54 



IMPORTANT TIMBER TREES 



sions it should be allowed to grow, if other features named 

 do not interfere. 



In order to illustrate the increase in growth and to de- 

 termine the ratio of that increase, it will be assumed that 

 the tree selected for illustration is one of the fast-growing 

 species, as some of the pines, and regularly increases one 

 fourth of an inch in diameter each year, or puts on an an- 

 nual layer of one eighth of an inch in thickness. It is 

 manifest that a slow-growing tree will not increase in con- 

 tents as rapidly, but the ratio of increase, when based on 

 age, will, if the growth is uniform, show the same results. 



The accompanying table shows the diameter of a tree at 



every inch of growth from five up to twenty inches, the 

 age corresponding to such diameter, the square of that dia- 

 meter, the number of square inches in area where the 

 diameter is taken, which is at the stump, and the ra- 

 tio of increase of wood contents of the tree from the five- 

 inch up to the twenty-inch diameter. It will be seen that 

 the ratio of increase is based on the mathematical fact that 

 the areas of circles are to each other as the squares of their 

 diameters in this case that of the tree's stump. Thus a 



