CHAPTER VIII 



OUR COMMON WOODS: THEIR IDENTIFICATION, 

 PROPERTIES AND USES 



WOODS have different values for various practical pur- 

 poses because of their peculiarities in structure. A knowl- 

 edge of the structural parts of wood is therefore necessary 

 as a means of recognizing the wood and of determining 

 why one piece is stronger, heavier, tougher, or better 

 adapted for a given service than another. 



Structure of wood: If one examines a cross-section of 

 the bole of a tree, he will note that it is composed of several 

 distinct parts, as shown in Fig. 145. At the very center 

 is a small core of soft tissue known as the pith. It is of 

 much the same structure as the pith of cornstalk or elder, 

 with which all are familiar. At the outside is the bark, 

 which forms a protective covering over the entire woody 

 system. In any but the younger stems, the bark is com- 

 posed of an inner, live layer, and an outer or dead portion. 



Between the pith at the center and the bark at the outside 

 is the wood. It will be noted that the portion next to the 

 bark is white or yellowish in color. This is the sapwood. It- 

 is principally through the sapwood that the water taken 

 in by the roots is carried up to the leaves. In some cases 

 the sapwood is very thin and in others it is very thi k, 

 depending partly on the kind of tree, and partly on its 

 age and vigor. The more leaves on a tree the more sap- 

 wood it must have to supply them with moisture. 



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