July 15, 192 x 
Effect of Length of Day on Seedlings of Alfalfa 
607 
SUMMARY 
When seed of Peruvian, Kansas-grown common, Grimm, and Turke¬ 
stan alfalfa are sown in the early fall in the approximate latitude of Wash¬ 
ington, D. C., the seedlings develop characteristics that make it easily 
possible for the casual observer to distinguish one variety from another. 
Seedlings from spring sowings did not develop differences at Washington 
or in northern latitudes in the United States that would be apparent to 
the untrained eye. Seedlings from greenhouse sowings in December at 
Washington showed essentially the same distinguishing characters that 
were shown by early fall sowings in the field at Arlington. 
At first it was concluded that the temperature of the fall days was 
responsible for the striking differences shown by the alfalfa seedlings. 
However, the results of Garner and Allard's work on the effect of the 
length of the day on the growth of plants suggested the advisability of 
growing alfalfa seedlings in the greenhouse under artificially lengthened 
and also under artificially shortened days. 
Three series of small flats were sown with seed of Peruvian, Kansas, 
Grimm, and Turkestan alfalfas, and Medicago falcata 011 January 20,1921. 
One series was allowed to have the effect of the normal day, one was given 
the effect of a day shortened by the use of a light-excluding box placed 
over the flat at 4 p. m. and allowed to remain until 9 a. m., and one was 
given the effect of a day lengthened by turning on an incandescent 
electric light at dusk and turning it off at 11 p. m. The seedlings grown 
under the normal and the shortened day behaved essentially the same 
as those from sowings made in the early fall at Arlington. In height, 
erectness, and lack of branching the varieties ranged as follows: Peru¬ 
vian, Kansas, Grimm, Turkestan, M. falcata . Seedlings under the length¬ 
ened day showed striking differences between the varieties but behaved 
in practically the reverse order from those under the normal and the 
shortened day. At the end of the first month the seedlings of M. falcata 
and Grimm exceeded those of the Peruvian and Kansas varieties in height. 
They were also quite as erect and unbranched. 
From these experiments it is evident that it is the day-night relation 
of alfalfas and not their reaction to temperature that causes the develop¬ 
ment of marked differences between the seedlings of the various varieties 
when seed is sown at certain times of the year. By the proper control of 
the length of day, which can be accomplished in the greenhouse at any 
time of the year with little trouble or expense, and by the method used 
in these experiments it is easily possible to distinguish between seedlings 
of the commercial groups of alfalfas. The tests can be so quickly and 
easily made that the method is offered especially to Experiment Station 
workers and those engaged in alfalfa seed certification work as a means 
of assisting in the identification of the various lots of seed. 
4849 G °—21 -8 
