THE FLOWER AND THE BEE 



elm are largely hernia i)]ir(){lite or perfeet, and self-pollination 

 is to a great extent prevented by the stigmas maturing earlier 

 than the anthers. Both the staminate and pistillate flowers 



Fig. 6. Gray Birch. BetvJa populifolia 



A, fertile catkin; B, staminate catkin. A wind-pollinated tree 



of the ash are in clusters, and in our sj)ecies are usually on 

 different trees. 



All of these genera possess certain contrivances or adapta- 

 tions which tend to prevent self-pollination and to strongly 

 favor cross-pollination. The stamens and pistils are often in 



