cit._] Specifications for paving blocks often require that longleaf pine be 90 per cent heart.

This is on the belief that sapwood is not only more subject to decay, but is also weaker than heartwood.

In reality there is no sound basis for discrimination against sapwood on account of strength, provided other conditions are equal.

It is true that sapwood will not resist decay as long as heartwood, if both are untreated with preservatives.

It is especially so of woods with deep-colored heartwood, and is due to infiltrations of tannins, oils, and resins, which make the wood more or less obnoxious to decay-producing fungi.