tropical species.
It is the source of considerable loss in the fancy veneer
industry, as the veneer from valuable logs so affected drops to
pieces.

The cause of heart break is not positively known. It is highly
probable, however, that when the tree is felled the trunk
strikes across a rock or another log, and the impact causes
actual failure in the log as in a beam.

_Resin_ or _pitch pockets_ are of common occurrence in the wood
of larch, spruce, fir, and especially of longleaf and other hard
pines. They are due to accumulations of resin in openings
between adjacent layers of growth. They are more frequent in
trees growing alone than in those of dense stands. The pockets
are usually a few inches in greatest dimension and affect only
one or two growth layers. They are hidden until exposed by the
saw, rendering it impossible to cut lumber with reference to
their position. Often several boards are damaged by a single
pocket. In grading lumber, pitch pockets are classified as
small, standard, and large, depending upon their width and
length.

INSECT INJURIES[37]

[Footnote 37: For detailed information regarding insect
injuries, the reader is referred to the various publications of
the U.S. Bureau of Entomology, Washington, D.C.]

The larvae of many insects are destructive to wood. Some attack
the wood of living trees, others only that of felled or
converted material. Every hole breaks the continuity of the
fibres and impairs the strength, and if there are very many of
them the material may be ruined for all purposes where strength
is required.

Some of the most common insects attacking the wood of living
trees are the oak timber worm, the chestnut timber worm,
carpenter worms, ambrosia beetles, the locust borer, turpentine
beetles and turpentine borers, and the white pine weevil.

The insect injuries to forest products may be classed according
to the stage of manufacture of the material. Thus round timber
with the bark on, such as poles, posts, mine props, and sawlogs,
is subject to serious damage by the same class of insects as
those mentioned above, particularly by the round-headed borers,
timber worms, and ambrosia beetles. Manufactured unseasoned
products are subject to damage from ambrosia beetles and other
wood borers. Seasoned hardwood lumber of all kinds, rough
handles, wagon stock, etc., made partially or entirely of
sapwood, are often reduced in value from 10 to 90 per cent by a
class of inse