428 POLLINATION OF FLOWERS 



evening primrose, is an example of an insect especially adapted 

 to reach deep into long tubular flowers. 



A little search among flowers, such as those of the columbine 

 and the foxglove, will usually disclose many which have had the 

 corolla bitten through by bees which are unable (or unwilling 

 to take the trouble) to get at the nectar by fair means, and 

 which therefore steal it. 



403. Bird-pollinated flowers. Some flowers with very long 

 tubular corollas depend entirely upon birds to carry their pollen 

 for them. Among garden flowers the gladiolus, the scarlet salvia, 

 the canna, and the trumpet honeysuckle are largely dependent ; 

 upon humming birds for their pollination. The wild balsam, 

 or jewelweed, the swamp thistle, and the trumpet creeper are 

 also favorite flowers of the humming bird. 



404. Prevention of self pollination. Dioacious flowers are, I 

 of course, quite incapable of self pollination. Pistillate monoe- 

 cious flowers may be pollinated by staminate ones on the same ^ 

 plant, but this does not secure as good seed as is secured by 

 having pollen brought to the pistil from a different plant of the 

 same kind. 



In bisexual flowers self pollination would commonly occur un- 

 less it were prevented by the action of the essential organs ' 

 or by something in the structure of the flower. In reality, 

 many flowers which at first sight would appear to be designed 

 to secure self pollination are almost or quite incapable of it. 

 Frequently the pollen from another plant of the same species I 

 prevails over that which the flower may shed on its own pistil, 

 so that when both kinds are placed on the stigma at the same 

 time it is the foreign pollen which causes fertilization. But 

 apart from this fact there are several means of insuring the 

 presence of foreign pollen, and only that, upon the stigma, just ? 

 when it is mature enough to receive pollen tubes. 



405. Stamens and pistils maturing at different times. If 

 the stamens mature at a different time from the pistils, self 

 pollination is as effectually prevented as though the plant were 



