are not yet out. This activity
commonly begins in January, February, and March, the exact time
varying with the kind of timber and the local atmospheric conditions.
And it has been found that green wood becomes lighter or contains less
water in late spring or early summer, when transpiration through the
foliage is most rapid. The amount of water at any one season, however,
is doubtless much influenced by the amount of moisture in the soil.
The fact that the bark peels easily in the spring depends on the
presence of incomplete, soft tissue found between wood and bark during
this season, and has little to do with the total amount of water
contained in the wood of the stem.

Even in the living tree a flow of sap from a cut occurs only in
certain kinds of trees and under special circumstances. From boards,
felled timber, etc., the water does not flow out, as is sometimes
believed, but must be evaporated. The seeming exceptions to this rule
are mostly referable to two causes; clefts or "shakes" will allow
water contained in them to flow out, and water is forced out of sound
wood, if very sappy, whenever the wood is warmed, just as water flows
from green wood when put in a stove.

Composition of Sap

The term "sap" is an ambiguous expression. The sap in the tree
descends through the bark, and except in early spring is not present
in the wood of the tree except in the medullary rays and living
tissues in the "sapwood."

What flows through the "sapwood" is chiefly water brought from the
soil. It is not pure water, but contains many substances in solution,
such as mineral salts, and in certain species--maple, birch, etc., it
also contains at certain times a small percentage of sugar and other
organic matter.

The water rises from the roots through the sapwood to the leaves,
where it is converted into true "sap" which descends through the bark
and feeds the living tissues between the bark and the wood, which
tissues make the annual growth of the trunk. The wood itself contains
very little true sap and the heartwood none.

The wood contains, however, mineral substances, organic acids,
volatile oils and gums, as resin, cedar oil, etc.

All the conifers--pines, cedars, junipers, cypresses, sequoias, yews,
and spruces--contain resin. The sap of deciduous trees--those which
shed their leaves at stated seasons--is lacking in this element, and
its constituents vary greatly in the different species. B