STUDY OF GRAPE POLLEN, 



247 



grapes varies considerably in size, but there is no apparent connection between 

 the size and germinating capacity. 



From these results it appears that one of the reasons why certain varieties 

 of grapes are self-sterile is a lack of viability or potency in the pollen itself.' 

 There may be other minor factors (quantity of pollen produced, etc.), but 

 this is sufficient to account for all of the phenomena observed in the field. 

 There are no distinct classes of self-fertile and self-sterile forms, but all 

 gradations exist from one extreme (pseudostaminate) to the other (pseudo- 

 pistillate). It further appears that pollen from the same variety may vary 

 in different years and in the same year in different localities.'' This gradua- 

 tion of pollen is quite readily noticed on examining pollen from a dozen or 

 two of varieties selected by chance. In selecting the varieties which are 

 given in the list in this bulletin extreme types were purposely sought so that 

 any differences which might exist would be most apparent. 



The grape is evidently, so far as its phaenological characters are con- 

 cerned, now in a state of evolution from an assumed older hermaphrodite'' 

 form to forms that are essentially staminate and pistillate. All of the stam- 

 inaAe forms which I have observed have small abortive pistils which con- 

 form with the observations of Engelmann. Others report staminate flowers 

 with no trace of pistil remaining. On the other hand, the most advanced 

 pistillate forms still retain their stamens and pollen although so far as their 

 true function is concerned they are abortive. There is considerable cor- 

 roborative evidence as to this being an incomplete evolution in the fact that 

 the forms are not fixed and separate, but blend together and are quite un- 

 stable even on the same plant. ^ These facts seem to show that our grape 

 is in a state of very unstable equilibrium coming from an ancestry of diverse 

 sexual types. ^ 



It might be interesting to consider the probable cause of this evolution. 

 It seems reasonable to suppose that there must be some advantage which the 

 staminate and pistillate vines have over the older hermaphrodite forms or 

 they would not have developed and persisted. This advantage probably lies 

 in the fact that cross fertilization is thus assured." The seedlings resulting 

 from cross fertilization being usually the stronger^ would have the better 

 chance in the struggle for existence with those from vines which were self- 

 fertilized. However, we should not lose sight of the fact that there are also 

 some advantages to the hermaphrodite forms, and the chief one of these lies 

 in the greater certainty of fertilization and consequent seed production. 

 Where vines are widely scattered, the hermaphrodites would have the ad- 



^Such plants are well known to botanists, and are called pseudo-hermaphrodite. 

 Kerner & Oliver: National History of Plants, 291. 



=Beach. Bui. 157. 



^Bailey. Survival of Unlike, 347, and Geddes & Thompson Evolution of Sex. 



■*There is a vine at this Station which bears both staminate and hermaphrodite 

 flowers. Mr. N. B. White, Norwood, Mass., reports a male rip. X lab. vine on his 

 ground which has fruited but twice in the last 30 years. See also Bushlicrg Catalogue, 8. 



^Kerner & Oliver, Natural History of Plants, 300. 



*Kerner & Oliver; /. c. 



^Darwin. Cross Fertilization f)f Plants. 



