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THE AMERICAN NATURALIST [Vol. XL VIII 



iar complex of hereditary physiological forces, each sensi- 

 tive in its own manner and degree to the impinging ex- 

 ternal stimuli, it is not surprising that the resultant (the 

 gross climatic reaction) should be sharply different in the 

 several varietal groups. 



The unequal effects upon the vegetative growth of the 

 different varieties brought about by the climatic changes 

 which occurred during the course of the summer may be 

 exhibited by calculating the place variation in yield. This 

 is best shown by correlating the first with each of the fol- 

 lowing cuttings throughout the season. The result is a 

 definite curve, beginning and ending high with a strong 

 sag in the middle. 



Correlation. + !75 n ± 2 .04 +-68 n ±?.05 + S ± .09 +!36±.09 + !58 n ±.07. 



These figures indicate the presence of some disturbing 

 factor which reached its maximum intensity during the 

 fourth and fifth cuttings, and to which certain plots were 

 more sensitive than others. The average period through 

 which the growth of these two crops extended was June 22 

 to August 27. The fact that these dates include the hottest 

 portion of the summer strongly suggests temperature as 

 the disturbing factor. 



The mean maximum temperature, mean minimum rela- 

 tive humidity and the correlation between yield and water 

 supplied are given in the following table : 



TABLE II 



