The layers of wood that are formed each year appear as rings on the cross section of the log, and by counting them the age of that portion of the tree may be determined.
The width of these yearly rings varies greatly in different trees and also in different parts of the same tree. The average width of the rings in well-grown old white pine will vary from 1/12 to 1/18 inch, while in the slower growing long-leaf pine it may be 1/25 to 1/30 of an inch. While these rings are approximately circular in shape, it is very seldom that they are a true circle; usually they are oval in shape, and at the stump they commonly form quite an irregular figure.
"The greater regularity or irregularity of the annual rings has much to do with the technical qualities of the timber."
Spring and Summer Wood. - If the annual rings are examined closely it will be noticed that each ring is made up of an inner, softer, light-colored portion, and an outer, firmer and darker colored portion. Being formed in the fore part of the season, the inner, light-colored part is termed spring wood, the outer, darker portion being the summer wood of the ring.
The summer wood is much firmer and heavier than the spring wood, and hence the greater the proportion of summer wood to the total volume the greater will be both the weight and strength of the timber.
The darker color of the summer wood also influences the shade of color of the entire piece of wood, and in the pines this color effect affords a valuable aid in distinguishing the heavy and strong from the light and soft woods.
"In some trees like the hard pines the dark summer wood appears as a distinct band, so that the yearly ring is composed of two sharply-defined bands - an inner, the spring wood, and an outer, the summer wood. But in some cases, even in hard pines, and normally in the wood of white pines, the spring wood passes gradually into the darker summer wood, so that a sharply-defined line occurs only where the spring wood abuts against the summer wood of its inner neighbor. It is this clearly-defined line which enables the eye to distinguish even the very narrow rings in old pines and spruces."
In a pine board, sawed from near the centre of the log, the spring and summer woods will appear about as shown in Fig. 3, an inner, lighter strip and its outer, darker neighbor always corresponding to one annual ring. If the tree was perfectly straight and the rings of uniform thickness, the spring and summer wood would appear on the face of the board as parallel bands, but, owing to the irregularity of the growth, the two kinds of wood usually form a variety of pleasing patterns on the face of bastard boards.
Where a saw cut passes through a bump or crook of the log, irregular concentric circlets and ovals are produced, and on almost all bastard boards arrow or V-shaped forms occur.
Although no dividing line between these two classes of woods is universally recognized, the "hard woods " are generally classed as those cut from broad-leaved trees and the "soft woods" as those from coniferous or needle-leaved trees, such as the pines, spruce and cedar.
" Though alike in their manner of growth, and therefore similar in their general make-up, conifers and broad-leaved trees differ markedly in the details of their structure and the character of their wood. The wood of all conifers is very simple in its structure, the fibres composing the main part of the wood being all alike and their arrangement regular.
"The wood of broad-leaved trees is complex in structure; it is made up of several different kinds of cells and fibres and lacks the regularity of arrangement peculiar to the conifers."*