294 



A TEXTBOOK OF BOTANY 



[Cn. VI, 5 



by the insect (Fig. 205). All of these matters are described 

 in detail in several works devoted to the subject. ThejJ 

 student will find that to the original investigators, these re-M 

 markable adjustments between flowers and insects seem most! I 

 reasonably explained as result of a gradual process of adapta- 1 1 

 tion of one to the other during the course of their evolutional 

 Insect-pollination prevails far more widely than any other M 

 method, and moreover is characteristic of the highest kinds N 

 of plants. A reason for its superiorij 



consists obviously in its greater economy and efficiency, for 



in the one case the 

 pollen is simply cast 

 forth and its access to 

 a stigma left to chance, 

 while in the other th( 

 pollen is carried di- 

 rectly from anthers 

 stigmas. ^__phase 

 this economy 

 Ing the most, so__to_ 

 speak, of insect visits 

 explains the pres- 

 ence of stamens :anct 

 (After H. "pistils in the same 



flowers. 



While insects are overwhelmingly the most important, 

 they are not the only animal cross-pollinators of flowers. 

 Some kinds of large bright flojyftra fl ro 

 by small nectar-eating birds. p,spftnifl,lly 



FIG. 206. Marcgravia nepenthoides, polli- 

 nated by humming birds ; much reduced. 



In the pouched nectaries below the flower, 

 there is secreted abundant nectar, in probing 

 for which the hovering birds bring their heads 

 successively against the flowers. 

 MOller.) 



(J^'ig. 2UbJ ' and others, growing close to the ground, are 

 pollinated by snails, which are attracted by a succulent tis- 

 sue formed in the spike among the flowers. But insects, 

 from their combination of small size, active habits, and 

 nectar diet, make the most effective cross-pollinators. 



As with other plant organs, flowers have not only their 

 primary function, which they perform as their contribution 



