Evening times-Republican. [volume] (Marshalltown, Iowa) 1890-1923, 1920-04-10
Length of Day
Controls Time
of EruitingI

| growth OF most kinds OF plants, ana
altho the summer sun might occa-
sionally become too hot, they have
understood that It could not cause
any injury except perhaps the Injury
due to burning. a recent discovery
by w. w. Garner and II, A. Alard'
OF the bureau OF plant industry, de-
partment of agriculture, shows that
entirely apart from any effect or
burning. II Is possible for plants to
have too much daylight or. I'm other
words. too many hours OF daylight In
comparison with the number OF hours
of darkness. Too long day ms well
las too short n day will prevent many
kinds -of plants from ever reaching
their stage of Towering and friuting'
Furthermore, the intensity of the
light has very much less significance
upon the growth of the plant than
has usually been supposed. Green
house experiments prove that the
Towering and fruitinS period Of
practically any plant can be made to
take place at any time of the year by
darkening the greenhouse in the
morning and evening If the day is
too long. or by lengthening the day
by artificial light If the day Is too
! short. This new theory OF controll-
ing Towering and fruiting OF plants
undoubtedly will be used by florists
and other greenhouse operators. For
example, violets bloom only during
the comparatively short days of
spring; but If violet plants are COW
cred with light proof boxes at night
and not uncovered until the sun is
about half an hour high each morn
| ing during the summer time. violcts
can be forced TO bloom again in the :
summer. Spring flowers and spring
crops happen to be spring flowers
and spring crops because the days at
he season of their Towering and
fiuiting have the proper number of
hours of daylight Correspondingly,
the early summer flowers and crops
must have a longer period of day
light. This has been proved as to
n large number of plants, and the
scientists believe that the principle
will hold thruout the higher forms of
plant life. and that i is prohah ly APP !
plicable To animal life as well
Reproduction Depends on Day.
lic pldnl can not Htlttln StNudl
reproduction. il has been shown. ex-
cept when it is exposed to a favor
able length Of day. The require
ments.. however differ widely with
species and varieties. But a length
or day that is unfavorable to repro
duction ma! he favorable to growth. |
Under that condition, the plant con-
tinues its vegetative development |
protusely and indefinitely without
bearing fruit. \ length of day may
be found that is favorable both to
sexual reproduction and vegetative
growth. That tends to bring about
the, "ercr-hearing' type Of fruiting.
BY employing dark chambers to
shorten the period of light and arti-
| fetal lights to extend it. scientists of
the department have shortened or
heightened the life. cycle of plants.
! haye made, some sof them complete
two cycles in ii single season, have
brought others into flower and fruit
months in Advance of their regular
time and. with still others. have
greatly delayed and even completely
prevented fruiting.
Long series of tests have been
made with soy beans, tobacco, wild
astor. climbing hempweed. beans,
ra@weed, radish, carrot lettuce, hib-
iscuS. cabbage, violets, goldenrOd
spinach, cosmos. iris. bcggartick
Luckwheat. and various other plants
y test made with Biloxi soybeans i
will show how the principle works
For the test plants the day was
hn h,. l.,
they were exposed to the light only
from 10 O'clock in the morning till 8
O'Clock in the afternoon. They were
first placed In the dark house on
May 20. Control plants, otherwise
treated exactly like the test plants.
were left exposed to the light from
dawn till dark. The first blossoms
appeared on the dark house plants
on June l6. No blossoms appeared
Until September on the plants that
were left in the light all day. But |
the dark house plants averaged only
8 or ! inches high, while. the plants
that were left in the light. all day
grew to an average height Of 81 or
So inches.
rhcse plants required q short day
and a long night for Towering and |
seed bearing. In tests with other
plants, just the opposite was found
to be true. The plants that were
left in the light all day did not grow |
luXuriantly, but produced flowers !
and seed, while those that were kept |
III the dark part of the day made |
abundant growth, but produced no |
seed or else were greatly retarded in |
producing seed
Temperature Has Little Influence.
temperature appeared to exert no |
Influence in these tests. The results
were the same. even when the tenn
perature was higher in the dark house
than on the outside. Another strik-
ing illustration of the relative unim-
portance OF temperature is the fact |
that plants kept in the dark for a
part of the day underwent, in mid
summer, the changes that in nature
come in the. fall and have always
been attributed to lower tempera-
lures. This. also. was true even when
the dark houses registered a higher
temperature than that Of the out
side summer atmosphere.
The results obtained by artificially
extending the period of light are just
as interesting as those obtained by
artificially shortening it. The arti- |.
fetal illumination, in test with iris.
was so arranged as to give Is hours
of continuous light in greenhouse
during the winter Control plants
were kept in n similar greenhouse
with no artificial light. The test was
begun on October 20, 1919. In the