800 LUTHER BrRBANK 



Whether or not the reoeptire lips hmrt secured 

 any poUen, they remain closed for four or five 

 minutes, so there is no danger that they will 

 encounter the bee as it leaves the flower laden 

 with a heth supply of pollen from the com- 

 panion anthers. But a few minutes later the 

 stigma lobes open again, like a trap set for the 

 next visitor. 



Human ingenuity could not well devise a 

 mechanism better adapted than this to secure 

 cross-pollination and insure against the possi 

 bi]it>' of self-fertilization. 



The foxglove (DigUaUi) also has stamcnii and 

 pistils lying along the roof of the ooroUa tube. 

 Its device to prevent sdf-fertilitation is the less 

 ingenious but equally effective one of ripening 

 the stigma only after the pollen has been dis- 

 charged — an esqiedient which, as we have seen, 

 is very oommonly icsorted to by other species of 

 plants, including the lilies. 



The Spanish broom (Spartium junceum) is a 

 typical butterfiylike flower, that, in common 

 with others of the same family, has developed 

 a peculiar mechanism to bring about cross- 

 pollination. The two lower petals are joined 

 together into a keel-shaped structure that con- 

 nects the stamens and pistils. The other three 

 petals are more enlarged, and are spread to 



