THE END OF THE STRUGGLE. 



61 



without the meaus of overtopping one another. When 

 the end of the period of principal height growth is 

 reached the trees are interfering with each other very 

 little, and the struggle for life begins again in a differ- 

 ent way. As the principal height growth ceases, and 

 the tops no longer shoot up rapidly above the side 

 branches, the crowns lose their 

 l)ointed shape and become com- 

 paratively flat. (See figs. 57, 58.) 

 The chief reason why trees stop 

 growing in height is that they are 

 not able to keep the upper parts 

 of their crowns properly supplied 

 with water above a certain dis- 

 tance from the ground. This 

 distance varies in different kinds 

 of trees, and with the health and 

 vigor of the tree in each species, 

 but there is a limit in every case 

 above which the water does not 

 reach. The power of the pumping machinery, more than 

 any other quality, determines the height of the tree. 



Fig. 59. — Diagram to show 

 why a sharply conical 

 crown receives more light 

 than a flat one. 



THE END OF THE STRUGGLE. 



Now that the tree can no longer expand at the top, 

 it must either suffer a great loss in the number of its 

 leaves or be able to spread at the sides; for it is clear 

 that not nearly so many leaves can be exposed to the 

 light in the flattened crown as in the pointed one, just 

 as a pointed roof has more surface than a flat one. 

 (See fig. 59.) It is just at this time, too, that the trees 

 begin to bear seed most abundantly, and it is of the 

 greatest importance to each tree that its digestive appa- 



