POLLINATION AND STERILITY 303 



It has been shown ^ that a marked difference in appearance 

 exists between the dry pollen of self-fertile and self-sterile 

 grape varieties. The former or normal pollen is oblong in 

 outline with slightly flattened ends, while the latter is quite 

 irregular and folded, and fails to genninate when placed in 

 a nutrient solution. 



Dorsey has shown that the development of the pollen in 

 self-sterile varieties of the grape is normal "up to the forma- 

 tion of the microspores, but here a degeneration takes place 

 which renders the pollen grains (microspores) sterile." A 

 careful study of the pollen produced by those varieties which 

 bagging tests have shown to be more or less self-sterile, show 

 that the generative nucleus and, in some cases, also the vege- 

 tative nucleus, degenerate. Such degeneration precludes the 

 possibility of nomial functioning in eveiy pollen-grain where 

 it occurs. Sterile pollen in the grape, then, is due to de- 

 generation in the generative nucleus. 



He has also shown that "the genn spores are not formed 

 in pollen borne by the reflexed type of stamen." 



To sunnnarize the causes and correlations in the sterility 

 of the grape, the following statements seem warranted from 

 present knowledge: 



1. Self-sterility in the grape is due to defective pollen 

 and not to the pistils. 



2. "All varieties tested set fruit when potent pollen was 

 used, which shows that the pistils are normal." 



3. Potent pollen can be distinguished from impotent by 

 its shape when diy. 



4. Impotent pollen is correlated with the reflexed type 

 of stamens. 



5. The defective pollen is due to an abortion of the gen- 

 erative nucleus. 



These studies lead to one veiy practical reconr.uenda- 

 ' Booth, N. O. N. Y. State Agr. Exp. Sta. Bull. 224, 291-302. 1902. 



