, the extra time

the seed was exposed to hot humid conditions in the Tropics could be

disastrous for the seed.

Some Hazards To Be Avoided

A person planning to ship seeds should anticipate the various hazards

to seeds during transit and while in storage immediately before and

after shipment. These hazards will vary depending on the method of

transportation—whether by truck, railroad car, ship, or airplane. Rapid

changes of temperature or relative humidity resulting from the movement of seeds between zones of different temperatures and humidities

can create hidden problems. Seeds chilled during air transportation are
196 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

likely to be covered with condensed water after landing of the plane at

warmer temperatures. Under some conditions this surface moisture can

be absorbed by the seeds rather rapidly. Proper storage immediately

after landing will obviate this problem.

Ching (1959) pointed out that under simulated shipping and storage

experiments Highland bentgrass seed absorbed water rapidly under

tropical conditions and lost its viability within a few weeks. It is

noteworthy that Ching found seed stored under arctic conditions tended

to absorb water gradually during prolonged storage and consequently

gradually lost viability. She recommended that shippers not send high

moisture seed, such as that stored at high humidities, during the winter

into areas where it would be exposed to high temperatures.

Harrington (1972) pointed out the peril of seeds becoming overheated

when shipped in boxcars placed on a railroad siding in a warm or hot

climate for several days. The boxcar acts as a heat trap whereby very

high temperatures may be reached. This hazard is greatest with high

moisture seeds.

Shipping seeds with borderline to high moisture contents is no doubt

the greatest of all hazards. Christensen (1969) stated that much grain is

shipped and stored at moisture contents slightly above safe levels at

anticipated temperatures. When the temperature rises purposely, accidently, or unexpectedly, respiration increases, storage molds appear,

and spoilage results. This is more likely to occur in grain shipped in bulk

than in seeds ordinarily shipped in bags or smaller containers.

Still another hazard is the possibility of shipping seeds as a part of a

mixed cargo. When considering this possibility, the shipper should be

sure that no chemicals that are deleterious to the seeds, such as certain

herbicides, are included in the cargo. Any substance that might increase

the concentration of oxygen should be excluded as oxygen hastens seed

deterioration. There is no objection to inclusion of the inert gases, such

as hydrogen, nitrogen, and carbon dioxide, which tend to retard deterioration.

Another hazard is the possibility of the seedsman or shipper failing to

carefully select the seed lots. Seeds of different crop species vary as to

their storability. Oily seeds deteriorate more rapidly than starchy

seeds. Storability differences may exist among cultivars of some crop

species and also among different crops of the same cultivars or species.

Such information when available should be used in choosing seed lots for

shipment. If seeds are to be shipped long distances under unfavorable

or questionable conditions, only fresh seeds of high viability and vigor

should be chosen.

General Recommendations

(1) Carefully select the seed lot for shipment. Consider the general

guidelines given previously.
PRINCIPLES AND PRACTICES OF SEED STORAGE 197

(2) Carefully consider such factors as the shipping quality of the

seed lot selected, method of shipment, distance to be shipped, time in

transit, and climatic zones through which the seed will pass.

(3) If the seed is not of safe moisture content for shipping, reduce

moisture to a safe level by an acceptable drying method.

(4) If feasible, ship the seed under controlled temperature and

relative humidity to assure viability. If not feasible, reduce the seed

moisture content to a safe level and ship in moisture-resistant or

moistureproof containers (Caldwell and Bunch, 1961). See the sections

on "Seed Storage Structures" and "Packaging and Packaging Materials."

THEORIES REGARDING SEED DETERIORATION

We have pointed out how growing, harvesting, processing, and

storage conditions affect seed longevity. We have also discussed ways to

slow down the rate of seed deterioration, but we have not discussed

what occurs inside a dry, sound, disease-free seed to cause it to weaken

and die. Several theories based on genetic and physiological principles

have been proposed.

Changes in Protein Structure

Ewart (1908) theorized that seed longevity depends not on available

food reserves but on how long the proteid molecules, into which

protoplasm disintegrates when drying, can recombine into active protoplasm with the absorption of water. According to this reasoning,

protein molecules should disintegrate excessively when seeds are dried

to very low moisture levels. Struve,io however, concluded that corn

dried to less than 4-percent moisture, sealed in nitrogen, and stored at a

low temperature would keep indefinitely. Nutile (1964b) found that

drying vegetable seeds to 0.4 percent caused some damage to carrot,

celery, eggplant, pepper, tomato, and Kentucky bluegrass seeds but not

complete loss of viability. Seeds of cabbage, cucumber, lettuce, onion,

and Highland bentgrass sealed with 0.4-percent moisture were not

injured.

Crocker (1938) suggested that protein coagulation caused loss of

viability. Later he (1948) reported that his protein coagulation theory

was too general because of the many kinds of protein in embryos and

because his studies did not show which protein coagulates with aging.

Depletion of Food Reserves

The theory that depletion of food reserves for the embryo causes

"See footnote 8, p. 61.
198 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

seeds to die did not persist long because it was soon evident that many

dead seeds still contained ample food reserves. Some Zea mays L.

seeds, more than 700 years old, found in the Mesa Verde cliff dwellings,

appeared sound visually, yet not a single viable seed was ever found

among them. Oxley (1948) suggested that exhaustion of an unnamed

organic compound results in loss of seed viability. Harrington (1960b)

reasoned that a seed may have an adequate food supply and still die

because of a breakdown in the food transport system. Seed moisture

content may be high enough for respiration but too low to transport

food from the reserve supply to the embryo (Harrington, 1967), Although food reserves are usually not entirely depleted when seeds die,

various changes may have occurred, such as increased acidity (Zeleny

and Coleman, 1938, 1939; Milner and Geddes, 1946) and decreased

lipids and proteins (Pomeranz, 1966; Ching and Schoolcraft, 1968;

Koostra and Harrington, 1969).

Development of Fat Acidity

The development of fat acidity in seeds has been shown to accompany

death. Germination declined 8 percent and fat acidity increased 14 units

when 8- to 9-percent moisture content soybeans were stored for 700

days. With increased seed moisture content, germination dropped rapidly and fat acidity increased sharply (Holman and Carter, 1952). A

drop in the germination of wheat seeds was accompanied by an increase

in fat acidity (Kelly et al., 1942). Increased fat acidity was also a major

cause of corn seed deterioration (Zeleny and Coleman, 1939). Fat

acidity of peanuts increased only after the stored seeds were dead

(Davis, 1961). Although fat acidity values have been established for

grain showing little or no deterioration (Baker et al., 1957)^ such values

may not constitute a reliable index of viability (James, 1967).

Enzymatic Activity

Attempts have been made to use enzymatic activity as a measure of

seed viability. However, only a few of the many enzymes in seeds have

been investigated. Early work with enzymes dealt principally with

catalase activity. Crocker and Harrington (1918) found catalase activity

in dead Johnsongrass and yet reported a relationship with viability.

They could not establish such a relationship with seeds of Amaranthus

retroflexus. Davis (1926) showed a relationship between catalase ratio

and viability of lettuce seeds, but the range of his study was not wide

enough to establish a linear relationship. Leggatt (1929-30) obtained a

correlation between catalase activity and germination of wheat seeds.

Because of the limited number of species studied and the inconsistent
PRINCIPLES AND PRACTICES OF SEED STORAGE 199

results, the relationship between catalase activity and seed viability

appears questionable.

Phenolase activity also does not appear to be an indicator of viability

(Davis, 1931), For wheat, Davis found a relationship with germination

but not age, and for oats a relationship with age but not germination.

Throneberry and Smith (1955) reported that malic dehydrogenase activity was more closely correlated with germination percentage than

was alcohol dehydrogenase and cytochrome dehydrogenase activity.

They believed inactivation of these enzymes was not a major cause of

viability loss. Linko and Sogn (1960), Bautista and Linko (1962), and

Grabe (1964) demonstrated a close relationship between glutamic acid

decarboxylase activity and viability. James (1968) found that the correlation coefficient between germination percentage and glutamic acid

decarboxylase activity for the average of all bean varieties studied

compared favorably with the coefficients reported by Grabe (1964); for

corn, the coefficients for individual varieties were variable. James

(1968) stated that the inconsistencies of the correlation coefficients

among the cultivars used definitely limit glutamic acid decarboxylase

activity as an indicator of viability of bean seeds. Because of the

conflicting reports on the relationship of enzymatic activity to seed

deterioration, much research remains to be done in this area.

Chromosomal Changes

In 1901 De Vries (m KostofF, 1935) observed that old Oenothera

lamarckiana seeds produced more abnormal plants than did fresh seed.

More recently chromosomal changes have been reported in old seeds of

a relatively large number of species: Crépis spp. (Navashin, 1933;

Navashin and Shkvarnikov, 1933; Navashin and Gerassimowa, 1936),

corn (Peto, 1933), onion (Nichols, 1941, 1942), sugar beet (Lynes,

1945), barley, pea, rye, and wheat (Gunthardt et al., 1953), Datura spp.

(Avery and Blakeslee, 1936; Blakeslee et al., 1942; Blakeslee, 1954),

and barley, broadbean, and pea (Abdalla and Roberts, 1969a).

Although numerous compounds are known to induce mutations, few

of them are normally found in seeds. Mutagenic compounds found in

plants include adenine, degradation products of adenine, uracil, thymine, adenosine desoxyribonucleic acid, and ribonucleic acid (D*Amato

and Hoffman-Ostenhof, 1956). The degrees of mutagenic action given

by these authors are (1) the lethal zone, where the accumulation of

mutagens becomes toxic and kills the seed, (2) the narcotic zone, which

affects the spindle mechanism, and (3) the subnarcotic zone, in which

the mutations occur. The mutagenic or chromosomal aberration theory

is supported further by the fact that (1) extracts from old seeds induce
200 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

mutations in fresh seeds, (2) the mutation rate increases with age, (3)

spontaneous mutations in dormant seeds become evident in the chromosome presplit phase and in adult plants, and (4) reactions of root and

shoot tips in old seeds closely parallel the reactions of the same kind of

seeds when treated with X-ray. Apparently mutagens do not develop

under good storage conditions, as all observations have been on seeds

affected by high temperature, relative humidity, or both.

Blakeslee's (1954) work with Datura demonstrated that age alone was

not responsible for the development of mutations. He found that

mutations developed in seeds at room temperature. The mutation rate

for seeds buried in the ground for 39 years was extremely low. James

(1967) suggested that seeds presently housed in the National Seed

Storage Laboratory at Fort Collins, Colo., may hold the ultimate

answer to the question of the relationship of mutations to seed age.

However, the answer will not be determined soon because the storage

conditions there are such that respiration in the stored seeds appears to

be near the minimum.

Membrane Damage

According to Villiers (1973), the immediate damage rendering aged

seeds incapable of germination is extranuclear. Free radical damage to

membranes and enzyme systems could affect essential metabolic processes when the seeds become imbibed for germination. Harrington

(1973)stated that seeds dried to 4- to 5-percent moisture content appear

to deteriorate sHghtly faster than seeds with 5- to 6-percent moisture,

probably from lipid autoxidation damage. Unsaturated lipids in seed

cells may break, producing two free radicals, which can react with other

lipids, destroying the structure of cell membranes. In imbibed cells

tocopherols made by enzymes combine with free radicals rendering

them harmless. Since enzymes are inactive at low seed moisture contents, the free radicals produced nonenzymically become destructive

when the tocopherols that were present when the seeds were dried are

depleted.

Respiration

The theories for seed deterioration, except possibly fat acidity, are

related to respiration. Respiration increases in proportion to the

amount of moisture in seeds, but it is very low at moisture contents

between 4 and 11 percent (Baily, 1940] Harrington, 1963). Respiration

rates up to about 50° C are also directly proportional to temperature.

With high temperatures and high moisture contents, seeds lose viability

very rapidly, usually in less than 3 months at 32° and 90-percent relative

humidity. Seeds stored at temperatures below 10° and at low relative

humidities will remain viable for a long time. According to James (1967),
PRINCIPLES AND PRACTICES OF SEED STORAGE 201

peanut seeds recognized as short lived were held at the Southern

Regional Plant Introduction Station, Experiment, Ga., for 8 years at

10° and 50-percent relative humidity without a significant decrease in

viability.

Summary

What really causes a seed to deteriorate? We examined the theory of

changes in protein structure and found that no specific changes have

been pinpointed. Depletion of food reserves is not a very sound theory

as almost all seeds contain an abundance of food long after the embryo is

dead. Although the development of fat acidity has been shown to

accompany the death of a seed, such development has not been firmly

estalished as the cause of death. No specific enzyme activity change has

been proved to cause the death of seeds. Chromosomal changes have

been noted in various kinds of seeds; however, no one has yet proved

conclusively whether such changes are really the cause of deterioration

or are just a result. Membrane damage, though not specifically established as the cause of deterioration, is definitely associated with it.

Although several theories have been proposed, none satisfactorily

explains how seeds deteriorate. Even though the process of deterioration is not clearly understood, the methods for preventing it are well

estabUshed. For more detailed information on theories of seed deterioration, see Streeter (1965X Roberts (1972), Abdul-Baki and Anderson (1972), and Heydecker (1973),

OLD AND ANCIENT SEEDS

Ewart (1908) wrote as follows about the longevity of seeds:

"Probably few sections of human knowledge contain a larger percentage of contradictory, incorrect and misleading observations than

prevail in the works dealing with this subject, and, although such fables

as the supposed germination of mummy wheat have long since been

exploded equally erroneous records are still current in botanical physiology. In addition, there are considerable differences of opinion as to the

causes which determine the longevity of seeds in the soil or air. The

works of de Candolle 1832, 1846, de Candolle and Picket 1895, Duvel

1905 and Becquerel 1934 are the most accurate and comprehensive

dealing with the question. The subject is still, however, in an incomplete and fragmentary condition."

The principal objectives here are twofold. First, we estabUsh that

very old seeds in some instances have retained vitality over a long

period, even more than a century. We differentiate (1) crop seeds

known to have survived for relatively long storage periods, (2) seeds of

native plants known to have survived longer than crop seeds, and (3)

circumstantial evidence of seed survival for a few to several centuries.
202 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

The second principal objective is to analyze the authenticity of so-called

mummified seeds or grains.

Maximum Known Survival of Crop Seeds

Unless crop seeds are kept under favorable storage conditions, they

lose viability within a few years. The information in the section on

"Examples of Storability of Different Plant Species" confirms this

broad-based general statement. On the other hand, there are several

authentic records of cereal crop seeds surviving up to 32 years. Aufhammer and Simon (1957) reported survival of barley and oat seeds for

123 years (table 29). Authentic records show that seeds of some of the

leguminous crops have survived up to 81 years (table 29).

All the results in table 29 are regarded as authentic. Some data have

been obtained from planned experiments and others from tests on seeds

stored in museums, cupboards, or laboratories under such conditions

that the history of the seed was known.

Maximum Known Survival of Primarily Weed and

Native Plant Seeds

Mature seeds of many weeds and native plants have dormant embryos, a condition that retards germination. In fact, seeds do not

germinate until they undergo physiological and biochemical changes

that permit afterripening. A dormant or quiescent embryo appears to

enhance longevity. Also, seeds with hard coats, which restrict imbibition of water and exchange of gases, are among those with the greater

lifespans. Many seeds of weeds and native plants are in this group,

which includes such plant families as the Convolvulaceae, Leguminosae,

Malvaceae, and Nymphaeaceae.

Plant species whose seeds have long lifespans are listed in table 30.

The data were obtained from seeds kept or stored dry with known

histories and from seeds buried in soil by planned experimentation.

Seeds Stored Dry

Perhaps the earliest authentic records of tests on the continued

vitality of air-dry seeds are those of Alphonse de Candolle (1846). He

(18S2) te^ieà seeds of different species harvested in 1831 and kept them

all air-dry until May 1846 (15 years), when he planted 20 seeds of each

species. There were 368 species representing 53 families. Five out of 10

species of Malvaceae, 9 out of 45 species of Leguminosae, and 1 out of 30

species of Labiatae showed some germination.

Ewart (1908) published the results of tests of over 1,000 species of

seeds, which he found locked in a cupboard in the botanical laboratory at

Melbourne, Australia. The seeds had been sent from Kew Gardens,
TABLE 29.—Examples of documented long lifespans of some com^m^on crop seeds when maintained under favorable

survival conditions

Crop Storage condition Place stored Storage period Germination Reference

Barley Ambient temperature

and relative humidity.

Eastern Washington;

dry climate.

Years

32

Percent

96 Haferkamp et al. (1953). ^

2

In glass vial embedded

in foundation stone of

building.

Nuremburg, Germany 123 12 Aufhammer and Simon

(1957).

o

Corn At low relative

humidity.

Fort Collins, Colo. 21 32 Robertson et al. (1943).

>

o

Ambient temperature

and relative humidity.

Eastern Washington;

dry climate.

32 11, 19, 23,

53, 70 (for

different

cultivars).

Haferkamp et al. (1953). >

a

o

w

o

Oats do do 32 84

22

Do.

Aufhammer and Simon

(1957).

In glass vial embedded

in foundation stone of

building.

Nuremberg, Germany 123 ö

i

Sorghum In laboratory, dry Fort Collins, Colo. 17 98 Robertson et al. (1943). >

Q

In envelopes in

laboratory.

Chillicothe, Tex 19 .5 Karper and Jones

(1936).

W

Wheat Ambient temperature

and relative humidity.

Eastern Washington;

dry climate.

32 85 Haferkamp et al. (1953).

In laboratory, dry Fort Collins, Colo. ____ 26 19.5 Fifield and Robertson gCO
TABLE 29.—Examples of documented long lifespans of some common crop seeds when maintained under favorable

survival conditions—Continued

Crop

Bluegrass,

Kentucky.

Alfalfa

Clover, red

Storage condition Place stored Storage period Germination Reference

Wheat—Con.

Ambient storage; dry Australia

climate.

Approx. 4.5- to 4.8- England

percent moisture

content.

In soil; buried seed Arlington, Va.

experiment.

Ambient temperature Eastern Washington;

and relative humidity. dry climate.

In loosely corked London, England

bottle in museum.

Same seed samples do

In soil; buried seed Arlington, Va.

experiment.

Pea (garden

and field):

Bluebell Ambient temperature Eastern Washington;

and relative humidity. dry climate.

Canada do do

Smilen do do

Solo do do

Percent

28 60 Brown and Myers (1960).

32

39

33

81

100

39

69 Whymper and Bradley

(1947).

1-2 Toole and Brown (1946).

49 Haferkamp et al. (1953).

2.6 Turner (1933).

1 Youngman (1952).

2, 16 Toole and Brown (1946).

31 46 Haferkamp et al.

(1953).

30 39 Do.

30 44 Do.

31 78 Do.

O

>

Q

2

o

d

r

H

a

w

>

aw

o

o

a

H

o

>

o

2

o

a

r

a
Sweetclover,

white.

Trefoil,

big.

Beet, sugar

In loosely corked

bottle in museum.

do__„_

London, England

^do

Same seed samples do

In metal containers Salt Lake City, Utah_

for 10 years, then

in cloth sacks; below

freezing.

TobaccoIn sealed containers,

desiccated, and

refrigerated.

In soil; buried seed

experiment.

CottonIn laboratory

Carrot do

Cucumber do

Muskmelon do

Onion do

Parsnip do

Pepper, red do

Watermelon do

Quincy, Fla.

Arlington, Va._

Knoxville, Tenn.

^Cheyenne, Wyo.

do_

do_

do_

do_

do_

do_

81

81

100

22

25

39

9.61

75

High

viability.

Turner (1968).

Do.

Youngman (1952).

Pack and Owen (1950).

Kincaid (1958).

Approx. 20 Toole and Brown (1946).

2SorM>a>o

Strawberry

_ At approx. -12°CBeltsville, Md.

256 Simpson (1946). C/2

31

7 James et al. (1964).

O

30 77 Do.

30 96 Do.

i

22 33 Do.

>o

28 30 Do.

K

28 69 Do.

30 92 Do.

23 89 Scott and Draper (1970). í^w
TABLE SO.—Records of seeds 75 years or older with some germination

Reference Source and condition

Ewart (1908) _

Becquerel

(1907, 1934).

Turner (1933)

SchjelderupEbbe (1936).

Seeds received from Kew Gardens,

London, and stored in a locked

cupboard in Melbourne, Australia.

Storage room in National Museum,

Paris; Cassia multijuga seed collected

in 1776, obtained from another source;

10 seeds used in each test except 2 for

C. multijuga.

From museums in England where

seeds were preserved in loosely corked

bottles.

Stored dry or in bottles or paper bags

in Norway.

Species Age when tested Germination

Years

Aleurites moluccana 79

Cytisus candicans 80

Goodia latifolia 105

Hovea linearis 105

Indigofera cytisoides 81

Melilotus alba 77

Melilotus gracilis 82

Astragalus massiliensis 86

Cassia bicapsularis 115

Cassia multijuga 158

Dioclea pauciflora 93

Leucaena leucocephala 99

Mimosa glomerata 81

Anthyllis vulneraria 90

Cytisus scoparius 81

Lotus uliginosus 81

Medicago orbicularis 78

Melilotus alba 81

Trifolium pratense 81

Trifolium striatum 90

Astragalus utriger 82

Kennedya apétala 77

Percent

74

62

8

17

5

18

22

10

40

100

20

30

50

4

.6

9.6

22

.6

2.6

14.1

6

13

to

O

>

o

2

o

c:

H

Cî

5Ö

M

Ä

>

a

DO

o

o

c!

o

>

Q

2

c:

5Ö
Anonymous (1942h) Stored in British Museum, London Albizia juííbríssiv

From Hans Sloane collection in British Nelumho nucífera

Museum.

Darlington and

Steinbauer (1960).

Kivilaan and

Bandurski (1973).

Beal's buried seed experiment at East Oenothera bie/nnü

Lansing, Mich. Riime.r crispufi

VerbascuM blattaria

do Verbascum blattaiia

147

150

237

80

80

80

90

Some seeds

germinated.

2 seeds

tested; both

germinated.

1 seed

tested; it

germinated.

10

2

70

20

2

2

o

r

w

>

o

O

M

O

w

W

Ö

C/2

H

O

>

O

O
208 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

England, in 1856 for the University Gardens, but they had been put

away in a dark, dry closet, where they had remained unopened for 50

years or longer. He soaked the seeds and placed them on moist filter

paper in glass dishes in germinators. Seeds that did not swell after 1 or

2 days in water were either filed or treated with concentrated sulfuric

acid. After washing, the seeds swelled readily. Out of 1,400 kinds

tested, Ewart (1908) found 58 that retained their vitality after 50 years

or more in storage. He also tested seeds from another source that

varied in age up to 105 years. Of these seeds, Goodia latifolia and

Hovea linearis germinated 8 and 17 percent, respectively. Of the 58

kinds surviving 50 years or more, 36 were in the Leguminosae, 4 in the

Malvaceae, 2 in the Euphorbiaceae, and the remainder in miscellaneous

plant families. Dry seeds of many leguminous species are frequently

hard. The results of some of Ewart's tests are in table 30.

Becquerel (1934) had access to a batch of old seeds in a storage room

in the National Museum of Paris. These seeds were collected from 1819

to 1853. He conducted germination tests on them in 1906 and again in

1934. Since they were all hard-coated seeds, they required special

treatment. They were sterilized, the coats were broken, and they were

put in tubes under sterile conditions at 28° C to germinate. The seed

stock was considered so precious that only 10 seeds of each kind were

used for the test. For the 1934 test he obtained from another source

about 20 seeds of Cassia multijuga, which were collected in 1776. Only

two of these seeds were tested. Table 30 shows the results obtained

with six species that germinated after 75 or more years. All these seeds

were Leguminosae. The seeds of C. multijuga germinated after 158

years of storage. Becquerel believed the long lifespan of all these seeds

was made possible by impermeability of the coats, which prevented any

exchange of gases or water between the interior of the seed and the

outside atmosphere, and by the high degree of desiccation (2- to

5-percent moisture) and absence of oxygen in which the embryos

existed within the hard coats.

Turner (1933) tested the viability of old seeds from different sources

kept in loosely corked bottles in a museum. Of nine species listed in his

publication, seven retained viability in excess of 75 years (table 30). All

were Leguminosae.

Schjelderup-Ebbe (1936) tested the viability of 1,254 batches (nearly

as many species) of seeds stored in bottles or paper bags for 34 to 112

years. Seeds of 3 species survived for 50 to 59 years, 10 for 60 to 69

years, 3 for 70 to 74 years, and 2 for over 75 years (table 30). Of 54

entries in the author's table, 19 species germinated after 50 or more

years of storage. One species belonged to the Cannaceae, 13 to the

Leguminosae, 4 to the Malvaceae, and 1 to the Convolvulaceae. Seeds of

some species in all these plant families produce hard seeds.
PRINCIPLES AND PRACTICES OF SEED STORAGE 209

Buried Seed Experiments

The first planned experiment in America to test the longevity of seeds

buried in soil was begun in Michigan. In the fall of 1879, Beal (1885) of

the Michigan Agricultural College began an experiment to determine

the longevity of seeds of 23 kinds of weeds growing near East Lansing,

Mich. Fifty freshly harvested seeds of each of the 23 kinds (2 woody and

21 herbaceous) were mixed with sand and placed in pint bottles. The 20

bottles were buried. They were inclined at a 45° angle 18 inches below

the soil surface on a sandy knoll of the college campus.

The plan was to dig up one bottle every 5 years and test the seeds for

germination. This schedule was followed until 1920, when it was decided

to remove bottles at 10-year intervals to extend the experiment. Seeds

of Brassica nigra and Polygonum hydropipershowed some germination

for the last time in the 50th year (Darlington, 1931). Seeds of Oenothera

biennis, Rumex crispus, and Verbascum blattaria germinated in each

succeeding test until the 80th year (Darlington and Steinbauer, 1960),

As indicated in table 30 for Real's experiment, V, blattaria was the only

species that germinated in the 90th year (Kivilaan and Bandurski,

1973).

Duvel (1905) set up a more elaborate buried seed experiment in 1902

at Arlington, Va. It was designed to test the longevity of 107 species of

crop and weed seeds. The seeds were mixed with sterilized soil, placed

in porous flowerpots, covered with inverted flowerpot saucers, and

buried at depths of 8, 22, and 42 inches. After 20 years' burial some

seeds of 51 of the 107 species were still alive. They were primarily weed

seeds and hard-seeded legume species. Of 31 cultivated species in the

experiment, 22 were dead after 20 years in the soil and most of them

after 1 year. The following cultivated species showed some germination

after 20 years: Alsike clover, beet, bushclover, celery, Kentucky bluegrass, red clover, timothy, tobacco, and white clover. Forty-four species grew after 30 years and 36 species after 39 years. The experiment

was discontinued in 1941 (after 39 years) just before the Arlington

Experimental Farm of the U.S. Department of Agriculture was occupied by the Defense Department.

A seed longevity experiment was started by sealing 20 lots of 120

kinds of seeds in 2,400 glass tubes (Went, 1948). The seeds were dried

before they were stored in vacuum tubes. One lot of each kind of seed

was to be removed at 10-year intervals at first and later at 20-year

intervals until A.D. 2307. The object of this experiment was to obtain

data on (1) how long seeds can be stored without losing their power to

germinate, (2) how they are affected by long storage, and (3) what

evolutionary changes occur from year to year in plants of the same

species.
210 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Circumstantial Evidence of Long Lifespans of Seeds

A large number of presumed long lifespans of seeds can be cited. The

age of the seeds has been estimated by such comparisons as with objects

of known age, surroundings, geological events, and carbon-14 dating. In

some cases, the seeds have been tested by reliable procedures, but in

other instances, germination in nature has been observed and accepted

as fact. Observations of the appearance of seedhngs cited as evidence of

seed longevity or persistence of life in seeds include the following

phenomena: Removal or burning of a building, disturbance of grassland

or forest soils, disturbance of old or ancient mounds, disturbance of the

earth's surface by bombing, drainage of old lake or pond beds, and

erosion and deposits left by glaciers. Superficially, events arising from

these phenomena appear as striking examples of seeds of great longevity. However, such observations are based largely on speculation without considering all the facts.

Turner (1933) pointed out the weakness of conclusions based on such

observations in the following words: "When the longevity of buried

seeds is estimated entirely from the circumstances in which they are

found, there is the possibility of error, and the only satisfactory

methods of ascertaining the length of time that buried seeds will remain

viable are by experiments such as those begun by Beal and Duvel in the

United States." Turner (1933) described 20 examples of claimed longevity of buried seeds about which the age of the seed can be questioned. We describe five examples, some of which were also described

by Turner (1933),

Seeds in Soil Disturbed by Digging Graves

In his "Flora of the Summe Battlefield," Hill (1917) gave the following

account: "In July poppies (Papaver rhoeas L.) predominated, and the

sheet of colour as far as the eye could see was superb; a blaze of scarlet

unbroken by tree or hedgerow. Here and there long stretches of

chamomile (Matricaria chamomilla L.) broke into the prevailing red

and monopoHzed some acres; and large patches of yellow charlock were

also conspicuous, but in the general effect no other plants were noticeable, though a closer inspection revealed the presence of most of the

common weeds of cultivation. . . . Charlock (Sinapis arvensis L.) not

only occurred in broad patches but was also fairly uniformly distributed, though masked by the taller poppies. Numerous small patches

were, however, conspicuous and these usually marked the more recently dug graves of men buried where they had fallen. ... No doubt

in the ordinary operations of ploughing and tilling of the ground in years

before the war much seed was buried which has been brought to the

surface by the shelling of the ground and subsequent weathering. In

this connection the presence of charlock on the more recently dug
PRINCIPLES AND PRACTICES OF SEED STORAGE 211

graves, where the chalk now forms the actual surface, is of interest,

since it adds further proof of the longevity of this seed when well buried

in the soil."

Actually there is no proof that the charlock seeds (Brassica kaber

(DC.) L. C. Wheeler) {=Sinapis arvensis) had been buried either deep

or for a long time. The seeds may have been lying in the soil but close to

the surface, where conditions were not conducive to germination until

they were brought to the surface, where light and oxygen were available and where any accumulated carbon dioxide within the seeds could

escape.

Seeds in Soil Under Forests of Known Age

Peter (1893) reported studies made of the seed content of soils of a

forest that had been planted on meadows and pastures for known

periods and kept free from open land plants by shading. In general, as

the age of the forests increased, seeds of field plants became more

scarce. He found seeds of Hypericum humifusum, Juncus bufonius,

and Stellaria media in deep soil layers of forests 100 years old. In soils

of forests 20 to 46 years old he found seeds of a large number of open

land plants belonging to such genera as Anagallis, Chenopodium,

Juncus, Plantago, Polygonum, Sinapis, Stachys, Stellaria, and Thlaspi. Peter (1893) concluded that seeds of some meadow and swamp

plants that may lie in the soil more than 50 years are still capable of

germination.

His conclusions appear to be correct, and in lieu of a planned experiment they provide some worthwhile data; however, his data would

be more valuable if there were no question about the age of the seeds.

Seeds Frozen in Arctic Tundra

Porsild et al. (1967) reported that seeds of arctic lupine, at least

10,000 years old, found in lemming burrows deeply buried in permanently frozen silt of the Pleistocene age, germinated and grew into

normal, healthy plants. A mining engineer found the seeds in the

permanently frozen burrows associated with the remains of a nest, fecal

matter, skulls, and skeletons of a rodent, later identified as the collared

lemming. According to Porsild et al. (1967)^ the mining engineer kept

the skeletons in a dry place for 12 years, when the authors learned of

the specimens and historical background.

Through carbon-14 dating, comparison with other archeological

artifacts, and natural and geological history of the central Yukon area

where the seeds were found, they concluded that the seeds had been

placed in the burrows by the lemmings and were at least 10,000 years

old. About two dozen seeds easily identified as those of the arctic lupine

were found, and about half were remarkably well preserved. Some of
212 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

the best preserved seeds yielded six seedlings when tested for

germination and eventually yielded normal, mature plants, indistinguishable from those grown from fresh seeds. The collared lemming no

longer occurs in the central Yukon, but the arctic lupine is a common

species of tundra and subalpine forests of northern and central Alaska,

the Yukon Territory, and the northern Mackenzie District.

A critical review of this account reveals the weaknesses of evidence

supporting the claimed age of these seeds.

Canna Seeds in Burial Mound

Researchers in Argentina (Sivori et al., 1968) reported that three

seeds of a Canna species (exact species not determined) were obtained

from a tomb being excavated in Santa Rose de Tastil. The seeds were

inside walnut shells strung in a necklace to form rattles. As determined

by carbon-14 dating tests of cameloid bones from overlying strata of the

site, the seeds were about 530 years old. This information, supplemented by the fact that no Incaic elements were found in the burial

mound, suggests that the city was developed before 1420. Two of the

three seeds were tested for germination and subsequent growth. The

first seed germinated, but the radicle ceased to grow, even after adding

gibberellic acid and indole-3-acetic acid. Another seed was tested under

aseptic conditions on a medium containing minerals and growth regulators. It germinated and continued growth after transplantation into

quartz gravel with a nutrient solution in a greenhouse. The roots of the

plant exhibited irregular geotropic response, even after being transplanted in the greenhouse.

The principal weakness in this account of seed longevity is the

accuracy of the carbon-14 dating test and the time relationship of the

cameloid bones tested and the Canna seeds. (See carbon-14 dating

results by Libby (1951) smd Godwin and WilHs (1964) ior Nelumbo seeds

in the next section.)

Indian Lotus Seeds Buried in Former Lakebed

Probably the longest claimed longevity for any seed is that recorded

by Ohga (1923), He obtained approximately 100-percent germination

with seeds of Indian lotus, which he found in a peat bed buried 2 feet

deep with loess in the Pulantien River valley in southern Manchuria.

The bed was 41 feet above the present water level of the river. Judging

from the age of the weeping willows on the bed of this former lake and

from the lowering rate of the water level, Ohga (1923) concluded that

the seeds were probably at least 120 years old. Possibly they were 400

years old or even older judging by the rate of erosion. Although the

supply of seeds was limited, Ohga deposited some with the Tohuku

Imperial University in Japan, and in 1926 he gave 30 seeds to the

British Museum in London.
PRINCIPLES AND PRACTICES OF SEED STORAGE 213

Later Chaney (1951) obtained a few seeds from the Ohga collection

and made them available for study in the United States. Records are

available (Wester, 1973) showing that in tests made in Japan, England, and the United States on 156 seeds all germinated except 2. A dry

seed from the Sloane collection in the British Museum germinated after

237 years (table 30). Two seeds from the Ohga collection, tested for

germination in 1951 by Wester, are illustrated in figure 33.

The age of these Nelumbo seeds is perhaps the most controversial

subject in the field of seed longevity with a legitimate basis. The

discoverer of the original seedbed and seeds estimated the seeds to be

at least 120 years old and perhaps as old as 400 years (Ohga, 1923),

Later Chaney (1951)y 2L paleontologist, reevaluated the information on

the age of the seedbed and concluded that the seeds might be as much as

50,000 years old.

Arnold and Libby (1951) reported that they had determined by

carbon-14 dating that the seeds were 1,040 ±210 years of age. This age

was generally accepted until Godwin and Willis (1964) conducted carbon-14 dating tests and concluded the correct age to be 100 ± 60 years.

Wester (1973) reviewed the entire history and arrived at an age of

1,024 years, which agrees with Libby's findings of 1,040 ± 210 years.

There is little question that these seeds are old, but their age has not

been established to the satisfaction of biologists. Like seeds of many

leguminous species, the seeds of the Indian lotus plant have very hard

seedcoats, which resist decay and are impervious to water and gases.

Also, the peat in which the seeds were found might have retarded the

deterioration of the seedcoat.

Life in Mummified Seeds

The following article on "Wheat 2,000 Years Old" appeared in the

Sunday magazine section of a Washington, D.C., daily newspaper,

dated January 13, 1957:

"This story begins more than 2,000 years ago, when relatives of a

deceased Egyptian nobleman buried some wheat kernels in his tomb,

presumably so the departed could grow his own in the land of the dead.

"The nobleman was hardly in any shape for showing as a museum

mummy when unearthed recently by a Swiss archeologist, but the wheat

seeds appeared to be in good condition. The archeologist, no farmer

himself, wondered if they might still sprout under proper cultivation.

"Reviewing his proposal to test the grain under various conditions of

soil and clime, the Egyptian government turned thumbs down on

experimenting anywhere but in Egypt. But placing agronomy ahead of

sovereignty, the scientist whisked a handful of the kernels out of the

country.
214 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

•WH

^.-.j'

«1 Tl

á ^^.^á

PN—5414. PN-5415

FIGURE 33.—Seeds of Nelumbo nucífera alleged to be over 1,000 years old: Above, before

absorbing water; below, after germination.
PRINCIPLES AND PRACTICES OF SEED STORAGE 215

"Distributing it to several experimental farmers in Europe, he seems

to have scored a major success with the wheat only in Sweden. There,

Oscar Johnson of Smaland planted three kernels, carefully nursed them

through the season and ended up with several thousand seeds for the

next planting. By present count, he has enough to sow 2}h acres. Should

he have a successful harvest next year, he expects to reap enough grain

to plant a few hundred acres. From then on, the wheat that had laid

dormant for ages may be available for others.

"Called "Osiris," the reborn wheat strain has thus far proved to have

tremendous hardiness. What other beneficial qualities it may have, Mr.

Johnson and other agriculturists the world over are interested in

finding out."

Two photographs accompanied the article. The caption to one photograph showing four spikes of branched grain reads as follows: "Buried

for centuries in an Egyptian tomb, wheat kernels were unearthed and

sown by Oscar John Johnson of Sweden, who produced this initial

yield." The other photograph, showing a man who apparently is transplanting seedlings of grain in soil, has the following caption: "Farmer

Johnson had only three grains of the 2,000-year-old wheat, so he planted

them in a special bed where he could keep a watchful eye on their

progress. All three grains prospered in spite of their age. The matured

wheat exhibited extreme hardiness, and he reaped enough to plant

more than two acres now."

This article was sent to the head of the Swedish Seed Testing Station

at Solna, Sweden, requesting that he comment on the article. Following

is his reply, dated February 1957:

"This is the same old story that appears in the world press at least

once in 10 years. The Egyptians by now know very well that it is a lie. If

living wheat kernels are found in ancient tombs, they were put there

rather recently by mice or other animals. Cereals deposited there 2,000

years ago have now turned to pure coal and are as dead as they can be.

When staying in Egypt 10 years ago I had an opportunity to convince

myself personally about this. Since no business can be done with such

seeds in Egypt, the kernels are sent to other countries and are sold at

fancy prices.

"The special case of Mr. Johnson first circulated in the Swedish press

a few years ago and then has been taken up by newspapers and journals

in most other countries. About a year ago I had a letter from Canada

asking my opinion of it. It is a pity that journalists always copy

sensational stories but never disprovals of them! Mr. Johnson's wheat is

a variety grown today in Egypt."

Other similar stories of mummy seeds are discussed by Brooke

(1935\ Luthra (1936\ and White (19461

A form of wheat sold to tourists as "miracle wheat" or "mummy
216 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

wheat" is a common branched form of Triticum turgidum, which grows

in southern Europe and northern Africa. It is commonly cultivated as a

curiosity (Turner, 1933). Similarly, fasciated forms of a pea similar to

the "mummy pea" were illustrated in a European herbal as early as

1590. One form of the pea was described and named Pisum umbellatum

(rose or crown pea) in 1771 (White, 1946).

Turner (1933) of Kew Gardens, London, indicated that there was no

authenticated evidence that wheat taken from undisturbed Egyptian

tombs will germinate. An experiment was made at Kew Gardens with

grain from a model granary found in a tomb of the 19th dynasty.

Samples were tested under various conditions. The effect of colored

glass was tried to induce germination, but after 3 months the grain had

turned to dust.

We have confiiTned these results in tests made at Beltsville, Md.,

using mummified grain from the Anatolian excavations at the site of

Alishar. Information from the Oriental Institute, University of Chicago, indicates that the material dates back to at least 700 to 1200 B.C.

and possibly to about 3000 B.C.

PN-5416

FIGURE 34.—Seeds of 1973 barley and wheat crops compared with carbonized structures

("seeds") of the same species from the Alishar excavations, dating from approximately 700 to 3,000 B.C.: Top to bottom, barley from Alishar and 1973 crop; wheat

from Alishar and 1973 crop.
PRINCIPLES AND PRACTICES OF SEED STORAGE 217

The printed word does not seem to dispel the story of life in mummy

seeds as such stories appear in the popular press from time to time. For

this reason, we are showing some of the seeds from the Alishar

excavations along with seeds harvested in 1973 (fig. 34). The so-called

mummy seeds have retained the shape of barley and wheat, but the

structure is similar to that of charcoal. There is no possibility of these

structures producing seedlings. Turner (1933) said, "It is popularly

asserted that miracle wheat and mummy peas originate from Egyptian

tombs and that such seeds germinate when sown, but in every instance

the statements prove to be without foundation."

GLOSSARY

Absolute humidity.—Amount of water vapor actually in the air, expressed either in its expansive force or in its weight per given

volume, as grains per cubic foot.

Absorption.—Imbibing of water by living cells or tissues in a seed.

Accelerated aging test.—Intentionally subjecting seeds to adverse

storage conditions for a short period to estimate their possible lifespan under favorable storage conditions.

Achene.—Small, dry, one-seeded fruit with thin distinct wall, which

does not split open.

Actinomycetes.—Bacterialike micro-organisms with ribbonlike form.

Activated alumina.—Highly porous, granular form of aluminum oxide,

with high adsorptive capacity for moisture.

Adsorption.—Taking up a gas, vapor, or dissolved material on the

surface of a solid; finely divided materials, as active carbon and silica

gel, can adsorb relatively large quantities of other materials.

Aeration.—Movement of outside air through stored seeds to prevent

heating and to facilitate drying.

Aging test— Any test to determine the deterioration of seeds with their

increased age, usually a germination or vigor test.

Air-dry.—Sufficiently dry so that no further moisture is given off on

exposure to air; i.e., in moisture equilibrium with the surrounding air.

Air-oven method.—Drying seeds in a forced-air oven to determine their

moisture content.

Alpha amylase.—An enzyme occurring widely in seeds, leaves, and

other plant parts; it accelerates starch hydrolysis.

Ambient.—That which encompasses or surrounds on all sides a designated object, state of matter, system, etc.; as used here, ambient

refers to temperature or relative humidity of the atmosphere in the

natural state without modification by man.

Anabolic process.—Process by which matter is changed into tissues of

living plants or ^eeds.
218 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Axillary bud,—Bud developed in the angle between leaf and stem.

Backcrossing,—Crossing a hybrid with one of the original parents.

Bacteria,—Simple microscopic vegetable organisms usually singlecelled and without chlorophyll, multiplying by fission (splitting apart)

and spore formation.

^^Baldheads.''—Bean seedlings with the primary leaves missing and the

terminal bud present or absent.

Batch drying,—Drying seeds in relatively small quantities while stationary as opposed to drying in a continuous moving line.

Biochemical change,—Change in the chemistry of a plant, plant part, or

seed.

Bracts,—More or less modified leaves subtending a flower or belonging

to an inflorescence.

Bruchids,—Family of small vegetarian beetles; the larvae live mainly in

the seeds of leguminous plants.

Bunt spores,—Reproductive units of certain fungi that attack cereal

plants.

Caryopsis,—One-seeded fruit with pericarp and seedcoat fused into one

covering, as in corn and other grains and grasses.

Catabolic process,—Pertaining to or characterized by the release of

energy.

Chaff.—Glumes or husks of grains and grasses separated from the seed

by threshing, winnowing, etc.

Chalcids.—Minute wasplike insects belonging to the order Hymenoptera, a few species of which invade seeds.

Check samples,—Samples of original seed lots used as a basis for

establishing the effects of any special treatment on the response of

seeds of the same lots. For example, seeds held at room temperature

constitute the check sample for seeds of the same lot stored at a high

temperature and high relative humidity and at a low temperature and

low relative humidity.

Chromosome aberrations,—Deviations from normal chromosome

structure.

Chromosome 10.—Geneticists have assigned numbers to various chromosomes; 10 identifies a specific chromosome.

Closed system,—Completely enclosed, sealed system; device, container, or combination of devices designed to perform a specific

function within a sealed environment, as the refrigeration system for

a domestic refrigerator.

'Void Test. ''—Special germination test; for corn, seeds are placed in a

very moist sand/soil/peat moss mixture, then held at 10° C for 7 days

before being placed in the regular germination temperature.

Coleoptile,—Sheathlike leaf of grasses and other monocotyledons; it

protects the delicate growing point as it emerges from the soil.
PRINCIPLES AND PRACTICES OF SEED STORAGE 219

Coleorhiza.—Sheath surrounding the radicle in some plants, through

which the root bursts.

Combine thresher.—Machine that cuts, threshes, and cleans grain while

moving over the field.

Convection.—A type of air current.

Cotyledons.—Seed leaves of the embryo, usually thickened for storage

of reserve food; they may serve as true foliage leaves.

Cultivar.—Cultural or cultivated variety.

Culture medium.—Laboratory substance on which micro-organisms

and excised embryos may be grown.

Cuticle.—Very thin detachable skin covering a plant, especially the

leaves.

Cytological change.—Change in the intrinsic character or function of a

cell.

Decorticated seed.—Seed with its outer covering removed.

Dehumidification.—Process by which the water is removed from a

substance; moisture vapor is removed from air.

Dehumidifier.—Equipment used to remove humidity (moisture) from

air.

Desiccant.—Drying agent.

Desiccator.—Usually a glass jar fitted with an airtight cover and

containing at the bottom some desiccating agent, such as calcium

chloride.

Desorption.—Removal of a substance from an absorbed state.

Dielectric properties.—Properties that make a material a nonconductor

of electricity.

Dough stage.—Stage in development of cereal grains when the interior

of the kernel (seed) is of doughlike consistency.

Dry-bulb thermometer.—Ordinary thermometer with its mercury-containing bulb kept dry. (See psychrometer.)

Dry heat.—Heat applied by dry air as opposed to moist heat, which is

applied by moist air.

Dry weight.—Moisture-free weight.

Dynamic method.—Procedure for determining equilibrium moisture

content by bubbling air through absorption towers containing an acid

or saturated salt solution, which controls the humidity around seeds

or other material.

Economic plants.—Plants of practical utility; commercial plants.

Ecosystem.—System involving all ecological or environmental factors,

such as cUmate, soil, physiography, and associated organisms.

Electric hygrometer.—Electric instrument for measuring the degree of

moisture in the atmosphere.

Electric moisture meter.—Electrical instrument that measures the

moisture content of seeds and other materials.
220 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Embryo,—Rudimentary plant within the seed.

Embryo axis.—Hypocotyl-root axis bearing at one end the root

meristem and at the other the cotyledon or cotyledons and the shoot

meristem.

Embryo transplant technique.—Procedure by which the embryo of one

seed is transplanted to the endosperm of another seed.

Endogeocarpic flora.—Certain microscopic plants that live or are found

in the soil and can invade plants.

Endosperm.—Tissue of seeds, developing from fertilization of the polar

nuclei of the ovule by the second male nucleus; it nourishes the

embryo.

Enzyme.—Catalyst produced in living matter; a specialized protein

capable of aiding in bringing about chemical changes; promotes a

reaction without itself being changed or destroyed.

Ergot.—Hard resting body produced by the fungus Claviceps purpurea; also the name of a disease of rye and other grasses.

Field emergence.—Emergence of seedlings from seeds planted in the

field; usually refers to percentage of seeds planted in the field that

germinates and produces seedlings strong enough to emerge through

the soil.

Field fungi.—Molds that live outside on growing crops.

Food transport system (in embryo).—System by which food is moved

from storage tissues of the seed to growing tips of the root and shoot.

Forage.—Vegetable food of any kind for animals, especially that consumed by domestic animals as pasture or browse.

Freeze-drying.—Process for drying seeds and other materials; it uses a

freezing temperature combined with moving dry air, which sublimes

frozen water to water vapor.

Fruit(s).—Ripened (matured) ovary of a plant, together with any intimately attached parts that developed with it from the flower. Fruits

of buckwheat, cereals, grasses, sunflower, and many others are

commonly called seeds.

Fumigant.—Chemical applied as a gas to destroy molds, insects, rodents, etc.

Fungi.—Lower plant forms devoid of chlorophyll and comprising

molds, mildews, rusts, smuts, mushrooms, toadstools, puffballs, and

allied forms that reproduce by spores.

Fungicide.—Chemical used to kill fungi.

Gall(s).—Swollen plant part caused by presence or action of an insect or

nematode.

Gaseous water.—Water vapor.

Gas storage.—Storage in an atmosphere composed of a gas other than

air.
PRINCIPLES AND PRACTICES OF SEED STORAGE 221

Genera.—Plural of genus; groups of structurally or phylogenetically

related species; categories of classification ranking between family

and species.

Genetic stock.—Strain of seeds used in studies pertaining to the genesis

of a particular plant; its mode of production and development; strain

used for genetic studies.

Genotype.—Hereditary makeup of an individual plant, which, with the

environment, controls the individual's characteristics, such as type of

flower or shape of leaf.

Germinate.—Initiate growth or development, especially when referring to a spore or seed.

Germ plasm.—Living substance of the cell nucleus that determines the

hereditary properties of organisms and that transmits these properties from makeup of organisms. For example, geneticists and plant

breeders often refer to the seeds and plants used in their research

and breeding as their "collection of germ plasm."

Glumes.—Chafliike bracts; specifically, two empty chaffy bracts at the

base of spikelets in grasses.

Grain.—Seed or seedlike fruit of any cereal grass, such as millet, oats,

rice, and wheat.

Grain head.—Attachment for a combine designed specifically for harvesting grain.

Hair hygrometer.—Instrument in which expansion and contraction of a

hair is used to measure changes in the amount of moisture in the air.

Hard seed.—Seed with seedcoat impervious to water or oxygen required for germination, or to carbon dioxide that may accumulate

within the seed and retard or prevent germination; sometimes overcome by scratching or scarifying the seedcoat or removal by brief

immersion in concentrated sulfuric acid and thorough washing.

Hectare.—1 ha is 2.4710 acres.

Herbarium specimen.—Dried and pressed specimens of plants mounted

or otherwise prepared for permanent preservation and systematic

arrangement in a room, building, or institution (herbarium) where

such collections are kept.

Hermetically sealed.—Sealed so that no gas or moisture can enter or

escape.

Hermetic storage.—Storage in an airtight container.

Hilum.—Scar or point of attachment of the seed.

''Hot spots. ""—Areas in a mass of stored seeds or grain where temperature is as high as 66° C or higher.

Hybrid.—Offspring of the union of a male of one race, variety, species,

genus, etc., with a female of another; a crossbred plant.

Hydrophobie.—Lacking a strong affinity for water.
222 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Hygroscopic.—Readily absorbing and retaining moisture, as caustic

potash, or becoming coated with water, as glass.

Hygroscopic equilibrium measurement.—Measuring the amount of

water in or on a substance when there is no movement of water

between the substance and the surrounding air.

Hygroscopicity.—Denotes sensitivity to moisture.

Hygroscopic moisture absorption.—Absorption of moisture from the

surrounding air.

Hygrothermograph.—Instrument that records both humidity and temperature on the same chart.

Hysteresis effect.—Phenomenon when at a given relative humidity

seeds or grain may reach two different equilibrium moisture contents—one by increasing the relative humidity from a low level and

another by decreasing the relative humidity from a high level.

Illumination.—Supplying light.

Immature seed.—Seed not fully developed.

Inbred.—Successively self-fertilized; also, a plant or progeny resulting

from successive self-fertilization.

Inert.—Lifeless.

Interstitial airspaces.—Air spaces between the cells in a plant tissue or

inside a seed.

Layer drying.—Drying seeds in thin layers as opposed to a large mass

of seeds.

Leguminous plants or legumes.—Members of the pea or legume plant

family (Leguminosae).

Lemma.—Small greenish bract that is part of the floret in grasses.

Lifespan.—Length of time a particular lot or kind of seeds will survive

under favorable storage conditions.

Lipids.—Group of substances comprising the fats and other esters that

possess analogous properties.

Lipolytic degradation.—Decomposition of fat.

Longevity.—Long duration of life, length of life, or lifespan.

Luteus genes.—Genes that carry a yellow plant color factor; they are

lethal as they prevent normal chlorophyll development.

Macromolecular water layer.—Water layer surrounding a macromolecule.

Macromolecule.—Large molecule; grouping together of simple molecules capable of independent existence as in cellulose.

Malt agar.—Culture medium used for laboratory cultivation of certain

fungi.

Malvaceous plant.—Plant belonging to the mallow family, as cotton and

okra.

Manifold.—Chamber from which air is distributed to more than one

duct.
PRINCIPLES AND PRACTICES OF SEED STORAGE 223

Mature stage.—Completely developed; full grown.

Membrane,—Any thin, soft, pliable sheet or layer of animal or vegetable origin; a limiting protoplasmic surface.

Mercurial,—Chemical compound containing mercury.

Metabolism,—Chemical changes occurring in an organic body in living

and growing processes.

Metabolites,—Products of metabolism.

Microflora,—Microscopic plants as a whole that inhabit a given area,

such as a seed.

Micropyle,—Pore or opening through which the pollen tube enters the

embryo sac during fertilization and through which the radicle frequently emerges when the seed germinates.

Milk stage.—Stage in the development of the kernel of a grain when its

contents are a milklike liquid.

Moisture-barrier material,—^Any material through which moisture either cannot move or moves very slowly.

Moisture content equilibrium.—State when the moisture content in the

air and in the seed remains constant; no movement of moisture either

into or out of the seed.

Moisture equilibrium,—Relative humidity of the air is in equilibrium

with the moisture content of the seed.

Moisture gradient,—Difference in moisture concentration inside and

outside a seed and between the seed surface and the air surrounding

the seed.

Moisture translocation,—Movement of moisture from one part of a

seed to another.

Multiwall bag,—Bag with multiple walls, usually two or more, composed of paper, foil, plastic film, or cloth, alone or in various combinations.

Mutagenic changes,—Change in the genetics of a seed; change in form

or qualities of chromosomes.

Mycoflora,—Fungal component of a microñora.

Nematode.—Microscopic wormlike animal.

Nomograph,—Alinement chart; graph that enables one, by the aid of a

straight edge, to read the value of a dependent variable when the

value of the independent variable is given.

Nutlet,—Any small nutlike fruit or seed, as in the mint and vervain

plant families.

Oilseed,—Any seed from which oil is expressed; a seed containing a

large percentage of oil in its storage tissues.

'Vnce-over harvesting,''—RRrwesting the entire crop at one time, as

opposed to going over a field several times to complete the harvest.

Open storage.—Storage with free access to normal atmospheric conditions.
224 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Ordinary storage,—Storage as usually practiced with no attempt to

control either temperature or relative humidity of the storage area.

Osmophilic,—Preferring to grow with very little water.

Overwinter storage,—Storage through the winter from harvest in the

fall to planting time in the spring.

Ovules.—Bodies within the ovary of a flower that become seeds after

fertilization and development.

Oxidation.—Act or process of being oxidized.

Palea,—Upper bract that with the lemma encloses the flower in

grasses. (See glumes.)

Pallet box,—Box in which seeds are placed for handling during processing and that is moved by forklift. (See totebox.)

Parasitic fungi,—Molds that exist at the expense of other organisms.

Percent germination,—Percentage of seeds that produces normal

seedlings when tested in a laboratory according to established procedures.

Pericarp.—Seed covering derived from the ovary wall; it may be thin

and intimately attached to the seedcoat as in a kernel of corn, fleshy

as in berries, or hard and dry as in pods and capsules.

Photoperiod,—Length of the light period on a given day.

Photoperiodism,—Response to the timing of light and darkness.

Photosynthetic organs,—Organs containing chlorophyll and capable of

photosynthesis.

Physiological dormancy,—Dormancy caused by disorganization of

functions or of metabolism as brought about by extremes of temperature, oversupply of water, etc.

Placenta,—Any sporangia-bearing surface; in seed plants that part of

the carpel bearing ovules.

Planting stock.—Seeds selected and preserved especially for planting,

as opposed to seeds held for human or animal food.

Plumule,—Major young bud of the embryo within a seed or seedling

from which the aerial part of the plant will develop.

Premilk stage,—Stage in the development of a seed that precedes the

milk stage.

Primary root,—First root of a plant that develops from the radicle.

Propagation.—Perpetuating and increasing plants vegetatively.

Protoplasm,—Essential, complex, living substance of cells on which all

the vital functions of nutrition, secretion, growth, and reproduction

depend.

Provenance.—Origin, source, place where found.

Psychrometer.—Hygrometer or instrument for measuring the water

vapor in the atmosphere, consisting essentially of two similar thermometers, the bulb of one kept dry, the other wet. The wet bulb is

cooled as a result of evaporation and consequently shows a tempera-
PRINCIPLES AND PRACTICES OF SEED STORAGE 225

ture lower than that of the dry-bulb thermometer. Since evaporation

is less on a moist day, the difference between the thermometer

readings is greater when the air is dry. This difference constitutes a

measure of the dryness of the surrounding air.

Psychrometric chart,—Graphical representation of psychrometric data,

showing the relationship between dry-bulb temperature, dewpoint,

wet-bulb temperature, and relative humidity.

Radicle,—Rudimentary root or lower end of the hypocotyl of the

embryo; it forms the primary root of the young plant.

Relative humidity,—Ratio of the quantity of water vapor actually in

the air to the greatest amount possible at a given temperature.

Respiration,—Oxidation-reduction process occurring in all living cells

whereby chemical action occurs, producing compounds and releasing

energy that are partly used in various life processes.

Respiration quotient (RQ),—Ratio of the volume of carbon dioxide

(COg) given off in respiration to that of the oxygen (0^) consumed—

RQ = CO^/Og.

Root axis.—Principal line along which a root may grow; hypothetical

central line of a root.

Sample,—Part of a seed lot presented for inspection or shown as

evidence of the quality of the whole lot.

Saprophytic fungi,—Molds that live off nonliving material.

Scarified seed,—Seed that has had its coat scratched to permit ready

entry of water and exchange of gases.

Schematic flow,—Movement of seeds according to a previously designed scheme or pattern.

Sclerotia,—Hard, resting bodies produced by certain fungi.

Scutellum,—Specially differentiated cotyledon in grass seeds; shieldshaped organ through which the embryo absorbs food from the

endosperm.

Sealed storage,—Storage in a sealed container; usually refers to hermetic storage.

Secondary root,—Lateral branch of the primary root.

Seed(s),—Mature ovule consisting of an embryonic plant together with

stored food, all surrounded by a protective coat.

Seedcoat,—Outermost tissues or "skin" of a seed; sometimes this coat is

extremely hard and waterproof, preventing entrance of water to

initiate germination unless it is broken, scratched, or eroded.

Seedling,—Young plant grown from a seed.

Seed lot.—Specific quantity of seed usually assigned an identifying

number or symbol; examples are the seed from a single field or a day's

harvest.

Seed physiology,—Branch of biology dealing with the organic processes

and phenomena collectively of seeds and their parts.
226 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Seed stock,—Quantity of seed reserved for planting for the production

of a new seed crop.

Shoot axis,—Principal line along which a shoot may grow; hypothetical

central line of a shoot.

Sigmoid,—Curved in two directions, like the letter "S."

Silica gel—Regenerable adsorbent consisting of amorphous silica.

Smut ball—Reproductive body produced by smut fungi.

Species,—Group of closely related organisms; for example, Medicago

sativa is the botanical name for alfalfa. Medicago is the genus and

sativa is the species. Several species belong to the genus Medicago;

for example, M, lupulina (black medic) and M, orbicularis (buttonclover).

Spine(s),—Any stiff sharp process distinguished from a thorn by the

absence of vascular tissue. Spines are frequently found on leaf

margins as in thistles.

Stand of plants,—Relative number or distribution of plants growing

over a given area, especially soon after germination.

Static efficiency,—Efficiency of static pressure in moving air through a

layer of seeds.

Static method,—Method by which a large fan builds up air pressure

against a mass of seeds in a dryer in order to move more air through

the seeds so as to speed up the drying process.

Static pressure,—Pressure acting by mere weight (force) without motion; pressure exerted by mere mass at rest.

Storage fungi,—Fungi that live off stored seeds and grains.

Stress test,—Test in which seeds are intentionally subjected to the

action of adverse external forces, usually unfavorable germination

conditions.

Strophiole,—Swollen appendage at the hilum of certain seeds, as that of

spurge.

Substrate,—Substratum, a substance acted upon.

Substratum,—Seedbed in a germination test; soil is a substratum for

germinating seeds.

Temperature gradient.—Rate of temperature change with increase in

height; lapse rate or change with distance from heat or cooling source.

Terminal bud,—Bud growing at the end of a branch or stem.

Testa,—Hard external coating or integument of a seed; seedcoat.

Thermocouple,—Thermoelectric couple used to measure temperature

differences.

Threshed,—Beat out from the head, pod, or capsule; separated from the

plant.
PRINCIPLES AND PRACTICES OF SEED STORAGE 227

Totebox.—Open or closed metal or wood box, which is placed on a pallet

and is moved by a forklift. (See pallet box.)

Treated seed.—Seed to which a poisonous chemical compound has been

applied to kill pests.

Umbel(s),—Inflorescence in which the peduncles or pedicels of a cluster

spring from the same point, as in carrot, coriander, or parsnip.

Unthreshed,—Not beat out; not separated from the pod, head, or

capsule.

Vacuum storage.—Storage in a sealed container from which all or

nearly all air was evacuated before sealing; storage in a (partial)

vacuum.

Vascular.—Furnished with vessels or ducts.

Viability.—(Quality as state of being alive; ability to live, grow, and

develop, as the viability of certain grains under dry conditions.

Viability test.—Test to determine whether a seed or the percentage of

seeds in a lot is alive or dead.

Viable.—Capable of growing or developing, as viable seeds.

Vigor.—Condition of active good health and natural robustness; when

seeds are planted, vigor permits germination to proceed rapidly and

to completion under a wide range of conditions.

Vims.—Extremely small, filterable body, which multiplies only in

living cells.

Vitality.—Germinating power.

Water-curtain germinator.—Germinator (germination chamber) that is

heated, cooled, aerated, and humidified by means of a curtain of

water falling down the back of the chamber; water is recirculated.

Weevils.—Snout beetles of the suborder Rhynchophora with snoutbearing jaws at the tip that damage stored seeds and grain.

Wet'bulb thermometer.—Ordinary thermometer with mercury-containing bulb that is kept wet. (See psychrometer.)

Wet weight.—Weight before drying.

Windrow.—Row of hay raked up to dry before being stacked or baled;

also any similar row for drying, as of grain or peanuts.

Xerophyte.—Plant structurally adapted for growth with a limited water

supply.

Yellow cuprocide.—Copper-containing fungicide used to protect seeds

from soil fungi.

Yield.—Aggregate of products resulting from growth or cultivation;

quantity produced, such as 100 bushels of corn per acre.

Zygote.—Fertilized egg^ potentially capable of developing into a seed.
228 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

VERNACULAR AND BOTANICAL-ZOOLOGICAL

NAME EQUIVALENTS!!

Plants

Achillea, the pearl—Achillea ptarmica L.

Ageratum—Ageratum mexicanum Sims

Alfalfa—Medicago sativa L.

Alyceclover—Alysicarpus vaginalis (L.) DC.

Alyssum—Alyssum maritimum (L.) Lam.

Amaranth, redroot—Amaranthus retroflexus L.*

Amaranthus—Amaranthus spp.

Anemone—Anemone spp.

Angel-trumpet—Datura arbórea L.

Anise—Pimpinella anisum L.

Apple—Malus sylvestris Mill.

Arabis—Arabis alpina L.

Armería—Armeria spp.

Artichoke—Cynara scolymus L.

Asparagus—Asparagus officinalis L.

Asparagus, fern—Asparagus plumosus Baker and A. sprengeri Regel

Asparagusbean, sitao—Vigna unguiculata subsp. sesquipedalis (L.)

Verde.

Aster—Aster spp.

Aster, China—Callistephus chinensis (L.) Nees

Babysbreath—Gypsophila spp.

Bachelor's button, cornflower—Centaurea cyanus L.

Bahiagrass—Paspalum notatum Fluegge

Balloonflower—Platycodon grandiflorum DC.

Balm—Melissa officinalis L.

Balsam—Impatiens spp.

Barley—Hordeum vulgäre L.

Barnyardgrass, jungleríce—Echinochloa spp.*

Basil, sweet—Ocimum basilicum L.

Basketflower—Centaurea americana Nutt. and Hymenocallis calathina Nichols

Bean:

Field—Phaseolus vulgaris L.

Garden (snap)—Phaseolus vulgaris L.

Kidney—Phaseolus vulgaris L.

Lima—Phaseolus vulgaris L.

Mung—Vigna radiata (L.) Wilczek (syn. Phaseolus aureus Roxb.)

" Since vernacular names are not commonly used for storage fungi, these organisms are

not listed. * = only scientific name is given in text.
PRINCIPLES AND PRACTICES OF SEED STORAGE 229

Bean—Continued

Navy—Phaseolus vulgaris L.

Scotch—Vicia faba L.

Tapilan—Vigna umbellata (Thunb.) Ohwi and Ohashi (syn. Phaseolus calcaratus Roxb.)

Beet:

Field—Beta vulgaris L.

Garden—Beta vulgaris L.

Sugar—Beta vulgaris L.

Beggarweed—Desmodium tortuosum (Sw.) DC.

Begonia—Begonia spp.

Bellflower:

Bluebell—Campanula spp.*

Peach—Campanula persicifolia L.

Bentgrass:

Colonial (including Astoria and Highland)—Agrostis tenuis Sibth.

Creeping—Agrostis palustris Huds.

Velvet—Agrostis canina L.

Bermudagrass—Cynodon dactylon (L.) Pers.

Betony—Stachys spp.*

Bindweed—Convolvulus spp.*

Bluegrass:

Bulbous—Poa bulbosa L.

Canada—Poa compressa L.

Kentucky—Poa pratensis L.

Nevada—Poa nevadensis Vasey ex Scribn.

Rough—Poa trivialis L.

Texas—Poa arachnifera Torr.

Wood—Poa nemoralis L.

Bluestem:

Big—Andropogon gerardii Vitm.

Little—Andropogon scoparius Michx.

Sand—Andropogon hallii Hack.

Borage—Borago oßcinalis L.

Broadbean or horsebean—Vicia faba L.

Broccoli—Brassica olerácea var. botrytis L.

Bromegrass:

Mountain—Bromus marginatus Nees ex Steud.

Smooth—Bromus inermis Leyss.

Browallia—Browallia spp.

Brussels sprouts—Brassica olerácea var. gemmifera DC.

Buckwheat—Fagopyrum esculentum Moench

Buffalograss—Buchloe dactyloides (Nutt.) Engelm.

Buffelgrass—Cenchrus ciliaris L. (syn. Pennisetum ciliare (L.) Link)
230 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Bugloss—Anchusa capensis Thunb.

Burclover:

California—Medicago polymorpha L.

Spotted—Medicago arabica (L.) Huds.

Burdock—Arctium lappa L. and A. minus (Hill) Bernh.

Bushclover—Lespedeza violácea (L.) Pers.

Butterflyflower—Schizanthus wisetonensis Hort.

Buttonclover—Medicago orbicularis (L.) Bartal.

Cabbage—Brassica olerácea var. capitata L.

Cabbage, Chinese—Brassica pekinensis (Lour.) Rupr.

Calceolaria—Calceolaria spp.

Calendula—Calendula officinalis L.

Calliopsis, dwarf and tall—Calliopsis spp.

Canarygrass—Phalaris canariensis L.

Canarygrass, reed—Phalaris arundinacea L.

Candlenut—Aleurites moluccana (L.) Willd.*

Candytuft:

Annual—Iberis umbellata L.

Perennial—Iberis gibraltarica L. and /. sempervirens L.

Canna—Canna spp.

Cantaloup—Cucumis melo L.

Canterbury-bells—Campanula medium L.

Caraway—Carum carvi L.

Cardoon—Cynara cardunculus L.

Carnation—Dianthus caryophyllus L.

Carpetgrass—Axonopus affinis Chase

Carrot—Daucus carota L.

Castorbean, Cambodia—Ricinus cambodgensis Benary*

Cathedral bells—Cobaea scandens Cav.

Catnip, nepeta—Nepeta spp.

Cauliflower—Brassica olerácea var. botrytis L.

Celeriac—Apium graveolens var. rapaceum (Mill.) Gaud.

Celery—Apium graveolens var. dulce (Mill.) Pers.

Centaurea:

Royal—Centaurea imperialis Hort.

Velvet—Centaurea gymnocarpa Moris and Denot

Chamomile, German (sweet false)—Matricaria chamomilla L.

Chard, Swiss—Beta vulgaris var. cicla L.

Charlock—Sinapis arvensis L. = (Brassica kaber(DC) L. C. (Wheeler))

Chervil—Anthriscus cerefolium (L.) Hoffm.

Chickweed, common—Stellaria media (L.) Vill.*

Chicory—Cichorium intybus L.

Chives—A^llium schoenoprasum L.

Chrysanthemum, annual—Chrysanthemum spp.
PRINCIPLES AND PRACTICES OF SEED STORAGE 231

Cinchona—Cinchona ledgeriana Moens ex Trim.*

Cineraria, common—Senecio cruentus (L'Her.) DC.

Cleome, spiderflower—Cleome gigantea Hort.

Clover:

Alsike—Trifolium hybridum L.

Berseem—Trifolium alexandrinum L.

Crimson—Trifolium incamatum L.

Ladino—Trifolium repens L.

Lappa—Trifolium. lappaceum L.

Large hop—Trifolium procumbens L.

Persian—Trifolium resupinatum L.

Red—Trifolium pratense L.

Rose—Trifolium hirtum All.

Strawberry—Trifolium fragiferum L.

Striate—Trifolium striatum L.*

Subterraneum—Trifolium subterraneum L.

Suckling (small hop)—Trifolium dubium Sibth.

White—Trifolium repens L.

Cockscomb—Celosia spp.

Cocksfoot (orchardgrass)—Dactylis glomerata L.

Cockvine, thunbergia—Thunbergia alata Bojer

Cocoa—Theobroma cacao L.

Coleus, common—Coleus blumei Benth

Collards—Brassica olerácea var. acephala DC.

Coltsfoot—Tussilago fárfara L.*

Columbine—Aquilegia spp.

Coneflower—Rudbeckia spp.

Coralbells—Heuchera sanguínea Engelm.

Coreopsis, perennial—Coreopsis lanceolata L.

Coriander—Coriandrum sativum L.

Corn (dent, field, flint, popcorn, sweet, white, yellow)—Zea mays L.

Cosmos—Cosmos spp.

Cotton—Gossypium spp.

Cowpea—Vigna unguiculata (L.) Walp. subsp. unguiculata

Cranesbill—Geranium spp.

Cress:

Garden—Lepidium sativum L.

Water—Nasturtium officinale R. Br.

Crested dogtail—Cynosurus cristatus L.

Crotalaria—Crotalaria intermedia Kotschy, C. júncea L., C, lanceolata E. Mey., C spectabilis Roth, and C. striata DC.

Crownvetch—Coronilla varia L.

Cucumber—Cucumis sativus L.

Cyclamen—Cyclamen europeum L.
232 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Cypressvine—Ipomoea quamoclit L.

Dahlia—Dahlia spp.

Daisy:

African—Dimorphotheca aurantiaca DC.

African lilac—Arctotis grandis Thunb.

English—Bellis perennis L.

Painted—Pyrethrum spp.

Shasta—Chrysanthemum leucanthemum L.

Swan river—Brachycome spp.

Dallisgrass—Paspalum dilatatum Poir.

Dames rocket, sweet rocket—Hesperis matronalis L.

Dandelion—Taraxacum officinale Weber

Delphinium, annual, perennial—Delphinium spp.

Dichondra—Dichondra repens Forst.

Dill—Anethum graveolens L.

Dock, curly—Rumex crispus L.*

Dodder—Cuscuta spp.*

Dropseed, sand—Sporobolus cryptandrus (Torr.) A. Gray

Dusty-miller—Centaurea candidissima Lam.

Eggplant—Solanum melongena L.

Endive—Cichorium endivia L.

Evening primrose—Oenothera biennis L. and 0. lamarckiana (0.

grandiflora Ait.)*

Fennel—Foeniculum vulgäre Mill.

Fescue:

Chewings—Festuca rubra subsp. commutata Gaud.

Creeping red—Festuca rubra L.

Hair—Festuca tenuifolia Sibth.

Meadow—Festuca pratensisYiná^. (syn. F. elatiorL.)

Sheep—Festuca ovina L.

Tall—Festuca arundinacea Schreb.

Firebush, Mexican—Kochia spp.

Flax:

Common—Linum usitatissimum L.

Flowering—Linum grandiflorum Desf.

Perennial—Linum perenne L.

Forget-me-not—Myosotis spp.*

Foxglove—Digitalis spp.

Foxtail—Setaria spp. *

Gaillardia—Gaillardia spp.

Geranium—Geranium spp.

Geum—Geum spp.

Gilia—Gilia spp.

Globe amaranth—Gomphrena globosa L.
PRINCIPLES AND PRACTICES OF SEED STORAGE 233

Gloxinia, common—Sinningia speciosa (Lodd.) Hiern

Godetia—Godetia amoena Lilija and G, grandiflora Lindl.

Goodia clover—Goodia latifolia Salisb.*

Goosegrass—Eleusine indica (L.) Gaertn.*

Gourds—Cucúrbita spp. and Lagenaria spp.

Grama:

Blue—Bouteloua gracilis (H.B.K.) Lag.

Side oats—Bouteloua curtipendula ÍMichx.) Torr.

Guar—Cyamopsis tetragonoloba (L.) Taub.

Guineagrass—Panicum maximum Jacq.*

Hardinggrass—Phalaris tuberosa var. stenoptera (Hack.) Hitchc.

Hawksbeard—Crépis spp.*

Heliopsis—Heliopsis spp.

Heliotrope—Heliotropium spp.

Hemp—Cannabis sativa L.

Hibiscus—Hibiscus spp.

Hollyhock—Althaea rosea (L.) Cav.

Hung tau—Vigna radiata (L.) Wilczek*

Hyacinth-bean—Dolichos lablab L.

Hyssop—Hyssopus officinalis L.

Indiangrass, yellow—Sorghastrum nutans (L.) Nash

Indigo—Indigofera cytisoides L.*

Indigo, hairy—Indigofera hirsuta L.

Iris, Japanese—Iris kaempferi Sieb.

Japanese lawngrass—Zoysia japónica Steud.

Jerusalem or Maltese cross—Lychnis chalcedonica L.

Jimsonweed—Datura spp.*

Jobs-tears—Coix lacryma-jobi L.

Johnsongrass—Sorghum halepense (L.) Pers.

Jute—Corchorus capsularis L. and C olitorius L.

Kale—Brassica olerácea var. acephala DC.

Kenaf—Hibiscus cannabinus L.

Kidneyvetch—Anthyllis vulneraria L.*

Kohlrabi (knolkol)—Brassica olerácea var. gongylodes L.

Kudzu—Pueraria lobata (Willd,) Ohwi (syn. P. thunbergiana{Sieh, and

Zuce.) Benth.)

Lambsquarters, pigweed—Chenopodium spp.*

Lantana—Lantana cámara L.

Larkspur:

Annual—Delphinium ajacis L.

Hybrids—Delphinium hybridum Steph.

Leadtree—Leucaena leucocephala (Lam.) de Wit*

Leek—Allium porrum L.

Lentil—Lens culinaris Medic.
234 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Lespedeza:

Kobe—Lespedeza striata (Thunb.) Hook, and Arn.

Korean—Lespedeza stipulacea Maxim.

Sericea or Chinese—Lespedeza cunéala (Dumont) D. Don

Siberian—Lespedeza hedysaroides (Pallas) Ricker

Striate—Lespedeza striata (Thunb.) Hook, and Arn.

Lettuce—Lactuca sativa L.

Lily—Lillium spp.

Linaria—Linaria spp.

Lobelia—Lobelia erinus L. and L. cardinalis L.

Locustbean (carob)—Ceratonia siliqua L.

Lotus, Indian—Nelumbo nucifera Gaertn.

Lovegrass, weeping—Eragrostis curvula (Schrad.) Nees

Lunaria, honesty—Lunaria annua L.

Lupine:

Annual types—Lupinus spp.

Arctic—Lupinus arcticus S. Wats.

Blue—Lupinus anguslifolius L.

Russell hybrids—Lupinus polyphyllus Lindl.

White—Lupinus albus L.

Yellow—Lupinus luteus L.

Maize (corn)—Zea mays L.

Mallow—Malva spp.

Manilagrass—Zoysia matrella (L.) Merr.

Marigold:

African—Tagetes erecta L.

French—Tagetes patula L.

Marjoram—Origanum majorana L.

Marvel of Peru, four-o'clock—Mirabilis jalapa L.

Matricaria—Matricaria spp.

Meadow foxtail—Alopecurus pratensis L.

Medic—Medicago spp.

Medic, black—Medicago lupulina L.

Mignonette—Reseda odorata L.

Milkvetch—Astragalus massiliensis Lam. (A. tragacantha) and A.

utriger Pallas*

Millet:

Foxtail (common, German, golden, Hungarian, Siberian)—Setaria

itálica (L.) Beauv.

Japanese—Echinochloa crusgalli var. frumentacea (Link) W. F.

Wight

Pearl—Pennisetum americanum (L.) Leeke

Proso—Panicum miliaceum L.

Mimosa—Mimosa glomerata Forsk.*
PRINCIPLES AND PRACTICES OF SEED STORAGE 235

Morningglory—Ipomoea spp.

Mullein, moth—Verbascum blattaria L.*

Muskmelon (cantaloup)—Cucumis melo L.

Mustard:

Black—Brassica nigra (L.) Koch*

India—Brassica júncea (L.) Czern.

Myosotis—Myosotis spp.

Nasturtium—Tropaeolum majus L.

Needlegrass—Stipa viridula Trin.*

Nemesia—Nemesia spp.

Nicotiana—Nicotiana spp.

Nigella—Nigella damascena L.

Nutgrass, nutsedge—Cyperus rotundus L.*

Oatgrass, tall—Arrhenatherum elatius (L.) Beauv. ex J. Presl and K.

Presl

Oats—Avena sativa L.

Okra—Hibiscus esculentus L.

Onion—Allium cepa L.

Onion, Welch—Allium fistulosum L.

Orchardgrass—Dactylis glomerata L.

Pakchoi—Brassica chinensis L.

Panicgrass—Panicum spp.*

Panicgrass, blue—Panicum antidotale Retz

Pansy—Viola tricolor L.

Parsley—Petroselinum crispum (Mill.) Nym. ex A. W. Hill

Parsnip—Pastinaca sativa L.

Partridgepea—Cassia fasciculata Michx.*

Paspalum—Paspalum spp.*

Path rush—Juncus bufonius L.*

Pea:

Austrian winter or field—Pisum sativum var. arvense (L.) Poir.

Garden—Pisum sativum L.

Rose or crown—Pisum umbellatum (P. sativum var. umbellatum

Ser.)

Peanut, Florida runner—Arachis hypogaea L.

Pechay (mustard)—Brassica júncea (L.) Czern.

VenmseiMm—^Pennisetum spp.*

Pennycress, fanweed—Thlaspi spp.*

Penstemon—Penstemon spp.

Pepper—Capsicum annuum L.

Pepper, red—Capsicum frutescens L.

Pe-tsai (Chinese cabbage)—Brassica pekinensis (Lour.) Rupr.

Petunia—Petunia hybrida Vilm.

Phacelia—Phacelia spp.
236 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Phlox—Phlox drummondii Hook, and Phlox spp.

Physalis—Physalis spp.

Pimpernel—Anagallis spp.*

Pine—Pinus spp.

Pinks, China—Dianthus spp.

Plantain—Plantago spp.*

Poppy:

California—Eschscholtzia califomica Cham.

Com, Shirley—Papaver rhoeas L.

Iceland—Papaver nudicaule L.

Mexican tulip—Hunnemannia fumariifolia Sweet

Oriental—Papaver orientale L.

Portulaca—Portulaca grandiflora Hook.

Potato—Solanum tuberosum L.

Primrose—Primula spp.

Primrose, Chinese—Primula sinensis Lindl.*

Pumpkin—Cucúrbita pepo L. and Cucúrbita spp.

Pyrethrum—Chrysanthemum spp.

Radish—Raphanus sativus L.

Radish, Japanese—Raphanus sativus L.

Rape, annual and winter—Brassica napus L.

Redtop—Agrostis gigantea Roth

Rescuegrass—Bromus unioloides Kunth

Rhodesgrass—Chloris gayana Kunth

Rhubarb—Rheum rhaponticum L.

Rice—Oryza sativa L.

Ricegrass, Indian—Oryzopsis hymenoides (Roem. and Schult.) Ricker

Rose campion—Lychnis spp.

Rosemary—Rosmarinus officinalis L.

Roughpea—Lathyrus hirsutus L.

Rush—Juncus spp.*

Rutabaga—Brassica napus var. napobrassica (L.) Reichb.

Rye—Sécale céréale L.

Ryegrass:

Annual—Lolium multiflorum Lam.

Italian—Lolium multiflorum Lam.

Perennial—Lolium perenne L.

Safflower—Carthamus tinctorius L.

Sage:

Mealycup—Salvia farinácea Benth.

Sage—Salvia officinalis L.

Scarlet—Salvia splendens Sello ex Nees

Sainfoin—Onobrychis viciifolia Scop.

St.-Johnswort—Hypericum humifusum L.*
PRINCIPLES AND PRACTICES OF SEED STORAGE 237

Salpiglossis—Salpiglossis sinuata Ruiz and Pav.

Salsify—Tragopogón porrifolius L.

Saponaria—Saponaria ocymoides L. and S. vaccaria L.

Savory—Satureja hortensis L.

Scabiosa—Scabiosa atropurpúrea L. and S. caucásica Bieb.

Scotch-broom—Cytisus candicans Lam. (C. monspessulanus) and C,

scoparius (L.) Link*

Senna—Cassia bicapsularis L. and C. ultijuga Rich.*

Sensitive plant—Mimosa spp.

Sesame—Sesamum indicum L.

Sesbania—Sesbania spp.

Silktree, mimosa—Albizia julibrissin Durazz.*

Sitao—Vigna unguiculata subsp. sesquipedalis (L.) Verde.

Smartweed—Polygonum spp.*

Smartweed, water—Polygonum hydropiperL."^

Smilo—Oryzopsis miliacea (L.) Aschers, and Schweinf.

Snapdragon—Antirrhinum spp.

Sneezeweed, helenium—Helenium spp.

Snow-on-the-mountain—Euphorbia marginata Pursh

Solanum—Solanum spp.

Sorghum, grain and sweet—Sorghum bicolor (L.) Moench

Soybean—Glycine max (L.) Merr.

Spinach:

Common—Spinacia olerácea L.

New Zealand—Tetragonia tetragonioides (Pall.) Ktze.

Squash:

Butternut—Cucúrbita pepo L.

Winter—Cucúrbita moschata Duchesne ex Poir. and C. maxima

Duchesne

Statice—Statice spp.

Stocks—Matthiola spp.

Strawberry—Fragaria x ananassa Duchesne

Strawflower—Helichrysum monstrosum Hort.

Sudangrass—Sorghum sudanense (Piper) Stapf

Sunflower—Helianthus annuus L.

Swede—Brassica napus var. napobrassica (L.) Reichb.

Sweetclover:

White—Melilotus alba Desr.

Yellow—Melilotus officinalis (L.) Pall.

Sweetpea:

Annual—Lathyrus odoratus L.

Perennial—Lathyrus latifolius L.

Sweet-william—Dianthus barbatus L.

Switchgrass—Panicum virgatum L.
238 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Thyme—Thymus vulgaris L.

Timothy—Phleum pratense L.

Tobacco—Nicotiana tabacum L.

Tomato—Lycopersicon esculentum Mill.

Trefoil:

Big—Lotus uliginosus Schkuhr

Birdsfoot—Lotus comiculatus L.

Turnip—Brassica rapa L.

Vaseygrass—Paspalum urvillei Steud.

Velvetbean—Mucuna deeringiana (Bort) Merr.

Verbena— Verbena spp.

Vetch:

Common—Vicia sativa L.

Hairy— Vicia villosa Roth

Hungarian—Vicia pannonica Crantz

Monantha— Vicia articulata Hornem.

Narrowleaf—Vicia angustifolia (L.) Reich.

Purple—Vicia benghalensis L.

Woollypod— Vicia dasycarpa Ten.

Vinca, periwinkle—Vinca rosea L. and F. minor L.

Viola—Viola comuta L.

Wallflower—Cheiranthus allioni Hort, and C. cheiri L.

Walnut—Juglans australis Griseb.

Watermelon—Citrullus lanatus (Thunb.) Matsum. and Nakai

Wheat:

Common—Triticum aestivum L.

Durum—Triticum durum Desf.

Hard red spring—Triticum aestivum L.

Hard red winter—Triticum aestivum L.

Poulard—Triticum turgidum L.*

Red Winter Speltz—Triticum spelta L.

Soft—Triticum spp.

Soft red winter—Triticum aestivum L.

Spring—Triticum aestivum L.

White—Triticum spp.

Wheatgrass:

Fairway crested—Agropyron cristatum (L.) Gaertn.

Intermediate—Agropyron intermedium (Host) Beauv.

Pubescent—Agropyron trichophorum (Link) Rieht.
PRINCIPLES AND PRACTICES OF SEED STORAGE 239

Wheatgrass—Continued

Slender—Agropyron trachycaulum (Link) Malte ex H. F. Lewis

Standard crested—Agropyron desertorum (Fisch, ex Link) Schult.

Tall—Agropyron elongatum (Host) Beauv.

Western—Agropyron smithii Rydb.

Wild rye:

Blue—Elymus glaucus Buckl.*

Canada—Elymus canadensis L.

Russian—Elymus junceus Fisch.

Willow, weeping—Salix babylonica L.

Zinnia—Zinnia spp.

Zoysia (see Japanese lawngrass and manilagrass)

Bromus polyanthus Scribn.*

Dioclea pauciflora Rusby*

Hovea linearis (J. E. Smith) R. Br.*

Kennedya apétala Loddiger*

Medicago orbicularis (L.) Bartal.*

Melilotus gracilis DC*

Insects

Beetle:

Flat grain—Cryptolestes pusillus (Schönherr)

Khapra—Trogoderma granarium Everts

Sawtoothed grain—Oryzaephilus surinamensis (L.)

Borer, lesser grain—Rhyzopertha dominica (F.)

Cadelle—Tenebroides mauritanicus (L.)

Chalcid—Bruchophagus spp.

Grain moth, Angoumois—Sitotroga cerealella (Oliver)

Weevil:

Granary—Sitophilus granarius (L.)

Rice—Sitophilus oryzae (L.)

Animals

Lemming, collard—Dicrostonyx spp.

Mouse—Muridae spp.

Rat—Rattus spp.

Squirrel—Sciurus spp.
240 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

CONVERSION TABLES FOR TEMPERATURES AND

MEASURES

Temperature Conversion 12

The numbers in the center of each column refer to the temperature in

centigrade or Fahrenheit. They can be converted to either scale. If

converting Fahrenheit to centigrade, the equivalent temperature is on

the left in each column. If converting centigrade to Fahrenheit, the

equivalent temperature is on the right.

Degrees De- Degrees Degrees De- Degrees Degrees De- Degrees

C grees F C grees F C grees F

-40.0 -40 -40.0 -24.4 -12 + 10.4 -8.9 + 16 +60.8

-23.9 -11 + 12.2 -8.3 + 17 +62.6

-39.4 -39 -38.2 -23.3 -10 + 14.0 -7.8 + 18 +64.4

-38.9 -38 -36.4 -7.2 + 19 +66.2

-38.3 -37 -34.6 -22.8 -9 + 15.8 -6.7 +20 +68.0

-37.8 -36 -32.8 -22.2 -8 + 17.6

-37.2 -35 -31.0 -21.7 -7 + 19.4 -6.1 +21 +69.8

-21.1 -6 +21.2 -5.5 +22 +71.6

-36.7 -34 -29.2 -20.6 -5 +23.0 -5.0 +23 + 73.4

-36.1 -33 -27.4 -4.4 +24 +75.2

-35.6 -32 -25.6 -20.0 -4 +24.8 -3.9 +25 + 77.0

-35.0 -31 -23.8 -19.4 -3 +26.6

-34.4 -30 -22.0 -18.9 -2 +28.4 -3.3 +26 + 78.8

-18.3 -1 +30.2 -2.8 +27 +80.6

-33.9 -29 -20.2 -17.8 0 +32.0 -2.2 +28 +82.4

-33.3 -28 -18.4 -1.7 +29 +84.2

-32.8 -27 -16.6 -17.2 + 1 +33.8 -1.1 +30 +86.0

-32.2 -26 -14.8 -16.7 +2 +35.6

-31.7 -25 -13.0 -16.1 +3 +37.4 -.6 +31 +87.8

-15.6 +4 +39.2 .0 +32 +89.6

-31.1 -24 -11.2 -15.0 +5 +41.0 + .6 +33 +91.4

-30.6 -23 -9.4 + 1.1 +34 +93.2

-30.0 -22 -7.6 -14.4 +6 +42.8 + 1.7 +35 +95.0

-29.4 -21 -5.8 -13.9 + 7 +44.6

-28.9 -20 -4.0 -13.3 +8 +46.4 +2.2 +36 +96.8

-12.8 +9 +48.2 +2.8 +37 +98.6

-28.3 -19 -2.2 -12.2 + 10 +50.0 +3.3 +38 + 100.4

-27.8 -18 -0.4 +3.9 +39 + 102.2

-27.2 -17 + 1.4 -11.7 + 11 +51.8 +4.4 +40 + 104.0

-26.7 -16 +3.2 -11.1 + 12 +53.6

-26.1 -15 +5.0 -10.6 + 13 +55.4 +5.0 + 41 + 105.8

-10.0 + 14 +57.2 +5.5 +42 + 107.6

-25.6 -14 h6.8 -9.4 + 15 +59.0 +6.1 + 43 + 109.4

-25.0 -13 +8.6 +6.7 + 44 + 111.2

i2Tabular data courtesy of Weksler Thermometer Corp., Freeport, Long Island,

N.Y, Absolute zero is -273.16° C or -459.69° F.
PRINCIPLES AND PRACTICES OF SEED STORAGE 241

Degrees De- Degrees Degrees De- Degrees Degrees De- Degrees

C grees F C grees F C grees F

+1.2 +45 +113.0 +30.0 -1-86 -hl86.8 +53.3 +128 +262.4

+30.6 +87 +188.6 +53.9 +129 +264.2

+7.8 +46 +114.8 +31.1 +88 +190.4 +54.4 +130 +266.0

+8.3 +47 +116.6 +31.7 +89 +192.2

+8.9 +48 +118.4 +32.2 +90 +194.0 +55.0 +131 +267.8

+9.4 +49 +120.2 +55.6 +132 +269.6

+ 10.0 +50 +122.0 +32.8 +91 +195.8 +56.1 +133 +271.4

+33.3 +92 +197.6 +56.7 +134 +273.2

+ 10.6 +51 +123.8 +33.9 +93 +199.4 +57.2 +135 +275.0

+ 11.1 +52 +125.6 +34.4 +94 +201.2

+ 11.7 +53 +127.4 +35.0 +95 +203.0 +57.8 +136 +276.8

+ 12.2 +54 +129.2 +58.3 +137 +278.6

+ 12.8 +55 +131.0 +35.6 +96 +204.8 +58.9 +138 +280.4

+36.1 +97 +206.6 +59.4 +139 +282.2

+ 13.3 +56 +132.8 +36.7 +98 +208.4 +60.0 +140 +284.0

+ 13.9 +57 +134.6 +37.2 +99 +210.2

+ 14.4 +58 +136.4 +37.8 +100 +212.0 +60.6 +141 +285.8

+ 15.0 +59 +138.2 +61.1 +142 +287.6

+ 15.6 +60 +140.0 +38.3 +101 +213.8 +61.7 +143 +289.4

+38.9 +102 +215.6 +62.2 +144 +291.2

+ 16.1 +61 +141.8 +39.4 +103 +217.4 +62.8 +145 +293.0

+16.7 +62 +143.6 +40.0 +104 +219.2

+ 17.2 +63 +145.4 +40.6 +105 +221.0 +63.3 +146 +294.8

+ 17.8 +64 +147.2 +63.9 +147 +296.6

+ 18.3 +65 +149.0 +41.1 +106 +222.8 +64.4 +148 +298.4

+41.7 +107 +224.6 +65.0 +149 +300.2

+ 18.9 +66 +150.8 +42.2 +108 +226.4 +65.6 +150 +302.0

+ 19.4 +67 +152.6 +42.8 +109 +228.2

+20.0 +68 +154.4 +43.3 +110 +230.0 +66.1 +151 +303.8

+20.6 +69 +156.2 +66.7 +152 +305.6

+21.1 +70 +158.0 +43.9 +111 +231.8 +67.2 +153 +307.4

+44.4 +112 +233.6 +67.8 +154 +309.2

+21.7 +71 +159.8 +45.0 +113 +235.4 +68.3 +155 +311.0

+22.2 +72 +161.6 +45.6 +114 +237.2

+22.8 +73 +163.4 +46.1 +115 +239.0 +68.9 +156 +312.8

+23.3 +74 +165.2 +69.4 +157 +314.6

+23.9 +75 +167.0 +46.7 +116 +240.8 +70.0 +158 +316.4

+47.2 +117 +242.6 +70.6 +159 +318.2

+24.4 +76 +168.8 +47.8 +118 +244.4 +71.1 +160 +320.0

+25.0 +77 +170.6 +48.3 +119 +246.2

+25.6 +78 +172.4 +48.9 +120 +248.0 +71.7 +161 +321.8

+26.1 +79 +174.2 +72.2 +162 +323.6

+26.7 +80 +176.0 +49.4 +121 +249.8 +72.8 +163 +325.4

+50.0 +122 +251.6 +73.3 +164 +327.2

+27.2 +81 +177.8 +50.6 +123 +253.4 +73.9 +165 +329.0

+27.8 +82 +179.6 +51.1 +124 +255.2

+28.3 +83 +181.4 +51.7 +125 +257.0 +74.4 +166 +330.8

+28.9 +84 +183.2 +75.0 +167 +332.6

+29.4 +85 +185.0 +52.2 +126 +258.8 +75.6 +168 +334.4

+52.8 +127 +260.6
242 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Degrees De- Degrees

C grees F

Degrees De- Degrees

C grees F

Degrees De- Degrees

C grees F

+76.1 +169 +336.2

+ 76.7 +170 +338.0

+ 77.2 +171 +339.8

+77.8 +172 +341.6

+ 78.3 +173 +343.4

+78.9 +174 +345.2

+ 79.4 +175 +347.0

+95.6 +204 +399.2

+96.1 +205 +401.0

+96.7 +206 +402.8

+97.2 +207 +404.6

+97.8 +208 +406.4

+98.3 +209 +408.2

+98.9 +210 +410.0

+ 115.0 +239 +462.2

+ 115.6 +240 +464.0

+ 116.1 +241 +465.8

+ 116.7 +242 +467.6

+ 117.2 +243 +469.4

+ 117.8 +244 +471.2

+ 118.3 +245 +473.0

+80.0 +176 +348.8

+80.6 +177 +350.6

+81.1 +178 +352.4

+81.7 +179 +354.2

+82.2 +180 +356.0

+99.4 +211 +411.8

+ 100.0 +212 +413.6

+ 100.6 +213 +415.4

+ 101.1 +214 +417.2

+ 101.7 +215 +419.0

+ 118.9 +246 +474.8

+ 119.4 +247 +476.6

+ 120.0 +248 +478.4

+ 120.6 +249 +480.2

+ 121.1 +250 +482.0

+82.8 +181 +357.8

+83.3 +182 +359.6

+83.9 +183 +361.4

+84.4 +184 +363.2

+85.0 +185 +365.0

+ 102.2 +216 +420.8

+ 102.8 +217 +422.6

+ 103.3 +218 +424.4

+ 103.9 +219 +426.2

+ 104.4 +220 +428.0

+ 122.4 +252 +485.6

+ 123.3 +254 +489.2

+ 124.4 +256 +492.8

+ 125.5 +258 +496.4

+ 126.7 +260 +500.0

+85.6 +186 +366.8

+86.1 +187 +368.6

+86.7 +188 +370.4

+87.2 +189 +372.2

+ 87.8 +190 +374.0

+ 105.0 +221 +429.8

+ 105.6 +222 +431.6

+ 106.1 +223 +433.4

+ 106.7 +224 +435.2

+ 107.2 +225 +437.0

+ 127.8 +262 +503.6

+ 128.9 +264 +507.2

+ 130.0 +266 +510.8

+ 131.3 +268 +514.4

+ 132.2 +270 +518.0

+ 88.3 +191 +375.8

+88.9 +192 +377.6

+89.4 +193 +379.4

+90.0 +194 +381.2

+90.6 +195 +383.0

+ 107.8 +226 +438.8

+ 108.3 +227 +440.6

+ 108.9 +228 +442.4

+ 109.4 +229 +444.2

+ 110.0 +230 +446.0

+ 133.3 +272 +521.6

+ 134.4 +274 +525.2

+ 135.6 +276 +528.8

+ 136.7 +278 +532.4

+ 137.8 +280 +536.0

+ 91.1 +196 +384.8

+91.7 +197 +386.6

+92.2 +198 +388.4

+92.8 +199 +390.2

+ 93.3 +200 +392.0

+ 110.6 +231 +447.8

+ 111.1 +232 +449.6

+ 111.7 +233 +451.4

+ 112.2 +234 +453.2

+ 112.8 +235 +455.0

+ 138.9 +282 +539.6

+ 140.0 +284 +543.2

+ 141.1 +286 +546.8

+ 142.2 +288 +550.4

+ 143.3 +290 +554.0

+ 93.9 +201 +393.8

+94.4 +202 +395.6

+95.0 +203 +397.4

+ 113.3 +236 +456.8

+ 113.9 +237 +458.6

+ 114.4 +238 +460.4

+ 144,4 +292 +557.6

+ 145.6 +294 +561.2

+ 146.7 +296 +564.8

+ 147.8 +298 +568.4
PRINCIPLES AND PRACTICES OF SEED STORAGE 243

Measures of Weight

Avoirdupois to metric:

1 ounce (oz) 28.3 grams

1 pound (lb) 453.6 grams

1 hundredweight (cwt) 50.8 kilograms

1 short ton (2,000 lb) 907.0 kilograms

1 long ton (2,240 lb) 1,016.0 kilograms

1 metric ton (1 tonne) 1,000.0 kilograms

Metric to avoirdupois:

1 gram (gm) 0.3533 ounce

1 kilogram (kg) 2.205 pounds

1 metric ton (1,000 kg) 1.102 short tons

Measures of Length

British or American to metric:

1 inch (in) 2.54 centimeters

1 foot (ft) 30.48 centimeters

1 yard (yd) 914 meter

1 mile (mi) 1.609 kilometers

Metric to British or American:

1 millimeter (mm) 0.039 inch

1 centimeter (cm) 394 inch

1 decimeter (dm) 3.397 inches

1 meter (m) 1.094 yards

1 kilometer (km) 621 mile

Measures of Area

British or American to metric:

1 square inch (in^) 6.452 square centimeters

1 square foot (ft2) 9.29 square decimeters

1 square yard (yd2) 836 square meter

1 acre 405 hectare

Metric to British or American:

1 square millimeter (mm2) 0.155 square inch

1 square meter (m2) 1.196 square yards

1 hectare (ha) 2.471 acres

1 square kilometer (km2) 386 square mile
244 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Measures of Volume

British or American to metric:

1 cubic inch (in 3) 16.387 cubic centimeters

1 cubic foot (ft3) 28.317 cubic decimeters

1 cubic yard (yd^) 765 cubic meter

Metric to British or American:

1 cubic centimeter (cm^) 0.061 cubic inch

1 cubic decimeter (dm3) 035 cubic foot

1 cubic meter (m^) 1.308 cubic yards

Measures of Capacity

American and British to metric:

1 pint (pt) (American) 0.473 liter

1 quart (qt) (American) 946 liter

1 gallon (gal) (American) 3.785 liters

1 gallon (British) 4.546 liters

Metric to American and British:

1 liter (1) 1.057 quarts (American)

1 liter 880 quart (British)

LITERATURE CITED

ANONYMOUS.

1942a. SEED STORAGE PROBLEMS. Puerto Rico Agr. Expt. Sta. Ann. Rpt.

1941/42: 39.

1942b. DURATION OF VIABILITY OF SEEDS. Gard. Chron. Ill: 234.

1959. SEEDS BAGGED TO KEEP. Agr. Res. 8: 10-11.

1968. 550-YEAR OLD SEED SPROUTS. Sci. News 94: 367.

ABDALLA, F. H., and ROBERTS, E. H.

1969a. THE EFFECTS OF TEMPERATURE AND MOISTURE ON THE INDUCTION OF

GENETIC CHANGES IN SEEDS OF BARLEY, BROAD BEANS, AND PEAS DURING

STORAGE. Ann. Bot. (N.S.) 33: 153-167.

and ROBERTS, E. H.

1969b. THE EFFECT OF SEED STORAGE CONDITIONS ON THE GROWTH AND YIELD OF

BARLEY, BROAD BEANS, AND PEAS. Ann. Bot. (N.S.) 33: 169-184.

ABDUL-BAKI, A. A., and ANDERSON, J. D.

1972. PHYSIOLOGICAL AND BIOCHEMICAL DETERIORATION OF SEEDS. In Kozlowski, T. T., Seed Biology, v. 2, pp. 283-315, illus. New York.

AGENA, M. U.

1961. UNTERSUCHUNGEN ÜBER KALTEEINWIRKUNGEN AUF LAGERNDE GETRIEDEFRUCHTE MIT VERSCHIEDENEM WASSERGEHALT. 112 pp. Bonn.

ALTSCHUL, A. M., KARON, M. L., KAYME, L., and HALL, C. M.

1946. EFFECT OF INHIBITORS ON THE RESPIRATION AND STORAGE OF COTTONSEED. Plant Physiol. 21: 573-587.
PRINCIPLES AND PRACTICES OF SEED STORAGE 245

AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS.

1972. ASAE DATA: ASAE D245.1. MOISTURE RELATIONSHIPS OF GRAIN. Agr.

Engin. Ybk. 1971, pp. 364-366.

ANDERSON, J. A., and ALCOCK, A. W., eds.

1954. STORAGE OF CEREAL GRAINS AND THEIR PRODUCTS. 515 pp., illus. St.

Paul, Minn.

ARNDT, C. H.

1946. THE INTERNAL INFECTION OF COTTON SEED AND THE LOSS OF VIABILITY IN

STORAGE. Phytopathology 36: 30-37.

ARNOLD, J. R., and LIBBY, W. F.

1951. RADIOCARBON DATES. Science 113: 111-120.

ASSOCIATED SEED GROWERS, INC. (ASGROW SEED CO.).

1949. A STUDY OF MECHANICAL INJURY TO SEED BEANS. AsgroW Monog. 1, 46

pp.

1954. THE PRESERVATION OF VIABILITY AND VIGOR IN VEGETABLE SEED. Asgrow Monog. 2, 32 pp.

ASSOCIATION OF OFFICIAL SEED ANALYSTS.

1954. RULES FOR TESTING SEEDS. Assoc. Off. Seed Anal. Proc. 44: 31-78.

1970. RULES FOR TESTING SEEDS. Assoc. Off. Seed Anal. Proc. 60: 1-116.

ATKIN, J. D.

1958. RELATIVE SUSCEPTIBILITY OF SNAP BEAN VARIETIES TO MECHANICAL INJURY OF SEED. Amer. Soc. Hort. Sei. Proc. 72: 370-373.

ATKINS, W. R. G.

1909. THE ABSORPTION OF WATER BY SEEDS. Roy. Dublin Soc. Sei. Proc. 12:

35-46.

AUFHAMMER, G., and SIMON, U.

1957. DIE SAMEN LANDWIRTSHAFTLICHER KULTURPFLANZEN IM GRUNDSTEIN

DES CHAMALIGEN NÜRNBERGER STADTTHEATERS UND IHRE KEIMFÄHIGKEIT. Ztschr. f. Acker- u. Pflanzenbau. 103: 454-472.

AUSTIN, R. B.

1972. EFFECTS OF ENVIRONMENT BEFORE HARVESTING ON VIABILITY. IN ROBerts, E. H., Viability of Seeds, pp. 114-149, illus. London.

AvERY, A. G., and BLAKESLEE, A. F.

1936. VISIBLE MUTATIONS FROM AGED SEEDS. Amer. Nat. 70: 36-37.

BABBITT, J. D.

1949. OBSERVATIONS ON THE ADSORPTION OF WATER VAPOR BY WHEAT. Ganad.

Jour. Res., Sect. F, Technol. 27: 55-72.

BACCHI, 0.

1955. SECA DA SEMENTÉ DE CAFE AO SOL. Bragantia 14: 225-236.

BAILEY, C. H.

1940. RESPIRATION OF CEREAL GRAINS AND FLAXSEED. Plant Physiol. 15: 257-

274.

BAINER, R., and BORTHWICK, H. A.

1934. THRESHER AND OTHER MECHANICAL INJURY TO SEED BEANS OF THE LIMA

TYPE. Calif. Bul. 580, 30 pp.

BAKER, D., NEUSTADT, M. H., and ZELENY, L.

1957. APPLICATION OF THE FAT ACIDITY TEST AS AN INDEX OF GRAIN DETERIORATION. Cereal Chem. 34: 226-233.

BAKER, K. F.

1972. SEED PATHOLOGY. In Kozlowski, T. T., Seed Biology, v. 2, pp. 317-416,

illus. New York.
246 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

BARRE, H. J.

1954. COUNTRY STORAGE OF GRAIN. In Anderson, J. A., and Alcock, A. W.,

eds.. Storage of Cereal Grains and Their Products, pp. 308-357. St. Paul,

Minn.

1963. IMPORTANT EQUIPMENT FOR DRYING SEEDS IN NORTH AMERICA. Internatl. Seed Testing Assoc. Proc. 28: 815-826.

BARROW, E. H. R.

1915. THE HEATING OF COTTONSEED—ITS CAUSES AND PREVENTION. INDUS.

Engin. Chem. 7: 709-712.

BARTHOLOMEW, D. P., and LOOMIS, W. E.

1967. CARBON DIOXIDE PRODUCTION BY DRY GRAIN IN ZEA MAYS. Plant Physiol.

42: 120-124.

BARTON, L. V.

1932. EFFECT OF STORAGE ON THE VITALITY OF DELPHINIUM SEEDS. Boyce

Thompson Inst. Contrib. 4: 141-153.

1939. STORAGE OF SOME FLOWER SEEDS. Boyce Thompson Inst. Contrib. 10:

399-427.

1941. RELATION OF CERTAIN AIR TEMPERATURES AND HUMIDITIES TO VIABILITY

OF SEEDS. Boyce Thompson Inst. Contrib. 12: 85-102.

1947. EFFECT OF DIFFERENT STORAGE CONDITIONS ON THE GERMINATION OF

SEEDS OF CINCHONA LEDGERIANA MOENS. Boyce Thompson Inst. Contrib.

15: 1-10.

1949. SEED PACKETS AND ONION SEED VIABILITY. Boyce Thompson Inst. Contrib. 15: 341-352.

1953. SEED STORAGE AND VIABILITY. Boyce Thompson Inst. Contrib. 17:87-103.

1954. EFFECT OF SUBFREEZING TEMPERATURES ON VIABILITY OF CONIFER SEEDS

IN STORAGE. Boyce Thompson Inst. Contrib. 18: 21-24.

1960a. STORAGE OF SEEDS OF LOBELIA CARDINALIS L. Boyce Thompson Inst.

Contrib. 20: 395-401.

1960b. LIFE SPAN OF FROST-DAMAGED CORN SEEDS. Boyce Thompson Inst.

Contrib. 20: 403-408.

1961. SEED PRESERVATION AND LONGEVITY. 216 pp., illus. London and New

York.

1966a. THE EFFECT OF STORAGE CONDITIONS ON THE VIABILITY OF BEAN

SEEDS. Boyce Thompson Inst. Contrib. 23: 281-284.

1966b. VIABILITY OF PYRETHRUM SEEDS. Boyce Thompson Inst. Contrib. 23:

267-268.

__ and GARMAN, H. R.

1946. EFFECT OF AGE AND STORAGE CONDITION OF SEEDS ON THE YIELDS OF

CERTAIN PLANTS. Boyce Thompson Inst. Contrib. 14: 243-255.
PRINCIPLES AND PRACTICES OF SEED STORAGE 247

BASS, L. N.

1953. RELATIONSHIPS OF TEMPERATURE, TIME AND MOISTURE CONTENT TO THE

VIABILITY OF SEEDS OF KENTUCKY BLUEGRASS. lowa Acad. Sci. Proc. 60:

86^8.

1960. PACKAGING AND STORAGE OF KENTUCKY BLUEGRASS AND CREEPING RED

FESCUE SEED. Assoc. Off. Seed Anal. Proc. 49: 173-181.

1965. EFFECT OF MATURITY, DRYING RATE AND STORAGE CONDITIONS ON LONGEVITY OF KENTUCKY BLUEGRASS SEED. Assoc. Off. Seed AnaL Proc. 55:

43-46.

1968. EFFECTS OF TEMPERATURE, RELATIVE HUMIDITY AND PROTECTIVE PACKAGING ON LONGEVITY OF PEANUT SEEDS. Assoc. Off. Seed Anal. Proc. 58:

58-62.

_ CHING, T. M., and WINTER, F. L.

1961. PACKAGES THAT PROTECT SEEDS. U.S. Dept. Agr. Ybk. 1961: 330-338.

_ and CLARK, D. C.

1974. EFFECTS OF STORAGE CONDITIONS, PACKAGING MATERIALS, AND SEED

MOISTURE CONTENT ON LONGEVITY OF SAFFLOWER SEEDS. Assoc. Off.

Seed Anal. Proc. 64: 120-128.

_ CLARK, D. C, and JAMES, EDWIN.

1962. VACUUM AND INERT-GAS STORAGE OF LETTUCE SEED. ASSOC. Off. Seed

Anal. Proc. 52: 116-122.

_ CLARK, D. C, and JAMES, EDWIN.

1963a. VACUUM AND INERT-GAS STORAGE OF CRIMSON CLOVER AND SORGHUM

SEEDS. Crop. Sei. 3: 425-428.

_ CLARK, D. C, and JAMES, EDWIN.

1963b. VACUUM AND INERT-GAS STORAGE OF SAFFLOWER AND SESAME

SEEDS. Crop. Sei. 3: 237-240.

_ and JAMES, EDWIN.

1961. DEVICE FOR VACUUM AND INERT-GAS SEALING OF TIN CANS. Agron. Jour.

53: 278.

BATTLE, W. R.

1948. EFFECT OF SCARIFICATION ON LONGEVITY OF ALFALFA SEED. Amer. Soc.

Agron. Jour. 40: 758-759.

BAUTISTA, G. M., and LINKO, P.

1962. GLUTAMIC ACID DECARBOXYLASE ACTIVITY AS A MEASURE OF DAMAGE IN

ARTIFICIALLY DRIED AND STORED CORN. Cereal Chem. 39: 455-459.

BEAL, W. J.

1885. THE VITALITY OF SEEDS BURIED IN THE SOIL. SOC. Prom. Agr. Sei. Proc. 6:

14-15.

BEATTIE, J. H., and BOSWELL, V. R.

1939. LONGEVITY OF ONION SEED IN RELATION TO STORAGE CONDITIONS. U.S.

Dept. Agr. Cir. 512, 23 pp.

and TATMAN, E. C.

1950. LONG-TERM STORAGE OF PARSNIP SEED. Amer. Soc. Hort. Sci. Proc. 55:

435-437.

BECK, J. M.

1966. GENERAL REQUIREMENTS FOR ECONOMICAL SEED STORAGE. Miss. State

Univ. Short Course Seedsmen Proc. 1966, pp. 39-42.

1972. SYSTEMS FOR CONTROLLING RELATIVE HUMIDITY AND TEMPERATURE. Miss. State Univ. Short Course Seedsmen Proc. 15: 77-85.
248 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

BECQUEREL, PAUL.

1907. RECHERCHES SUR LA VIE TATENTE DES GRAINES. Ann. des Sci. Nat., Bot.

5/6: 193-^11.

1934. LA LONGEVITE DES GRAINES MACROBIOTIQUES. [Paris] Acad. des. Sci.

Compt. Rend. 199: 1662-1664.

1953. LA SUSPENSION DE LA VIE AUX CONFINS DU ZERO ABSOLUET SES CONSEQUENCES. Extrait des Actes due Congrès de Luxembourg. 72d Sess.

Assoc. Franc, pour l'Avane, des Sci., pp. 487-491.

BLACK, J. N.

1959. SEED SIZE IN HERBAGE LEGUMES. Herbage Abs. 29: 235-241.

BLACKSTONE, J. H., WARD, H. S., JR., BUTT, J. L., and others.

1954. FACTORS AFFECTING GERMINATION OF RUNNER PEANUTS. Ala. Agr. Expt.

Sta. BuL 289, 31 pp.

BLAKESLEE, A. F.

1954. THE AGING OF SEEDS AND MUTATION RATES. N.Y. Acad. Sci. Ann. 57:

488-490.

AvERY, A. G., BERGNER, A. D., and SATINA, S.

1942. DATURA STUDIES. Carnegie Inst. Wash. Ybk. 41 (1941-42): 176-180.

BoDGER SEEDS LTD.

1932. SOME INTERESTING STATISTICS ON THE LONGEVITY OF FLOWER

SEEDS. Seed World 31 (11): 17.

BONVICINI, M.

1951. SEMENTÉ DI GRANO SENZA LESIONI. Commun. Cong. Assoc. Franc. Prog.

Sci., p. L

BORTHWICK, H. A.

1932. THRESHER INJURY IN BABY LIMA BEANS. Jour. Agr. Res. 44: 503-510.

BoswELL, V. R., TooLE, E. H., TooLE, V. K., and FISHER, D. F.

1940. A STUDY OF RAPID DETERIORATION OF VEGETABLE SEEDS AND METHODS

FOR ITS PREVENTION. U.S. Dept. Agr. Tech. Bui. 708, 40 pp.

BRANDENBURG, N. R., SIMONS, J. W., and SMITH, L. L.

1961. WHY AND HOW SEEDS ARE DRIED. U.S. Dept. Agr. Ybk. 1961, pp.

295^06.

BRéESE, M. H.

1955. HYSTERESIS IN THE HYGROSCOPIC EQUILIBRIA OF ROUGH RICE AT 25°

c. Cereal Chem. 32: 481^87.

BRETT, C. C.

1952A. FACTORS AFFECTING THE VIABILITY OF GRASS AND LEGUME SEED IN

STORAGE AND DURING SHIPMENT. Intematl. Grassland Conf. 6: 878-884.

1952b. THE INFLUENCE OF STORAGE CONDITIONS UPON THE LONGEVITY OF SEEDS,

WITH SPECIAL REFERENCE TO ROOT AND VEGETABLE CROPS. 13th Internatl. Hort. Cong. Rpt., pp. 1016-1018.

BREWER, H. E., and BUTT, J. L.

1950. HYGROSCOPIC EQUILIBRIUM AND VIABILITY OF NATURALLY AND ARTIFICIALLY DRIED BLUE LUPINE SEEDS. Plant Physiol. 25: 245-268.

BRISON, F. R.

1941. INFLUENCE OF STORAGE CONDITIONS UPON THE GERMINATION OF ONION

SEED. Tex. Acad. Sci. Proc. and Trans. 25: 69-70.

1942. THE INFLUENCE OF STORAGE CONDITIONS UPON THE GERMINATION OF

ONION SEED. Amer. Soc. Hort. Sci. Proc. 40: 501-503.
PRINCIPLES AND PRACTICES OF SEED STORAGE 249

BROOKE, C. L.

1935. MUMMY WHEAT WON'T GROW. Northwest. Miller 181: 456.

BROWN, C. W., and MYERS, A.

1960. LONG TERM CEREAL STORAGE. Agr. Gaz. N.S. Wales 71: 348-355.

BROWN, E.

1939. PRESERVING THE VIABILITY OF BERMUDA ONION SEED. Science 89: 292-

293.

STANTON, T. R., WIEBE, G. A., and MARTIN, J. H.

1948. DORMANCY AND THE EFFECT OF STORAGE ON OATS, BARLEY, AND

SORGHUM. U.S. Dept. Agr. Tech. Bui. 953, 30 pp.

BROWN, E. B.

1922. EFFECTS OF MUTILATING THE SEED ON THE GROWTH AND PRODUCTIVENESS

OF CORN. U.S. Dept. Agr. Bui. 1011, 14 pp.

BROWN, H. T., and ESCOMBE, F.

1897-98. NOTE ON THE INFLUENCE OF VERY LOW TEMPERATURES ON THE GERMINATIVE POWER OF SEEDS. Roy. Soc. London, Proc, Sect. B, 62:

160-165.

BUNCH, H. D.

1958. MORE RESEARCH, EDUCATION, "PREACHING" NEEDED TO CUT DOWN ON

HIGH SEED MOISTURE. Seedsmen's Digest 9 (5): 13.

BUNTING, R. H.

1930. PROCEEDINGS OF THE ASSOCIATION OF ECONOMIC BIOLOGISTS. II. MYCOLOGICAL ASPECTS. Ann. Appl. Biol. 17: 402^07.

BURGESS, J. L.

1938. REPORT ON PROJECT TO DETERMINE THE PERCENTAGE AND DURATION OF

VIABILITY OF DIFFERENT VARIETIES OF SOYBEANS GROWN IN NORTH CAROLINA. Assoc. Off. Seed Anal. Proc. 23: 69.

BuRLisoN, W. L., VAN DOREN, C. A., and HACKLEMAN, J. C.

1940. ELEVEN YEARS OF SOYBEAN INVESTIGATIONS, VARIETIES, SEEDING,

STORAGE. 111. Agr. Expt. Sta. Bui. 462, pp. 121-167.

BURNS, R. E.

1957. EFFECT OF AGE OF SEED ON SURVIVAL UNDER ADVERSE STORAGE CONDITIONS. (Abstract) Assoc. South. Agr. Workers Proc. 54: 226.

CALDWELL, W. P.

1962. SAFER SEED STORAGE FOR SHIPMENT ABROAD. Crops and Soils 61-62: 17.

and BUNCH, H. D.

1961. EFFECTS OF SEED MOISTURE AND PACKAGING CONTAINER UPON VIABILITY

AND VIGOR OF WHEAT, CABBAGE AND SOYBEAN SEEDS DURING TRANSOCEANIC SHIPMENT AND SUBSEQUENT STORAGE. AgTOn. Abs. 1961: 72.

CALIFORNIA DEPARTMENT OF AGRICULTURE.

1973. CALIFORNIA SEED LAW AND REGULATIONS. 46 pp. Sacramento, Calif.

CARLSON, G. E., and ATKINS, R. E.

1960. EFFECT OF FREEZING TEMPERATURES ON SEED VIABILITY AND SEEDLING

VIGOR OF GRAIN SORGHUM. Agron. Jour. 52: 329-333.

CHANEY, R. W.

1951. HOW OLD ARE THE MANCHURIAN LOTUS SEEDS? Gard. Jour. N.Y. Bot.

Gard. 1: 137-139.

CHING, T. M.

1959. KEEPING FIELD SEED QUALITY IN STORAGE AND TRANSIT. West. Feed and

Seed 14: 21-22.

1961. RESPIRATION OF FORAGE SEED IN HERMETICALLY SEALED CANS. Agron.

Jour. 53: 6-^.
250 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

CHING, T. M., and ABU-SHAKRA, S.

1965. EFFECT OF WATER VAPOR TRANSMISSION RATES OF PACKAGE MATERIAL

AND STORAGE CONDITIONS ON SEED QUALITY. Agron. Jour. 57: 285-287.

and CALHOUN, W., JR.

1968. PRODUCTIVITY OF 10-YEAR-OLD CANNED FORAGE SEEDS. Agron. Jour. 60:

393-394.

PARKER, M. C, and HILL, D. D.

1959. INTERACTION OF MOISTURE AND TEMPERATURE ON VIABILITY OF FORAGE

SEEDS STORED IN HERMETICALLY SEALED CANS. Agron. Jour. 51: 680-684.

and SCHOOLCRAFT, I.

1968. PHYSIOLOGICAL AND CHEMICAL DIFFERENCES IN AGED SEEDS. Crop Sci. 8:

407^09.

TAYLOR, H. L., and ROWELL, P. T.

1960. CHANGE OF FORAGE SEED QUALITY UNDER DIFFERENT SIMULATED SHIPPING CONDITIONS. Agron. Jour. 52: 37-40.

CHIRKOVSKIY, V. I.

1953. [THE INFLUENCE OF AGING OF SEEDS ON THE DEVELOPMENT OF TOBACCO

PLANTS.] Akad. Nauk. SSSR Dok. 92: 439-442. [In Russian.] (From Hort.

Abs. V. 24, No. 1658. 1954.)

1956. [THE DEVELOPMENT OF TOBACCO PLANTS IN RELATION TO THE AGE OF

SEEDS AND SOME OTHER FACTORS.] Krasnodar Vsesoyuzn. Nauch. Issled.

Inst. Tabaka i Makhorki, Sborn. Nauch. Issled. Rabot No. 149: 147-161. [In

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CHOPINET, R.

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256 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

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260 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

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262 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

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264 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

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266 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

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1929. EFFECT OF VARIOUS FUMIGANTS ON THE GERMINATION OF SEEDS. JOUR.

Agr. Res. 39: 925-927.

YOUNG, R. E.

1949. THE EFFECT OF MATURITY AND STORAGE ON GERMINATION OF BUTTERNUT

SQUASH SEED. Amer. Soc. Hort. Sei. Proc. 53: 345-346.

YOUNGMAN, B. J.

1952. GERMINATION OF OLD SEEDS. Kew Bul. 6, pp. 423-426.

ZELENY, LAWRENCE.

1954. CHEMICAL, PHYSICAL, AND NUTRITIVE CHANGES DURING STORAGE. In

Anderson, J. A., and Alcock, A. W., eds.. Storage of Cereal Grains and

Their Products, pp. 46-76, illus. St. Paul, Minn.

1961. WAYS TO TEST SEEDS FOR MOISTURE. U.S. Dept. Agr. Ybk. 1961:443^47.

_ and COLEMAN, D. A.

1938. ACIDITY IN CEREALS AND CEREAL PRODUCTS, ITS DETERMINATION AND

SIGNIFICANCE. Cereal Chem. 15: 580-595.

^ and CoLEMAN, D. A.

1939. THE CHEMICAL DETERMINATION OF SOUNDNESS IN CORN. U.S. Dept. Agr.

Tech. Bul. 644, 24 pp.
INDEX

Abnormal seedlings, 13, 23, 24, 29, 52

Absorption, 15, 36, 38, 48, 49, 196

Accelerated aging test, 172-174

Achillea, the pearl, 179

Adsorption, 38, 49

Ageratum, 179

Ageratum, 158

Agropyron, 17

A. cristatum, 18

Air-dry seeds, 57, 202

Air ducts, 97, 102

Air - sealed in (see Sealed storage)

Alhizia, 7

A. julibrissin, 207

Alcohol dehydrogenase, 199

Aleurites molucanna, 206

Alfalfa, 14, 15, 16, 24, 30, 33, 42, 43, 48, 88,

90, 99, 154, 158, 173, 175, 204

Alpha amylase, 11

Althaea, 16

Aluminum foil (see Packaging materials)

Alyceclover, 15, 175

Alysicarpus, 15

Alyssum, 179

Alyssum, 158

Amaranthus, 179

Amaranthus retroflexus, 198

Ambient conditions, 11, 173, 174, 183, 204

Ambient relative humidity, 9, 15, 20, 83, 95,

204

Ambient temperature, 9, 20, 156, 171, 183,

203, 204

Anabolic process (changes), 91

Anagallis, 211

Anatolian excavations (at the site of Alishar), 78, 79, 216-217

Ancient seeds, 7, 201-217

Anemone, 179

Angel-trumpet, 179

Anise, 179

Anthyllis vulneraria, 206

Antirrhinum, 95, 158

Apple, 30

Arabis, 179

Arctic lupine, 211, 212

Arctic tundra, 211, 212

Argon - sealed in (see Sealed storage)

Armería, 179

Artichoke, 178

Asparagus, 16, 157, 178

Asparagus, 16, 177

Asparagus, fern, 32, 179

Asparagusbean, sitao, 16

Aster, 15, 56, 61, 62, 94

Aster, 158

Aster, China, 179

Astragalus:

A. massiliensis, 206

A. utriger, 206

Avena sativa, 169

Babysbreath, 179

Bachelor's button, cornflower, 179

Bacteria, 78, 80, 81, 86, 171

Bahiagrass, 175

Balloonflower, 179

Balm, 179

Balsam, 179

Barley, 4, 7, 8, 11, 20, 22, 27, 30, 35, 41, 53,

57, 78, 80, 86, 90, 91, 93, 95, 121, 158,

175, 199, 202, 203, 216, 217

Basil, sweet, 179

Basketflower, 15

Bean, 2, 3, 4, 8, 13, 16, 17, 18, 23, 24, 30, 37,

40, 51, 90, 94, 121, 146, 156, 158, 168,

173, 199

Genetic differences, 24, 25

Kinds:

Field, 175

Garden (snap), 16, 40, 51, 56, 159, 178

Kidney, 59, 60, 156

Lima, 13, 16, 40, 59, 60, 90, 159, 178

Mung, 94, 156

Navy, 23, 25

Scotch, 83

Tapilan:

Black seeded, 156

White seeded, 156

Yellow seeded, 156

Beet, 59, 60, 90, 157, 158, 159, 178, 209

Field, 159, 175

Garden, 40

275
276 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Beet—Continued

Sugar, 32, 33, 44, 94, 95, 116, 121, 122,

159, 175, 199, 205

Beggarweed, 15

Begonia, 179

Bellflower, peach, 179

Bellis, 158

Bentgrass, 158

Colonial (including Astoria and Highland), 42, 43, 53, 164, 175, 196, 197

Creeping, 42, 175

Velvet, 175

Bermudagrass, 42, 175

Biochemical change, 7, 91-92, 202

Biochemical deterioration, 6, 13, 86, 92

Bluegrass, 158

Bulbous, 175

Canada, 175

Kentucky, 21, 30, 42, 43, 51, 53, 62, 108,

113, 117, 153, 159,164, 175, 197, 204,

209

Effect of moisture content on viability,

21, 22, 30, 113, 153

Effect of temperature on viability, 113,

117, 153

Nevada, 175

Rough, 42, 43, 175

Texas, 175

Wood, 175

Bluestem:

Big, 175

Little, 175

Sand, 175

Borage, 179

Brassica:

B. kaher, 211

B. nigra, 209

Broadbean or horsebean, 27, 40, 44, 93, 95,

116, 122, 178, 199

Broccoli, 159, 178

Bromegrass, 118, 119, 158, 173

Mountain, 175

Smooth, 42, 43, 113, 120, 152, 175

Bromus, 17

B. marginatuSy 18

B. polyanthus^ 18

Browallia, 179

Brussels sprouts, 157, 159, 178

Buckwheat, 2, 41, 90, 175

Buffalograss, 175

Buffelgrass, 21

Bugloss, 180

Burclover, 16

California, 175

Spotted, 175

Burdock, edible, 18

Buried seeds, 204, 205, 207, 209-213

Burlap bags (see Storage containers)

Bushclover, 209

Butterflyflower, 180

Buttonclover, 16, 175

Cabbage, 18, 27, 40, 49, 53, 59, 60, 64, 77,

88, 90, 157, 158, 159, 164, 178, 197

Chinese, 18, 40, 159, 179

Calceolaria, 180

Calendula, 180

Calliopsis, dwarf and tall, 180

Campanula, 158

Canarygrass, 175

Reed, 43, 175

Candytuft:

Annual, 180

Perennial, 180

Canna, 13, 180, 212

Canna, 7, 13, 212

Cannaceae, 13, 208

Cantaloup (see also Muskmelon), 97, 158,

178

Canterbury-bells, 180

Capsicum annuum, 169

Caraway, 179

Carbon dioxide and respiration, 79-80

Carbon dioxide - sealed in (see Sealed

storage)

Carbon-14 dating, 210-213

Cardboard seed containers (see Storage

containers)

Cardoon, 178

Carnation, 180

Carpetgrass, 175

Carrot, 18, 19, 27, 40, 49, 54, 59, 60, 90, 156,

157, 158, 159, 178, 197, 205

Cassia, 7

C bicapsularis, 206

C. multijuga, 206, 208

Catabolic process (changes), 91-93

Catalase activity, 198, 199

Cathedral bells, 180

Catnip, 13, 15

Cauliflower, 77, 157, 158, 159, 178

Celeriac, 159, 178

Celery, 40, 54, 158, 159, 178, 197, 209

Cellophane (see Packaging materials)

Waxed (see Packaging materials)

Cenchrus celiaris (Pennisetum ciliare), 21

Centaurea:

Royal, 180

Velvet, 180
PRINCIPLES AND PRACTICES OF SEED STORAGE 277

Centaurea, 15

Cereals, 7, 12, 20, 24, 81, 83, 87, 88, 145,

148, 202, 215

Chamomile, 210

Chard, Swiss, 159

Charlock, 210, 211

Chenopodmm.y 211

Chervil, 179

Chicory, 178

Chives, 159

Chlorinated rubber (see Packaging materials)

Chromosome 10, 8

Chromosome aberrations (changes), 7, 94,

95, 199, 201

Chrysanthemum, annual, 180

Civ chova le(igenana, 77

Cineraria, common, 180

Cleome, spiderflower, 180

Climatological data, 184-193

Use of, 182, 183

Clover, 16, 20, 23, 30, 42, 80, 90, 158

Kinds:

Alsike, 14, 15, 42, 43, 175, 209

Berseem, 175

Crimson, 33, 42, 45, 63, 65, 66, 67, 74,

75, 76, 80, 99, 149, 150, 153, 159,

164, 165, 166, 173, 175

Ladino, 42, 43, 90, 176

Lappa, 176

Large hop, 176

Persian, 176

Red, 10, 14, 15, 42, 43, 63, 90, 154, 173,

176, 204, 209

Rose, 42

Strawberry, 42, 176

Subterraneum, 42, 176

Suckling (small hop), 176

White, 14, 15, 33, 42, 63, 176, 209

Cockscomb, 180

Cocksfoot (orchardgrass), 115

Cockvine, thunbergia, 180

Cocoa bean, 83

Cold storage rooms, 129-134

Coleus, common, 180

Collards, 159, 178

Columbine, 180

Compositae, 15

Compressor capacity, 136

Condensing units, 136

Coneflower, 180

Conifers, 32

Controlling—

Fungi, 81, 89-91, 174

Humidity, 136-141

Insects, 81, 87, 88, 89, 126, 148, 174

Rodents, 81, 89, 126, 148, 160

Storage atmosphere, 133-141

Temperature, 133-136

Convolvulaceae, 13, 15, 202, 208

Convolvulus, 13

Coralbells, 180

Coreopsis, perennial, 180

Coriander, 179

Corn (maize), 2, 3, 7, 9, 11, 13, 18, 22, 30,

34, 35, 38, 41, 44, 45, 46, 47, 48, 53, 57,

61, 62, 80, 83, 88, 89, 90, 91, 93, 94, 95,

102, 103, 108, 112, 116, 117, 121, 122,

123, 143, 145, 146, 148, 149, 164, 170,

173, 197, 198, 199, 203

Kinds:

Dent, 34, 41

Field, 158, 176

Flint, 34

Popcorn, 41, 176

Sweet, 8, 34, 40, 59, 60, 146, 158, 159,

169, 178

White, 41, 91

Yellow, 41, 91

. Coronilla, 15

Cosmos, 180

Cotton, 13, 15, 16, 18, 21, 25, 36, 37, 44, 50,

63, 83, 89, 91, 93, 94, 123, 146, 154, 176,

205

Cotton bags (see Storage containers)

Cotyledon cracking, 51

Cowpea, 16, 90, 156, 176, 178

Cranesbill, 13

Crepif^, 95, 199

Cress, 30

Garden, 178

Water, 178

Crested dogtail, 10, 176

Crotalaria, 15, 176

Crotalaria, 15

Crownvetch, 15, 43

Crucifers, 23

Cucumber, 8, 18, 40, 53, 88, 94, 97, 105, 156,

158, 159, 164, 178, 197, 205

CucumAs i^ativus, 169

Cucúrbita pepo, 169

Cucurbits, 20

Cuscuta, 13, 15

Cyawopsis, 15

Cyclamen, 180

Cyperus rotundus, 21

Cypressvine, 180
278 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Cytisus candicans (C. monspessulanus),

206

C. scoparius, 206

Cytochrome dehydrogenase, 199

Cytological change, 94, 95

Dahlia, 180

Daisy:

African, 180

African lilac, 180

English, 180

Painted, 180

Shasta, 180

Swan river, 180

Dallisgrass, 42, 176

Dames rocket, sweet rocket, 180

Dandelion, 64, 178

Datura, 95, 199, 200

Decorticated seeds, 35

Dehumidification:

By desiccants, 138

By refrigeration, 138

Dehumidified rooms, 129-133

Dehumidifiers:

Rotary, 107, 111, 112, 138, 139, 140

Cylinder, 138, 139

Disc, 138, 140

Two tower, 107, 110

Delphinium, annual, perennial, 31

Desiccants:

Activated alumina, 138

Calcium chloride, 14, 16, 27, 63, 94, 123,

163, 168, 169

Avena sativa, 169

Bean, 16, 168

Cabbage, 27

Capsicum annuum, 169

Carrot, 27

Clover, red, 63

Cottonseed, 123

Cucumis sativus, 169

Cucúrbita pepo, 169

Eggplant, 157, 168

Lettuce, 27, 168

Onion, 27, 94

Oryza sativa, 169

Parsley, 27

Pechay (mustard), 27

Radish, 27

Raphanus sativus, 169

Rice, 123, 168

Sitao, 27

Solarium melongena, 169

Sweetclover, 14

Tobacco, 168

Tomato, 168

Vegetables, 27

Zea mays, 169

Zoysia japónica, 168

Calcium oxide (quicklime), 123, 167, 168,

169

Oryza sativa, 169

Phaseolus radiata var. pendalus

(= Vigna radiata), 169

Rice, 123, 168

Sweet com, 169

Tobacco, 168

Vicia sativa, 169

Viola tricolor, 168

Magnesium chloride, 123

Magnesium sulfate, 123

Phosphorus anhydride, 52

Silica gel, 107, 138, 168

Timothy, 168

Sodium chloride, 123

In sealed containers, 168-169

Desiccation, 50, 51, 208

Injury, 50, 51, 52

Desiccator, 94, 157, 163

Desmodium, 15

Desorption, 38, 49

Detection of—

Fungi, 174

Insects, 174

Deterioration, 14, 21, 23, 24, 25, 36, 86, 87,

199

Changes associated with, 91-95

Chemical effects on, 87-91

Definition, '6

Moisture content effect on, 35-^6, 38,

52-77, 113-121, 14^159, 164-169

Relative humidity effect on, 35-38, 195

Temperature effect on, 52-77, 113-121,

148-158, 195

Theories regarding, 197-201

Dewpoint, 38, 50

Dichondra, 15

Dichondra, 15

Dill, 179

Dioclea pauciflora, 206

Dolichos, 15

Dormancy, 14, 15, 19-21, 52, 121

Dropseed, sand, 176

Dryer:

Airflow diagram, 104, 105

Costs, 110, 111, 121
PRINCIPLES AND PRACTICES OF SEED STORAGE 279

Efficiency, 104, 111

Types:

Batch, 97, 102-106, 123

Bin, 96, 97-98, 102, 103, 121

Column, 103

Layer, 97, 98, 101, 102, 103

Rotary drum, 103

Wagon, 102

Continuous flow, 97, 106, 107, 123

Special purpose, 108, 114, 115

Dryeration process, 106, 108

Drying, principles of, 96

Drying capacity, 109-110

Drying rate, estimation of, 121-123

Fast, 121-123

Normal, 121-123

Slow, 121-123

Drying rates for—

Broadbean, 122

Garden pea, 121, 122

Lupine, 121, 122

Maize, 122

Oats, 122

Rape, 121, 122

Rye, 121, 122

Ryegrass, 122

Sugar beet, 121, 122

Wheat, 122

Drying seeds, methods, 4, 87, 95-123

Artiñcial drying, 97-123

Batch drying, 97, 102-106, 121

Bulk drying, 96-113, 121

Continuous flow drying, 97, 106, 107, 121

Dehumidified air, 96, 106, 107, 109

Desiccant drying, 14, 16, 96, 123

Freeze drying, 96, 108

Heated air, 96, 97-123

Heated dehumidified air, 96, 106, 109

In storage, 96, 97, 121

Infrared radiation, 108

Layer drying, 97, 101, 102, 121

Natural drying, 96, 97

Solar heat, 97, 98

Sun drying, 96, 97, 106, 148

Unheated air, 96, 97

Vacuum, 96, 108

Drying systems (batch dryers), 123

Double or two pass, 103, 104, 105, 123

Single pass, 103, 104, 105

Single pass reversing, 103, 104, 105

Suction, 103, 104, 105

Tunnel, 103, 105, 106

Drying temperature, 22, 113-121

Drying time, 113, 115, 116, 118-120

Effect of weather on, 121

Dusty-miller, 180

Echinochloa, 152

Eggplant, 18, 40, 54, 90, 157, 158, 159, 168,

178, 197

Eleusine, 152

Elymus glaucus, 17

Embryo:

Damage, 23, 24

Excision test, 170

Transplant technique, 92

Endive, 178

Endogeocarpic flora, 87

Enzymatic activity, 6, 7, 92, 198-201

Equilibrium moisture content, 37, 40, 50, 95

Average decrease per 10° C increase,

43-44

Determination method:

Dynamic, 39

Static, 39

Vapor pressure, 39

Of cereal seeds, 41

Of grains, 41

Of grasses, 42, 43

Of small seeded legumes, 42, 43

Of various crops, 37, 39, 40, 41, 44, 48, 49,

50, 80

Of vegetable seeds, 40

Equilibrium relative humidity curves, 41,

45, 46, 47

Euphorbiaceae, 208

Excess moisture, 10

Excessive drying, 51, 121

Extreme desiccation, 50-52

Farm storage (see Storage, types)

Fat acidity, 198, 201

Fennel, 179

Fescue, 43, 158, 173

Chewings, 25, 30, 31, 42, 43, 53, 62, 164,

176, 195

Creeping red, 42, 43, 62, 153, 164

Hair, 176

Ky. 31, 99

Meadow, 10, 42, 69, 176

Red, 53, 159, 176

Sheep, 176

Tall, 33, 42, 43, 164, 176

Festuca:

F. arundinacea, 84

F. pratensis, 18

F. rubra, 84
280 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Fiberboard (see Packaging materials)

Boxes (see Storage containers)

Cans (see Storage containers)

Drums (see Storage containers)

Field crops, 6, 15, 18, 26, 78, 88, 90, 159,

174, 175, 195

Field emergence, 12, 17, 153

Firebush, Mexican, 180

Flax:

Common, 10, 28, 36, 37, 44, 48, 80, 154,

176

Flowering, 180

Perennial, 180

Flowers, 1, 6, 15, 20, 26, 32, 62, 78, 88, 142,

146, 158, 174, 175, 179-182

Foil bags (see Storage containers)

Food reserves, depletion of, 78-79, 197,

198, 201

Food transport system (in embryo), 198

Forage, 1, 40, 146

Forest trees, 7

Foxglove, 180

Free radicles, 200

Freezing injury, 11, 34, 35

Fruit trees, 7

Fumigants:

Carbon tetrachloride, 91

Ethylene dichloride, 90

Ethylene oxide, 90

Hydrogen cyanide, 91

Isopropyl formate, 90

Methyl bromide, 89, 90, 91

Methyl chloroacetate, 90

Phosphine gas, 91

Tertiary butyl chloride, 90

Trichloroethylene, 90

Fumigation, 87-91

Fungi (molds), 2, 4, 12, 22, 23, 24, 25, 35, 40,

50, 78, 80, 81-88, 125, 171, 174, 196

Kinds:

Absidia, 86

Actinomycetes, 81, 86

Altemaria, 81, 86

Aspergillus, 82, 83, 85, 86

A. amstelodami, 83, 85, 87

A. candidus, 83

A. chevalieri, 83, 87

A. flavus, 83, 85, 86, 87

A. fumigatus, 86

A. glaucus, 84, 87

A. niger, 85, 86, 87

A. ochraceus, 82, 83, 85

A. parasiticus, 85

A. repens, 83, 87

A. restrictus, 83, 87

A. ruher, 83, 87

A. tamarii, 83, 87

A. terreus, 85, 86

A. versicolor, 83, 86

Chaetomium, 81

Cladosporium, 81, 87

Fusarium, 81, 86

Helminthosporium, 81

Mucorales, 87

Pénicillium, 83, 86, 87

P. citrimum, 86, 87

P. cyclopium, 86

P. funiculosum, 86

P. ruhrum, 86

Rhizopus, 81, 86

Sclerotium bataticola, 86

Streptomyces, 86

Torula sacchari, 87

Trichoderma viride, 81

Types:

Field, 81, 83, 86

Osmophilic, 83

Parastic, 81

Saprophytic, 81

Soil, 125

Storage, 50, 81, 83, 86, 87, 88, 125,

196

Xerophytic, 87

Fungicides:

Arasan, 90

Ceresan, 89

Ethyl mercuric chloride, 90

Mercurials, liquid organic, 89

Mercuric acetate, 90

Mercuric chloride, 89

New Improved Ceresan, 89, 90

Organic mercury compounds, 90

Organic sulfur compounds, 90

Semesan, 90

Sodium hypochlorite, 84

Spergon, 90

Volatile mercury compounds, 90

Yellow cuprocide, 90

Fungus:

Control, 81, 87-88

Detection, 174

Identification, 174

Gaillarida, 180

Gas storage (see Sealed storage)
PRINCIPLES AND PRACTICES OF SEED STORAGE 281

Genes:

Luteus 2, 8

Luteus 4, 8

Genetic effects, 7, 24, 35

Genetic stock, 1, 2, 94

Genetic variation, 24, 25, 29

Geraniaceae, 13, 15

Geranium, 13, 15

Geranium, 15

Germ plasm storage, 7, 127-129, 167

Germination (viability), 4-7, 10, 12-15, 18-

19, 22, 24-36, 50-77, 92-94, 113-121,

148-158, 164-169, 194-195

Of ancient seed, 201-217

Test:

Evaluation, 169

Methods, 169-170

Rules, 170

Geum, 180

Gilia, 180

Glass jars (tubes, bottles) (see Storage containers)

Globe amaranth, 180

Gloxinia, common, 180

Glutamic acid decarboxylase, 170, 199

Glycine, 15

Godetia, 180

Goodia, 3, 7

G. latifolia, 206, 208

Gossypium, 16

Gourds, 180

Grains, 2, 5, 22, 34, 35, 36, 37, 41, 50, 80, 81,

83, 86, 92, 102, 103, 106, 123, 148-149,

198

Gramma:

Blue, 176

Side oats, 176

Grasses, 2, 4, 9,10,11,17, 20, 23, 29, 33, 42,

43, 49, 58, 62, 81, 83, 121, 146,152, 153,

159

Guar, 15

Guidelines for storing seeds, 174-183, 194-

197

Handling and labor, 121

Hard seed, 7, 10, 13, 14, 15, 16, 17, 36, 202,

208, 213

Hardinggrass, 42, 176

Heat:

Input, 113, 115, 116, 118, 119, 120, 121

Load, 134

Sealer (see Sealer for)

Sealing requirements, 144

Heating during storage, 4

Heating time (effect on viability), 21-22,

113-121

Heliopsis, 181

Heliotrope, 181

Helium - sealed in (see Sealed storage)

Hemp, 30, 33, 52, 55, 56, 154, 164, 176

Herbs, 6, 15, 174, 175, 179

Hibiscus, 16, 181

Hibiscus, 16

Hollyhock, 13, 16, 181

Hot spots, 83, 86, 172, 174

Hot-water treatment, 89

Hovea linearis, 206, 208

Humidity control systems:

Desiccant type, 138, 139, 140

Refrigeration type, 138, 140

Hyacinth-bean, 15, 181

Hygroscopic equilibrium measurement, 39

Hygroscopic moisture absorption, 48, 49

Hygroscopicity, 39

Hygrothermograph, 172

Hypericum humifusum, 211

Hyssop, 179

Hysteresis effect, 37

Illumination effects, 77-78

Impaction damage, 4, 5

Impermeable seeds, 13, 14, 15, 16

In-transit seeds, 4

Care, 194

Hazards, 4, 5, 195, 196

Recommendations, 196, 197

Inbred lines, 8

Indiangrass, yellow, 176

Indigo, hairy, 15

Indigofera, 15

/. cytisoides, 206

Infrared light (see Light, effects on longevity)

Insects, 86, 88-89, 148, 174, 194

Control, 81, 87, 88, 89, 126

Detection, 174

Identification, 174

In stored seeds, 81, 86

Kinds:

Beetle:

Flat grain, 88

Khapra, 88

Sawtoothed grain, 88

Borer, lesser grain, 88

Cadelle, 88

Chalcid, 88
282 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Insects—Continued

Kinds—Continued

Grain moth, Angoumois, 88

Weevil:

Granary, 88

Rice, 88, 90

Ipomoea, 13, 15

Iris, Japanese, 181

Japanese lawngrass, 176, 178

Jerusalem or Maltese cross, 181

Jobs-tears, 181

Johnsongrass, 53, 176, 198

Juncus, 211

J. bufonius, 211

Jute, 90, 94, 147

Kale, 159, 178

Kenaf, 154, 164

Kennedya apétala, 206

Kohlrabi (knolkol), 157, 159, 178

Kudzu, 16, 176

Labeling of packages (see Package labeling)

Labiatae, 13, 15, 202

Laminations (see Packaging materials)

Lantana, 181

Larkspur:

Annual, 181

Hybrids, 181

Larva-infested seeds (see Seed)

Lafhynis, 15

Leek, 159, 178

Legumes, 7, 9, 10, 13, 14, 15, 16, 20, 23, 24

33, 42, 43, 62, 63, 146, 153, 154, 174,'

202, 208, 209, 213

Leguminosae, 7, 13, 15, 16, 202, 208

Lens, 16

Lentil, 16, 178

Lespedeza, 16, 173

Kobe, 33, 99, 100

Korean, 33, 176

Sericea or Chinese, 33, 100, 176

Siberian, 176

Striate, 176

Lespedeza, 16

L. sericea (now L. evenata (Dumont) D

Don), 100

Lettuce, 7, 11, 21, 26, 27, 28, 36, 37, 40, 49

53, 64, 65, 67, 68, 71, 72, 74, 75, 76^ 94,'

150, 157, 158, 159, 168, 173, 178 197'

198

Leucaena leucocephala, 206

Lifespan, 8, 9, 11, 12, 13, 14, 17, 19, 21, 26

27, 28, 33, 37, 174, 202-217

Light:

Effects on longevity:

Blue violet, 77

Diffused, 77

Infrared, 78

No light (darkness), 77

Orange yellow, 77

Ultraviolet, 77, 78

White, 77

Treatment:

Heat lamp, 77

Mercury quartz lamp, 77

Lilaceae, 16

Lily, 16

Linaria, 181

Lipids, 36, 200

Liquid refrigerants, 135

Lobelia, 30, 181

Lobelia cardinalis, 62

Locustbean, 83

Lolium multiflorum, 84

Long lifespans:

Circumstantial evidence, 210-217

Examples, 7-9, 202-213

Lotus, Indian, 13, 212, 213

Lotus, 7, 16

L. uliginosus, 206

Lovegrass, weeping, 176

Lunaria, honesty, 181

Lupine, 15, 16, 44, 116, 121, 122

Annual types, 181

Arctic, 211, 212

Blue, 25, 45, 99, 176

Russell hybrids, 181

White, 176

Yellow, 176

Lupinus, 7, 16, 158

Macromolecular water layer, 78

Maize (corn), 7, 9, 30, 53, 61, 116, 122

Malic dehydrogenase, 199

Mallow, 13, 16

Malt agar, 85

Malvaceae, 13, 16, 202, 208

Malvaceous plants, 15

Manifold, 97

Manilagrass, 176, 178

Marigold:

African, 181

French, 181

Marjoram, 179

Marvel of Peru, four-oclock, 181

Matricaria, 181
PRINCIPLES AND PRACTICES OF SEED STORAGE 283

Matricaria chamomilla, 210

Maturity:

Of seeds, 5-7, 17, 18, 19

Stages:

Dough, 17, 18

Immature, 9, 10, 14, 17, 18, 19, 34

Mature, 9, 11, 17, 18, 19, 21, 34, 202

Milk, 17, 18

Premilk, 17, 18

Maximum survival (see Old seeds)

Meadow foxtail, 176

Measuring devices, seed, 144

Measuring moisture vapor transmission,

163-164

Mechanical damage, 6, 9, 10, 12, 13, 22, 23,

51

Mechanical injuries, 6, 12, 22, 23, 24, 25

Mechanical refrigeration systems, 135-136

Medic, 23

Black, 16, 176

Medicago, 16

M. orbicularis, 206

MelilotuSy 16

M. alba, 206

M. gracilis, 206

Membrane damage, 200, 201

Metabolic processes, 200

Metal cans (see Storage containers)

Micro-organisms, 9, 49, 80, 81, 83, 87

Mignonette, 181

Millet, 103

Foxtail (common, German, golden, Hungarian, Siberian), 176

Japanese, 177

Pearl, 177

Proso, 177

Mimosa, 16

M. glomerata, 206

Mint family, 2, 13, 15

Moisture absorption, 48-50

Moisture-barrier containers, 108, 127, 164-

168, 194

Moisture-barrier materials, construction of,

167, 168

Moisture-barrier storage, 164-168

Moisture content equilibrium, 38, 39, 95

Moisture content of seeds, 4, 11, 21-23, 26,

30, 31, 34-57, 95, 158-159, 170-171, 194

Effect on storage life, 21-22, 35-38, 50-

77, 148-159, 164-166

Moisture effects, 35-52

Moisture equilibrium, 48. 49, ^0, 149

Determination method:

Dynamic, 39

Static, 39

Vapor pressure, 39

Moisture gradient, 96

Moisture levels for sealed storage, 158-159

Moisture movement in—

Seeds, 48, 49, 137

Storage structures, 137

Moisture-resistant structures, 129-134

Moisture stress, 5, 96

Moisture/temperature/atmosphere interactions, 66-77

Moisture test methods:

Air oven, 37, 38, 170, 171

Dry weight, 38, 95

Electric moisture meter, 170, 171

Wet weight, 38, 83, 95

Moistureproof storage, 148-159 (see also

Sealed storage in)

Monitoring:

Fungi and bacteria, 171, 172

Germination and viability, 169

Insects, 174

Relative humidity, 171, 172

Seed moisture content, 170, 171

Storability of seed lots, 172-174

Temperature, 172

Vigor, 170

Morningglory, 13, 15, 181

Multiwall bags (see Storage containers)

Mummy seeds, 201, 202, 213-217

Muskmelon (cantaloup), 49, 105, 159, 178,

205

Mustard, 30, 40

India, 159, 178

Mutagenic changes, 7, 94, 199, 200

Mutagenic compounds, 199

Ademine and its degradation products,

199

Adenosine deoxyribonucleic acid, 199

Ribonucleic acid, 199

Thymine, 199

Uracil, 199

Mutation rate, 200

Myosotis, 181

Myosotis, 158

Nasturtium, 181

National Seed Storage Laboratory, 65, 108,

127-131, 200

Nelumbo, 212, 213

N. nucifera, 207, 214
284 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Nemesia, 181

Nemesia, 158

Nepeta, 15

Nicotiana, 181

Nicotiana, 95

Nigella, 181

Nitrogen - sealed in (see Sealed storage)

Nomograph, 27

Normal seedlings, 5, 23, 65

Nymphaeaceae, 13, 202

Oatgrass, tall, 177

Oats, 4, 7, 8, 11, 12, 20, 30, 41, 83, 86, 90,

91, 100, 116, 121, 122, 158, 177, 199^

202, 203

Oenothera biennis, 199, 207, 209

0. lamarckiana (O. grandiflora), 199

Okra, 13, 16, 17, 40, 158, 178

Old seeds:

From a tomb, 212-214

From herbarium specimens, 6

Lifespans, 7-9, 201-217

Maximum survival, 202-217

Stored dry, 202-208

Yield from, 93-94

Onion, 7, 13, 27, 28, 31, 36, 37, 40, 49, 53,

56, 60, 64, 94, 95, 155, 156, 158, 'l59Í

164, 173, 178, 197, 199, 205

Effect of relative humidity on, 36, 49, 56,

59, 60

Welsh, 18, 40, 159

Onobrychis, 16

Open storage (see Storage, types)

Orchardgrass, 33, 42, 43, 115, 116, 122, 177

Ordinary storage (see Storage, types)

Oryza sativa, 169

Osnaburg bags (see Storage containers)

Overwinter storage (see Storage, types)

Oxygen - sealed in (see Sealed storage)

Package-filling equipment, 143

Package labeling, 147

Packaging materials:

Acetate, 146, 168

Burlap (jute), 50, 142, 143, 145, 147, 149,

162

Cellophane (waxed), 146, 156, 158, 161,

162, 167, 168

Chlorinated rubber, 156, 158

Cotton, 127, 142, 143, 145-147, 160-162

Fiberboard (cardboard), 142, 145-147,

160-162

Foil (aluminum), 142, 146, 149, 161, 162,

164, 168

Glass, 7, 51, 77, 142, 143, 146, 148, 149,

152, 154, 156, 157

Laminations, 142, 145, 146, 160-162

Linen, 156, 158, 162, 164-168

Metal, 65-77, 142, 143, 145-156, 158, 205

Moisture resistant, 159-162

Moistureproof, 148

Paper, 42, m, 127, 143,145-147, 149, 153,

156, 158, 160-162, 164, 167, 168

Plastic films, 127, 142, 144, 145, 159-162,

167

Mylar, 167, 168

Pliofilm, 161, 162

Polyester, 161, 162, 164, 168

Polyethylene, 143, 145, 146, 159-162,

164, 167, 168

Polypropylene, 167

Polyvinyl, 161, 162

Saran, 167

Porous, 147-148

Packaging of seeds:

Field, 145

Flower, 146

Turf grass, 146

Vegetable, 146

Pakchoi, 178

Pallet box (totebox) (see Storage containers)

Panicgrass, blue, 177

Panicum, 152

P. maximum var. trechoglume, 21

Pansy, 32, 181

Papaver rhoeas, 210

Parsley, 7, 27, 30, 32, 158, 159, 178

Parsnip, 7, 30, 40, 54, 64, 156, 159, 178, 205

Paspalum, 152

Pea, 8, 16, 30, 40, 44, 64, 83, 90, 93, 95, 116,

121, 143, 146, 158, 159, 199, 216, 217

Austrian winter or field, 9, 177, 204

Garden, 121, 122, 178, 204

Rose or crown, 216

Peanut, 7, 13, 18, 20, 21, 24, 36, 37, 44, 55,

56, 59, 60, 83, 86, 87, 155, 164, 177, 198'

201

Pechay (mustard), 27

Pennisetum, 152

Penstemon, 181

Penstemon, 158

Pepper, 40, 54, 88, 90, 94, 158, 159, 178, 197

Red, 205

Permeable seeds, 14, 15, 16

Pests and seed deterioration, 81-89

Pe-tsai (Chinese cabbage), 179
PRINCIPLES AND PRACTICES OF SEED STORAGE 285

Petunia, 30, 32, 181

Petunia, 158

Phacelia, 181

Phalaris arundinacea, 18

PhaseoluSy 16

P. radiata var. pendulus (Vigna radíala), 169

P. vulgaris, 23

Phenolase activity, 199

Phleum pratense, 18

Phlox, 181

Phlox, 158

Physalis, 181

Physiological changes, 92, 202

Physiological dormancy, 14

Physiological maturity, 5

Pine, 36, 37

Pinks, China, 181

Pisum, 16

P. umbellatum (P. sativum var. umbellatum), 216

Plantago, 211

Planting units, 2

Poa pratensis, 18, 84

Polygonum, 211

P. hydropiper, 209

Poppy,177, 210

California, 181

Corn, Shirley, 181

Iceland, 181

Mexican tulip, 181

Oriental, 181

Portulaca, 181

Potato, 157

Preharvest factors, 9, 10, 11, 22

Primrose, 181

Primula sinensis, 62

Protein:

Coagulation, 197

Structure changes, 197, 201

Provenance effect, 10

Psychrometer, 171, 172

Psychrometric chart, 137

Pueraria, 16

Pumpkin, 18, 97, 159, 179

Purpose of seed storage, 1-2

Pyrethrum, 28, 33

Radish, 4, 27, 29, 30, 40, 88, 157, 159, 173,

179

Japanese, 18

Rape, annual and winter, 44, 116, 121, 122,

177

Raphanus sativus, 169

Redtop, 42, 43, 177

Refrigerants, 134-135

Refrigerated dehumidified storage, 129-134

Refrigeration:

Of storage rooms, 133-136

System capacity, 136

Rehydration damage, 52

Relative humidity:

Curves, 41, 45, 46, 47

Determination by—

Electric hygrometer, 39

Hair hygrometer, 39

Psychrometric chart, 137

Thermometer, wet and dry bulb, 137,

171

Effect on seed moisture, 35-52

Relative storability index of—

Field crops, 175-178

Flowers, 179-182

Herbs, 179

Vegetable crops, 178-179

Removing seeds from cold storage, 141

Repair systems, 92

Rescuegrass, 45, 46, 47, 100, 177

Respiration, 49, 78-81, 200

During storage, 78-80, 86, 196

Factors affecting, 80

Heat, 78-80, 86

Measurement, 79-80

Preservatives for reducing, 80-81

Products, 79

Quotient, 80

Rhodesgrass, 177

Rhubarb, 179

Rice, 4, 20, 21, 36, 41, 63, 64, 91, 121, 123,

148, 149, 168, 177

Moisture content, 36, 48, 49

Storage life, 27, 148

Ricegrass, Indian, 177

Ricinus cambodgensis, 30

Rodents, 2, 81, 89, 148, 160, 194, 211, 212

Lemming, collared, 211, 212

Mice, 89, 160, 215

Rats, 89, 160

Squirrels, 89

Root crops, 9, 10

Rose campion, 181

Rosemary, 179

Roughpea, 15, 177

Rumex crispus, 207, 209

Rutabaga, 157, 159, 179
286 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Rye, 4, 7, 11, 20, 30, 33, 35, 42, 83, 90, 95

116, 121, 122, 158, 177, 199

Ryegrass, 115, 116, 122, 153, 158, 159, 164

Annual, 42, 43, 159

Italian, 177

Perennial, 10, 30, 37, 42, 43, 50, 53, 80,

115, 153, 158, 159, 177

Safe moisture content for sealed storage,

40, 51, 158-159

Safflower, 63, 65, 68, 69, 71, 72, 74, 75, 76,

150, 151, 154, 155

Sage, 179

Mealycup, 181

Scarlet, 181

Sainfoin, 16, 177

Salpiglossis, 181

Salsify, 179

Salvia spendens, 62

Saponaria, 182

Savory, 179

Scabiosa, 182

Scarified seed, 23, 24

Sealed storage, 28, 37, 57-77, 148-159

InAir, 28, 37, 57, 62-74, 77

Argon, 63-74, 76

Carbon dioxide, 57, 61-75, 79

Ethylene oxide, 63

Helium, 63-76

Nitrogen, 57, 61-75, 197

Oxygen, 57, 61, 62, 64

Vacuum, 52, 57, 62-76, 209

Sealer for—

Heat-sealable materials, 144, 145

Metal cans, 145

Vacuum and gas, 65, 145

Sealing metal cans, 145

Seed:

Defined, 2-3

Drying room, 108, 115

In soil, 21, 204, 205, 210-213

In-transit storage:

Historical background, 194, 195

Larva-infested, 88

Living organism, 2

Longevity, 6, 8, 17, 18, 19, 21, 22, 25, 26,

62, 201-217

Moisture content, expressed as—

Dry weight, 5, 9, 17, 38, 95

Wet weight, 38, 95

Packages (see Storage containers)

Size, 19

Storability, 9, 10, 17, 148, 172-182, 196

Storage structures, 123-142

Construction, 129-134

Structure, 2, 3, 4, 11, 15

Weighing devices, 144

Weight, 19

Seedbome micro-organisms, 171

Seedcoat, 13, 15

Permeability, 13-17

Selecting a dryer system, 109-110

Sensitive plant, 16

Sesame, 63, 65, 69, 71, 73, 74, 75, 76, 151,

154, 155

Sesbania, 16

Sesbania, 16

Setaria, 152

Shipping:

Hazards, 195-196

Recommendations, 196-197

Significance of seed storage, 1

Sinapis, 211

S. arvensis, 210, 211

Sitao, 27

Smilo, 177

Snapdragon, 32, 182

Sneezeweed, helenium, 182

Snow-on-the-mountain, 182

Sodium chloride - malt agar, 84

Solanum, 182

Solarium melongena, 169

Sorghum, grain and sweet, 4, 20, 22, 35, 41,

42, 45, 46, 47, 48, 50, 51, 52, 64, 65, 66,

69, 70, 71, 73, 74, 75, 76, 79, 91, 103,

145-149, 152, 173, 177, 203

Soybean, 4, 8, 15, 22, 24, 28, 29, 31, 36, 50,

55, 58, 59, 75, 76, 79, 91, 101, 102, 103,

145-149, 152, 155, 158, 164, 173, 177,

203

Field plantings, 29

Mechanical damage to, 24

Moisture content, 28, 29, 36, 44

Spinach:

Common, 23, 40, 59, 60, 158, 159, 179

New Zealand, 179

Squash, 19, 159, 179

Butternut, 19

Winter, 40

Stachys, 211

Stacking bags, 141

Static efficiency, 101

Static pressure, 99, 100, 101

Static pressures for drying:

Alfalfa, 99
PRINCIPLES AND PRACTICES OF SEED STORAGE 287

Blue lupine, 99

Crimson clover, 99

Fescue, Ky. 31, 99

Kobe lespedeza, 99, 100

Lespedeza sericea, 100

Oats, 100

Rescuegrass, 100

Soybean, 101

Wheat, 101

Statice, 182

Sfellaria, 211

S. media, 211

Sfipa viridula, 17

Stizolohium (now Mucuna), 16

Stocks, 182

Storage, types:

Bulk, 79, 124-126, 146

Bin, 50, 86, 96, 97, 124, 126

Silo, 50, 126

Commercial, 9

Controlled atmosphere, 57-77, 127-133

Controlled conditions, 9, 20

Controlled relative humidity and temperature, 129-133

Controlled temperature, 26-35, 52-56

Conventional, 5

Country elevator, 126

Farm, 9, 86, 126

Germ plasm, 7, 127-131

In transit, 4, 5, 194-197

Open, 7, 28, 57, 62, 79, 194

Overwinter, 14

Processor, seed, 126

Research, 127

Retail, 127

Sealed, 14, 16, 27, 28, 37, 57-77, 79, 90,

127, 194

Storage conditions, 9, 183-184

Favorable, 9

Unfavorable, 9

Storage containers:

Bags (envelopes), 66-70, 79, 88, 106, 124,

125, 126, 127, 142, 143, 145, 146, 147,

149, 150, 152, 153, 196

Acetate, 146

Burlap, 142, 143, 144, 145, 146, 147,

149, 152

Cellophane, 146, 158

Cotton, 89, 127, 142, 143, 144, 145-146,

147, 205

Osnaburg, 145, 147

Seamless, 145, 147

Laminated materials, 142, 145, 146,

147, 149, 164

Linen, 156, 158

Paper, 66-70, 127, 142, 143, 145, 146,

147, 149, 152, 153, 156, 158, 203,

206, 208

Polyethylene (plastic), 91, 127, 143,

144, 145, 146, 159

Rubber, chlorinated, 156, 158

Boxes:

Fiberboard (cardboard), 142, 145, 146,

147

Wood, 1

Cans:

Fiberboard, 142, 145, 146, 147

Metal, 65-77, 142, 143, 145, 146, 147,

148, 149, 150, 151, 152, 153, 154,

155, 156, 157, 158, 167

Drums:

Fiberboard, 142, 145, 146, 147

Metal, 142, 145, 147, 149

Jars (bottles, tubes):

Glass, 7, 52, 62, 77, 142, 143, 146, 149,

152, 154, 155, 156, 157, 203, 204,

205, 206, 208, 209,

Tank, metal, 1

Totebox (pallet box), 124, 125, 126, 146

Metal, 146

Wood, 146

Storage life, 7-26, 36, 37, 148, 174

Effect of seed moisture content on, 35-48,

52-77

Effect of temperature on, 26-35, 52-77

Storage period, 18, 183, 194

Storage potential, 4, 7, 8, 25, 27

Storage structures, 123-142, 194

Basic features, protection from—

Contamination, 124

Fire, 125

Fungi, 125

Insects, 124-125

Rodents, 124

Water, 124

Stored-product insects, 88

Strawberry, 205

Strawflower, 182

Stress damage, 5, 51

Stress test, 30, 170

Sudangrass, 42, 53, 90, 164, 177

Piper, 43

Sunflower, 2, 30, 90, 177, 182

Survival curve, 25-26

Swede, 157

Sweetclover, 14, 15, 16, 30

White, 14, 177, 205

Yellow, 42, 43, 177
288 AGRICULTURE HANDBOOK 506, U.S. DEPT. OF AGRICULTURE

Sweetpea, 15, 37

Annual, 182

Perennial, 182

Sweet-william, 182

Switchgrass, 177

Temperature:

Effects, 26^5, 113, 117

Above freezing, 20, 26-30, 149-158

Below freezing, 10, 11, 20, 29, 30-35,

55, 149-152, 154-157, 205

Gradient, 86

Temperature/atmosphere/moisture interactions, 57, 61-77

Temperature-moisture relationships, 52-57,

113, 117, 118, 119, 120

Testa, 15

Testing for—

Bacteria, 171

Fungi, 171

Germination, 169-170

Storability, 172-174

Viability, 169-170

Vigor (see Vigor tests)

Tetrazolium test (see Vigor tests)

Thermocouple, 172

Thermograph, 172

Thermometer, 171-172

Thlaspi, 2, 11

Thumb rules, 27, 37, 183

Thyme, 179

Timothy, 4, 12, 43, 50, 90, 115, 116, 122,

158, 168, 173, 177, 209

Tobacco, 30, 94, 146, 168, 177, 205, 209

Tocopherols, 200

Tomato, 18, 22, 28, 36, 40, 49, 54, 60, 90, 94,

97, 105, 157, 158, 159, 168, 179, 197

Dehydration of seeds, 22

Effect of relative humidity, 36, 56, 59, 60

Totebox (pallet box) (see Storage containers)

Treated seeds, 89-90

Trees, 20, 81

Trefoil, 16, 88, 158

Big, 177, 205

Birdsfoot, 43, 49, 177

Broadleaf, 42

Narrowleaf, 42

Trifolium, 7, 16

T. pratense, 206

T. striatum, 206

Triticum turqidum, 216

Turnip, 30, 40, 88, 159, 179

Tussilago fárfara, 31

Unscarified seed, 23, 24

Vacuum - sealed in (see Sealed storage)

Vapor pressure, 48

Variation among species, 7, 9

Variation between cultivars, 8, 11, 24

Vaseygrass, 177

Vegetables, 1, 6, 9,10,15, 18, 20, 26, 27, 32,

36, 37, 40, 45, 49, 55, 64, 78, 88, 90, 105,

142, 146, 155, 159, 174, 175, 178, 195,

197

Velvetbean, 4, 16, 18, 177

Ventilation of storehouse for—

Heat dissipation, 133, 141

Moisture dissipation, 125, 141

Verbascum blattariüj 207, 209

Verbena, 62, 182

Vetch, 16, 30, 158

Common, 177

Hairy, 15, 17, 43, 177

Hungarian, 177

Monantha, 177

Narrowleaf, 177

Purple, 177

Woollypod, 177

Viability (see Germination)

Viability curve, 25, 26

Viability test (see Testing for)

Vicia, 16

V. sativa, 169

Vigna, 16

V. radiata, 169

Vigor, 5, 6, 7, 14, 17, 18, 19, 25, 26, 29, 30,

57, 62, 92, 93, 170, 175

Vigor tests:

Cold, 170

Glutamic acid decarboxylase activity,

170, 199

Respiration, 170

Stress, 170

Tetrazolium, 170

Vinca, periwinkle, 182

Viola, 182

Viola tricolor, 168

Viruses, 81

Wallflower, 182

Walnut, 212

Warehouse cleanliness, 142

Water:

Absorption, 15, 36

Characteristics, 95-96

Water-curtain germinator, 65, 164, 165, 166

Watermelon, 8, 18, 40, 97, 158, 159, 173,

179, 205
PRINCIPLES AND PRACTICES OF SEED STORAGE 289

Weather:

Effects on drying, 10, 11

Injury, 10, 11

Weeds, 7, 20

Wheat, 4, 7, 8, 11, 20, 22, 24, 26, 27, 30, 35,

38, 45, 46, 47, 48, 49, 53, 64, 78, 79, 80,

83, 86, 88, 89, 90, 91, 95, 101, 121, 122,

158, 164, 173, 198, 199, 203, 204, 213,

215, 216, 217

Kinds:

Common, 177

Durum, 41,

Hard, 48,

Hard red spring, 41

Hard red winter, 41

Red Winter Speltz, 11

Soft, 48

Soft red winter, 41

Spring, 11

White, 41

2,000 years old, 213, 215

Wheatgrass:

Fairway crested, 177

Intermediate, 42, 152, 177

Pubescent, 178

Slender, 178

Standard crested, 152, 178

Tall, 178

Western, 178

Wild rye:

Canada, 178

Russian, 178

Willow, weeping, 212

X-ray, 200

Yield potential, 7, 17, 19

Zea mays, 169, 198

Zinnia, 182

Zoysia (see also Japanese lawngrass and

manilagrass), 178

Zoysia japónica, 168

U.S. GOVERNMENT PRINTING OFFICE: 1978 0—228-808