20.] FROST SPLITS A common defect in standing timber results from radial splits which extend inward from the periphery of the tree, and almost, if not always, near the base.

It is most common in trees which split readily, and those with large rays and thin bark.

The primary cause of the splitting is frost, and various theories have been advanced to explain the action.
R.Hartig[35] believes that freezing forces out a part of the imbibition water of the cell walls, thereby causing the wood to shrink, and if the interior layers have not yet been cooled, tangential strains arise which finally produce radial clefts.
[Footnote 35: Hartig, R.: The diseases of trees (trans.

by Somerville and Ward), London and New York, 1894, pp.

282-294.] Another theory holds that the water is not driven out of the cell walls, but that difference in temperature conditions of inner and outer layers is itself sufficient to set up the strains, resulting in splitting.