PRINCIPLES OF AMERICAN FORESTRY. 



wood were it not for the fact that the outer layers of bark 

 fall off as the tree grows older. 



Wood once hardened never changes, and the branches 

 are practically always at the same height from the ground 

 They might be raised a little by the thickening of the 

 main roots. 



FIG. 1. Cross-section of Woody Stem. Diagram showing (a) outer 

 bark, (ft) inner bark or bast, (r) cambium, (d, e, f, g, and h) annual 

 rings of wood, and ({) pith. 



In some experiments the bark of rapidly growing 

 branches was peeled back in the spring for a few inches, the 

 wood covered with tin-foil and the bark replaced. At 

 the end of the season there was found a ring of wood out- 

 side of the tin-foil, thus showing where the annual growth 

 of the tree was made. 



The Bark covers the whole exterior surface of the trunk, 

 branches, and roots and serves as a protection. It is made 



