No. 124 

1961 

BIRCH SEEDS WILL GERMINATE 

UNDER A WATER-LIGHT TREATMENT 

WITHOUT PRE-CHILLING 

The seed of yellow and paper birches, like that of many other species, 

often exhibits delayed germination, which apparently is due to embryo 

dormancy.' Stratification is usually recommended for overcoming this 

dormancy before the seed is sown or before it is tested for germination. 

This involves a chilling treatment for 1 to 2% months, which is best 

done under controlled temperatures with the seeds layered in a moistened 

porous material such as sand or sphagnum moss. For testing germination, 

seeds are transferred after stratification treatment to flats or germinators 

held at about room temperature. Since the seeds must be kept moist, this 

requires either a special setup to provide the moisture, or frequent manual 

watering. The method is time-consuming, and the requisite facilities are 

not always available. 

Two reports in the literature led us to suspect that prolonged coldstratification and the customary procedure for testing germination could 

be bypassed by placing the seeds in water under suitable conditions of 

light. Wareing and Black had found that unchilled seeds of Betula 

pubescens will break dormancy in light.2 And Redmond and Robinson 

had reported that yellow birch seed coats contain a water-soluble substance that inhibits growth of the embryos, but that this substance loses 

its inhibiting properties when exposed to light.3 

1U. S. Forest Service. Woody plant seed manual. U. S. Dept. Agr. Misc. Pub. 654. 416 pp., 

illus. 1948. 

2Wareing, P. F., and Black, M. Photoperiodism in seeds and seedlings of woody species. In 

Physiology of forest trees (Ed., K. V. Thimann). 678 pp. New York. 1958. 

"edmond, D. R., and Robinson, R. C. Viability and germination in yellow birch. Forestry 

Chron. 30: 79-87. 1954. 
We accordingly undertook some simple tests to see whether unchilled 

yellow birch and paper birch seeds would break dormancy and germinate 

in water when exposed to artificial light. 

Procedure 

The work discussed here was all informal and exploratory, and was 

done in a piecemeal manner as time permitted over a 2-year period. There 

were no refined experiments, no rigorously controlled comparisons of 

variables. 

Mature strobili of paper and yellow birches were collected, air-dried 

for a day at room temperature, and stored at room temperature in paper 

containers. The first tests were started 1 week later. Other tests were 

conducted from time to time. The longest storage periods tested were 

14 months for paper birch and 26 months for yellow birch. Size of the 

test samples ranged from 100 to more than 1,000 seeds per species. 

All together, some 20 separate tests were made, involving more than 

15,000 seeds of each species. 

In the tests, the seeds were placed in petri dishes partly filled with 

tap water, and then exposed to one of several types of artificial light. 

The same light sources were not always available, but those used always 

were either fluorescent room light, fluorescent or incandescent desk lamp 

light, or a combination of these types. Lights were left on for either 8 

or 24 hours per day. Intensities varied from 80 to 420 foot-candles. In 

addition, more than 1,000 seeds of each species were tested in total 

darkness. 

A single test period was always 3 weeks or longer. Observations were 

made 3 times per week. Emergence of the radicle from the seed coat 

was accepted as evidence that dormancy was broken and germination 

had started. 

Results 

The results clearly demonstrated that unchilled seeds of paper and 

yellow birches will break dormancy and germinate when immersed inwater and exposed to artificial light. That is the basic finding from the 

tests. With immersion and illumination, some seeds of both species 

germinated in every trial, regardless of seed age (within the limits tested) 

or type of light. 

The test of immersed seeds in total darkness showed that light is 

essential to prompt breaking of dormancy and germination. In darkness, 

none of the yellow birch seeds and less than 1 percent of the paper birch 

seeds germinated in 30 days. With illumination, germinations as high 

as 95 percent for paper birch and 75 percent for yellow birch were 
obtained in 20 days. Germinations higher than 50 percent were obtained 

in many of the tests. The lowest germination in any water-light test 

was 11 percent. 

The 11-percent germination was on a small (100-seed) sample of 

paper birch seed after 4 months' storage. The light treatment was 350 

foot-candles, 8 hours per day, from a fluorescent lamp of the "daylite" 

type. Yellow birch seeds also germinated. rather poorly under this treatment. It is suspected that the daylite type of light is comparatively 

ineffective. However, this light type was used in only one test of each 

species, so the evidence against it is by no means conclusive. In all other 

tests involving fluorescent light, the "cool-white" type was used. 

The first germination in a test usually appeared in 3 to 8 days. The 

main surge of germination occurred at about 2 weeks (fig. I), and was 

Figure 1. - Unchilled paper birch seeds germinating in tap water 

in a petri dish. The light treatment was 80 foot-candles of coolwhite fluorescent room light for 8 continuous hours per day. Seeds 

had been in storage for 3 weeks. Photographed on the 15th day 

after treatment was started. 
completed, or practically so, within 3 weeks. When placed in the water, 

some seeds sank and others floated, but all seemed to germinate equally 

well. Fungi appeared on some seeds during the tests, usually at the point 

where the radicle emerges. Most such seeds did not germinate. 

Germination data from three selected tests are presented in table 1. 

The first two columns (tests 1 and 2) show some results for the two 

species under the same test conditions. The second and third columns 

(tests 2 and 3) show results for two samples of yellow birch seed from 

the same lot under different test conditions. These data merely represent 

some of the better test results; no conclusions as to species differences or 

effects of different treatments should be drawn from them. The data do 

show that fairly high, and probably almost complete, germination can 

be obtained by the immersion method. 

Table 1.-Germination data fros 3 selected tests 

* 

Samples of 1,000 seeds, placed in tap water and exposed to 

80 foot-candles of cool-white fluorescent room light for 8 continuous hours per day. Seeds stored 2 weeks before the test was started. 

No. of days 

after start 

of test 

** 

Sample of 1,000 seeds, placed in tap water and exposed to 

80 foot-candles of cool-white fluorescent room light for 8 continuous hours per day plus 320 foot-candles of incandescent desk lamp 

light for 24 hours per day. Same seed lot as in Test 2, but stored 

4 weeks. 

Fresh seed (less than 1 month old) usually germinated faster and 

in higher percentages than year-old or older seed. This might be expected, 

since birch seeds have been reported to lose viability rapidly after about 

18 months of open storage at room temperature.' The oldest seeds that 

were tested germinated as follows ( 1,000-seed samples) : 

3 11 1 -- 5 -- -- 8 

7 56 14 30 

11 87 22 6 1 

15 9 1 40 72 

19 92 43 75 

Germinat ion percent (cumulative) 

Yellow birch, stored 26 months - 36 percent. 

Paper birch, stored 14 months - 24 percent. 

These samples were exposed to 80 foot-candles of cool-white fluorescent 

light for 8 hours per day. 

Test No. 3 

yellow birch** 

TestNo.1 

Paper birch* 

TestNo.2 

yellow birch* 
Although the results of these tests do not justify conclusions regarding 

the comparative efficacy of different light treatments, it was observed that 

yellow birch seeds seemed to require more intensive light treatment than 

paper birch seeds for maximum germination. 

Discussion 

Two major points are brought out in this report: 

That seeds of yellow and paper birches will tolerate excessive moisture 

and will, in fact, germinate in a free water medium. 

That, under artificial light, seeds of these birches will germinate in a 

water medium without benefit of pre-chilling or other treatment to break 

dormancy. 

The practical implications of the above findings are that germination 

tests could be run on these two species (and perhaps others) by the 

simple procedure of placing the seed in water under suitable illumination. 

The customary prolonged cold-stratification could be bypassed, and no 

special germinators or frequent manual waterings would be required. 

The results reported here represent only the basic demonstration that 

untreated yellow and paper birch seeds will germinate in water under 

lights. Additional experimentation is needed to determine optimum light 

and temperature conditions, effects of age of seed, importance of fungi 

and, if necessary, how to control them, and relationships of other possible 

contributing factors, such as acidity of the water. 

-GEORGE YELENOSKY 

Research Forester, Laconia Research Center 

Northeastern Forest Experiment Station 

Forest Service, U. S. Dept. Agriculture 

Laconia, N. H.