Wood has a relatively high strength with a small volumetric weight, easy workability, elasticity, low thermal conductivity and frost resistance. Under favorable operating conditions, wood is stored for a very long time.
Thanks to these advantages, along with a relatively low cost, wood has found a very wide application in construction (log and panel walls, partitions, ceilings, roofs, floors, etc.).
This mechanical support is provided by a fabric called wood. Thanks to this strong structure, trees are vegetables that have big weight and life for several years. Like most vegetables, trees have three main parts, the roots, the trunk, and the leaves, which contain the branches, which in turn contain the leaves. In a very general and functional way, the roots provide attachment to the soil and absorb water and minerals, thanks to which the tree lives. In general, the trunk provides mechanical support to the plant and acts as a conduit between roots and foliage, allowing water and nutrients to circulate in both directions, i.e. up and down.
However, how construction material wood has some disadvantages. Among them should be indicated:
· structural heterogeneity(anisotropy), which determines the difference in strength and thermal conductivity along and across the fibers, which creates significant difficulties when using wood in construction;
The bowl, formed by branches and twigs, contains leaves, which are the main plant organs in which photosynthesis takes place. A very important principle for the functioning of vegetables in general is that there is a close relationship between the growth of roots and branches, so it must be taken into account that what happens to some happens to others. This is a guide as it relates to trimming wood or ornamental trees, does not pay attention to the production or care of flowers or fruits that are present on the tops of trees.
· hygroscopicity, i.e., the ability to absorb and evaporate moisture when the humidity and temperature of the surrounding air change. With increasing humidity, the wood swells (its volume increases), with a decrease in humidity it dries out (its volume decreases). Since, due to the anisotropy, these changes in the dimensions of the wood in different directions are not the same, they cause internal stresses, leading to the formation of cracks and warping;
Following the intimate relationship between the development of the crown and the root system, it must be taken into account that the roots require sufficient space for growth. The main tree roots extend predominantly in the area immediately below the crown and in the drip zone. Therefore, for optimal and balanced growth of cups, there must be adequate development of the roots, and this is achieved by leaving room for the growth of the latter and therefore the branches and leaves themselves. The drip zone is the main area where the roots perform their absorption and exchange of gases with the atmosphere.
· decay i.e. the ability to be destroyed by the action of microorganisms, observed in wood that is in adverse conditions;
· combustibility because of which wooden structures are flammable unless special measures are taken to protect them from fire.
Builders must be well aware of both positive and negative building properties wood, in order to be able to mitigate negative properties, and use positive ones to the maximum extent,
A cross-section of a branch or trunk of a tree shows a series of tissues that, like layered tubes, cover the tissues of these plants. Then follow the growth tissue, which is actually the really living part of the branches and trunk. This is a very thin layer compared to the previously described layer, the earth's crust and the sapwood and length that follows it inwards. Despite its size, this layer of growth is what binds all the tissues of the tree, in which there are channels that transport water and minerals, as well as photosynthetic products, that is, products produced by the plant and from which it nourishes.
The structure of wood can be studied with the naked eye yali at some magnification.
A structure that is visible to the naked eye or at low magnification (through a magnifying glass) is called a macrostructure, and visible only at high magnification (through a microscope) is called a microstructure.
macrostructure
It is most convenient to get acquainted with the macrostructure by three sections of a tree trunk (Fig. 1). A cut by a plane passing along the chord of the cross section at some distance from the axis of the trunk (Fig. 1, a) is called tangential; a plane perpendicular to the axis of the trunk (Fig. 1,b), - transverse or end; a plane passing through the axis of the trunk (Fig. 1, c) - radial.
This layer is necessary for the connection between the roots and foliage of the tree. Whatever happens to this layer of growth will certainly affect cup and root development. Then, towards the center of the cut, is the sapwood and then the heartwood, both are actually very similar and form what we call the tree of the tree, and its function is to support the plant mechanically and is formed mainly by dead cells.
Energy Energy can be defined as the ability to respond that a person has before the pressure of an external agent. In the case of trees, this is the ability to respond to and survive biotic and abiotic agents. Energy, in general, is related in inverse proportion to the age of the individual, that is, younger, more energetic and vice versa. On the same scale, the force is more towards the center and bottom of the tree than up and out.
Rice. 1. Tree cuts
Rice. 2. The structure of the tree according to the end section
When considering the end section of the trunk, it is possible to distinguish the parts shown in Fig. 2. The bark, consisting of the outer layer 1 - crust - and the inner 2 - bast, protects the tree from mechanical damage. In a growing tree, the bast layer serves to carry nutrients down from the crown of the tree; it stores these substances. Under the bast there is a thin layer of cambium 3, consisting of living cells. In the cambium layer, bast cells are deposited towards the bast, and wood cells are deposited towards the center of the tree. Number of wood cells deposited more quantity bast cells, as a result of which the wood grows faster than the bark.
Structure For the purposes of this Guide, the structure of a tree refers to the physical structure that allows free and healthy growth. This is a set of cells that make up woody tissue. It can be divided into three parts. It is usually located in the central part of the trunk. It is formed by weak or dead cells, sometimes consistent. Its diameter varies from less than one millimeter to more than one centimeter depending on the species.
Also called the heart, this is the area that surrounds the bone marrow. It is dark in color and is made up of dead, ligated cells, which give it greater resistance to attack by fungi and insects. Its proportion depends on the type and age of the tree. This is the brightest staining zone, consisting of young cells. It has less resistance to biological attacks. The sapwood is more abundant, and the tree is younger.
The thick layer of wood behind the cambium consists of a series of thin concentric layers. On a cross section of a tree trunk of some species, one can distinguish the outer part of the wood - sapwood 4 - and the inner part - core 5. The sapwood consists of younger ones, the core - of completely dead cells.
In trees of some species (pine, oak, cedar), the color of the core is darker than the color of sapwood; in others (spruce, fir, beech), the central part of the wood, which has all the properties of the core, does not differ in color from the peripheral and is called ripe wood. There are species (birch, maple, alder), the so-called sapwood, in which the core is absent.
It arises from an increase in the thickness of the trunk, forming concentric layers of woody cells or xylem, largely in relation to the interior and cells of the phloem or bark, in a small proportion, to outside. Periodically mentioned layers constitute the so-called growth rings.
Its outer layer, called the suer or cork, consists of dead cells and acts as a protection for the shaft. Its inner layer is called freedom or phloem and is formed by living cells through which the transfer and deposition of nutrients in the stem is carried out.
All tree species can be divided into heartwood, having a core and sapwood, sapwood, devoid of a core, having only sapwood, and ripe woody, having ripe wood and sapwood.
Rice. 3. Pine wood cuts
Forest constitution, anatomically
Wood consists of longitudinal and transversal cells different characteristics according to the functions they perform in the tree. The longitudinal cell extends from the roots to the crown, while the transverse cell extends from the marrow to the bark of the tree.
Chemical wood is made up of three main compounds
Cellulose, hemicellulose and lignin; and other secondary compounds such as tannins, gums, oils, dyes and resins.Anatomical description of the tree
Recommendations for the description of wood The description of the properties of wood is carried out in three main directions.
- Longitudinal: This is the direction parallel to the axis of the tree.
- Radial: This is the direction in which the medullary rays travel from the cord to the cortex.
- Tangent: This is the tangent direction to the growth rings.
The core 6 is located along the entire trunk in its central part. It consists of cells with thin walls, weakly interconnected. The core and the shoots of wood formed in the first year of existence form a core tube with a diameter of 1 to 10 mm, depending on the species and age of the tree. This part of the trunk is usually the weakest, crumbles easily and rots more easily than others.
fruit tree structure
Longitudinal section: an area or surface parallel to the axis of the brainstem, which in turn can be: radial: resulting from a longitudinal section parallel to the radius, from the cortex to the brain. Tangent: If the cutting plane follows a direction perpendicular to the spokes or tangent to the growth rings. Section: This is a section or face that is perpendicular to the axis of the trunk. . The anatomical description of wood is carried out in order to develop identification keys based on the structure observed in transverse, radial and tangential sections.
On the transverse (end) section of a tree trunk, you can see a large number of concentric layers. Each such layer corresponds to one year of the tree's life, which is why it is called the annual layer, or annual ring.
In spring, thin-walled cells of early wood of the annual ring are formed, in summer - strong thick-walled cells of late wood. On fig. 3 shows radial, end and tangential sections of pine wood; they clearly show the difference in the tissues of early and late wood.
The anatomical description of wood can be done at the macroscopic or microscopic level. The description of wood is made by observing the structure of wood tissues with the naked eye or with a magnifying glass 10 times. In the sections shown in the figure below, the specialist can identify different types of pores, parenchyma, radii, resins and resins. They can then be classified according to their size, number and type of grouping and thus identify at least the family to which the wood belongs.
Depending on the growth conditions, the annual layers are of different widths, even in trees of the same species. The width of the annual layers does not affect the properties of wood as much as the percentage of mechanically most valuable late wood in it.
in wood hardwood moisture moves through the vessels / tubs) located along the trunk. On the transverse section of the trunk, they look like rounded holes.
The anatomical structure of conifers
Microscopic description is the observation of the type and structure of the cells that make up wood tissues using a microscope. This allows us to describe and classify different kinds and serves to determine, roughly speaking, the properties of wood. It is hard to believe, but in conifers, even on the largest pines, woody tissue consists of tracheids, parenchyma, and sometimes resin canals. Tracheids are very long, up to 75 times longer than their diameter. They are the basis wood structure. They also allow liquids to pass through.
In the wood of some hardwoods (oak, ash, elm), large and small vessels are located; large ones are located in the early part of the annual layer, small ones are collected in groups or distributed evenly over the area of the late part (Fig. 4). Such breeds are called k-plmtevascular.
They are the most common element in wood conifers, of which they make up 90% of their volume. We also find parenchyma formed by cells of shorter length, whose function is conduction and storage. Finally, resin channels are often found in conifers, which are formed by a hollow space in which the cells that form their walls pour resin.
The structure of the tree and the scheme of its nutrition
The woody tissue of broad-leaved trees has a more complex cellular structure than that of conifers. This is formed by fibers, vessels, parenchyma, and sometimes rubber channels. The fibers are elongated cells, and the main component of hardwoods, such as the tracheid in conifers, is the support of the woody body. They also allow the passage of nutrients through small holes called scores. Vessels or pores are the true channels of sap within the tree by the conductive elements, they form a set of cells in the form of a tube connected by their usually open ends.
Rice. 4. Section of the annular vascular rock
In the wood of other hardwood species (birch, aspen, linden), there are no large vessels; there is no sharp difference between the early and late parts of the annual layer. These breeds are called disseminated vascular (Fig. 5).
The parenchyma can be longitudinal or radial, the first has the function of storing reserve substances, and the second, that is, radial, stores and distributes nutrients from the bark to the bone marrow of the tree. Sometimes there are gomiferos channels formed by specialized parenchyma cells located longitudinally or inside the medullary radii.
Anatomy and physiology of wood. The anatomy describes the various tissues of the tree and its cellular compositions. Physiology studies functions and relationships various types cells and tissues that make up wood. The study of wood anatomy and wood physiology allows one to understand its internal structure, its characteristics, defects and classification.
Rice. 5. Cross-section of the seed-vascular breed
Coniferous trees do not have vessels, but consist mainly of closed elongated cells (tracheids). In most conifers, between tracheids (mainly in the late part of the annual layer) there are so-called resin ducts - intercellular spaces filled with resin (see Fig. 3).
The three main constituents of wood are carbon, oxygen and hydrogen. Cellulose, hemicellulose and lignin are the main substances that make up wood. Cellulose is a natural linear polymer formed by combining β-glucose molecules, a product of photosynthesis.
Segment of the cellulose chain. Because it is formed by repeating glucose monomers, cellulose is therefore a polysaccharide. Hydrogen bonding of neighboring cellulose chains forms crystalline regions called microfibrils. About 65% of cellulose is found in these regions; the rest form amorphous regions.
In addition to annual rings, on a cross section of a tree, narrow stripes can be seen with the naked eye, directed along the radii and called core rays. In crafts, many tree species are easiest to distinguish precisely by the shape and arrangement of the core rays and the characteristic pattern formed by their section.
microstructure
Cellulose, which makes up about 60% of wood, gives stability and supports plant life. However, although cellulose is a homopolysaccharide, that is, a polysaccharide consisting of only one type of base unit, hemicelluloses are heteropolysaccharides. Because they are hydrophilic, hemicelluloses contribute to the elasticity and dimensional variation of the wood.
Lignin - a word derived from the Latin lignoum - is a three-dimensional polymer whose basic functional unit is phenylpropane. Finally, a small part of the wood is made up of other compounds such as extracts, organic and inorganic compounds.
When examining the microstructure of wood under a microscope, one can see that it consists of a very large number of living and dead cells of various shapes and sizes.
Each living cell has a shell and inside it the protoplasm, cell sap and nucleus. Protoplasm is a plant protein composed of carbon, hydrogen, oxygen, nitrogen and sulfur.
Nucleus on chemical composition very close to protoplasm and differs from it only in the content of phosphorus. Nuclei meet various forms, for the most part oval.
shell cells mainly form a substance called cellulose, or fiber. As the cell grows, a very important change in the shell occurs - lignification, which is caused by the appearance of lignin cell walls in the substance. Wood cells are diverse in shape and purpose. According to their purpose, there are conductive, mechanical and storage cells.
Conductive cells serve mainly to transfer nutrients from roots to branches and leaves. These are the vessels mentioned above and some tracheids.
mechanical cages elongated, have thick walls and narrow internal cavities. They are tightly interconnected and in hardwoods are evenly distributed over the annual layer, which gives the wood greater strength.
In hardwood, the functions of mechanical (supporting) cells are performed by libriform, which makes up the bulk of the trunk, in coniferous wood - tracheids of late wood.
storage cells are found mainly in the medullary rays. They serve to store nutrients and substances and transfer them to living cells in a horizontal direction.
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Trunk- this is the main and most valuable part of the tree, giving 60-90% business wood. The thin part of the trunk is called the top, the thick part is called the butt. The structure of a tree trunk, visible to the naked eye, is called a macrostructure. It is clearly visible on three main sections of the trunk.
Distinguish end section, perpendicular to the longitudinal axis of the trunk (see figure), radial cut, perpendicular to the end section and passing through the core of the trunk; tangential cut passing tangentially to the annual layers at some distance from the core.
The structure and properties of wood are not the same for different cuts. On the transverse section of the trunk, the bark, its cork and bast layers, and the cambium are distinguished; wood is visible, its sapwood and core, where annual layers, core rays and core are different (see figure).
Core located in the center of the tree trunk along its entire length. It has a loose structure, is fragile and is subject to rapid decay. In conifers, the diameter of the core is 3-4 cm, while in hardwoods it is slightly larger. Each year, wood growth occurs by one annual ring formed by the cambium under the bark.
With the growth of the tree, the wood of the core is destroyed, so its diameter gradually increases towards the crown. In some species, such as pine, larch, oak, ash and cedar, the part of the wood located closer to the core has a darker color and low humidity. This most valuable piece of wood is called core, and the rest, located towards the bark, - sapwood. There are breeds that do not have a nucleus, they have same color wood throughout.
The wood of the core is distinguished by strength, density and hardness, as well as greater resistance to decay than sapwood, which consists of young cells, which are characterized by a lower density of wood. Sap flow - the movement of water with nutrients dissolved in it - occurs along the sapwood. The thickness of the sapwood depends on the type of tree, its age and growing conditions. The growth of the core with the death of the sapwood cells turns into the wood of the core.
In birch, beech, maple, aspen and alder, the center of the trunk has a dark color, indicating the initial stage of decay. This part of the trunk is called false core.
Between the sapwood and the bark is a thin layer of living cells - cambium. During the growing season, the division of cambial cells forms new wood and bark cells. At the same time, the tree grows both in thickness and in length. The bark consists of an outer cork layer and an inner bast layer.
The outer layer protects the tree from atmospheric influences and mechanical damage, while the inner layer transfers organic nutrients developed in the crown leaves down the trunk.
Most conifers in the cross section of the trunk have different annual layers in the form of concentric circles. Annually, with normal growth, one annual layer is formed. Its thickness (in the direction of the radius) for different tree species different. The early wood of the annual core layer differs from the late wood, which is closer to the bark. This is explained by the growth of the early wood of the annual layer in spring and early summer. At this time, there is little moisture in the soil and the cells of early wood are loose and light, providing sap flow. The late wood of the annual layer grows in late summer and autumn.
In hardwoods, the cells of late wood (annual layer) consist of supporting tissues, and in conifers, they consist of thick-walled tracheids, darker in color and distinguished by density and strength.
The width of the annual layers depends on the age of the tree, on the species and growth conditions. In young trees, the annual layers are usually wider, except for the willow, which has only narrow annual layers. In the pine growing in the north, the annual layers are narrower than in the pine growing in the southern latitudes. The properties of wood are characterized by the width of the annual layers. Conifers with narrow annual layers are more durable and resinous.
Pine with narrow annual layers of reddish brown color is more valuable than with wide annual layers. Coniferous wood, on the end section of which in the radial direction of 1 cm there are at least three and no more than 25 annual layers, is considered the best. In hardwood species, on the contrary, the wider the annual layers, the denser, harder and more durable wood. This is typical for oak, chestnut, elm, ash, elm. These breeds have spring period regardless of climatic, soil and other conditions, 2-3 rows of large conductive tissue (tracheids) are formed, and then - the late wood of the annual layer, consisting of mechanically strong tissues.
In birch, beech, hornbeam, maple, linden, alder, aspen, the wood does not have pronounced annual layers and the width of the annual layer does not affect the quality of the wood.
The core rays are located in the trunk in the radial direction. Distinguish between primary and secondary rays. The primary core rays start from the core and reach the cortex, the secondary ones start near the core and continue to the cortex. Water, nutrients and air move along the core rays in a horizontal direction. On the transverse section of the trunk, large core rays are distinguishable in the form of shiny stripes, on the radial section - in the form of stripes or spots, and on the tangential section - in the form of dots or stripes. The wood splits well in the direction of the core rays. Core rays are found in most tree species, but their size, type and number depend on the species and growing conditions. Trees grown in the sun have more core rays than those grown in the shade.
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