APPENDIX. 207 



under the stimulus of hiyh cultivation. Second, we can never be perfectly 

 sure that any variety will be self-fertile on our soil and under our culture , 

 even those varieties which are self-fertile elsewhere may be partially self- 

 sterile with us. Third, most self-fertile as well as self-sterile varieties are 

 tienefited by cross-pollination. It is taking risks to plant a very large block 

 of one variety. The trees may bear just as much and just as fine fruit as 

 though other varieties were with them, but the chances are against it. 



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 im- 

 portant. In a wild thicket of plums or other fruits, they are usually numer- 

 ous 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 

 thoroughness of cultivation increases, the number of these natural insect 

 aids to cross-pollination decreases ; hence, it may become necessary to keep 

 domestic honey-bees foi- this purpose. 



SUMMARY. 



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

 seasons and with 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 degi-ees. Even flowers which appear 

 to be uninjured may be so weakened that they cannot set fruit. 



5. Rain during the blooming season prevents the setting of fruit "chiefly 

 ty 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 

 irom isolated trees or solid blocks of one variety. 



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

 "variety may be self-sterile in one place and nearly self-fertile in another. 



II. Poorly nourished trees are more likely to be sterile \yith their own 

 pollen than well-fed trees are. 



12. The loss of fruit from self-sterility usually maybe prevented by plant- 

 ing other varieties among the self-sterile trees. 



