INSECTS IN RELATION TO PLANTS 261 
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 tlHey 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 aoe 
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 (fris 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 Oe Hats) ath, anthers, 2, siematte sips 
an overhanging anther(an) and 
becomes powdered with grains of pollen as the insect pushes 
n, nectary; s, sepal. 
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 1s 
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 
