II Прочтите 4-ый абзац текста и исьменно ответьте на следующий вопрос:

Why can we clearly see the annual rings on a cross-section of a tree?

Контрольная работа № 5

(для специальности ТД)

Вариант 2

I Прочтите и устно переведите с 1-го по 5-ый абзацы текста.

Перепишите и письменно переведите 3, 4, 5 абзацы текста.

SAPWOOD AND HEARTWOOD

1. On a cross-section of a tree stem you can usually see a dark-coloured centre and light-coloured wood nearer to the bark. The light-coloured wood is called sapwood. It is made of living cells and is in communication with the cambium and inner living bark. The dark-coloured wood in the centre is called heartwood. It consists of dead cells. Its main function is mechanical support of the stem and the crown.

2. When the tree is young it has no heartwood. The formation of heartwood begins when the tree grows to a certain height. This process begins at different time in different species. It also depends on conditions in which the tree grows.

3. As the tree becomes older the heartwood grows wider. The tree, of course, retains a layer of sapwood under the bark which pro­vides sap conduction. The layer of sapwood may consist of only a few growth rings in some species and of more than 100 in others. The sapwood is usually widest when the tree is young and becomes narrower as the tree increases in diameter. The sapwood is wider in the upper portion of the trunk than in the base of the tree.

4. In most trees heartwood can be clearly seen because of its darker colour, but some species such as spruce, true firs, hem­locks, aspen and poplar usually do not show a darkening of the heartwood. In some other species the formation of heartwood begins much later and the stems of smaller size may be composed of sapwood only.

5. The formation of heartwood is an enigma. There are a lot of questions about it that still have no answers (e.g. At what time does the formation of heartwood begin in a tree? Why cannot some sapwood be transformed into heartwood? etc.). It should be mentioned that one part of a growth ring may be in the sapwood and the other in the heartwood.

II Прочтите 2-ой абзац текста и письменно ответьте на следующий вопрос:

When does the formation of heartwood begin?

Контрольная работа № 5

(для специальности ТД)

Вариант 3

I Прочтите и устно переведите с 1-го по 5-ый абзацы текста.

Перепишите и письменно переведите 1, 2, 3 абзацы текста.

WOOD GRAIN

1. Wood consists of a multitude of cells, which differ from each other in shape, size, thickness of walls, contents, and arrangement. They are more or less firmly grown together. These cells may be as long as 1/3 inch in spruce or only 1/25 inch in some of the hardwoods. Cells of this sort are called fibres, in the softwoods they conduct water longitudinally in the tree. Cells of another kind which have greater diameter are called vessels; we can see them in the hardwoods. In the cells that make up wood rays water or sap is conducted in a radial direction.

2. No two woods have identical structure. The firs, pines, ce­dars, spruces and other needle-leaved softwoods have relative­ly few kinds of cells, while the hardwoods, such as oaks, beeches and maples have many kinds. These cells have various functions, such as conducting water, storing materials and reinforcing the structure.

3. The differences in cell structure produce a distinct pattern within the wood. This pattern becomes characteristic for each kind of wood, but it is never identical in any two pieces of the same wood. The grain figure is affected by the way the log is sawed. The woods that have considerable difference between springwood and summerwood are called coarse-grained; when there is little contrast, they are called fine-grained.

4. Here are the main types of wood grain. Straight-grained wood has the fibres running in the same direction as the main axis of the tree. Interlocked grain, occurs when layers of the wood alternate in direction. Such wood is difficult to split or to plane; for example, mahogany and elm. Wavy grain is almost a regular pattern of waves in the grain. Curly grain is a grain pattern with a definite curly appearance.

5. The grain pattern about the knots is circular and is usually more varied in direction than wood above or below the knot.