TIM'; TR I'!-. 17 



The actual shape of trees depends on the space they have to 

 grow in, on the soil, situation, and on the age of the trees. 

 Where trees have plenty of room to grow, and their natural 

 development is not interfered with, their individual character- 

 istics are most apparent. 



TREE GROWTH. 



Assimilation. Plants are made up of various tissues and 

 these are formed of numerous cells. The material of which the 

 cells are composed is largely carbon. This carbon is derived 

 from the carbon dioxide of the air which enters into the leaves 

 and under the action of light, air and water is there decom- 

 posed; the oxygen is given off and the carbon is retained, and, 

 combined with water obtained from the roots, forms starch, 

 sugar, gum and other plant foods. 



This process of food making is called assimilation and can 

 be carried on only in the green parts of the plant, and in these 

 only when exposed to light and air. Hence, foliage, air and 

 light at the top are essential prerequisites for tree growth, and, 

 other conditions being favorable, the greater quantity and bet- 

 ter development of foliage and the more light this foliage has 

 at its disposal for its work, the more vigorously will the tree 

 grow. 



In general, therefore, the growth of wood may be reduced 

 either by the removal of foliage, which reduces the working 

 surface, or by shading, which somewhat checks the activity of 

 tlic foliage by hindering light action. 



Transpiration. The flow of sap in trees is not well under- 

 stood. In a general way it may be said that the sapwood trans- 

 mits the water from the roots to the leaves, where a part enters 

 into the assimilated sap and goes to build up the plant, and the 

 remainder, which is by far the greater part, passes off as vapor. 

 The amount thus transpired varies greatly with the species, age 

 of the tree, amount of foliage at work, amount of light at its 

 disposal, climatic conditions and the condition of tree growth. 

 The amount of water transpired is so large in comparison to 

 the amount retained in the tree that while an acre of forest may 

 store in its trees i,oco pounds of carbon, 15 -or 20 pounds of 

 mineral substances and 5.000 pounds of water in a year, it may 



