DETERMINING NEED OF CROSS-POLLINATION 399 



The following varieties will set a limited amount of fruit 

 in certain years with their own pollen^ but set much better 

 crops if pollen of other Japanese varieties is available for cross- 

 pollination purposes. 



Beauty Methley 

 Climax Santa Rosa 



Practically all varieties of Japanese plums with the excep- 

 tion of Formosa and Gaviota are cross-fruitful. 



Several of the European varieties of plums are self-un- 

 fruitful. The European species {Primus domestica and Primus 

 insititia) do not have as high a percentage of self-unfruitful 

 varieties as the Japanese and American species. Of those 

 studied, the following are self-unfruitful for all practical pur- 

 poses and should not be planted in solid blocks: 



Bavay Jefferson Sergeant 



Clyman Imperial Standard 



German Prune McLaughlin Tragedy 



Golden Drop President Washington 



Quackenboss 



The following varieties set fair crops with their own pollen: 



Agen Reine Claude 



California Blue Sugar 



Giant Victoria 



Italian Prune Yellow Egg 



Certain other varieties set light crops with their own pollen 

 in some years, but much better crops are produced if pollen 

 of other varieties is available. This list includes Diamond 

 Grand Duke, Pond, and Shropshire. 



There seems to be practically no-cross-incompatibility 

 between European varieties of plums; therefore satisfactory 

 crops should be produced if any two varieties are interplanted, 

 provided that their blossoming seasons overlap. 



Practically all varieties of American species of plums that 

 have been observed in pollination studies are self-unfruitful 



