Heartwood and sapwood

Heartwood and sapwood

a)     Heart wood: Heartwood (or “xylem”) is wood that as a result of tylosis become more resistant to decay. Tylosis is the deposition of chemical substances (a genetically programmed process). Once heartwood formation is complete, the heartwood is dead. Some uncertainty still exists as to whether heartwood is truly dead, as it can still chemically react to decay organisms. Usually heartwood looks different; in that case it can be seen on a cross-section. Heartwood may (or may not) be much darker than living wood. It may (or may not) be sharply distinct from the sapwood. However, other processes, such as decay, can discolor wood, even in woody plants. The term heartwood derives from its position and not from any vital importance to the tree. A tree can thrive with its heart completely decayed.

b)     Sapwood: Sapwood is the younger, outermost wood. In the growing tree it is living wood. Its principal functions are to conduct water from the roots to the leaves. It also store up and give back aecording to the season the reserves prepared in the leaves. All xylem tracheids and vessels have lost their cytoplasm and the cells are therefore functionally dead in sapwood. All wood in a tree is first formed as sapwood. The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees grown in the open may become of considerable size, 30 cm or more in diameter, before the formation of heartwood. Some species begin to form heartwood very early in life. Therefore, they have only a thin layer of live sapwood. But in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut, black locust, mulberry, osage-orange, and sassafras. But it is thick in maple, ash, hickory, hackberry, beech, and pine. Some others never form heartwood.