igo 



MENDELISM 



It does not matter much to him whether the colour 

 of a pea flower is purple or pink or white. But it 

 does matter whether the plant bears rather larger 

 seeds than usual, or rather more of them. Even a 

 small difference when multiplied by the size of the 

 crop will effect a considerable difference in the profit. 

 It is the general experience of seedsmen and others 

 that differences of this nature are often capable of 

 being developed up to a certain point by a process 



U.300 



U200 



B 

 1 100 



/ ^ \ ^ 



4= — ^ 



4 6 8 10 12 14 16 18 20 

 Weight of individual seeds 



Fig. 47. 



Curves to illustrate the influence of selection. 



of careful selection each generation. At first sight 

 this appears to be something very like the gradual 

 accumulation of minute variations through the corf- 

 tinuous application of a selective process. Some 

 recent experiments by Professor Johannsen of Copen- 

 hagen set the matter in a different light. One of 

 his investigations deals with the inheritance of the 

 weight of beans, but as an account of these experi- 

 ments would involve us in the consideration of a 

 large amount of detail we may take a simple 

 imaginary case to illustrate the nature of the con- 



