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 
freefrom signs of decay. 
