Spruce
impregnated with crude resin and dried is greatly increased in
strength thereby.

[Footnote 28: Bul. 70, U.S. Forest Service, p. 92; also p. 126,
appendix.]

Since the late wood of a growth ring is usually darker in color
than the early wood, this fact may be used in judging the
density, and therefore the hardness and strength of the
material. This is particularly the case with coniferous woods.
In ring-porous woods the vessels of the early wood not
infrequently appear on a finished surface as darker than the
denser late wood, though on cross sections of heartwood the
reverse is commonly true. Except in the manner just stated the
color of wood is no indication of strength.

Abnormal discoloration of wood often denotes a diseased
condition, indicating unsoundness. The black check in western
hemlock is the result of insect attacks.[29] The reddish-brown
streaks so common in hickory and certain other woods are mostly
the result of injury by birds.[30] The discoloration is merely
an indication of an injury, and in all probability does not of
itself affect the properties of the wood. Certain rot-producing
fungi impart to wood characteristic colors which thus become
criterions of weakness. Ordinary sap-staining is due to fungous
growth, but does not necessarily produce a weakening effect.[31]

[Footnote 29: See Burke, H.E.: Black check in western hemlock.
Cir. No. 61, U.S. Bu. Entomology, 1905.]

[Footnote 30: See McAtee, W.L.: Woodpeckers in relation to trees
and wood products. Bul. No. 39, U.S. Biol. Survey, 1911.]

[Footnote 31: See Von Schrenck, Hermann: The "bluing" and the
"red rot" of the western yellow pine, with special reference to
the Black Hills forest reserve. Bul. No. 36, U.S. Bu. Plant
Industry, Washington, 1903, pp. 13-14.

Weiss, Howard, and Barnum, Charles T.: The prevention of
sapstain in lumber. Cir. 192, U.S. Forest Service, Washington,
1911, pp. 16-17.]

CROSS GRAIN

_Cross grain_ is a very common defect in timber. One form of it
is produced in lumber by the method of sawing and has no
reference to the natural arrangement of the wood elements. Thus
if the plane of the saw is not approximately parallel to the
axis of the log the grain of the lumber cut is not parallel to
the edges and is termed diagonal. This is likely to occur where
the logs have considerable taper, and in this case may be
produced if sawed parallel to the axis of growth instead of
parallel to the growth ring