stion. One is concerned with the
physiological changes which might take place during the year in
the wood of a living tree. The other deals with the purely
physical results due to the weather, as differences in
temperature, humidity, moisture, and other features to be
mentioned later.

Those who adhere to the first view maintain that wood cut in
summer is quite different in composition from that cut in
winter. One opinion is that in summer the "sap is up," while in
winter it is "down," consequently winter-felled timber is drier.
A variation of this belief is that in summer the sap contains
certain chemicals which affect the properties of wood and does
not contain them in winter. Again it is sometimes asserted that
wood is actually denser in winter than in summer, as part of the
wood substance is dissolved out in the spring and used for plant
food, being restored in the fall.

It is obvious that such views could apply only to sapwood, since
it alone is in living condition at the time of cutting.
Heartwood is dead wood and has almost no function in the
existence of the tree other than the purely mechanical one of
support. Heartwood does undergo changes, but they are gradual
and almost entirely independent of the seasons.

Sapwood might reasonably be expected to respond to seasonal
changes, and to some extent it does. Just beneath the bark there
is a thin layer of cells which during the growing season have
not attained their greatest density. With the exception of this
one annual ring, or portion of one, the density of the wood
substance of the sapwood is nearly the same the year round.
Slight variations may occur due to impregnation with sugar and
starch in the winter and its dissolution in the growing season.
The time of cutting can have no material effect on the inherent
strength and other mechanical properties of wood except in the
outermost annual ring of growth.

The popular belief that sap is up in the spring and summer and
is down in the winter has not been substantiated by experiment.
There are seasonal differences in the composition of sap, but so
far as the amount of sap in a tree is concerned there is fully
as much, if not more, during the winter than in summer.
Winter-cut wood is not drier, to begin with, than
summer-felled--in reality, it is likely to be wetter.[47]

[Footnote 47: See Record, S.J.: Sap in relation to the
properties of wood. Proc. Am. Wood Preservers' Assn., Baltimore,
Md., 1913, pp.