Structure of a Timber Tree

The trees which grow outwards about the centre are called exogenous trees. The cross sectional details of such a tree are shown. Exogenous trees such as Sal, Babul, Teak, etc. are used for all engineering purposes. If trunk of tree is cut in transverse direction, the annual rings can be seen which are useful in predicting the age of tree. The cross- sectional parts of tree and their functions are described below (parts from outer to inner).

(i) Bark or skin:

It is the outermost portion of tree. The outer bark protects the tree from high temperature and mechanical harm. The inner bark covering the cambium layer protects cambium layer from injury and also supplies food to those parts where it is needed most.

(ii) Cambium layer:

This layer of sap between inner bark and sapwood is known as cambium layer. This layer makes bark on the outer side and wood on inner side. It is an immature sap wood.

(iii) Sap wood:

The outer annual rings between cambium layer and heart wood are known as sap wood. It is usually light in colour and weight as compared to heart wood. Sap (i.e., plant juice and moisture ) actually is the food of tree which is made available to the tree from the ground through roots. Sapwood is not used for any engineering work because it contains large amount of moisture and is liable to quick decay.

(iv) Medullary rays:

These are thin radial fibres between cambium layer and pith of tree. The function of these rays is to hold together the annual rings of sapwood and heartwood. In addition to this, these rays store the food of the tree and distribute to different parts according to the necessity.

(v) Heart wood:

The annual rings between sapwood and pith form the heart wood. The rings of heartwood are closer than rings of sapwood. Heartwood is darker in colour and is strong and durable. Actually, the sapwood gets converted to heartwood in due course of time, usually 10 to 30 years. Heartwood is dead portion of tree and does not take part in the growth of tree. Heartwood is used for all engineering works.

(vi) Medullary sheath:

It is a layer between heart wood and the pith. It covers the pith from all around.

(vii) Pith:

It is the innermost portion of the tree. Pith is very soft portion and varies in size and shape for different types of trees. It consists entirely of cellular tissues.

Find More About,

Timber
Structure of a Timber Tree
Properties or Characteristics of Timber
Defects of Timber
Diseases of Timber - Dry and Wet Rot
Decay of Timber
Seasoning of Timber
Methods of Seasoning of Timber
Preservation of Timber