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THE AMEBIC AN NATURALIST [Vol. XLVIII 



in the number of nodes, each with its accompanying leaves 

 and side branches. Above fifteen inches, however, the 

 principal growth in height consists in a lengthening of the 

 internodes and, consequently, a relatively greater produc- 

 tion of stem as compared with leaf tissue. In this phys- 

 iological correlation lies the core of the difficulty in breed- 

 ing at once for quality and quantity. The act of high pro- 

 duction within itself cuts down the quality of the product 

 by reducing the ratio between the leaves and the stems. 



This difficulty, moreover, occurs in the composition as 

 well as the percentage of the leaves. The correlation ex- 

 isting between the nitrogen content of the leaves and the 

 number of days required to mature a cutting is shown in 

 the following table : 



Quickly maturing varieties thus have leaves richer in 

 nitrogen than those which require a greater length of time 

 for completion of growth. When, however, we take the 

 average number of days required throughout the season 

 to mature a cutting for each plot and compare this with 

 the total seasonal yield we find a correlation of + .43. 

 Thus we are again confronted by a minus correlation be- 

 tween quality and yield which must be overcome if we 

 would make progress simultaneously in both lines. 



As further examples of antagonistic correlations, a few 

 instances may be taken from the data furnished by forty- 

 three plots of pure races of alfalfa grown during the sum- 

 mer of 1910. The correlation between height and percent- 

 age of leaves was again constant and marked. The results 

 here paralleled those found for the regional varieties. 

 Whereas yield was uniformly correlated positively with 

 both stooling capacity (av. No. stems per plant) and 

 height, it is interesting to note that there was also a uni- 



