400 



POLLINATION AND FRUIT SETTING 



Most of them will intercross satisfactorily. Varieties of these 

 species are of minor commercial importance in many regions. 



Certain Plum Species Do Not Intercross Satisfactorily. Ap- 

 parently varieties of the Japanese and American species are 

 interfruitful, and these can be planted together if desired for 

 cross-pollination purposes. The European species {Prunus 

 domestica and Prunus insititia) likewise appear to be inter- 

 fruitful. Varieties of Prunus domestica do not, for the most 

 part, cross satisfactorily with those of the Japanese and Ameri- 

 can species. 



{d) Cherries, The pollination problem with cherries de- 

 pends upon whether sweet, sour, or Duke (crosses between 

 sweet and sour) varieties are grown. Practically all varieties 

 of sweet cherries are self-unfruitful. Provision should always 

 be made for cross-pollination when planting a sweet cherry 

 orchard. Most varieties produce plenty of viable pollen, but 

 certain ones appear to be better pollenizers than others. Some 

 varieties are intersterile. Thus, Napoleon, Bing, and Lambert, 

 three very important commercial varieties on the Pacific Coast, 

 will not fertilize each other. However, varieties such as Re- 

 publican, Black Tartarian, Wood, Early Purple, Rockport, 

 Windsor, and certain others pollinate these three varieties 

 successfully. 



Sour cherry varieties are self-fruitful in most sections. Ex- 

 perimental studies and field observations show that in many 

 sections the common varieties of sour cherries such as Early 

 Richmond, Montmorency, English Morello, Wragg, and Dye- 

 house are usually self-fruitful and will set good crops without 

 cross-pollination. Reports from Oregon, however, indicate 

 that several varieties, including the IMontmorency, are self-un- 

 fruitful for all practical purposes under local conditions. So 

 far as is known, varieties of sour cherries blossoming at the 

 same time pollinate each other readily. 



Many varieties of Duke cherries are self-unfruitful. Ex- 

 perimental evidence available in this country suggests that 

 much better crops would result in all Duke varieties if at 



