116 INBREEDING AND OUTBREEDING 



the same conditions, but it is easy to see why lie held so 

 tenaciously to this view if one remembers the faith he had 

 in the effect of environment on organisms. Such a view 

 he deemed supported by the fact that crosses of selfed 

 lines with the intercrossed lines (also inbred, but to a less 

 degree) did not give as great increases in growth as 

 crosses of selfed lines with fresh stock from other local- 

 ities. His crosses between inbred lines did give noticeable 

 increases in growth, however, in many cases equaling the 

 original variety. This is well illustrated by Dirnithus, in 

 which the selfed line was crossed both with the inter- 

 crossed line and with a fresh stock. The ratio of each 

 crossed population to the selfed population in height, 

 number of seed capsules, and weight of seed, produced is 

 as follows: 



Selfed Selfed 



X X 



Intercrossed Fresh Stock 



HeigM, coimipared to selfed plants 100 :95 100 :81 



No. capsules oompared to selfed' plants 100 :67 100 :39 



Weight of seed compared to selfed plants 100 :73 100 :33 



With Darwin we still attribute the greater increase 

 of vigor in crosses of distinct stocks to a greater germinal 

 diversity, but we differ from him as to the way in which 

 that diversity is brought about. Be that as it may, great 

 credit is due Darwin for being the first to see it was not 

 the mere act of crossing which induced vigor but the union 

 of different germinal complexes. This he states clearly 

 in the following sentences ("Cross and Self -Fertilization 

 ia the Vegetable Kingdom," p. 269) : "A cross between 

 plants that have been self -fertilized during several suc- 

 cessive generations and kept all the time under nearly 



