A tree as a living organism consists of a huge number of living and dead cells, which vary according to their functions and form solid tissues, to which they belong: mechanical (strengthening), covering, conductive, crumb (granary, assimilation), and creative tissues (meristems), from which all solid tissues arise through division and differentiation. The individual parts of the tree are made of these tissues: Crown, consisting of boughs, branches and leaves, trunk and root system. As in any living organism, individual parts form an inseparable whole, each of them performs specific tasks, and disorders in one part of the body affect others.
The trunk is that part of the tree, which distinguishes them from other forms of plant growth. In dendrology, two main types of trunks are distinguished: arrow and log. We call an arrow a trunk in an accident, when it has the character of a central axis and is visible up to the top of the tree (spruce, larch). This is due to the constant domination of the apical bud. On the other hand, we call a trunk a trunk, when it separates into branches at a certain height (oaks, clones). Free-standing trees, exposed to strong wind influences, according to the laws of mechanics, they produce so-called conical trunks - conical in shape, which are more durable. Dense trees, not exposed to direct wind, produce a full trunk, close to a cylinder.
Trunk, boughs, annual branches and shoots usually consist of the following elements: core, wood, pulp (cambium) and the so-called. kory, including the bast and the cork layer. The core is located in the middle of the trunk and branches; it develops from an apical meristem. It is made of parenchyma, which here can act as a storage tissue. In older tree trunks, the core often dies, for example, in the trunk of a beech - after 40 years. The core is connected by primary core rays to the tissues of the primary cortex. During the secondary thickness increase, secondary core rays are produced. Core rays - depending on the needs - perform the functions of conducting water and assimilates, and accumulating spare substances. Rays, just like the core, they are made of living parenchyma cells.
During the differentiation of tissues in the apex of growth, a pulp cell ring is formed (cambium). It is a meristem (creative tissue) lateral, ensuring secondary growth of the trunk in thickness. The pulp is made of thin-walled cells with a high plasma content. As a result of rapid cell division, two basic tissues of the trunk are formed: wood is formed from cells deposited in the centripetal direction (xylem), and deposited in a centrifugal phloem (phloem). The process of growth is repeated every year and this is how concentric rings of annual increments of both wood are formed, and a sip, the so-called annual rings. The dividing pulp deposits much more cells in the centripetal direction as wood, than in the centrifugal direction as a bast.
Diagram of the longitudinal and transverse section of an annual shoot of a woody dicotyledonous plant: 1 - peel (epidermis), 2 - cork, 3 - cork-making pulp (fellogen), 4 - primary cortex, 5 — łyko (phloem), 6 - cambium, 7 - wood (xylem), 8 - core radius, 9 - core.
Both cells set aside towards the wood, and sip they change and adapt to new functions. Because the cells produced by cambium at different times are distinctly different in size, and wood grain formation takes a relatively long time during the growing season, the structure of this jar is varied. Early wood is distinguished (spring) - about large cells, thin-walled and late wood (summer) - about smaller cells, thick-walled. Early wood cells, with high lights, enable intensive water conduction during this period (ascending current), whereas late wood performs mainly mechanical functions (increasing endurance) and contains about 50-60% (by volume) wood fibers. In wood, conductive elements are distinguished (trachealne), wood fibers (sclerenchymatic) and crumb (parenchymę), about storage functions and, partially conduction.
So the tasks of wood are as follows:
1) water conduction;
2) ensuring the mechanical strength of the trunk and roots ;
3) storage of nutrients.
There are two types of tracheal elements: coils and dishes. Coils are the more primitive element of wood, characteristic of conifers, although the wood of some deciduous trees also contains coils. They are elongated, woody, dead cells. Due to the presence of funnel-shaped pits in their common walls, water can penetrate into adjacent coils. The coils, apart from conducting water, act as reinforcing elements.
The coils have evolved into vessels and wood fibers. Dishes form long, continuous tubes made of connected members, the so-called. perforation plates, through which water penetrates. The dishes are characteristic of the wood of deciduous trees.
Among deciduous trees we can distinguish trees with vascular wood (clone, birch, buk, Poplar, lime and others) and trees with ring-vessel wood (oak, ash, elm and others). The wood of deciduous trees has much more pith tissue than softwood. This results in a much greater possibility of vegetative reproduction, regeneration and wound healing.