THE AMERICAN NATURALIST [Vol. XL VIII 



curves are almost exactly alike, the greatest relative yield 

 of each being in the heated part of the summer after the 

 beginning of the water famine. In like manner, the 

 American and Turkestan varieties made similar relative 

 yield curves, that for the Turkestan being slightly above 

 the curve for the American strains. Here, however, the 



curves bend strongly downward in mid and late summer, 

 as if these types were much less resistant to the accumula- 

 tive effects of drought and heat. In fact, it would seem 

 that during the hot period included within the fifth cutting 



