SPECIFICITY IN FERTILIZATION 215 



East and Park (191 7), however, demonstrate very 

 conclusively in Nicotiana that ''self-sterility is a condi- 

 tion determined by the inheritance received, but can 

 develop to its full perfection only under a favorable 

 environment." Thus at the end of a flowering period 

 and under conditions adverse to vegetative growth, a 

 certain amount of self-fertility may obtain in plants 

 that are entirely self-sterile at other times. The extent 

 of this change varies with the species; but the offspring 

 arising from such self-fertilization are self-sterile, a fact 

 that demonstrates the fluctuating character and envi- 

 ronmental origin of the self-fertilization to which the 

 oft'spring owe their existence. Such self-fertility does 

 not differ from other cases of suppression of characters 

 by environment. When this principle was borne in 

 mind the results of the extensive experiments became 

 intelligible and permitted a consistent genetic analysis. 



The view of Darwin that too great uniformity of 

 organization of the gametes operates to prevent success- 

 ful fertilization recurs in one form or another up to the 

 present time. Darwin cited the infertility that some- 

 times arises as a result of inbreeding as an analogous 

 phenomenon. It is obvious that Jost's and Correns' 

 interpretations also rest on the ground of too close rela- 

 tionship, assumed by them to be chemical, and related 

 by Correns to heritable genes. East assumes the neces- 

 sity for the secretion of stimulating substances by the 

 pistils for the growth of the pollen tube that can be 

 ''called forth only by a gamete that differs from the 

 somatic cells between which the pollen tube passes'' 

 (quoted from Stout, 1916). Morgan (1913) holds that 

 "the failure to self- fertilize, which is the main problem, 



