76 THE WHITE PINE 



It is undoubtedly true that a tree which is the 

 average tree at one period will not always be 

 so; but by the use of the average trees of 

 groups of different ages the error which may 

 arise is almost wholly eliminated. The ques- 

 tion is a very complicated one, and for the pur- 

 pose in hand this method is sufficiently correct. 



The height growth reaches its maximum rate 

 earlier as the quality of the locality improves. 

 The most rapid growth in height takes place 

 between 15 and 20 years on soil of quality I, 

 between 20 and 30 years on quality II, and be- 

 tween 30 and 40 years on quality III. 



The diameter of the average tree was found 

 by plotting the growths of the average trees of 

 the various groups, and by constructing curves 

 in the same way as for the height growth. (See 

 Plate II.) 



The basal areas of the valuation survey acres 

 were computed for fully stocked acres and 

 plotted on cross-section paper, and curves were 

 constructed in the same manner as the curves 

 for the volume yield. These curves were found 

 to rise very rapidly at first, then to lay them- 

 selves over, and finally to run on a straight line. 



The number of trees per acre is found from 

 the material already obtained. The total basal 

 area per acre at different periods is divided by 



