POLLINATION AND STERILITY 291 



259. Cross-pollination. — The experiments of Waite and 

 many subsequent workers have shown that, with many- 

 kinds and varieties of fruits, it is necessary to have a trans- 

 fer of pollen from one variety to another in order to insure 

 fertilization and the setting of fruit. This transfer between 

 varieties, instead of from the stamens to the pistils of the 

 same flower, has come to be known as cross-pollination 

 in contradistinction to self-pollination. That cross-pollina- 

 tion should be the rule with many fruits will be shown 

 later. 



In selecting a pollinizer, the chief concern is to choose a 

 variety that possesses the following characteristics: 



1. It must blossom at the same time and preferably at 

 the same age as the variety which is to be pollinated. 



2. It must be inter-fertile with it. 



3. Should be a standard variety, i. e., be of high value 

 for the purpose grown. 



4. Should \)c a good ]wllon-producer. 



260. Means of effecting cross-pollination. — Two agencies 

 have usually been considered instrumental in the transfer 

 of pollen: wind and insects. Experimental work and exten- 

 sive observation, however, have shown that wind is of little 

 or no importance with the tree-fruits, the nuts being ex- 

 cepted. Insects play a most vital part in pollinating the 

 blossoms. Chief among the insects are the bees, particu- 

 larly the honey bees. 



Nature has provided for the visitation of insects in a most 

 conspicuous way. Students of nature, particularly Darwin 

 and his followers, are in full agreement that the insects are 

 attracted by the bright or showy flowers and by the nectar 

 secreted at the basal parts, thus bringing about the transfer 

 of the pollen-grains which adhere to them, from flower to 

 flower. When the flowers are so constructed as to permit 

 pollination by the wind, they are said to be anomophilous 



