88 PLANT LIFE 



The lateral branches, which in isolated trees 

 spread out and constitute its charm, here 

 compete with each other, and all are over- 

 shadowed by the topmost branches which 

 alone get properly illuminated. Consequently 

 the lower leaves become useless, and they, 

 together with the branches which bear them, 

 become starved and are destined to perish. 

 The tops are constantly growing higher, while 

 the trunk is as perpetually being denuded 

 of its lower lateral branches. In this way 

 the grand boles or trunks are formed which the 

 woodman delights to see, and they are the 

 distinguishing features of forests managed with 

 skill and intelligence. The forester's aim is 

 always secured, broadly speaking, in this 

 way, though of course there are differences 

 in actual treatment depending on the par- 

 ticular kind of tree or association of trees 

 it is desired to produce. The tall trunks are 

 the result of a sort of natural pruning, brought 

 about by growing the trees at the correct 

 distances apart, the actual distance being 

 regulated by the size, age, and other conditions 

 which affect the growth as a whole. 



The amount of leaf surface is not only 

 influenced by the available exposure to light, 

 but is influenced by other conditions as well. 

 Thus mechanical requirements need to be 

 satisfied, and they may easily limit the dimen- 

 sions practically attainable by the green 

 surface as a whole. A leaf too weak in itself, 

 or too feebly supported to retain a suitable 



