Speaking

Speak about:

1. The wide use of timber in our life.

2. The use of timber in prehistoric times.

3. A scientific study of wood.

4. The use of wood residues.

Unit 4

Indefinite, Continuous, Perfect Tenses Active Voice

Grammar:

Wood formation

Wood is a fascinating natural material to use, study and admire. From the very earliest times man has used wood for tools and weapons, buildings, furniture, or just as fuel for his fires. Nowadays wood serves very many purposes too. As a matter of fact, it is adaptable to both structural and decorative use.

But it is impossible to use valuable qualities of wood without gaining some knowledge of the structure and chemical composition of this material. Being a representative of the woody plants a tree has three main parts: roots, a stem and leaves.

A stem or a trunk has always been of the greatest value in the manufacture of wood products. The trunk has an outer covering called the bark which protects the wood from extremes of temperature, mechanical injury and harmful fungi and insects.

Between the bark and the wood there is a thin delicate tissue known as cambium. This tissue produces both the bark and the wood. The enlargement of the trunk in girth is brought about entirely by the activity of the cambium.

The production of wood and bark tissue occurs only when the cambium is growing. In temperate regions this occurs during the spring and summer months. During this period of time leaves in the tree's crown have to work hard. They are winning carbon dioxide from the air and transforming it into the new carbon

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compounds the wood is composed of.

The roots are working hard as well. To supply the tree with mineral salts needed for its life processes the roots are carefully exploring the soil under the tree. All this time sap is actively flowing from the roots up the stem.

No wood is formed during autumn when the rhythm of growth slows down, nor in winter when the tree rests. Many trees are leafless at that time of the

year. New cells produced due to the activity of the cambium form layers of wood

called sapwood. The function of sapwood is to carry sap. A tree is getting older, slow chemical changes are taking place in its inner layers. As a result, sapwood is turned into heartwood.

Heartwood is harder and stronger than sapwood. In the majority of timbers heartwood is more resistant to decay. Therefore it is desirable to exclude the use of sapwood in situations where the likehood of fungi infection is considerable.

General understanding

Read the text attentively and answer the questions.

1. What purposes did ancient people use wood for?

2. Does wood serve many purposes nowadays?

3. Why is it necessary to know the structure and composition of wood?

4. What part of the tree is of the greatest value in the manufacture of wood products?

5. What is the function of the bark?

6. Where is cambium located?

7. When does the production of wood and bark tissue occur?

8. Why are the roots carefully exploring the soil under the tree?

9. What is the function of sapwood?

10. What is heartwood?