ECOLOGY OF FLOWERS 355 



characteristics of such flowers are the inconspicuous char- 

 acter of their perianth, which is usually green or greenish, 

 the absence of odor and of nectar, the regularity of the 

 corolla, and the appearance of the flowers before the leaves 

 or their occurrence on stalks raised above the leaves. 



Pollen is, in the case of a few aquatic plants, carried 

 from flower to flower by the water on which it floats. 



425. Insect-Pollinated Flowers. Most plants which 

 require cross-pollination depend upon insects as pollen- 

 carriers, 1 and it may be stated as a general fact that the 

 showy colors and markings of flowers and their odors all 

 serve as so many advertisements of the nectar (commonly 

 but wrongly called honey) or of the nourishing pollen 

 which the flower has to offer to insect visitors. 



Many insects depend mainly or wholly upon the nectar 

 and the pollen of flowers for their food. Such insects 

 usually visit during any given trip only one kind of flower, 

 and therefore carry but one kind of pollen. Going straight 

 from one flower to another with this, they evidently waste 

 far less pollen than the wind or water must waste. It is 

 therefore clearly advantageous to flowers to develop such 

 adaptations as fit them to attract insect visitors, and to 

 give pollen to the latter and receive it from them. 



426. Pollen-Carrying Apparatus of Insects. 2 Ants and 

 some beetles which visit flowers have smooth bodies, to 

 which little pollen adheres, so that their visits are often of 

 slight value to the flower, but many beetles, all butterflies 

 and moths, and most bees have bodies roughened with 

 scales or hairs which hold a good deal of pollen entangled. 



1 A few are pollinated by snails ; many more by humming-birds and other 

 birds. 2 gee Muller's Fertilization of Flowers, Part II. 



