246 LUTHER BURBANK 



they were growing large, it would be hard 

 to say. 



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 messen- 

 gers. 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 obtain 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 adopted their method be- 

 cause 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 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 



