POLLINATION AND STERILITY 297 



vial and applied with a camel's-hair brush or the finger. 

 Others pick the flowers and brush the anthers over the pis- 

 tils of the female parent. 



THE STERILITY PROBLEM 



When it is recognized that many varieties of fruit exhibit 

 self-sterility, inter-sterility, and self-barrenness, and hence 

 require cross-pollination with some other variety, the sub- 

 ject becomes one of great economic importance. There is 

 considerable variation of opinion in regard to the ultimate 

 causes of sterility, and consideration here can well be con- 

 fined to some of the established facts which closely pertain 

 to pomology. 



265. Definition of terms. — Self-sterility refers to the 

 inability of a plant to develop fertile seeds when the pistil 

 is pollinated with pollen from its own flower or from one of 

 the same variety of fruit. Other meanings are given to it, 

 such as lack of development of any fruit at all when the 

 flower is self-pollinated. It must be understood that such a 

 condition does not mean that either 'the pistils or stamens 

 are defective but merely that fertilization does not take 

 place, even though the pollen may germinate on the stigma, 

 as often occurs; or if fertilization does take place, the young 

 embiyo does not complete its development. The ultimate 

 reason for this phenomenon is not clear, but the phrase 

 "lack of affinity" has been given to it. In other cases, the 

 pollen may be defective and hence cause self-sterility, or 

 the embryo sacs may be defective. 



Self-fertility, on the other hand, refers to the ability of a 

 plant to produce genninable seeds when its pistils are pol- 

 linated from the same flower, tree, or variety, i. e., in the 

 fertilization of the ovule, the male gametes were not derived 

 from another variety or species. 



Varieties are said to be inter-sterile when certain ones fail 



