ne to one-half inches at the
stump to one-tenth inch near the top of the tree, and forms in general
about ten to fifteen per cent of the entire trunk. The pith is quite
thick, usually one-eighth to one-fifth inch in southern species,
though much less so in white pine, and is very thin, one-fifteenth to
one twenty-fifth inch in cypress, cedar, and larch.

In woods with a thick pith, the pith is finest at the stump, grows
rapidly thicker toward the top, and becomes thinner again in the crown
and limbs, the first one to five rings adjoining it behaving
similarly.

What is called the pith was once the seedling tree, and in many of the
pines and firs, especially after they have been seasoning for a good
while, this is distinctly noticeable in the center of the log, and
detaches itself from the surrounding wood.

Sap and Heartwood

Wood is composed of duramen or heartwood, and alburnum or sapwood, and
when dry consists approximately of 49 per cent by weight of carbon, 6
per cent of hydrogen, 44 per cent of oxygen, and 1 per cent of ash,
which is fairly uniform for all species. The sapwood is the external
and youngest portion of the tree, and often constitutes a very
considerable proportion of it. It lies next the bark, and after a
course of years, sometimes many, as in the case of oaks, sometimes
few, as in the case of firs, it becomes hardened and ultimately forms
the duramen or heartwood. Sapwood is generally of a white or light
color, almost invariably lighter in color than the heartwood, and is
very conspicuous in the darker-colored woods, as for instance the
yellow sapwood of mahogany and similiar colored woods, and the reddish
brown heartwood; or the yellow sapwood of _Lignum-vitae_ and the dark
green heartwood. Sapwood forms a much larger proportion of some trees
than others, but being on the outer circumference it always forms a
large proportion of the timber, and even in sound, hard pine will be
from 40 per cent to 60 per cent of the tree and in some cases much
more. It is really imperfect wood, while the duramen or heartwood is
the perfect wood; the heartwood of the mature tree was the sapwood of
its earlier years. Young trees when cut down are almost all sapwood,
and practically useless as good, sound timber; it is, however, through
the sapwood that the life-giving juices which sustain the tree arise
from the soil, and if the sapwood be cut through, as is done when
"girdling," the