314 ELEMENTARY BIOLOGY 



out just because of the inability to produce sufficient seed to replace 

 the old individuals, the suitable insects not being numerous enough. 

 In general, the plants that are most decidedly dependent upon the 

 wind for their pollenation seem to be at least as successful as those that 

 are dependent upon insects. Thus, the grasses and the common catkin- 

 bearing trees and the cone-bearing trees are widely distributed over 

 the surface of the earth, and none of the insect-pollenated plants seem 

 to have any decided advantage over them. 



The insects that are able to get food from highly specialized flowers, 

 because of their peculiar instincts or structure, may seem to have some 

 advantage over insects that cannot make use of those particular flowers. 

 Nevertheless we find it extremely difficult to understand what advan- 

 tage a species may derive from such extreme adaptation, since such 

 dependence often leads to complete extermination (as in the case of 

 Blastophaga in the absence of fig trees), and in any case means pay- 

 ing a high price for benefits received. 



