372 BOTANY OF CROP PLANTS 



Pollination and Fertilization. — The literature on this 

 subject is extensive. Cross-pollination is the rule and 

 self-polHnation the exception in the apple and pear. Ex- 

 periments have shown that the wind aids but Httle in cross- 

 polhnation, and that insects, chiefly the honey bee, are 

 relatively more important The bee is attracted to the 

 flowers by the nectar which is produced rather abundantly. 



Fig. 156. — Floral diagram of apple (Malus sylvestris). Note that the sta- 

 mens are in three distinct whorls. {After Kraus.) 



Self -sterility and Self -fertility.- — Many apples and pears 

 are self-sterile, that is, will not fertilize their own pistils. 

 In such cases, pollen from another variety will usually result 

 in fertilization. Self-steriHty and self-fertility probably 

 vary with different climatic conditions. In Oregon, Lewis 

 and Vincent found that the Spitzenburg is self-sterile but 

 capable of being fertiUzed with pollen from a number of other 

 varieties, such as Yellow Newton, Arkansas Black, Jonathan, 

 and Baldwin. Evidently, the mutual affinities of apple 

 varieties must be considered in setting out an orchard. It 

 would not be well to plant soHd blocks of Spitzenburg, for 

 example. It should be alternated with rows of some one of 



