No. 531] GENOTYPE CONCEPTION OF HEREDITY 143 



make hypotheses as to the nature of heredity and varia- 

 bility. Darwin has somewhat exaggerated the scientific 

 value of breeders' testimonies, as if a breeder eo ipso 

 must be an expert in heredity. As to the principle of 

 pure lines it has been occasionally vindicated by Her- 

 man authors, e. g. y K. v. Riimker, that pure line breeding 

 is a thing old and well known. This is quite true ; nearly 

 sixty years ago L. Vilmorin not only emphasized in a 

 lucid manner the importance of pure breeding, but he 

 even tried a little to use his experiences theoretically. 

 But it can not be denied that the principle of pure lines, 

 as a true scientific analytical implement, as an indispen- 

 sable method of research in heredity — not merely as a 

 questionable and, at any rate, unilateral and insufficient 

 method of practical breeding — is a novelty from recent 

 years. Had this analytical principle been used in the 

 times of Darwin, or had it even been appreciated in due 

 time by the biometric school, certainly the real bearing 

 of selection might long since have been rightly under- 

 stood also by the practical breeders of pure strains. 



The genotypes may then be characterized as some- 

 thing fixed and may be, to a certain degree, parallelized 

 with the most complicated molecules of organic chem- 

 istry consisting of " nuclei" with a multitude of "side- 

 chains. ' ' Continuing for a moment such a metaphor, we 

 may even suggest that the genes may be looked upon as 

 analogs of the "radicals" or "side-chains." All such 

 ideas may as yet be premature; but they are highly 

 favored by the recent researches of Miss Wheldale. 



The fixity of a genotypical constitution in question is 

 the conception arrived at by Mendelian and pure line 

 work. Hence there is a discontinuity between different 

 genotypes. This discontinuity has been energetically 

 contested by several biologists, among whom Woltereck 

 roay be pointed out as an important representative. In 

 his very interesting report on experiments with Daph- 

 nias, Woltereck indicates, as said above, that selection 

 was as yet ineffective; moreover he describes a case of 

 discontinuous alteration of type (mutation), and his ex- 



