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.