THE FACTOR HYPOTHESIS AS APPLIED TO PLANTS 387 



a possible explanation, which, as will be recalled, did not long sur- 

 vive. Weismann oflFered in explanation his genninal selection, which 

 was soon discarded because it was beyond the possibility of experi- 

 mental testing. Aside from these two attempts to explain individual 

 variation no other comprehensive scheme had been presented. Biolo- 

 gists had simply recognized the fact of individual variation without 

 any conception of the mechanism. They knew that individual varia- 

 tion existed but had even stopped asking why it existed. 



The importance of this new theory, therefore, is obvious. It is 

 an ingenious explanation of the inheritance of quantitative characters 

 and of the existence of individual variations. Furthermore, the theorv 

 has not been developed through meditation, but has its basis in 

 scientific experiments. It is imaginative to a certain extent, of course, 

 as is every other valuable theory, but unlike most such theories it has 

 a substantial foundation, namely, Mendel's law. 



