468 THE AMERICAN NATURALIST [Vol. XL VI 



The belief that any strain of alfalfa is made up of 

 many substrains with various steps of hardiness has 

 been arrived at largely by a priori methods. We find 

 that there are distinct morphological types of alfalfa 

 within a strain which breed true, and that with other 

 plants there are physiological types within any strain or 

 variety likewise breeding true. It is reasonable to sup- 

 pose that the same is true in regard to hardiness in al- 

 falfa. 



One of the Utah strains of the 201 series killed 42.8 per 

 cent, from a total of 76 plants, and at the same time this 

 strain of the 202 series sown from seed secured from 

 three mother plants killed but 3.5 per cent, from a total 

 of 131 plants. We have established at once a compara- 

 tively hardy alfalfa from one quite tender. With this 

 Utah alfalfa, as with several others, it is difficult to avoid 

 the conclusions that the strain is made up of many bio- 

 types, relative to hardiness, which show their indepen- 

 dent character even when no precaution is taken against 

 interbreeding 



We have also experimental evidence upon this point. 

 Alfalfas that were selfed in 1909 were from both hardy 

 and tender strains of alfalfa. A selfed Mexican plant 

 had progeny that showed absolute hardiness during the 

 winter of 1910-11, while the mother strain killed 24.5 

 per cent. Others of the selfed alfalfas acted in the same 

 manner, producing offspring behaving radically differ- 

 ent from the behavior of the parent strain. In some 

 cases progenitors of non-hardy strains were selected from 

 hardy strains. 



It seems likely then that any regional strain of alfalfa 

 as far as hardiness is concerned, is made up of biotypes 

 with different cold resistant qualities. An alfalfa of 

 this nature when moved to a colder region loses the rep- 

 resentatives of the tender biotypes leaving the hardy 

 ones for propagation. But this explanation accounts in 

 no measure for the absolute changes of hardiness which 

 some alfalfas must have undergone to have allowed the 



