Logs are sawed into timber, planks, or boards, and these forms are called lumber.
Fig. 71. A Large Band Saw
Timber refers to all of the largest sizes, such as beams and joists. Planks are wide strips over one inch thick, and boards are one inch or less in thickness, varying in width and length. Lumber may be planed at a planing mill, and is then known as dressed lumber. It may be dressed on one, two, or all sides. Dressed stock which is free from knots, shakes, and sapwood is called clear.
Fig. 72. End of Log, showing Annual Rings and Medullary Rays
By examining the end of a log we can learn a great deal of the life of the tree. It is made up of a number of irregular rings and of lines radiating from the center and running in nearly straight lines toward the bark.
The number of rings tells us the age of the tree, as a new ring is added each year.
As the tree grows, the old wood near the center becomes compressed and dry and is known as the heartwood, while that portion between the heartwood and bark is called sapwood.