Timber
Wood which is suitable for building and other construction purposes is called timber.
Structure And Growth of Tree:
Pith Or Medulla:
- Pith is the centre of the trunk.
- It is the first formed portion of the stem of the tree.
- It consists entirely of cellular tissues.
- It contains large amount of fluid and nourishes the plant.
- When the plant becomes old it dies and decays.
Annual Ring:
- The annual ring of woody fiber arrange in concentric circle around the pith.
- One ring is added every year.
Heart Wood:
- Innermost rings surrounding the pith.
- Dark colour, stronger ,compacted and durable.
Sap Wood:
- Outer annual rings of the tree.
- Transmit the sap from root to branches.
- Lighter in colour , weaker and more liable to decay.
Cambium Layer:
- Outer most one ring between the bark and sapwood.
- . Not converted into wood.
- In due course of time cambium layer is changes to sapwood.
- If exposed by removing bark ,result in death of tree.
Mudullary Rays:
- Thin horizontal veins radiating from the pith towards bark.
- Carry sap from outside to the inner parts of tree and nourish it.
- . Keep annual rings tightly together.
Growth and structure of tree:
Growth:
- In spring season the roots of the tree suck the solution of salts from the soil.
- The salts act as food and transmit to the trunk ,branches and leaves of the tree.
- In the presence of sun the solution of salts looses moisture because of evaporation and absorbs carbondioxide from the air.
- This transformation makes a viscous solution known as sap.
- In autumn season ,this viscous sap descends below the bark and leaves a thick layer.
- This thick layer below the bark gets transformed to wood known as cambium layer
- .With the passage of time this cambium layer gains the strength
- .Every year a fresh layer is formed which represents the age of the tree in years.
- Medullary rays carry the sap from below the bark to the interior thereby nourishing the tree.
Characteristics Of Hard And Soft Wood
Hard Wood:
- Heavier and dark in colour.
- Annual rings are not distinct.
- Comparatively hard and difficult to work upon.
- Contains large percentage of acid.
- Resists shearing stresses.
- Close-grained, strong and non resinous.
- Examples are Shisham , Sal, Teak ,Oak, Mahagony and Babul.
Soft Wood:
- Light in weight and colour.
- Annual rings are very distinct.
- Comparatively weaker and split easily.
- Contains straight fibers resins and turpentine and peculiar fragrance.
- Strong for resisting tensile force.
- Weak in direction across the grains.
- Texture is soft and regular.
- Examples are Spruce ,Deodar, Chir, Kail, Pines, Fir, and Walnut.
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