DEVELOPMENT OF PLANTS 



425 



commonly appear and the pistils are normally reduced to two. 

 More frequently the flowers are imperfect, either the pistils or 

 stamens of each flower being aborted (Fig. 318, B) . These two 

 kinds of imperfect flowers are arranged on the same or different 

 trees and they are adapted to small short-tongued lapping in- 



Fig. 318. A common form of the Sapindales : A, inflorescence of sugar 

 maple {Acer saccharum) — s, staminate flowers; p, pistillate flowers. B, 

 staminate (right-hand) and pistillate flower enlarged. C, section of a 

 pistillate flower, showing the two sterile stamens and nectar disc at base 

 of filaments. D, section of ovary, showing early development of the wings 

 of the fruit and the pendulous ovules with micropyle pointing down. 



sects which visit these open types of flowers. The intelligent 

 long-tongued bees and butterflies generally avoid such flowers, 

 having learned by experience with colors and odors that a surer 

 supply of food is to be found in those flowers that conceal their 

 nectar and so exclude the promiscuous crowd of insects that 

 swarm about the simpler types. It should be stated that the 

 development of imperfect or incomplete flowers appearing in 

 many of the orders is not to be looked upon as a primitive con- 

 dition, though common in the lower monocotyledons and dicoty- 

 ledons, since, throughout the Angiospermae, forms will constantly 

 appear in which one or another set of organs fails to develop. 

 The formation of anemophilous flowers, however, as in the box 

 maple, is a return to a primitive condition. 



