PROPERTIES OF WOOD AND THEIR USES 57 



finishes more readily and on account of the narrowness 

 of the growth rings presents a more uniform appearance 

 after it has been planed and polished. 



Durability. The length of time a given species will 

 resist decay in use depends upon the species, the rate 

 of growth of the individual and to a certain degree 

 upon the soil which produced the tree. Broadleaf 

 species are usually more durable than evergreens, 

 although the wood of the hard pines will outlast that 

 produced by the willow or cottonwood. In fact the 

 cypress, one of our most durable woods, belongs to the 

 evergreen group. So lasting is this wood that it has 

 been called "the wood eternal," and after seeing the 

 splendid condition of the shingles upon some of the 

 old Southern plantation houses, the description does 

 not seem inept. Certain woods, like chestnut and the 

 oaks, contain substances called tannins which are anti- 

 septic and retard bacterial action; the oil in cedar has 

 the same effect. , 



Dense hardwoods are usually quite durable, although 

 such heavy woods as maple, birch and beech are by no 

 means lasting. In these cases the large amount of 

 moisture and starch contained in the wood makes them 

 especially subject to the action of the agencies of decay. 

 Mesquite, a heavy dark wood of the Southwest, is 

 especially durable. This tree grows in such arid 

 surroundings that it develops a deep wide-spreading 

 root system. It is this tree which gives rise to the 

 remark that in certain parts of New Mexico it is neces^ 

 sary to dig for firewood as more of the tree is found 

 below than above the surface of the ground. It is an 

 actual fact that a tie made from this species has remained 

 in position for thirty-two years and was then absolutely 

 free from signs of decay. 



