The Garden Magazine, October, 1920 
99 
on the dark-house plants on June 16. On the plants that were 
left in the light all day no blossoms appeared until September^ 
or 80 days later. But, while the dark-house plants averaged only 
6 or 7 inches in height, those that were left in the light all day 
grew to an average height of 57 or 58 inches. This test proved 
conclusively that the Soy Bean requires a short day and a long 
night for flowering 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 seeds, while those 
that were kept in the dark a part of the day made abundant 
growth. The latter, however, were either greatly retarded in 
producing seed or produced none at all. Temperature more- 
over, appeared to exert no influence in the tests. A striking 
illustration of the relative unimportance of temperature lies 
in the fact that plants kept in the dark for a part of the day 
underwent, in midsummer, the changes that naturally come in 
the fall and that, heretofore, have been attributed to lower 
temperatures. This was true even when the dark houses 
registered a higher temperature than the outside temperature. 
Equally interesting were the results obtained by artificially 
extending the period of light instead of shortening it. In a test 
with Iris, for example, the artificial illumination was so arranged 
as to give 18 hours of continuous light in a greenhouse during 
the winter, a large number of tungsten filament incandescent 
lights being used for the purpose. Control plants were kept in 
a similar greenhouse with no artificial light. This test was be- 
gun on October 20, 1919. In the greenhouse where daylight 
was supplemented with electric light the plants made rapid 
growth, soon attained normal size and produced blossoms on 
December 24. On the other hand, the plants in the greenhouse 
where no artificial light was used, remained practically dormant 
and showed no tendency to blossom as late as February 12, 1920, 
notwithstanding that this greenhouse was kept at the same 
temperature as the other. 
Another test was conducted with the seed of Spinach, which 
was sowed November 1, 1919, and came up in both green- 
houses on November 6. The plants in the control house, 20 to 
25 in number, grew very slowly, producing low, compact, leafy 
growths or rosettes, and gave no evidence of blossoming as late as 
February 12, 1920. The plants in the lighted house, however, 
elongated very rapidly, soon developed flower stalks, and all blos- 
somed in the period between thedates of December8and23, 1919. 
These continued to elongate more or less throughout January and 
February, 1920, blossoming and shedding pollen continuously, 
thus becoming in effect “ever-blooming” plants. 
The advance in agricultural practice which may come through 
this new discovery will have to be brought about largely by 
plant breeders and other crop specialists. For instance, it will 
prove of material significance in the future planning of cropping 
systems for different regions, especially where consideration of 
new crops from different latitudes is necessary. The new 
principle undoubtedly explains the erratic behavior which has 
been observed with many crops when they are shifted to 
different latitudes, and may also clear up the conflicting re- 
sults of variety tests and field tests conducted with the same 
crops in different regions. 
The experiments have shown, for instance, that Ragweed 
requires for flowering a stimulus that is afforded by the shorten- 
ing of the days and lengthening of the nights. It does not 
come into flower until the period of daylight falls below 1 5 
hours. In the latitude of Washington D. C., that comes about 
July 1. But if Ragweed should be taken to northern Maine 
and planted, the plants would not experience a proper length 
of day until after August 1 and. though the vegetative growth 
might be very rank, they could not mature seed before killing 
frosts intervened. The long days, therefore, might make it 
impossible for Ragweed to perpetuate itself in that latitude. 
On the other hand, plants that get their flowering stimulus from 
a long day could not perpetuate themselves through seed forma- 
tion at the equator, where the day never exceeds 12 hours. 
This principle seems to clear up the puzzling fact that many 
plants grow most luxuriantly near the northern limit of their 
range. The long northern day allows them to attain their 
maximum growth before the shorter day intervenes to check 
vegetative growth and start the reproductive process. 
RADISHES ARE DECIDED LOVERS OF LIGHT 
this is conclusively proved by the response of plants (on left) 
raised under usual conditions, and the marked dejection of those 
(on right) whose light supply was restricted to seven hours daily 
AND THE SOY BEAN IS JUST THE REVERSE 
The almost tropical abundance of the plants (on right) matured in 
comparative night (their daily light-exposure was only from ten to 
three) convincingly indicates the magical properties of darkness 
