2 PRINCIPLES OF AMERICAN FORESTRY. 



by their being smaller than adjoining rings and less dis- 

 tinctly defined. The age of trees could be told by the 

 rings of the outer bark nearly as well as by those of the 

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

 fall off as the tree grows older. 



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

 bark, (h) inner bark or bast, (c) cambium, (d, e, /, g, and h) annual 

 rings of wood, and {i) 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 



