194 



THE EVOLUTION THEORY 



produced in enormous quantities, fell like clouds of dust into the air, 

 were carried by the wind hither and thither, and some occasionally 

 alighted on the stigma of a female flower. In these plants the sexes 

 often occur separately on different trees or individuals, and there must 

 be a certain advantage in this when the pollination is effected by the 

 wind. 



The male flowers of the Archisperms would be visited by insects 

 in remote ages, just as they are now ; but the visitors came to feed 

 upon the pollen, and did not render any service to the plant in 

 return'; they rather did it harm by reducing its store of pollen. If it 

 was possible to cause the insect to benefit the plant at the same time 

 as it was pillaging the pollen, by carrying some of it to female 

 blossoms and thereby securing cross-fertilization, it would be of great 



Fig. 50. Flowers of the Willow (Salix cinerea) ; after H. Miiller. A, the 

 male, B, the female catkin. C, individual male flower ; n, nectary. D, indi- 

 vidual female flower ; n, nectary. E, Poplar, an exceptional hermaphrodite 

 flower. 



advantage, for the plant would no longer require to produce such 

 enormous quantities of pollen, and the fertilization would be much 

 more certain than when it depended on the wind. It is obvious that 

 the successful pollination of anemophilous plants implies good weather 

 and a favourable wind. 



It is plain that the utilization of the insect- visitors in fertilization 

 might be secured in either of two ways ; the female blossoms might 

 also offer something attractive to the insects, or hermaphrodite flowers 

 might be formed. As a matter of fact, both ways have been followed 

 by Nature. An example of the former is the willow, the cross- 

 fertilization of which was forced upon the insects by the development 

 in both female and male blossoms of a nectary (Fig. 50, G and D), a 

 little pit or basin in which nectar was secreted. The insects flew now 

 to male and now to female willow-catkins, and in doing so they 



