ects only one or two central boards
when cut into lumber, but in spiral-grained timber the damage is
much greater. When shake consists of several radial clefts it is
termed _star shake_. In some instances one or more of these
clefts may extend nearly to the bark. In felled or converted
timber clefts due to heart shake may be distinguished from
seasoning cracks by the darker color of the exposed surfaces.
Such clefts, however, tend to open up more and more as the
timber seasons.

_Cup_ or _ring shake_ results from the pulling apart of two or
more growth rings. It is one of the most serious defects to
which sound timber is subject, as it seriously reduces the
technical properties of wood. It is very common in sycamore and
in western larch, particularly in the butt portion. Its
occurrence is most frequent at the junction of two growth layers
of very unequal thickness. Consequently it is likely to occur in
trees which have grown slowly for a time, then abruptly
increased, due to improved conditions of light and food, as in
thinning. Old timber is more subject to it than young trees. The
damage is largely confined to the butt log. Cup shake is often
associated with other forms of shake, and not infrequently shows
traces of decay.

The causes of cup shake are uncertain. The swaying action of the
wind may result in shearing apart the growth layers, especially
in trees growing in exposed places. Frost may in some instances
be responsible for cup shake or at least a contributing factor,
although trees growing in regions free from frost often have
ring shake. Shrinkage of the heartwood may be concentric as well
as radial in its action, thus producing cup shake instead of, or
in connection with, heart shake.

A local defect somewhat similar in effect to cup shake is known
as _rind gall_. If the cambium layer is exposed by the removal
of the entire bark or rind it will die. Subsequent growth over
the damaged portion does not cohere with the wood previously
formed by the old cambium. The defect resulting is termed rind
gall. The most common causes of it are fire, gnawing, blazing,
chipping, sun scald, lightning, and abrasions.

_Heart break_ is a term applied to areas of compression failure
along the grain found in occasional logs. Sometimes these breaks
are invisible until the wood is manufactured into the finished
article. The occurrence of this defect is mostly limited to the
dense hardwoods, such as hickory and to heavy