No. 587] SHORTER ARTICLES AND DISCUSSION 709 



That we are dealing with a real measure of the relatively per- 

 manent differentiation of individuals, and not with merely tem- 

 porary differences due to growth, is indicated by the fact that 

 the correlations between a first and a third year are about the 

 same as those between a first and a second or a second and a 

 third. 



In other fields of plant industry such methods may be profit- 

 ably applied. For example Sievers 7 after discussing at some 

 length the question of the differentiation of belladonna plants 

 with respect to alkaloidal content, warns the reader that " the 

 investigation has hardly progressed far enough to yield any defi- 

 nite conclusions ' ' but says in summarizing his data : 



A considerable number of plants with leaves rich in alkaloids in one 

 season are found to have equally rich leaves in the following season. 

 Furthermore, they frequently manifest the same characteristics at the 

 various stages of growth during the season in comparison with other 

 plants. The same facts are true with regard to plants which bear 

 leaves with a low percentage of alkaloids. 



How much more definite is the information conveyed by the 

 simple statement that the inter-annual correlation 8 between the 

 alkaloidal content for 1911 and 1912 is 



r = . 513 ±.066! 

 Such studies as those by Stockberger on individual perform- 

 ance in hops 9 may be facilitated by the use of inter-annual corre- 

 lation coefficients. He gives only the extremes of his series of 

 individuals, but from these the correlations between ^vield per 

 hill for different years are : 



1909 and 1910 29 ± .17 .59 ± .13 - 



1910 and 1911 55 ± .13 .52 ± .14 



1909 and 1911 43 ± .15 .30 ± .18 



Such constants, deduced from materials which almost certainly 

 idonna Plants, " Jour. Agr. Bes., 1, 129-146, 1913. 



8 In computing this coefficient a number of inconsistencies in the data 

 ible were discovered. The constant as given is probably as nearly correct 



9 Stockberger, W. W., ' < A Study of Individual Perl 

 Prac. Amer. Breed. Ass., 7, 452-457, 1912. 



