1 8 Characteristics, Structure, Life of Trees 



for next year's growth all the way down to the root tips. 

 The stored material is then used the following spring to form 

 leaves and shoots and new rootlets. 



The whole mechanism of the tree can be compared to a 

 sytsem of water works — water being the most important 

 factor in the life of the plant — the root tips being the pumps 

 or \'alves taking up water with minerals in solution from the 

 soil. The roots and stem and branches are the conducting 

 pipes; the leaves are the engines where the power is apphed 

 which sets the current in motion: namely, heat, light, wind, 

 and other causes of transpiration (evaporation). 



In the leaves, which may also be regarded as the stomach 

 of the plant, the raw food is digested and assimilated into 

 a form in which it may be used by the plant, and thence it 

 is carried by osmosis ^ to places where it is needed. 



It stands to reason that the amount of foliage which is 

 active under the intluence of light, determines the amount 

 of assimilated food material which will be at the disposal of 

 the tree and hence the amount of growth. The leaves and 

 their healthy function are, therefore, of the highest im- 

 portance to the tree; but just as important is the number 

 of root tips capable of securing water and the necessary 

 minerals. 



For best results the amount of active foUage and of active 

 rootlets must be in direct proportion; and, indeed, there is 

 such a close relation between the two, that if for some rea- 

 son the normal amount of active leaf surface is reduced, as 

 by insect injury, a corresponding amount of rootlets may 

 die because not fed, unless a surplus of stored material is 

 available. Even more surely, if the root system is in any 

 way curtailed, as for instance when a cut for a street is made, 



' Osmosis is the name for the process l^y which h'tjuids are diffused 

 through membranes. 



