The structure of a tree, its main parts
The plant world is divided into lower and higher plants, which are characterized by the presence of roots, stems and leaves.
A number of physiological processes necessary for the growth and development of plants occur in them. In a growing tree, roots, trunk and crown are distinguished (Fig. 1). Rice. 1. Parts of a growing tree: 1 - roots; 2 - trunk; 3 – crown
Roots 1 constitute an entire system, which includes small roots that absorb water with minerals dissolved in it, and thick roots that conduct water and store nutrients, and also help maintain the tree itself in an upright position.
Trunk 2 supports the tree crown and connects it to the roots. Solutions of mineral substances move along the trunk in an ascending current, and solutions of organic substances formed in the foliage move in a descending current. The trunk also accumulates and stores nutrients.
Crown 3 is a collection of branches covered with leaves or needles. In the green leaves of the crown, during the process of photosynthesis, complex organic substances are produced that are necessary for the life and growth of the tree, the formation mechanism of which is the process of absorbing carbon dioxide from the air and water coming from the soil, as well as the action of light. The tree crown is currently not widely used, although its biomass contains many valuable substances.
The study of the trunk is carried out on three main sections (Fig. 2): transverse, or end, when the section plane is perpendicular to the axis of the trunk; radial, when the section plane runs along the axis of the trunk; tangential, when the section plane runs along the axis of the trunk perpendicular to the radius of the end.
Rice. 2. Main sections of the trunk (b): P - transverse section, P - radial section, T - tangential section
The trunk makes up the bulk of the tree. In some breeds it accounts for up to 90% of the mass. The structure of a tree trunk is shown in Fig. 3.
The trunk is a cone-shaped body covered with bark 6. The bark protects the tree from external influences and damage. The inner part of the bark, which conducts organic nutrients formed in the leaves down the trunk, is called bast 5. In the center of the trunk there is a small-sized core 1. This low-quality part of the tree in cross section looks like a speck with a diameter of 2...5 mm of brown or brown color , most often round or oval in shape. The main part of the trunk is wood 3. Between the bark and wood there is cambium 4 - a thin layer of living educational tissue that serves to nourish and form wood and bark. As the diameter of the trunk increases, the proportion of bark decreases (the thickness of the bark decreases in the direction from the butt to the top).
Rice. 3. The structure of a tree trunk in transverse (P), radial (R) and tangential (T) sections: 1 – core; 2 - core; 3 - sapwood; 4 - cambium; 5 - bast; 6 – bark
Use in shipbuilding
Source nationalclass.ru
Of course, all the shipbuilders of the world in the old days used exclusively wood to build their ships, since they did not know other technologies. Times are changing and now amazing metal giants are being launched from shipyards, which are not only larger, but stronger and faster than their ancestors. Nevertheless, wood is still in demand in shipbuilding to this day, especially among yachtsmen. Also, dinghies, longboats and boats are made from wooden planks - this is cheaper and looks more beautiful.
Note: the expression “mast timber” is still in use among builders, joiners and carpenters.
Wood structure
2.1. Macroscopic structure of wood
The structure of wood can be studied with the naked eye, in which case the macroscopic structure of the wood can be examined. The microscopic structure can only be carefully studied using various types of microscopes.
By studying the macroscopic structure of wood, you can find that in some species the wood is unevenly colored: in the inner part of the trunk it is darker than on the periphery. In these cases, the dark-colored part of the wood is called heartwood, and the lighter-colored part is called sapwood. Such species are called sound wood (pine, larch, ash, oak, etc.).
In other breeds, the central part of the trunk does not differ in color from the outer part; such breeds are usually called coreless. Among this group of tree species, one can distinguish those in which the central zone in a growing tree has less moisture than the peripheral one; such species are usually called mature wood (beech, aspen, etc.). Species that do not have a core and do not differ in moisture content (for example, spruce, fir, birch, aspen, linden, etc.) are called sapwood.
Every year, layers of wood are formed on the trunk in the form of concentric, less often wavy, rings of different widths - these are annual layers (Fig. 4), which are especially noticeable in coniferous and some deciduous species. In sections they look like longitudinal stripes and winding lines. Their width depends on the species, age of the tree, position in the trunk, and growing conditions. In many species, it is clear that the annual layer consists of two parts: a light-colored soft part - early wood (it is formed in the first half of the growing season) - and an outer, darker and harder part, facing the bark - late wood. Early wood carries water up the trunk, while late wood performs mainly mechanical functions.
In a cross section of some species, such as oak, bright shiny lines are clearly visible, radiating from the pith to the bark, called pith rays. All species have rays - both deciduous and coniferous. Their width depends on the breed, growing conditions and ranges from 0.05 to 1 mm. They serve to move water laterally and store nutrients in winter.
Core repetitions (veins) are brownish or brownish lines, stripes or specks, located mainly at the boundaries of the annual layers in some deciduous trees (for example, birch, alder, maple, aspen, willow, pear, rowan). In their color and structure, they resemble the heartwood and are overgrown insect passages, which are usually found in the lower part of the trunk in deciduous trees and, less often, in conifers. Core repetitions deteriorate the quality of products made from this wood and are considered one of the defects of wood.
Vessels are structural elements of deciduous wood (conifers do not have them), having the shape of tubes of different sizes. In a growing tree, water rises through vessels from the roots to the crown. In cross-section, they appear as small holes and are divided into large and small.
Rice. 4. Scheme of trunk formation (a) and type of annual layers (b) on transverse (P), radial (R) and tangential (T) sections (light - early wood; dark - late wood
Large vessels are often concentrated in the early zone of the annual layers, small ones are collected in groups and located in the late zone, where they are visible due to their light color. Based on the location of the vessels in the wood, hardwoods are divided into ring-vascular, with a ring of large vessels in the early zone, and scatter-vascular, in which all vessels, regardless of size, are more evenly distributed throughout the annual layer.
Resin ducts are structural elements of conifers, which are thin channels filled with resin. Moreover, only pine, cedar, larch and spruce have resin passages; other conifers (fir, yew and juniper) do not have them. There are vertical and horizontal passages that form a common resin-bearing system, which in the total volume of wood is less than 1%.
2.2. Microscopic structure of wood
A deeper understanding of the structure of wood is given by the microscopic structure of wood. Wood consists of various kinds of cells, and the cell is made of a shell that is filled with living protoplast. Based on their shape, cells are divided into parenchymal and prosenchymal. Parenchyma cells have a round shape and a thin membrane and retain a living protoplast. Prosenchymal cells have an elongated shape with thickened walls and resemble a fiber.
A collection of cells with the same structure and functions forms tissues. The following types of tissues are represented in a growing tree: integumentary, mechanical, conductive, storage, educational and assimilation (the process of photosynthesis).
The main substance that makes up the cell membrane, or cell wall, is cellulose, bundles of which are micro- and macrofibrils. There are primary (thin) and secondary (thicker) shells. The secondary shell contains pores. The overhanging secondary shell over the pore cavity in the form of an arch forms a bordered pore. If it is missing, then it’s time for a simple one. Between the pore cavities there is a permeable membrane. In the center of the membrane in the bordered pores of conifers there is a torus - an impenetrable thickening that can have different shapes. The space between the fibrils is filled with lignin and hemicelluloses.
The structure of coniferous and deciduous wood.
Coniferous wood consists of two interpenetrating systems of cells located along and across the axis of the trunk. Conductive and mechanical functions are performed by tracheids - vertically located prosenchymal cells with dead protoplast.
There are early tracheids (Fig. 5, a), which are formed at the beginning of the growing season and perform a conducting function, and late tracheids (Fig. 5, b), which play the role of mechanical elements.
Rice. 5. Anatomical elements of coniferous wood (pine): a - early tracheid (radial section): 1 - large bordered pores, 2 - simple (terminal) pore at the point of contact with the pith rays, 3 - small bordered pore; b — late tracheid (radial section); c — medullary ray (radial section): 1 — ray tracheids, 2 — parenchyma cells; d — resin duct (cross-section): 1 — accompanying parenchyma cell, 2 — lining cell (epithelium), 3 — dead empty cell, 4 — medullary ray; e - core beam with a horizontal resin path (tangential section): 1 - core beam; 2 – horizontal resin passage
Early tracheids contain many large bordered pores. The storage function is performed by living parenchyma cells (Fig. 5, c), which are mainly part of the medullary rays (Fig. 5, c-e). They accompany resin ducts and are sometimes located in the form of woody parenchyma.
Hardwood wood consists of a larger set of anatomical elements arranged in a less orderly manner. The conductive function in hardwood is performed by vessels (Fig. 6, a) with pores on the walls and tracheids, the mechanical function is performed by libriform fibers (Fig. 6, b) and fibrous tracheids, storing – parenchyma cells forming cords (Fig. 6, c). The vessels consist of segments - individual short cells with wide cavities and thin walls. When the side walls of cells are destroyed, round or slit-like openings are formed, which are called simple and scalariform perforations, respectively (Fig. 6, d).
Rice. 6. Anatomical elements of hardwood: a - a vessel of segments with simple perforation; b — libriform fiber; c — part of a strand of woody parenchyma; d — ladder perforation; d - spiral thickening; e - tills (swellings) in the vessel: 1 - vessel wall, 2 - tills; g - heterogeneous medullary ray: 1 - with recumbent parenchyma cells; 2- with standing parenchyma cells
Furniture making
Furniture made of wood never loses popularity, although in our century plastic and metal began to be used for this. For serial and custom (elite) production, almost all types of wood are used, including soft, hard and very hard, so in this case there is plenty to choose from. You can always find cabinets, chairs, tables, beds, sofas, etc. at home or on sale. and so on. Of course, for the most part, cabinets are made from chipboard and OSB, but in any case this refers to lumber. Elite options are usually made from solid wood - such furniture is very beautiful and high-quality, regardless of the type of wood. Garden furniture is also made from wood, which is sometimes not removed from the street all year round, remaining exposed to rain and snow, but at the same time it lasts for a very long time.
Chemical composition of wood and bark
Wood consists predominantly of organic substances (at least 99% of the total mass) in the form of cellulose, hemicellulose and lignin, which contain carbon, hydrogen, oxygen and some nitrogen. In addition to the main ones, wood contains extractive substances (tannids, resins, gums, pectins, fats, etc.), soluble in water, alcohol or ether. The chemical composition of wood of different species is almost the same. Absolutely dry wood on average contains 49-50% carbon, 43-44% oxygen, 6% hydrogen and 0.1. 0.3% nitrogen.
When wood is burned, its inorganic part remains - ash (0.1... 1%). Its composition includes calcium, potassium, sodium, magnesium and in smaller quantities phosphorus and sulfur. They form minerals, most of which (75-90%) are insoluble in water. Among the soluble ones are alkaline ones (potash and soda), and among the insoluble ones are calcium salts.
The chemical composition of the bark differs little from the composition of wood and branches, but the bark contains much less cellulose and much more lignin (especially pine bark), extractives and minerals, and also contains suberin, which is not found in wood.
