BIOMETRIC IDEAS AND METHODS 69 



(r = 0) under similar circumstances means that 

 the character studied is not inherited. But the 

 work of Johannsen and Jennings indicates that 

 in general there is no correlation (r = 0) between 

 parent and offspring within the genotype (i.e., 

 within the same pure line). Are we to conclude 

 then that there is no inheritance within the geno- 

 type — within a group of individuals where the 

 offspring breed absolutely true generation after 

 generation ? 



What a correlation coefficient deduced from a 

 parent-offspring correlation table which includes 

 a random sample of parents in general, or offspring 

 in general, really measures, is what may be called 

 the orderly heterogeneity of the material which 

 goes into the table. One gets out of the table by 

 way of the correlation coefficient merely a measure 

 of what was put into the table as raw data. If 

 the table includes individuals belonging to several 

 distinct genotypes, we may expect to get from it, 

 in many cases at any rate, a sensible correlation 

 coefficient between parent and offspring. But 

 this coefficient does not measure the intensity of 

 inheritance between parent and offspring with 

 reference to the character considered. It simply 

 measures the mutual interrelation (as to range and 

 distribution of variation) of the several genotypes 

 which went into the table. The coefficient 

 indicates, in other words, that there are certain 

 groups of individuals within the table which are 



