No. 531] THE GENOTYPE HYPOTHESIS 163 



both parents, segregation can not be proved, for the char- 

 acter breeds true. 



In fact the many results of experimental breeding dur- 

 ing the past few years have convinced me that De Vries's 

 general conception of this matter is incorrect. There may 

 be finally a considerable modification of our ideas regard- 

 ing the ultimate nature of Mendelian unit characters and 

 the exact meaning of segregation, yet the universal appli- 

 cability of a strict Mendelian system to interpret the 

 facts of heredity becomes more and more apparent every 

 day. And the point that I wish to emphasize is that 

 Mendelian inheritance is a genuine corollary of the geno- 

 type hypothesis if the latter is applicable to a popula- 

 tion in a state of natural hybridity. In my work with 

 maize where free intercrossing does occur I am convinced 

 of the existence of genotypes in a state of natural 

 hybridization. Furthermore, these genotypes can be iso- 

 lated by inbreeding. If it were true, then, that only 

 certain markedly discontinuous characters such as color 

 Mendelize, how could genotypes which differ from each 

 other in size characters be isolated? It is not expected, 

 however, that the statement that Mendelian inheritance 

 and the genotype hypothesis are interdependent will be 

 received without proof. Data that are believed to fur- 

 nish such proof are submitted here. 



When Mendelism was a new idea it was natural that 

 the behavior of many hybrids should be regarded as 

 irreconcilable to such a system of interpretation. The 

 earlier criticisms arose largely through the misconception 

 that dominance instead of segregation was its essential 

 feature. Later, when so many complex results from pedi- 

 gree cultures were fitted into a strict and simple Men- 

 delian notation, it was objected that the investigators 

 could by expert juggling of a sufficient number of factors 

 interpret according to their system any experimental 

 results they might obtain. Perhaps a few biologists re- 

 garded as a personal affront the gradual growth of the 

 idea that the facts of heredity were complex, but it is 



