48 Plant Genetics 



In the first place botanists suggested parthenogenesis 

 or vegetative apogamy in the Fi, which of course would 

 mean vegetative propagation and would not involve the 

 segregation of characters and recombinations in fertiliza- 

 tion. In such a case, of course, the hybrid characters 

 would be continued. This is true, but why should the 

 Fi generation exhibit apogamy any more than any other 

 generation ? An ingenious theoretical answer to this 

 pertinent question has been suggested by East (5) as 

 follows. "May not the difficulty of maturing sexual 

 cells in a wide cross sometimes cause apogamous develop- 

 ment, and therefore a continued propagation of a con- 

 stant and uniform race?" This suggestion seems 

 reasonable, for it conforms to two other recognized 

 phenomena. 



Jeffrey (7) and his followers have shown that in 

 wide crosses the resulting hybrid produces more or less 

 sterile pollen. An investigation of wild plants has indi- 

 cated that much hybridizing occurs in nature, especially 

 in certain families, as indicated by the amount of sterile 

 pollen, which is sometimes as much as 100 per cent. 

 Such plants, which reveal their hybrid character only 

 by the presence of sterile pollen, are called by Jeffrey 

 " crypthybrids." This fact has also been brought out by 

 many experimental breeders. 



A second significant fact in this connection was 

 aimounced by East, who says "apogamy is evidently 

 induced by the extraordinary irritation of foreign pol- 

 len." The mechanism involved should be considered. 

 A study of the development of the ovule and female 

 gametophyte shows that stages are passed through before 

 pollination, bringing the ovule to a certain stage of 



