218 A BOOK OF INSECTS 



but the reader should at once fix in his mind the fact that 

 a vast number of plants only escape barrenness through 

 the intervention of circumstances over which they exercise 

 no direct control. 



Dry, dust-like pollen is carried about by wind, many 

 kinds of trees and grasses being thus cross-fertilised. They 

 have inconspicuous flowers — almost without exception. 

 On the other hand, plants whose flowers have bright- 

 coloured petals and fragrant scents rely chiefly upon the 

 assistance of insects ; and their pollen is usually more or less 

 adhesive. Probably insects began to visit inconspicuous 

 flowers at a very remote period of the world's history ; for 

 they are adventurous creatures, alert to discover fresh 

 sources of food. That these primitive flower- visitors insti- 

 tuted the system of cross-pollination which obtains to-day 

 seems certain. The stages of the wonderful evolutionary 

 process which must have followed can only be guessed 

 at ; but the secretion by plants of nectar in the region 

 of the essential organs marked a great step in advance. 

 The sweet liquid constituted a counter attraction to the 

 insects, which thus devoured less of the valuable pollen, 

 albeit they did not carry less of it away upon their hairs. 

 Indeed, at the present day, many kinds of insects visit 

 flowers solely for the sake of nectar, and eat no pollen at all. 



In the case of the buttercup, pollination is a relatively 

 simple process. Many insects, especially two-winged flies, 

 visit the flower, which is rendered conspicuous by its 

 yellow petals. The flies feed, according to their taste, 

 either upon the pollen or upon the nectar which is 

 secreted at the bases of the petals. Some of the pollen 

 may be transferred to the stigmas of the same flower, 

 while some may be carried to the flowers of a distant 

 plant, the chances in favour of self- and cross-pollination 

 being about equal. We may contrast the buttercup with 



