Pollination in Orchards. 385 



The Pollen-Carriers. 



The pollen of one variety is carried to the pistils of another in 

 two ways : by the wind and by insects. There are many kinds of 

 insects which aid more or less in the cross-pollination of orchard 

 fruits, principally bees, wasps and flies. Of these, the wild bees of 

 several species are probably the most important. In a wild thicket 

 of plums or other fruits, they are usually numerous enough to insure 

 a good setting of fruit. But few if any wild bees can live in a large 

 orchard, especially if it is well tilled. As the extent and thorough- 

 ness of cultivation increases, the number of these natural insect aids 

 to cross-pollination decreases ; hence it may become necessary to 

 keep domestic honey bees for this purpose. 



SUMMARY. 



1. Scarcely one fruit blossom in ten sets fruit, even in the most 

 favorable seasons and w4th the most productive varieties. 



2. Trees making a very vigorous growth may drop their blossoms. 



3. Brown rot, apple or pear scab, and pear blight may kill the 

 blossoms. 



4. Frost injury to blossoms is of all degrees. Even flowers which 

 appear to be uninjured may be so weakened that they cannot set 

 fruit. 



5. Pain during the blooming season prevents the setting of fruit 

 chiefly by destroying the vitality of the pollen, injuring the stigma, 

 or by preventing fertilization because of the low temperature. The 

 washing of pollen from the anthers seldom causes serious loss. 



6. Much of the unsatisfactory fruiting of orchards all over the 

 country is due to self-sterility. A tree is self-sterile if it cannot set 

 fruit unless planted near other varieties. 



7. The main cause of self-sterility is the inability of the pollen of 

 a variety to fertilize the pistils of that variety. 



8. Poor stamens and pistils or the premature ripening of either 

 are but minor causes of self-sterility. 



9. An indication of self-sterility is the continued dropping of 

 young fruit from isolated trees or solid blocks of one variety. 



10. Self-sterility is not a constant character with any variety. 



26 



