CHAPTER VII. 



FLOWERS AND INSECTS. 



83. Insects as agents of pollination.— The use of insects 

 as agents of pollen transfer is very extensive, and is the pre- 

 vailing method of pollination among monocotyledons and 

 dicotyledons. All ordinary flowers, as usually recognized, 

 are related in some way to pollination by insects, but it 

 must not be supposed that they are always successful in 

 securing it. This mutually helpful relation between flow- 

 ers and insects is a very wonderful one, and in some cases 

 it has become so intimate that they cannot exist without 

 each other. Flowers have been modified in every way to be 

 adapted to insect visits, and insects have been variously 

 adapted to flowers. 



84. Self-pollination and cross-pollination.— The advantage 

 of this relation to the flower is to secure pollination. The 

 pollen may be transferred to the carpel of its own flower, 

 or to the carpel of some other flower. The former is known 

 as self-pollination, the latter as cross-pollination. In the 

 case of cross-pollination the two flowers concerned may be 

 upon the same plant, or upon different plants, which may 

 be quite distant from one another. It would seem that 

 cross-pollination is the preferred method, as flowers are so 

 commonly arranged to secure it. 



85. Advantage to insects.— The advantage of this relation 

 to the insect is to secure food. This the flower provides 

 cither in the form of nectar or pollen ; and insects visiting 

 flowers may be divided roughly into the two groups of 

 nectar-feeding insects, represented by butterflies and moths, 



