July 15, 1921 
Effect of Length of Day on Seedlings of Alfalfa 
605 
Grimm alfalfa from that of other domestic varieties. Analysts, it is 
true, become very expert in identifying kinds of alfalfa seed by various 
pieces of evidence, including weed seeds, dust, and all incidental impuri¬ 
ties, as well as by color, size, and percentage of hard seed. But even 
seed analysts can not always make the critical determinations that are 
necessary. To the less well-trained person the seed of all varieties of 
alfalfa is very much alike. 
By sowing seed in the greenhouse, as was done in the experiment 
herein described, it is possible within three or four weeks to distinguish 
seedlings of one kind from another. If this method is used, it is highly 
desirable to have on hand viable seed of the most important commercial 
alfalfas and of at least one strain of Medicago falcata to be used in making 
the necessary comparisons of the seedlings. As a simple method to follow, 
it is suggested that the seed of the lot or lots to be identified be sown in 
rows in small flats in which adjoining rows are sown with seed of the 
Peruvian, Kansas, or some southern-grown common strain, Montana, 
Dakota, or some northern-grown common strain, Grimm, and a strain of 
M. falcata. For best results there should be three flats, each sown in 
the same way—one flat to be subjected to a short day, one to an abnor¬ 
mally long day, and one to the normal day as it exists at the time the 
tests are made. The normal day series may not be necessary, but there 
are some advantages in including it as a control. It is suggested that 
the day be shortened for the first series by putting the flat in a room with 
light excluded or in a box such as is shown in Plate 121, B, at 4 p. m., 
and leaving it in total darkness until 9 a. m. This gives a sufficiently 
long day for the necessary photosynthetic action and at the same time 
it is short enough to produce quick and striking differences in the seed¬ 
lings of at least certain of the varieties. The length of day may be 
augmented for the second series by using a tungsten bulb of 100 watts 
and a reflector as shown in Plate 121, B. It is suggested that the light 
be turned on at dusk and turned off about 11 o’clock p. m. This gives 
an abnormally long period of constant illumination, but such a period 
is helpful in producing striking results quickly. By the use of both the 
short and the long day the differences between the northern and southern 
alfalfas are better shown. The normal-day series adds evidence when 
the differences of the seedlings are studied. 
While it is not possible by this, method to distinguish between certain 
closely related varieties or strains such as the Grimm, Baltic, and Cana¬ 
dian variegated, these strains as a group can be positively distinguished 
from the common and other commercial strains by the general habit 
of growth and lack of uniformity of the seedlings. While the Turkestan 
seedlings can easily be distinguished from the Kansas by their height 
and lack of uniformity, they resemble those of the Grimm closely enough 
to make positive identification difficult. Since there is great diversity 
in the various lots of Turkestan seed that are imported commercially, 
