GROWTH 9 



ter under the present demands of the market. 

 A glance at it shows that, while over 85 per 

 cent, of the length of a tree 40 inches in diam- 

 eter is valuable for lumber, the proportion falls 

 to 80.5 per cent, at the diameter of 20 inches, and 

 to 68.3 per cent, when the diameter is only 10 

 inches. The comparatively slow increase of 

 the percentage of lumber length after a diame- 

 ter of 20 inches has been reached is interest- 

 ing in connection with the slow rate of height 

 growth in old trees. 



The thickness of bark on the White Pine va- 

 ries with the situation, among trees of the same 

 age, and is different on different sides of the 

 tree. Pines standing in the open have thicker 

 bark, as well as a larger diameter and thicker 

 sap-wood, than those in crowded woods. On 

 old trees the bark is often exceedingly thick. 

 A conspicuous instance is supplied by the very 

 old tree already mentioned. Its bark measured 

 3.8 inches on the stump, whereas the average 

 thickness for first-growth Pine is between one 

 and two inches. On suppressed trees two hun- 

 dred years old it is frequently as little as half 

 an inch. 



In trees over one hundred years old the bark 

 varies from 9 to 12 per cent, of the total vol- 

 ume, and reaches an average of 11 per cent. 



