40. Wood, as a building material, is divided into three general groups, namely, the evergreen class, the tropical class, and the hardwoods.

In the first of these are classed the pine, spruce, hemlock, cedar, cypress, etc. The tropical woods include palm, rattan, bamboo, etc. The hardwoods are oak, chestnut, walnut, locust, maple, hickory, ash, boxwood, whitewood, and a number of others.

Each of these woods has peculiarities and characteristics which render it fit and useful for some building purposes, and utterly unfit and useless for others.