FEETILIZATION. 181 



both. In some the stamens are exserted and pistil 

 included, while in others the stamens are included and 

 style exserted. This arrangement also favors cross- 

 fertilization through insect agency. 



447. The service thus performed by insects in be- 

 half of vegetation is very important. Numerous spe- 

 cies are wholly dependent on bees, moths, flies, for the 

 dissemination of their pollen, and consequently for 

 their very existence. Many other species, although 

 capable of self-fertilization, are still greatly benefited 

 by the intercrossings of pollen which the visits of 

 insects occasion. Of course the bees have no idea of 

 these benefactions. They visit the flowers solely for 

 their own good. The nectar which they seek is always 

 so situated as to oblige them to disturb the pollen or 

 pollinia as they pass and repass, get besprinkled with 

 it, and so encounter the stigmas from flower to flower. 



448. It would seem important that the bee or moth 

 should confine its visits during any one excursion to 

 plants of the same species. And this it often does, as 

 shown 4 by observation, avoiding the mingling of its 

 nectars as well as the confusion of its pollens. In 

 accomplishing this, the insect may be led by habit, 

 becoming accustomed, for the hour, to one form of 

 nectary ; or it may be drawn by uniform odor of the 

 flowers, or by their gay and special colors. For we 

 observe that the flowers of grasses and of forest trees 

 whose pollen is wafted by the wind, requiring no aid 

 from insects, are destitute both of bright colors and of 

 fragrance, and of honey. 



449. From these observations and many others of 

 similar import, it is inferred that Nature insists on the 

 fertilization of the stigma in every plant by all means, 



