FRUIT SETTING AS AN ORCHARD PROBLEM 543 



with Yellow Egg, while 114 flowers set and matured fruit when polli- 

 nated with Burbank. Though both crosses evidently may be classed 

 as interfertile, there is a great difference in the degree of fertility exhibited. 

 Marshall, ^° working with varieties of P.domestica, iound anyone combina- 

 tion to give as good set of fruit as any other; Sutton, ^^^ working with other 

 varieties of the same species, reached the same conclusion, except that 

 intersterility appeared in three varieties. However, two of these three 

 varieties originated as bud sports from the third. The European plums 

 are not interfruitful to any considerable degree with those of either the 

 Japanese or American groups. 



Except for certain varieties of the several European groups known to 

 be self fruitful, plums always should be planted so they will secure the 

 advantages of cross pollination. 



Apparently both self and cross unfruitfulness in the plum is due to 

 incompatibilities and not to degeneration of the pollen or of the embryo 

 sacs. 



Apricot. — Experimental data are not available on the pollination 

 responses of the apricot; however, circumstantial evidence indicates 

 that at least a number of the leading varieties grown in America are 

 self fruitful. 



Cherry. — Until a comparatively recent time cherries have been 

 assumed to be self fruitful. In 1915, Gardner^" reported several varieties 

 of the sweet cherry, all that were tested, as self unfruitful under Oregon 

 conditions and a little later Tufts^^^ reported a number of the same 

 varieties self barren in California. All the sweet cherries tested have been 

 reported self barren in' England. ^^^ The conclusion seems warranted 

 therefore that self barrenness is the general rule in this group. Gardner*" 

 also found May Duke self unfruitful in Oregon, but Sutton^^^ found 

 both May Duke and Archduke partly self fertile and Late Duke fully 

 self fertile in England. Experimental data on the sour cherries are not 

 available but Hedrick*'^ concludes from his observations that self fruit- 

 fulness is the general rule in that group. 



, Inter-unfruitfulness has been found among some of the varieties of 

 the sweet cherry- — notably Napoleon, Lambert and Bing — in both 

 Oregon*" and California, ^^s 



Self unfruitfulness and cross unfruitfulness in the cherry are due to 

 incompatibilities rather than to any structural defects of pollen or ovules. 



Grape. — As mentioned already, conditions in the grape range all the 

 way from complete self fruitfulness to complete barrenness. Varieties 

 of hybrid origin particularly are likely to be self barren, though this 

 condition is found in many varieties descended from a single species.^*' ^^ 

 Among some of the more common self fruitful varieties may be men- 

 tioned: Clinton, Champion, Concord, Isabella, Moore Early, Niagara, 

 Worden, Agawam, Catawba, Delaware, Diamond and Norton. Among 



