214 PROBLEMS OF FERTILIZATION 



but he agrees as to the chemical foundation of the 

 phenomenon; each stuff depends on a gene in the germ 

 plasm, and it is the combination of stuffs that is formed 

 by each gametic union that is specific or individual. 

 He thus bases the phenomenon on line combinations of 

 stuffs. Correns must receive the credit of being the first 

 to relate self-sterility to cross-sterility within the species. 

 Stout (1916, 1917) has carried out a very elaborate 

 and finely executed series of experiments on Cichorium. 

 In a combination similar to Correns he made sixty- 

 nine back crosses of offspring on a known parent, of 

 which thirty-five were fertile and thirty-four sterile, 

 thus agreeing with Correns' ratios. He observes that 

 "the range of variation in the actual fertility, how- 

 ever, is so great in both cases that the grouping of 

 all offspring into two classes with reference to cross- 

 fertility with a parent is of little significance." He 

 confirms in general the relation of self- and cross- 

 sterility within the species which Correns discovered, 

 but believes that Correns' conception of line stuffs is 

 fundamentally wrong. As demonstration of this he 

 shows that self-fertile plants may arise in certain 

 crosses between self-sterile individuals; when these 

 self-fertile offspring of the F x generation were selfed he 

 obtained forty-one self-sterile and thirty-nine self-fertile 

 plants in F 2 ; in F 3 of selfed plants, self-fertile and self- 

 sterile plants arose again in about equal numbers. He 

 also shows that neither self-sterility nor self -fertility is a 

 dominant or recessive character in any consistent sense, 

 "and there is a very irregular and sporadic inheritance 

 both of the character as such and the degree of its 

 expression, if the two can in any sense be separated." 



