The wood surrounding the center of a tree is heart wood and outside of this is the sap wood, usually lighter in color than the heart. Sap wood, except in certain trees, as ash and hickory, is less hard and durable than heart wood. However when the heart wood at the center of the tree is exposed in the surface of a board, it tends to split away from the board. The amount of sap or heart wood in a piece of sawed timber may be seen by the difference in color of the sawed surface, also end inspection will show from which part of the tree the piece is taken.

In Fig. 4 the large radii of curvature of the rings show these as sap pieces, the points A being nearest the bark. Fig. 5 shows heart pieces, indicated by the curvature of the rings. The heart of the tree is at B.

Fig. 4.

Fig. 5.