34 INBREEDING AND OUTBREEDING 



oped, has its analogue in the complemental males charac- 

 teristic of the Cirripedes. 



But by far the most numerous and most interesting 

 adaptations for cross-pollination are characteristic of 

 plants alone. These are the thousands of structural modi- 

 fications which utilize external agencies. Wind and water 

 have not been despised, but the real servants they are 



Fio. 8. Adaptation for crosa-pollination, transference of pollen by insecta. (After Kerner.) 



not slaves for they are paid for their services are the 

 lower animals and in particular the insects. 



The ideas of Darwin resulting in the tremendous labors 

 of Miiller,Delpino, Kerner, Knuth and others have made it 

 no longer necessary to describe the facts concerning the 

 dispersal of pollen by animals. 124 ' 157 The subject has 

 been so fascinating that it is common knowledge how the 

 insects are attracted to flowers by odor and by color; how 

 they are rewarded for visits by nectar and by pollen ; how 



