540 JOURNAL OF FORESTRY 



1892 was less than 20 centimeters in diameter and which from 1892 to 

 1900, or in eight years, has grown to a 20-centimeter class. Since there 

 are 10,206 20-centimeter trees in 1900, of which 7,399 came from the 

 15-centimeter diameter class, the difference, 2,807, represents the ma- 

 terial which in 1892 was already 20 centimeters and which has not as 

 yet passed this class. 



On the other hand, there were in 1892 6,826 trees, 20 centimeters of 

 which, 2,807, have not passed the class; the difference, 4,019, have then 



passed the class in eight years and entered the 25-centimeter class. 



o 

 For a tree to reach the 25-centimeter class it required years, and 



Q 



for the 6,826 trees it will require X 6,826= 13.5 years. Rea- 



soning similarly for the following age classes, 4,019 trees have passed 

 in eight years from 20 to 25. In 1900 there were 6,521 trees 25 centi- 

 meters ; of this number 4,019 came from the 20-centimeter class ; the 

 difference, 2,502, represents the trees which were 25 centimeters in 

 1892 and which have not passed the 30-centimeter class. In 1892 there 

 were 5,575 trees of 25 centimeters, of which 2,502 had not passed the 

 class ; the difference, 3,075, thus passed in eight years to the 30-centi- 

 meter class, and for the 5,575 trees of 25 centimeters to pass it re- 





 quires X 5,575 = i4-5 years, and similarly for the other classes. 



We have thus found, after having corrected several discrepancies of 

 the curve, the results given in column 5 of Table i. The figures ob- 

 tained are naturally subject to revision when they differ materially 

 with the density of the stands, and we believe that when the trees are 

 properly spaced, as we intend progressively to do, they will pass into 

 the different classes in less time. 



Table I 



(b) Price per cubic meter standing for each diameter class. — Ac- 

 cording to the results of sales and the data furnished by sales, the price 



