96 



ELEMENTARY STUDIES IN INSECT LIFE 



pollen does fall upon its own stigma, by rendering this 

 sterile to its own ovule but fertile when transferred to 

 the flower of another variety of the same stock. Briefly 

 and in a general way, this sums up the advance of our 

 knowledge upon this interesting subject. Many subse- 

 quent investigations have elaborated these principles by 

 the detailed study of various forms of flowering plants. 



cP 



P 



FIG. 72. Enlarged section of a Bartlett pear flower : sf, style ; sp, sepal ; /, 

 filament ; a, anther ; s, stigma ; p, petal ; d, disk ; ov, ovule. (After Waite.) 



Plants whose Flowers are Sterile to their Own Pollen but 

 Fertile to Pollen Brought from Other Plants of Same Species. 



More than fifty species of plants have been found to be 

 partially or wholly sterile to their own pollen, but fer- 

 tile to pollen transferred from other plants of the same 



