July 15, 1921 
Effect of Length of Day on, Seedlings of A Ifalfa 
603 
grown in that State from original stock probably produced in southern 
latitudes, must therefore be regarded as a southern strain. The M. fal- 
cata was from the original stock secured by the Department of Agri¬ 
culture from eastern Russia. The Grimm strain is a hybrid between M. 
saliva L. and M. falcata that has been locally grown in northern latitudes 
for more than half a century. The Turkestan used in this case behaved 
much the same as the Grimm; but other lots will doubtless show con¬ 
siderable variation in this respect because of the great range in compar¬ 
ative length of day in different parts of Turkestan. The relation between 
locality of origin of the various alfalfas and their reaction to the day- 
night period is shown consistently. . 
The day-night experiments herein described throw light on some ques¬ 
tions that have perplexed students of alfalfa in this country. It is well 
known that the Peruvian variety in the Southwest continues growth 
later in the fall than the other commercial varieties and begins growth 
earlier in the spring. This fact led Brand 1 to conclude that it was able 
to grow at a lower temperature than the other varieties. He applied 
the term “zero point" to the minimum temperature at which growth 
takes place and classed Peruvian alfalfa as a variety with a low zero 
point. Prom subsequent investigations it was found that while Peruvian 
alfalfa continues growth late in the fall and begins it early in the spring in 
the Southwest and even as far north as Washington, D. C., it does not do so 
at Redfield, S. Dak., and other northern points. Oakley and Garver 2 3 were 
of the opinion that this phenomenon was due to the effect of very low 
temperature to which the variety was subjected in the North. It is 
quite clear now that this explanation is not the proper one, for although 
temperature bears an important relation to growth, it is its day-night 
relation that causes Peruvian alfalfa to'have a longer growing period 
than the other varieties in the South and to have the same or even a 
shorter growing period in the North. The northern varieties do not 
thrive under the short day of southern Arizona and California, but they 
can more than compete with the Peruvian under the long day of the 
North. At Redfield the growing season does not extend far into the 
short days of late fall or winter, neither does it begin in the spring until 
the long days have arrived. Low temperature in the fall checks the 
growth of Peruvian alfalfa in the North before the short days give it the 
advantage over Medicago falcata , Grimm, and other northern alfalfas. 
Low temperature also holds the Peruvian back in the spring until the 
long days arrive under which the northern alfalfas grow most rapidly. 
An explanation is now found for the fact that while Grimm alfalfa gives 
better yields than the Kansas in the North it does not do so as far south 
1 Brand, Charles J. Peruvian alfalfa: a new long-season variety for the southwest. U. S. 
Dept. Agr. Bur. Plant Indus. Bui. 118, 35 p., 11 fig., 3 pi. 1907. 
3 Oakley, R. A., and Garver, Samuel, medicago falcata, a yellow-flowered alfalfa. U. S. 
Dept. Agr. Bui. 428, 70 p., 23 fig., 4 pi. 1917. literature cited, p. 67-70. 
