INSECTS IN RELATION TO PLANTS 



26l 



FIG. 253. 



insects actually do associate color and nectar, even though 

 they will fly to bits of colored paper almost as readily as they 

 will to flowers of the same colors. It is not to be supposed, 

 however, that insects realize that they confer any benefit 

 upon the plant in the flowers of which they find food. At 

 any rate, most flowers are so 

 constructed that certain insects 

 cannot get the nectar or pollen 

 without carrying some pollen 

 away, and cannot enter the next 

 flower of the same kind without 

 leaving some of this pollen upon 

 the stigma of that flower. Take 

 the iris, for example, which is 

 admirably adapted for pollina- 

 tion by a few bees and flies. 



Iris. In the common blue-flag (Iris versicolor, 

 Fig. 252), each of the three drooping sepals forms 

 the floor of an arched passageway leading to the nec- 

 tar. Over the entrance and pointing outward is a 

 movable lip (Fig. 253, /), the outer surface of which 

 is stigmatic. An entering bee hits and bends down 

 the free edge of this lip, which scrapes pollen from 

 the back of the insect and then springs back into 



place. Within the passage, the Section to illustrate cross pollination 



hairy back of the bee rubs against of Iris - an > anthe ;' ; '- stigmatic lip; 



* n, nectary; s, sepal. 



an overhanging anther (aw) and 



becomes powdered with grains of pollen as the insect pushes 

 down towards the nectar. As the bee backs out of the pass- 

 age it encounters the guardian lip again, but as this side of 

 the lip can not receive pollen, immediate close pollination is 

 prevented. Of course, it is possible for bees to enter another 

 part of the same flower or another flower of the same plant, 

 but as a matter of fact, they habitually fly away to another 

 plant; moreover, as Darwin found, foreign pollen is prepotent 

 over pollen from the same flower. It may be added that bees 



