304 POMOLOGY 



tion, viz., mixed plantings of the grape will be more fruitful 

 than those of one variety only, 



271. The plum. — Some of the most extensive investi- 

 gations on the self-sterility problem have been with the plmn, 

 notably by Bailey/ Waugh,- Hendrickson,^ and Dorsey.^ 

 There is a general tendency throughout the plum species 

 to self-sterility but there are many exceptions, as would be 

 anticipated from a knowledge of the problem. The salicina 

 (Japanese) varieties are as a rule self-sterile and self-barren. 

 The Climax is the only one of several kinds observed by 

 Hendrickson to be self-fertile in California. He also reported 

 that, in general, the early blooming Japanese varieties such 

 as Combination, Kelsey, and Satsuma, are scanty pollen- 

 producers and not effective poUinizers, while the later blos- 

 soming sorts such as Burbank, Wickson, Climax, Sultan, and 

 Abundance produce pollen abundantly and are effective 

 pollinizers. 



Varieties of the native American species of plums vary- 

 in regard to the sterility character but are much inclined to 

 be self-sterile, as is notable in the case of the Wild Goose 

 which is perhaps more generally grown than any other single 

 kind. They are for the most part fully inter-fertile, however, 

 so that one given variety will pollinate any other, providing 

 the two bloom at the same time.'' Waugh has shown that 

 in the P. americana group the pistils are frequently defec- 

 tive, averaging 21.2 per cent in the trees studies. The an- 

 thers are also defective in some cases but not so frequently 

 as the pistils. In some cases, the anthers mature before the 



1 Bailey, L. H. Cornell Agr. Exp. Sta. Bull. 52, 106, 139, 175. 



2 Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Rept. 1897-98, 1898-99. 



3 Hendrickson, A. H. Plum pollination. Calif. Agr. Exp. Sta. BuU. 

 310. 1919. 



^ Dorsey, E. J. Jour. Agr. Res. 17: No. 3, 1919. 

 ^Waugh, F. A. Standard Cycl. Hort. V: 2719. (1916.) 



