CLIMATIC REQUIREMENTS 



385 



Climatic Requirements. Alfalfa originated in a region with 

 an extremely hot dry climate. It seems to flourish in a hot climate 

 if it is also dry, but will not withstand a hot humid climate. The 

 common cultivated 'forms are limited in their northern extension by 

 winter killing. In general the northern limit of common alfalfa is 

 through South Dakota to central New York. However, there 13 great 

 variation in the winter resistance of different strains. This is well 



FIG. 168. Distribution of alfalfa in United States. (From U. S. Census, 1910.) 



illustrated by very extensive experiments conducted at Dickson, 

 North Dakota, in the years 1908-1909. The following data are 

 selected to illustrate the difference in hardiness : 



Hardiness of Alfalfa 



Source of seed Per cent surviving 



4 strains from Arabia 00.00 



5 strains from South America 00.40 



5 strains from Germany 16.90 



3 strains from Nebraska 23.60 



12 strains from Turkestan 27.70 



3 strains from Montana 34.60 



2 strains from Canada 54.60 



3 strains from Mongolia 66.50 



1 strain Grimm alfalfa (Minn.) 93.00 



1 strain Grimm alfalfa (Dakota) 97.20 



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