602 
Journal of Agricultural Research 
Vol. XXI, No. 8 
favor of the Peruvian. Ten days after the seedlings emerged some 
differences were evident. These differences increased rapidfy, and on 
March 3 typical plants from each series were removed to the laboratory 
and photographed. The photographs tell the story. (PI. 116-121, A.) 
The seedlings given the normal day which, at this time, was of about the 
same length as the average October day, behaved in practically the same 
manner as those grown in the greenhouse from December sowings and 
the same as those produced from early fall field sowings at Arlington. 
The seedlings under the light of the short day—from 9 a. m. to 4 p. m.— 
exhibited the same varietal differences as those under the normal day; but 
the differences were accentuated, as the photographs indicate. The seed¬ 
lings grown under the long day—under the day with added illumination 
from twilight until 11 p. m.—behaved quite differently from the others. 
The seedlings of M. falcata instead of being short and rosettelike in 
habit, grew erectly with no branching and attained practically as great 
a height as any of the seedlings in the three series, up to the time photo¬ 
graphed. Later on, however, these seedlings were overtaken by the 
other varieties. The Grimm and Turkestan behaved similarly to M. 
falcata; and, whereas the Peruvian and Kansas seedlings were erect, 
they failed to keep the relative position with regard to height which 
they held under the normal and short day. In brief, the abnormally long 
day produced almost a reversal of order in the matter of height and to 
a degree a reversal in the habit of growth. The temperature of the 
greenhouse in which the tests were conducted ranged from 50° to 6o° P.; 
and while the electric light under which the long-day seedlings were 
placed produced a slight rise of temperature, this did not quite equal the 
temperature inside of the dark chamber and is considered insignificant so 
far as its effect on the general results is concerned. The dark chamber 
was a wooden box 3 by 3 by 3 feet, of -Ms-inch material with light-tight 
ventilators, top and bottom. (PI. 121, B.) With the factor of tempera¬ 
ture virtually eliminated, it seems fair to conclude that the phenomenon 
of difference in habit of growth of seedlings of alfalfa varieties obtained 
both in the field and greenhouse experiments herein described was due, 
for the most part, to the day-night relation of the varieties. 
REACTION OF VARIETIES AND SPECIES TO LENGTH OF DAY IN ACCORD- 
ANCE WITH REGIONAL DEVELOPMENT 
The evidence is quite clear that Peruvian alfalfa grows best in com¬ 
parison with others under the relatively short day while the strain of 
Medicago falcata used in these experiments produces its best growth 
under the relatively long day. It also seems to be true that the Kansas 
strain resembles the Peruvian in its day-night relations while the Grimm 
resembles the M. falcata. This is not surprising. The Peruvian variety 
was developed near the Equator where the days are always about 12 
hours long. The Kansas, which is the result of several seed generations 
