s.

Lumber and timber with diagonal grain is always weaker than
straight-grained material, the extent of the defect varying with
the degree of the angle the fibres make with the axis of the
stick. In the vicinity of large knots the grain is likely to be
cross. The defect is most serious where wood is subjected to
flexure, as in beams.

_Spiral grain_ is a very common defect in a tree, and when
excessive renders the timber valueless for use except in the
round. It is produced by the arrangement of the wood fibres in a
spiral direction about the axis instead of exactly vertical.
Timber with spiral grain is also known as "torse wood." Spiral
grain usually cannot be detected by casual inspection of a
stick, since it does not show in the so-called visible grain of
the wood, by which is commonly meant a sectional view of the
annual rings of growth cut longitudinally. It is accordingly
very easy to allow spiral-grained material to pass inspection,
thereby introducing an element of weakness in a structure.

There are methods for readily detecting spiral grain. The
simplest is that of splitting a small piece radially. It is
necessary, of course, that the split be radial, that is, in a
plane passing through the axis of the log, and not tangentially.
In the latter case it is quite probable that the wood would
split straight, the line of cleavage being between the growth
rings.

In inspection, the elements to examine are the rays. In the case
of oak and certain other hardwoods these rays are so large that
they are readily seen not only on a radial surface, but on the
tangential as well. On the former they appear as flakes, on the
latter as short lines. Since these rays are between the fibres
it naturally follows that they will be vertical or inclined
according as the tree is straight-grained or spiral-grained.
While they are not conspicuous in the softwoods, they can be
seen upon close scrutiny, and particularly so if a small hand
magnifier is used.

When wood has begun to dry and check it is very easy to see
whether or not it is straight- or spiral-grained, since the
checks will for the most part follow along the rays. If one
examines a row of telephone poles, for example, he will probably
find that most of them have checks running spirally around them.
If boards were sawed from such a pole after it was badly checked
they would fall to pieces of their own weight. The only way to
get straight material would be to split it