In common usage wood is said to be "coarse grained" when its annual rings are wide and "fine grained" when they are narrow. The term " fine grained " is also sometimes applied to those woods which are capable of high polish, and this depends chiefly on the hardness of the wood. When the direction of the fibres is parallel to the axis of the stem or limb the wood is "straight grained," and when the course of the fibres is spiral or twisted around the tree the wood is "cross grained." Sometimes the fibres take the shape of fine waves, when the wood is said to be wavy or "curly" grain. The latter is frequently seen in maple.
Generally the surface of the tree under the bark is not uniform and smooth, but has more or less elevations or depressions, and the same is also true of the layers in the interior. In some woods these depressions or elevations are maintained in only a few layers, while in others they increase from year to year. On tangent boards of such woods the section of these pits and prominences appear as circlets and give rise to beautiful figures. In maple the tendency to preserve any particular contour is very great, and as the depressions and elevations are usually small and very numerous, they appear on the face of the boards as very fine circlets, and hence the term "bird's-eye" maple.
*Filbert Roth, Bulletin No. 10, U. S. Department of Agriculture.
The branches or limbs of a tree also affect the grain and the appearance of a board cut through or near them.
"At the junction of a branch with the stem of the tree the fibres on the upper and lower sides of the branch behave differently. On the lower side they run from the stem into the limb, forming an uninterrupted strand or tissue and' a perfect union [as shown in Fig. 4]. On the upper side the fibres bend aside and are not continuous into the limb."
Owing to this arrangement of the fibres the cleft made in splitting never runs into the knot if started above the limb, but is apt to enter the knot if started below.
When limbs die, decay and break off the remaining stubs are surrounded and finally covered by the growth of the
So long as these knots preserve their natural color they are not classed as dead, but are nevertheless dead from the point where they cease to be united with the living wood.
Dead knots in pine and spruce almost always become loose, so that when the log is sawed into boards the sections of the knots drop out 7. Color and Odor. - The color of wood lends to its beauty, aids in its identification and is of great assistance in judging of its quality. Each different variety of wood has its own peculiar color, at least for the heartwood, and this when known offers a reliable mark of distinction.
Newly-formed wood, like that of the outer few rings, has little Fig. 4. - Section of Wood Showing limb -which lived four years, then died and broke off near the stem, leaving the part to the left of a, b a right a "dead" 'knot, which would color. In all trees the sapwood is generally light, and in the hard woods there is often a great difference in the color of the sapwood and heartwood.
The color of good timber should be uniform throughout the heart-wood; when it is blotchy or varies much in color from the heart outward, or becomes pale suddenly toward the limit of the sapwood, it is probably diseased.
"When wood is attacked by fungi it becomes more opaque, loses its brightness, and in practice is designated 'dead' in distinction to 'live' or bright timber.
"Exposure to air darkens all wood; direct sunlight and occasional moistening hasten this change and cause it to penetrate deeper. Prolonged immersion has the same effect, pine wood becoming a dark gray, while oak changes to a blackish brown."
The odor of wood is caused by chemical substances contained in it, but which form no part of the wood substance itself. Exposure to weather reduces and often changes the odor, but most of the soft woods exhale apparently as much odor as ever when a fresh surface is exposed.
Many kinds of wood are distinguished by strong and peculiar odors, which aid in identifying the variety, and in some cases give the wood a peculiar value.
Decomposition is usually accompanied by pronounced odors; decaying poplar emits a disagreeable odor, while red oak often becomes fragrant, its smell resembling that of heliotrope.