448 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



Particular idioplasmic elements of the nucleus of the sex cells 

 must, it would seem from the occurrence and only sporadic inherit- 

 ance of self-sterility, have less direct influence on the possibility 

 of successful fertilization than has the individually developed 

 epigenetic cell organization of the parent individual and the grade 

 of relative constitutional differentiation that may arise in the 

 development of the two sexes even on a single individual. 



Inbreeding and self-fertilization are often highy beneficial, as 

 Darwin noted. Burck ('08) argues at length from good grounds, 

 as noted above, that self-fertilization is the most effective means 

 of reproduction. The evidence is clear that self-sterility prevails 

 in plants that are necessarily cross-bred and that when self- fertile 

 plants do appear inbreeding does not decrease the fertility. Speak- 

 ing broadly, similarity favors gametic fusion. 



Self-sterility due to differentiation giving dissimilarity, when it 

 occurs, may have manifest advantages in evolution on the assump- 

 tion of an increased number of variants that come from crossing 

 and the direct increase of the intensity of variation that may 

 thus appear over that in self-fertilized strains or that which 

 arises by somatic variation. With the development of self- 

 incompatibility a certain amount of cross-incompatibility comes 

 unavoidably by heredity either between closely related (simi- 

 lar) or between more distantly related individuals. Types and 

 grades of sex differentiation that are essentially physiological, 

 if such are to be assumed as determining fertilization, have doubt- 

 less been acquired just as proterandry or heterostyly, and other 

 numerous anatomical incompatibilities have been acquired. Their 

 transmission in out-crosses, however, is an unusually perfect 

 example of sporadic inheritance in which vague tendencies only 

 can be recognized. 



The results in chicory show that the development of self-incom- 

 patibility is not to be closely correlated with conditions in the 

 immediate parentage. Every plant is, of course, the product of 

 the fusion of two gametes, yet when self-sterile its gametes are 

 inhibited from fusing. The apparent contradiction is equally 

 present on any theory of sex. Such considerations, as already 

 noted, emphasize the sporadic quality of the jjlicnomenon of self- 

 sterility. 



Thus far the development of self-sterility, due to physiological 



