ch such
layer forms an envelope around its inner neighbor, and is in turn
covered by the adjoining layer without, so that the whole stem is
built up of a series of thin, hollow cylinders, or rather cones.

A new layer of wood is formed each season, covering the entire stem,
as well as all the living branches. The thickness of this layer or the
width of the yearly ring varies greatly in different trees, and also
in different parts of the same tree.

In a normally-grown, thrifty pine log the rings are widest near the
pith, growing more and more narrow toward the bark. Thus the central
twenty rings in a disk of an old long-leaf pine may each be one-eighth
to one-sixth inch wide, while the twenty rings next to the bark may
average only one-thirtieth inch.

In our forest trees, rings of one-half inch in width occur only near
the center in disks of very thrifty trees, of both conifers and
hardwoods. One-twelfth inch represents good, thrifty growth, and the
minimum width of one two hundred inch is often seen in stunted spruce
and pine. The average width of rings in well-grown, old white pine
will vary from one-twelfth to one-eighteenth inch, while in the slower
growing long-leaf pine it may be one twenty-fifth to one-thirtieth of
an inch. The same layer of wood is widest near the stump in very
thrifty young trees, especially if grown in the open park; but in old
forest trees the same year's growth is wider at the upper part of the
tree, being narrowest near the stump, and often also near the very tip
of the stem. Generally the rings are widest near the center, growing
narrower toward the bark.

In logs from stunted trees the order is often reversed, the interior
rings being thin and the outer rings widest. Frequently, too, zones or
bands of very narrow rings, representing unfavorable periods of
growth, disturb the general regularity.

Few trees, even among pines, furnish a log with truly circular
cross-section. Usually it is an oval, and at the stump commonly quite
an irregular figure. Moreover, even in very regular or circular disks
the pith is rarely in the center, and frequently one radius is
conspicuously longer than its opposite, the width of some rings, if
not all, being greater on one side than on the other. This is nearly
always so in the limbs, the lower radius exceeding the upper. In
extreme cases, especially in the limbs, a ring is frequently
conspicuous on one side, and almost or entirely lost to view on the