Wood and its properties

The tree consists of vein, tree, branch i leaves. The trunk represents the main mass of the tree and represents 50 - 90% of its cubic volume; veins and branches make up 10 - 50% of the wood mass.

There are the following basic parts in a tree: heart, pith, cambium and bark. The bark is the outer part of the tree, which is distinctly different from the heart. Between the bark and the pith there is a thin ring, which is not visible to the naked eye and is called cambium. The cells of the cambium, through division, each year separate heart cells inside the tree trunk, and bark cells on the outside of the tree. Since the cambium gives off more heart cells than bark cells, there is much more heart than bark.

The heart is the most valuable part of the tree; it is located between the heart and the bark. The heart is located in the center of the tree. It consists of soft, porous tissue, which has very weak mechanical properties. When there are hearts in boards, laths or beams, then this material gets cracks over time. Therefore, for many more important elements, the presence of the heart in the material is not allowed.

A proper representation of the tree can be obtained by looking at it in three sections: transverse, radial i tangentially.

Cross section is the one directed to the axis of the tree, radial section goes along the trunk, passing through the heart, a tangential is the one that goes along the trunk outside the heart (Fig. 1).


Sl. 1. Three main cuts of wood: 1 - tangential; 2 - radial; 3 - transverse

On the cross-section of the tree, circles can be seen, which increase from the center to the periphery, and which are called annual rings (years). Each annual ring consists of an inner and an outer layer. The inner layer is called early wood, and the external one late wood. Early wood is formed in spring, and late - in summer. Early wood is porous, it consists of hollow tissues, water passes through it with dissolved mineral substances, which are needed for the nutrition of the tree. Late wood consists of cells with thick walls that carry mechanical properties.


Sl. 2. Core rays on transverse, radial and tangential sections: 1- bark; 2 - characters; 3 - years; 4 - heart; 5 and 6 - wide core rays

On the radial section, the annual layers are seen in the form of straight longitudinal lines, on the tangential section - in the form of curved curved lines.

On the transverse, radial and tangential sections, in addition to the annual layers, you can also see core rays (Fig. 2). On the cross section, they have the form of narrow strips, on the tangential section - dark lines with narrowed ends. Core rays serve to conduct water and air through the trunk of the tree in the transverse direction, as well as to store reserve nutrients. The number of core rays in different types of wood is different and in pine it is about 3000 per 1 cm2, and in spruce 143000. In coniferous species, core rays occupy 3 - 10%, and in deciduous trees 9 - 36% of the volume of wood mass.

Core rays consist of cells, which have a low mechanical strength, due to which they increase the splitting of the wood.

In some types of wood, e.g. white or dark spots can be seen in the cross-section of alder, birch, yew, chub, ash. These spots are caused by insects or frost damaging the cambium and are calledcore stains''. These core stains reduce the mechanical strength of the wood. All types of wood can be divided into four groups:

  1. Sailing species (oak, walnut, white acacia, pine, ke dar, larch, etc.);
  2. Species with mature heartwood (beech, linden, spruce, fir, common Siberian and Caucasian fir, etc.);
  3. Types with core and mature pith (ordinary ash, elm, etc.);
  4. Quack types (birch, aspen, black and white alder, hornbeam, maple, horse chestnut, maple, etc.).

In soft wood species, the darker colored central part is called core, and part of the light color — grandmother. In the case of wood species with a mature heartwood, the central part of the section is characterized by a lower amount of moisture than the peripheral part. In a growing tree, sapwood serves to conduct water and accumulate nutrients. In some wood species, a double sapwood can be seen in the cross-section. This is nothing but the initial stage of wood rot caused by special wood-destroying fungi.

In terms of its mechanical strength, the sapwood does not differ from the heartwood, but it is weakly resistant to rotting. With the growth of the tree, the sapwood gradually moves into the heartwood. In the process of this transition, special outgrowths, called tile, and the cavities and cell envelopes are filled with cellular and extractive materials.

Tiles fill the elements of the heart, which make it poorly permeable to liquids. Therefore, srcica is used to make barrels, wooden tanks, etc. At the same time, the heart that contains tiles is very difficult to impregnate with antiseptics. This also applies to the beech tree, which has a false core, created as a result of the tree being infected with fungi that destroy it during its growth.

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