No. 551] THE MENBEL1AN NOTATION 



643 



Mendel's Law and Gr Alton's Law 

 The above statement leads into a discussion of Men- 

 del's law of heredity as compared with Galton's law, for 

 in itself it is almost a statement of the difference. As 

 Bateson was the first to emphasize, organisms inherit 

 from parental germ cells only, therefore a law of an- 

 cestral heredity is a fallacy and a misnomer. The 

 simple illustration that of two individuals alike in ap- 

 pearance one is homozygous for a character and the 

 other heterozygous for the same character, shows the 

 superficial reasoning that leads to the correlation coeffi- 

 cient as a measure of heredity. Parental and filial pop- 

 ulations may show correlation, but that is only a matter 

 of averages and not a measure of the inheritance. 



Professor Castle has recently disclosed the probable 

 Mendelian basis for Gait on 's data on coat color of 

 Bassett hounds by showing the inheritance of tricolor 

 coat in guinea-pigs, yet he makes the surprising state- 

 ment that "as regards height, however, and other size 

 characters, Galton's law is quite as good a basis for pre- 

 dicting the result of particular matings as is Mendel's." 

 The arch priest of biometry, Karl Pearson, does not 

 claim that Galton's law can predict the result of individ- 

 ual matings. Similarly, Mendel's law predicts only by 

 averages. It says that where DR meets DR, there will be 

 on the average WD.WR.IRR produced. Where the 

 classes are larger the prediction in increasingly compli- 

 cated. But the prediction is as good for size characters as 

 for qualitative characters of the same complication. And 

 there are such qualitative complications, as is manifest by 

 Castle's formula of A A CC UUIIYYBBB rBrEE for a 

 wild rabbit's coat color. The difference between Gal- 

 ton's law and Mendel's law is that the true criterion of 

 the germ plasm of any individual is its breeding power 

 and not the somatic appearance of its back ancestry. 

 This is as true of size characters as of any other char- 

 acters. 



