CHAPTER VII 

 NEO-MENDELISM {Continued) 



5. Inheritance of quantitative characters. — 

 This phase of the factor hypothesis, if true, is of funda- 

 mental importance not only to genetics but to general 

 biology. It is based upon the conception of cumula- 

 tive factors, and as it is presented it will be realized 

 that it throws Ught not only upon numerous breeding 

 experiments but also upon variation in general, which 

 means evolution also. A cumulative factor was defined 

 as one which, when added to another similar factor, 

 affects the degree of development of the character. 



It will be recalled that Correns crossed red and 

 white strains of Mirabilis and obtained pink hybrids. 

 The suggested explanation of this result was that a 

 single dose of the re(J determiner gives pink while a 

 double dose gives red. When Correns inbred these 

 pink hybrids, he obtained the result presented in fig. 8,' 

 that is, I red, 2 pink, i white. This result is obvious 

 and the mechanism is plain. 



With this diagram in mind we shall consider some of 

 the experiments of Nilsson-Ehle (2) at the Swedish 

 Experiment Station. He crossed two strains of wheat 

 with red and white kernels. The Fi individuals had 

 light red kernels, which of course suggests a repetition of 

 the situation shown by Mirabilis in the experiment of 

 Correns. The F2 generation, however, showed a very 

 different result. The reds and whites appeared in the 



63 



