POMACES 



373 



the other varieties the pollen of which is capable of fertilizing 

 it. It is no doubt true that the failure of many varieties to 

 set fruit is due, in part, to self-sterility. 



Effects of Strange Pollen. — The secondary effects of for- 

 eign pollen on the mature fruit have received considerable at- 

 tention. It is claimed by many that the pollen from one va- 

 riety when placed on the stigma of another, immediately 



Fig. 157. — Apple (Malus 



sylvestris). Median 

 flower. 



longitudinal section of 



impresses its characteristics upon the fruit. It is difficult to 

 understand how foreign pollen could have any considerable 

 effect of this kind. The flesh of the apple is receptacle for the 

 most part. The sperm nuclei of the pollen, of course, do not 

 come into contact with the nuclei of the receptacle cells. It is 

 altogether possible, however, that uniformity of crop, percent- 

 age of set, and size of fruit are immediately affected by 

 strange pollen. 



