176 HORTICULTURE FOR SCHOOLS 



ample, the Bartlett pear is self-sterile in the East, but is 

 self-fertile in the Pacific Coast states, although cross-polli- 

 nation may increase the crop even in the Pacific states. 



274. Requisites of good pollinizer. In choosing trees for 

 pollinating any variety, several requisites of good pollinizers 

 should be carefully considered. 



1. Varieties must not only be able to pollinate each other, 

 but must produce pollen at the time it is needed by the other 

 trees; that is, they must bloom at approximately the same 

 time. If one variety blooms early and the other late, the 

 pistils of the early-blooming sort will be past the receptive 

 stage when pollen of the late-blooming kind is ready, and 

 the pistils of the late-blooming variety will not be receptive 

 until sometime after the pollen from the early-blooming 

 tree has been shed. For example, it would be of no use to 

 inter-plant Chapman and Napoleon sweet cherries for inter- 

 pollination, because the Napoleon does not blossom until the 

 Chapman has finished its blooming period. 



2. Any variety intended for pollinizing another kind must 

 produce viable pollen in abundance. The Combination 

 Japanese plum has already been mentioned as being unsuit- 

 able for pollination purposes, as it produces pollen very 

 sparingly. 



3. Late-blooming varieties escape frost more often than 

 early-blooming ones. This is not only the case with fruit 

 that has already set, but is true also of the flowers just after 

 they have been pollinated, and before the pollen-tube has 

 reached the ovary. Some species of early bloomers will stand 

 frost better than others. Japanese plums, for example, 

 will stand more frost than apricots, even in case of those 

 varieties blooming at the same time. 



4. Varieties which are good from a commercial stand- 

 point should be chosen for inter-pollination. For example, 

 if it is desired to plant varieties of pears for pollinating the 

 Bartlett, a kind should be chosen which will pollinate the 



