CHAPTER XXXI 

 TREES 



434. Industrial Advantages of Wood. Wood is the most 

 important material used by carpenters, cabinetmakers, 

 shipwrights, and other wood-workers in carrying on their 

 respective trades. It possesses certain physical character- 

 istics that make it very valuable for industrial purposes 

 it is easily worked with tools into desired shapes and sizes; 

 it is easily penetrated by fastening agents, such as nails and 

 screws; it is strong, light, and easy to handle; it is a non- 

 conductor of heat and electricity; and it can be protected 

 by paint from the effects of air and moisture. 



435. Characteristics of Trees. Wood is, of course, ob- 

 tained from trees of various kinds. Though each kind of 

 tree produces a distinct type of wood, all trees have cer- 

 tain characteristics in common. Trees consist of three 

 parts: (1) the roots, which extend into the ground to a length 

 of 30 to 40 ft., or still farther when the soil is not too hard and 

 they do not find moisture enough near the surface; (2) the 

 trunk or stem, which supports the crown and supplies it with 

 mineral food and water from the roots; (3) the crown, a 

 network of branches, buds, and leaves. 



436. Sap-wood and Heart-wood. A cross-section view 

 of a tree shows the bark on the outside, the heart-wood in 

 the center of the trunk, and the sap-wood between the two. 



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