November, 1921 



SCIENTIFIC AGRICULTURK 



87 



pectively in the generations 1 to 12 will be 

 as follows: 



It will be noted in the above table that 

 in 4 generations tlie proportion of indivi- 

 dnals in the lower yielding strain is almost 

 halved and that in the 12t]i generation so 

 lednced as to become practically negligible. 



The rapid increase in the higher yielding 

 line X is represented in Fig. 1. 



The conclusion may be drawn from the 

 above discussion that in populations con- 

 sisting of pure lines having different yield 

 values, those strains exhibiting the lower 

 capacities in this respect tend to become 

 automatically eliminated. It might be 

 shown also that the greater tlie difference 

 in yield the more rapidly will this elimina- 

 tion proceed. Although it has been a mat- 

 ter of colnmon knowledge among agrono- 

 mists that mixtures of oats and barley, for 

 instance, fail to maintain their original pro- 

 portions on being grown from seed mix- 

 tures taken from successive crops, this pro- 

 perty of pure line populations has not been 

 previously emphasized as a self-regulating 

 factor in maintaining the oiiginal quali- 

 ties of a superior strain when degressive 

 mutations take place. 



Fig. 1.- — Graph showing the number of individuals in Line X per single indi- 

 vidual in Line Y in 12 successive generations, the initial proportion of plants 

 being 100 to 1 respectively. 



