27.) If evaporation proceeds more rapidly on the outside than inside, the greater shrinkage of the outer portions is bound to result in many checks, the number and size increasing with the degree of inequality of drying.
In cold weather, drying proceeds slowly but uniformly, thus allowing the wood elements to adjust themselves with the least amount of rupturing.

In summer, drying proceeds rapidly and irregularly, so that material seasoned at that time is more likely to split and check.
There is less danger of sap rot when trees are felled in winter because the fungus does not grow in the very cold weather, and the lumber has a chance to season to below the danger point before the fungus gets a chance to attack it.

If the logs in each case could be cut into lumber immediately after felling and given exactly the same treatment, for example, kiln-dried, no difference due to the season of cutting would be noted.
WATER CONTENT[48] [Footnote 48: See Tiemann, H.D.: Effect of moisture upon the strength and stiffness of wood.Bul.70, U.S.Forest Service, Washington, D.C., 1906; also Cir.

108, 1907.] Water occurs in living wood in three conditions, namely: (1) in the cell walls, (2) in the protoplasmic contents of the cells, and (3) as free water in the cell cavities and spaces.

In heartwood it occurs only in the first and last forms.