THE WOOD

CHARACTERISTICS OF WOOD

Wood is a I–41 fibrous tissue found in many plants. It has been used for centuries ice noth fuel and as a construction material. It is composed of 2 natural composite of cellulose fibers (which are strong in tensio .) embedded in a matrix of lignin. Lignin resists compression. W md is produced as secondary xylem in the stems of trees. In a living tree it transfers water and nutrients to the leaves and other growing tissues. It has a support function, enabling woody plants to reach large sizes or to stand up for themselves.

1. Formation

Wood is yielded by trees. A tree increases in diameter by the formation of new woody layers between the existing wood and the inner bark. It envelops the entire stem, living branches, and roots. Technically this is known as secondary growth. Secondary growth takes place by the cell division in the vascular cambium, a lateral meristem, and subsequent expansion of the new cells.

2. Growth rings

In some areas like Pakistan, there are clear seasons. Here growth can occur in a discrete annual or seasonal pattern, leading to growth rings. These rings can be clearly seen on the end of a log. These are also visible on the other surfaces. If these seasons are annual these growth rings are called as annual rings. Where there is no seasonal difference growth rings may be indistinct or absent. In some cases, there are differences within a growth ring. Wood is divided into two types on the basis of type of growth rings:

a) Early wood or springwood: The part of a growth ring nearest

the center of the tree arc formed early in the growing season. Growth is rapid during these seasons. They are composed of wider elements. It is lighter in color than that near the outer portion of the ring. It is known 3S early wood or springwood.

h) Late wood or summer wood; The outer portion formed later in the season is then known as fir: latewood or suminerwood.

3. Knots

A knot is a particular type of imperfection in a piece of wood. It will affect the technical properties of the wood. It makes the wood imperfect. But knots may be exploited for artistic effect. In a longitudinally sawn plank, a knot will appear as a roughly circular solid piece of wood. The grains of the rest of the wood flow around this piece of wood. Within a knot, the direction of the wood (grain direction) is up to 90 degrees different from the grain direction of the re ular wood.