ds of medium growth afford stronger material than when
very rapidly or very slowly grown. In many uses of wood,
strength is not the main consideration. If ease of working is
prized, wood should be chosen with regard to its uniformity of
texture and straightness of grain, which will in most cases
occur when there is little contrast between the late wood of one
season's growth and the early wood of the next.

HEARTWOOD AND SAPWOOD

Examination of the end of a log of many species reveals a
darker-colored inner portion--the _heartwood_, surrounded by a
lighter-colored zone--the _sapwood_. In some instances this
distinction in color is very marked; in others, the contrast is
slight, so that it is not always easy to tell where one leaves
off and the other begins. The color of fresh sapwood is always
light, sometimes pure white, but more often with a decided tinge
of green or brown.

Sapwood is comparatively new wood. There is a time in the early
history of every tree when its wood is all sapwood. Its
principal functions are to conduct water from the roots to the
leaves and to store up and give back according to the season the
food prepared in the leaves. The more leaves a tree bears and
the more thrifty its growth, the larger the volume of sapwood
required, hence trees making rapid growth in the open have
thicker sapwood for their size than trees of the same species
growing in dense forests. Sometimes trees grown in the open may
become of considerable size, a foot or more in diameter, before
any heartwood begins to form, for example, in second-growth
hickory, or field-grown white and loblolly pines.

As a tree increases in age and diameter an inner portion of the
sapwood becomes inactive and finally ceases to function. This
inert or dead portion is called heartwood, deriving its name
solely from its position and not from any vital importance to
the tree, as is shown by the fact that a tree can thrive with
its heart completely decayed. Some, species begin to form
heartwood very early in life, while in others the change comes
slowly. Thin sapwood is characteristic of such trees as
chestnut, black locust, mulberry, Osage orange, and sassafras,
while in maple, ash, gum, hickory, hackberry, beech, and
loblolly pine, thick sapwood is the rule.

There is no definite relation between the annual rings of growth
and the amount of sapwood. Within the same species the
cross-sectional area of the sapwood is roughly proporti