216 PROBLEMS OF FERTILIZATION 



would seem to be due to the similarity in the hereditary 

 factors carried by eggs and sperm." Stout on the other 

 hand, arguing from hybrid incompatibilities, maintains 

 that "the most fundamental principle of sexual fertility 

 is that a marked degree of similarity in constitution is 

 necessary' for the existence of compatibility. He is 

 thus inclined to refer self-incompatibility to constitu- 

 tional dissimilarity between gametes, which must 

 therefore be strictly of epigenetic origin. He cannot, 

 however, deny the occurrence of a certain amount of 

 cross-incompatibility as a result of heredity; so that 

 his views seem to lack consistency in this respect. 



It is obvious that genetic studies cannot solve the 

 problem of self-incompatibility in a physiological sense; 

 on the other hand, if a physiological solution were 

 found the genetic results would be more readily inter- 

 pretable. The elementary fact that the gametes which 

 produced any hermaphrodite individual were ipso facto 

 compatible, though they may themselves transmit 

 incompatibility, proves that the latter property is 

 cytoplasmic, belonging to the duplex organization and 

 not to the genes of the mature gametes. Confusion 

 between the possession and transmission of incompati- 

 bility must be avoided. 



East and Park (1917) have shown that the differ- 

 ence in behavior between compatible and incompatible 

 pollen on the stigma and in the style is that the compat- 

 ible pollen tube grows with constant acceleration, exhib- 

 iting an autocatalytic curve, whereas the incompatible 

 pollen tubes grow at a constant rate and hence fail to 

 reach the ovule before the style withers and growth 

 becomes impossible. They therefore assume that com- 



