THE WOOD 217 



THE WOOD 



Having learned something about forests, let us now 

 examine a little more closely their main product, the wood. 



SOME STRUCTURAL FEATURES 



Sap and Heart. We have observed on some of the 

 stumps and ends of logs that different kinds differ in 

 appearance. On the oak we saw the rough bark outside, 

 then a layer of lighter colored wood, the sapwood ; and 

 within this the darker heartwood, containing, somewhere 

 near the center, the tiny brownish pith. This same 

 arrangement of sapwood and heartwood we find in the 

 majority of our useful timber trees. In some, like hick- 

 ory and elm, the sapwood is wide ; in others, like the 

 locust and catalpa, it is narrow ; and in some trees, like 

 spruce, balsam, hemlock, and maple, it has no distinct 

 color at all. The sapwood and heartwood differ not only 

 in color, but also in durability ; the sapwood part of our 

 oak post decays in a very short time, while the heartwood 

 part lasts for years. This difference is very important, 

 and particularly in those kinds of woods where the heart 

 is durable. 



Annual Rings. We have also noticed that the wood 

 at the end of the log appears to be made up of rings ; 

 and we learned that these are called annual or yearly 



