PRACTICAL POLLENATION 



We know that, in the main, insects tend to 

 keep near the surface of the earth, and it may 

 be that the plants that tended to grow very tall 

 were relatively neglected by the insect messengers. 

 But on the other hand, there are insects that haunt 

 the highest trees, and we can hardly doubt that 

 had even the tallest of plants desired to retain the 

 services of insect messengers, races of these would 

 have been developed that would have proved 

 equal to the most exacting demands. 



What seems on the whole most probable, then, 

 is that the trees have changed their allegiance 

 from insect messengers to wind because of the 

 very nature of the conditions under which they 

 grew. 



By raising their heads high and higher into the 

 air they obviously put themselves more in contact 

 with the wind and thus make it increasingly 

 possible to spread their pollen broadcast across 

 wide stretches of territory. 



As a matter of fact we know that the pollen 

 of pine trees in particular may be carried almost 

 in clouds for scores and even hundreds and 

 hundreds of miles. 



So there is every opportunity for the cross- 

 fertilization of individual trees growing in widely 

 separated territories; and there is therefore no 

 restriction put upon the possibilities of progress 



[71] 



