MORPHOLOGY OF HIGHER PLANTS. . 399 



(Mitchella repens) two kinds of flowers are produced, viz.: (a) 

 one with short styles and long filaments, and another (b) with 

 long styles and short filaments, and thus the flowers appear to be 

 especially adapted for insect cross-pollination and are called 

 DIMORPHIC. In still other cases one species gives rise to three 

 kinds of flowers, depending upon the difference in the relative 

 lengths of the styles and filaments, as in the purple loosestrife 

 (Lythrum calcaratum), and such flowers are called TRIMORPHIC. 

 The external agents which are instrumental in carrying pollen 

 from one flower to another and thereby promoting cross-pollina- 



FIG. 229. Visitation of flowers by insects showing how they gather the pollen and 

 assist in cross-pollination, the one on the left being Lilium Martagon visited by a hawk 

 moth, showing that while the proboscis is removing honey from the nectary the under 

 side of the body is becoming covered with pollen; at the right Cydonia vulgaris, the common 

 quince, visited by a bee, whose legs are becoming covered with pollen. After Dodel-Port. 



tion are the wind, water currents, insects, small animals and birds, 

 such as humming-birds, which are, even in temperate regions, 

 to be observed visiting the garden nasturtium. 



In many of the early-flowering trees, as well as pines, Indian 

 corn, etc., the flowers are devoid of showy, attractive features, 

 but produce large quantities of pollen which is more or less dry 

 and powdery and carried by the wind to other flowers. Flowers 

 which are wind-pollinated are classed as ANEMOPHILOUS, and it is 

 estimated that about one-tenth of all the flower-producing plants 

 belong to this class. 



Plants which are pollinated by the aid of water currents are 



