tree quickly dies, as it can derive no further
nourishment from the soil. Although absolutely necessary to the
growing tree, sapwood is often objectionable to the user, as it is the
first part to decay. In this sapwood many cells are active, store up
starch, and otherwise assist in the life processes of the tree,
although only the last or outer layer of cells forms the growing part,
and the true life of the tree.

The duramen or heartwood is the inner, darker part of the log. In the
heartwood all the cells are lifeless cases, and serve only the
mechanical function of keeping the tree from breaking under its own
great weight or from being laid low by the winds. The darker color of
the heartwood is due to infiltration of chemical substances into the
cell walls, but the cavities of the cells in pine are not filled up,
as is sometimes believed, nor do their walls grow thicker, nor are the
walls any more liquified than in the sapwood.

Sapwood varies in width and in the number of rings which it contains
even in different parts of the same tree. The same year's growth which
is sapwood in one part of a disk may be heartwood in another. Sapwood
is widest in the main part of the stem and often varies within
considerable limits and without apparent regularity. Generally, it
becomes narrower toward the top and in the limbs, its width varying
with the diameter, and being the least in a given disk on the side
which has the shortest radius. Sapwood of old and stunted pines is
composed of more rings than that of young and thrifty specimens. Thus
in a pine two hundred and fifty years old a layer of wood or an annual
ring does not change from sapwood to heartwood until seventy or eighty
years after it is formed, while in a tree one hundred years old or
less it remains sapwood only from thirty to sixty years.

The width of the sapwood varies considerably for different kinds of
pine. It is small for long-leaf and white pine and great for loblolly
and Norway pines. Occupying the peripheral part of the trunk, the
proportion which it forms of the entire mass of the stem is always
great. Thus even in old long-leaf pines, the sapwood forms 40 per cent
of the merchantable log, while in the loblolly and in all young trees
the sapwood forms the bulk of the wood.

The Annual or Yearly Rings

The concentric annual or yearly rings which appear on the end face of
a log are cross-sections of so many thin layers of wood. Ea