What is a cork in biology definition. Technical jam. Features of the material, characteristics and application. Application of technical sheet cork

Phellems. First, a layer of phelloderm cells is formed, which forms a layer of phellogen cells. Phelogen cells are divided into two parts: upper and lower. The upper cell (phellema) immediately dies and becomes covered with a thick layer of suberin (a substance that does not allow water and gases to pass through). The lower cell continues to divide, forming a phellem. In some plants (for example, pine, tulip tree, euonymus), the cork consists of thin-walled suberized cells and phelloids - layers of cells with lignified, but not suberized walls.

The plug performs the following functions:

protection against mechanical damage,
protection against penetration of pathogenic organisms,
protection from drying out,
mechanical support due to the rigidity of the phellem cells.

Notes

Literature

Biological encyclopedic dictionary / Ch. ed. M. S. Gilyarov; Editorial team: A. A. Baev, G. G. Vinberg, G. A. Zavarzin and others. - 2nd ed., corrected.. - M.: Soviet Encyclopedia, 1989. - P. 506. - 864 With. - 150,600 copies. - ISBN 5-85270-002-9

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See what “Cork (biology)” is in other dictionaries:

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Periderm is the integumentary tissue of plants and plays a very important role in their life. It is this that protects trees from environmental influences. What is the periderm? How is it formed? How does it perform its protective functions? How does the periderm differ between different breeds?

Cover layer

The term "periderm" (from the Greek. peri– “near”, “around” and derma– “skin”) denotes a complex, multilayered complex of secondary integumentary tissues – phellogen, phelloderm and cork(or phellems, from Greek. phellos- "cork"). The presence of a peridermal covering layer is characteristic of gymnosperms and dicotyledonous angiosperms.

The periderm is formed on branches, trunks and wintering shoots of trees of various species, on stems, roots, roots, tubers, rhizomes, on the surface of the covering scales of wintering buds, and it also covers leaf scars in place of fallen leaves.

Phellogen and phelloderm

The formation of the periderm occurs due to phellogen (cork cambium). The phellogen of above-ground organs - shoots, trunks, branches - is most often formed in the epidermis, subepidermal layers, and less often in the primary bark and phloem. It is located parallel to the outer surface of plant organs and represents a layer of educational tissue ( meristems, from Greek. meristos- “divisible”), consisting of small short rectangular (in cross section) cells with relatively thin membranes.

As a result of cell division, parenchymal phelloderm cells, often containing chloroplasts, are formed on the inner side of the phellogen. It can be seen as a green layer when stripping branches, for example, from elderberry or beech. Phelloderm cells are living; various reserve substances, in particular starch, are often deposited in them.

Cork

The phellogen separates the cork tissue from the outer surface - phellem. As the phellem forms, previously formed cells are pushed to the periphery and differentiate - suberin and wax are deposited on their surface, the cellulose membrane thickens, protoplasts die; cellular cavities can be filled with air, tannins or resinous substances. For example, birch cork cells are filled with betulin, a white powdery substance; oak cork cells may contain druses of calcium oxalate crystals.

The resulting plug can consist of only a few cell layers (the peel of root crops, the birch bark of young birches), or can reach several centimeters. The most famous examples are cork oak and Amur velvet, the cork layer of which often exceeds 5 cm.

Beech is very sensitive to sunburn, since its trunk is covered with only a thin layer of superficial periderm. On the contrary, oaks grow well in open sunny places, the trunks of which are covered with a thick crust with numerous cork layers.

Lentils

Total suberization of phellem cells, as well as the absence of intercellular spaces, prevents gas exchange. To prevent “suffocation” of internal tissues, the outer cork layer is interrupted in places lentils. At the site of lentil formation (most often under former stomata), a layer of phellogen in the form of a concave lens deposits loosely connected round parenchyma, weakly suberized cells, between which water vapor, oxygen, and carbon dioxide can diffuse. Together, the lentil cells form a powdery mass, partially covered with wax and therefore non-wettable.

Externally, the lenticels look like small tubercles above the surface of the periderm. They can be clearly visible, for example, on the surface of trunks and perennial branches of birch in the form of black horizontal lines; in aspen and poplar, lenticels have rhombic outlines.

Age-related changes

The first layers of periderm that arise in the outer outer part of the primary cortex are called superficial periderm. In a number of species of woody plants, it remains the main integumentary tissue for many years, stretching in proportion to the thickening of the trunk. The thin outer layers of cork tissue are constantly peeled off and replaced with new ones due to the active phellogen. For example, smooth trunks are formed in beech, hornbeam, aspen, hazel, young rowan and bird cherry trees. Such trees are sometimes called peridermal.

In most tree species, as they grow, there is a constant formation of additional layers of periderm in the deeper living zones of the primary bark. The phellogen of such an internal periderm dies off quite quickly, and along with it, the areas of the primary cortex and phloem limited by the layers of the peridermal plug die off. A complex of alternating dead tissues appears on the surface of the trunks, the outer layers of which crack as the trunk thickens under the pressure of constantly growing internal tissues, which ultimately leads to the formation of a crust (or rhytidoma), the thickness of which can reach several centimeters.

Such age-related changes are of the same type, but not the same. For example, if the layers of the internal periderms are located parallel to the outer surface, forming closed cylinders ( in young trunks of juniper, cypress), – arises ring(ringed) crust. With longitudinal cracking, the ring crust can turn into banded (honeysuckle, grapes). Its fall is accompanied by tears into long ribbon-like pieces, which are subsequently discarded.

Often, on a cross section, the peridermal layers form a pattern in the form of short arcs, “resting” on each other. In this case, the crust peels off in the form of plates or scales, this is scaly crust (typical for pines, sycamore, plane trees).

Under protection

The periderm functions as a covering tissue. Due to the tight closure of cork cells and the presence of a suberin layer (virtually impermeable to water) in their shells, the peridermal layers protect the internal tissues of plants from excessive moisture loss due to evaporation. Cork is quite difficult to ignite and almost doesn't burn, which is important for trees in the event of ground forest fires.

Cutting the trunk of a young apple tree:
1- periderm, 2 – collenchyma, 3 – parenchyma (remains of the primary bark), 4 – areas of bast fibers, 5 – secondary phloem, 6 – cambium, 7 – secondary xylem of the second year of life, 8 – secondary xylem of the first year of life, 9 – primary xylem, 10 – pith.

The high content of air and various pigments in the cells of the cork layers help protect plant organs from direct exposure. sunlight And temperature changes(in case of overheating or prolonged frosts).

For example, beech is very sensitive to sunburn, since its trunk is covered with only a thin layer of superficial periderm.
On the contrary, oaks grow well in open sunny places, the trunks of which are covered with a thick crust with numerous cork layers.

On lignified trunks and branches under natural conditions (for example, as a result of impacts in windy weather), injured areas often form. The wounds are slowly filling wound callus(from lat. callus- “influx”), on the surface of which a protective layer of periderm is gradually formed, which is also called the wound layer.

1What is the significance of the skin and the cork? 2Where is the phloem located and what cells does it consist of? 3What is cambium and where is it located? and got the best answer

Answer from Anastasia Popova[guru]
1) The skin and cork are classified as integumentary tissues. The main function is to protect the plant from mechanical damage, penetration of microorganisms, sudden temperature fluctuations, excessive evaporation, etc.
Epidermis (epidermis, skin) is the primary integumentary tissue located on the surface of leaves and young green shoots. It consists of a single layer of living, tightly packed cells that do not have chloroplasts. The cell membranes are usually tortuous, which ensures their strong closure. The outer surface of the cells of this tissue is often covered with a cuticle or waxy coating, which is an additional protective device. The epidermis of leaves and green stems contains stomata that regulate transpiration and gas exchange in the plant.
Periderm is the secondary integumentary tissue of stems and roots, replacing the epidermis in perennial (less often annual) plants. Its formation is associated with the activity of the secondary meristem - phellogen (cork cambium), the cells of which divide and differentiate in the centrifugal direction (outward) into the cork (phellema), and in the centripetal direction (inward) - into a layer of living parenchyma cells (phelloderm). Cork, phellogen and phelloderm make up the periderm.
The cells of the cork are impregnated with a fat-like substance - suberin - and do not allow water and air to pass through, so the contents of the cell die and it fills with air. The multilayer cork forms a kind of stem cover that reliably protects the plant from adverse environmental influences. For gas exchange and transpiration of living tissues lying under the plug, the latter has special formations - lentils; These are gaps in the plug filled with loosely arranged cells.
2) Bast is a conductive tissue. Another name is phloem. Phloem conducts organic substances synthesized in the leaves to all plant organs (downward current). It is a complex tissue and consists of sieve tubes with companion cells, parenchyma and mechanical tissue. Sieve tubes are formed by living cells located one above the other. Their transverse walls are pierced with small holes, forming a kind of sieve. The cells of the sieve tubes are devoid of nuclei, but contain cytoplasm in the central part, strands of which pass through through holes in the transverse partitions into neighboring cells. Sieve tubes, like vessels, stretch along the entire length of the plant. Companion cells are connected to the segments of the sieve tubes by numerous plasmodesmata and, apparently, perform some of the functions lost by the sieve tubes (enzyme synthesis, ATP formation).
3) Cambium is a secondary educational tissue. Located in the roots and stems of plants. Gives rise to secondary conducting tissues and ensures plant growth in thickness. Cambium also plays an important role in wound healing in plants. If the outer tissues of the stem are damaged, the cambium grows into the damaged area and differentiates into new xylem, phloem and cambium, each of these tissues continuing continuously with the corresponding tissue type in the undamaged part of the plant.

Reply from 3 answers[guru]

Hello! Here is a selection of topics with answers to your question: 1What is the significance of the skin and cork. 2Where is the phloem located and what cells does it consist of? 3What is cambium and where is it located?

Wood is one of those building materials that have been known to mankind since ancient times. The volume of its consumption is growing every year, and therefore many species are on the verge of complete extinction.

The latter also includes cork, which has been used by humans for thousands of years.

It belongs to the oak genus. The difference from its relatives is that by about five years its branches and trunk are covered with thick bark with unique properties. But you can only remove it by the age of 20. Note that this can be done up to the age (of the tree, of course) of 200 years!

After the first collection, it takes at least 8-9 years, during which the bark is restored. A tree aged 170-200 years produces approximately 200 kg of high-quality raw materials.

The peculiarity of this oak is also that it belongs to the evergreen species. The leaves resemble those of Russian oaks, but are covered with a significant layer of fluff underneath. The cork tree itself is quite large: the height can reach 20 meters, and the trunk diameter can be a meter.

Latin name - Quercus suber. It grows at an altitude of no higher than 500 meters above sea level. Most oaks of this type are found in Portugal, which is why the country's budget receives considerable cash injections from the export of cork, which increases its value every year.

Since ancient times, man has known that the cork tree provides this most valuable raw material, and therefore it has been cultivated for a long time. Note that there is a false representative of this genus, Q. crenata, which is quite widespread in southern Europe. Its cork layer is so small that the tree is grown exclusively for decorative purposes.

In Portugal alone, Quercus suber oak plantations cover more than 2 million hectares! In addition, approximately the same amount of territory is used for this throughout Southern Europe.

During the year, all plantations produce more than 350 thousand tons of bark, but this amount has long been insufficient to meet demand. That is why the wild cork tree was almost completely destroyed.

By the way, what is unique about cork as a material? The fact is that it is a structure whose structure resembles a honeycomb in a bee hive.

Each cubic centimeter of this material can contain up to 40 million of these honeycombs, which are separated from each other using partitions made of a cellulose component.

Simply put, each capsule is filled with air, so even a small piece of cork is very elastic. This property gives the material complete waterproofness and the ability to restore its original state even after strong pressure.

This is why balsa wood (a photo of which is in the article) has received such wide appreciation among furniture makers.

In addition, the bark contains suberin (a mixture of fatty acids, waxes and alcohols). It is unique in that it gives the wood fire-resistant and anti-rot qualities. There are known cases when, during forest fires, cork oaks remained completely intact, except for the scorched bark and leaves dried from the heat.

Thus, the bark of the cork tree is a unique material given to man by nature.

Periderm

Cork. The primary covering tissue - the skin - in stems with secondary growth usually does not function for long. To replace the skin, which collapses under the pressure of secondary growth, a secondary integumentary tissue is formed - phellem (cork), which is part of a tissue complex called periderm.

Many plants develop several periderms over time.

The formation of the first periderm begins with the formation of a special, secondary meristem - phellogen (cork cambium)). A phellogen cell is formed by isolating its tangential partitions from a skin cell or deeper lying living tissue (Fig. 149). Collectively, the phellogen cells form a phellogen ring. First, in the stem and branches, phellogen is laid down in the skin (in willows, pears and rowan), or in the primary bark, in its outer layer (in bird cherry, cherry), or in a deeper layer adjacent to the endodermis (in currants). In other plants (raspberries, rose hips, fireweed), phellogen is formed in the pericycle. The phellogen ring for the most part consists of tightly closed living parenchyma cells, having a relatively small rectangular shape in cross section.

Rice. 149. Formation of cork cambium (phellogen) in the skin of the skullcap stem ( Scutellaria splendens, from the family Lamiaceae); partial cross sections of the stem:

1 - one of the initial stages of phellogen formation: in some skin cells, partitions have formed, parallel to the surface of the skin; 2 - later stage: phellogen has formed and formed a layer of plug cells (phellem).

radial size, and on a longitudinal tangential section - the outline of a polygon with 4-6 sides.

Phellogen generates by tangential divisions of its cells cork and phelloderm. The cork is formed outward from the phellogen, phelloderm - inward from it. Phelloderm cells are very similar to neighboring cells of the primary cortex or pericycle: they are living parenchyma cells, usually containing chlorophyll. They can be distinguished from the cells of the primary cortex by the fact that they are a continuation of the radial rows of cork and phellogen cells. Little phelloderm is formed, rarely more than one or two layers (Fig. 150). The main product of phellogen activity is cork. The cork cambium forms numerous layers of cells arranged in radial rows (Fig. 151).

On transverse sections, the cork cells have the outlines of rectangles, on longitudinal tangential sections, they have the outline of quadrangles and hexagons.

The cork may consist entirely of thin-walled cells (in bird cherry and elderberry) or of alternating layers of thin-walled and thick-walled cells (in birch). The thickening of the shell can be uniform (in birch), or predominant on the outer tangential wall (in some willows), or on the inner (in viburnum).

Suberin is deposited in the cell membranes of the cork, and they become almost impenetrable to water and air. The living contents in the cork cells die early, and the cell cavities are filled with air. Sometimes they contain granular contents, rich in tannins and their breakdown products or resins. The cells of the birch cork contain betulin in the form of a white fine-grained substance; the cells of the cork oak contain cerine in the form of needle-shaped crystals and sometimes calcium oxalate in the form of druses.

In birches, phellogen annually produces from 3 to 6 layers of thin-walled cork and by the end of the growing season 2-4 layers of thick-walled cork; in the cork one can distinguish the annual layers. In pine cork, layers of thin-walled cells with weakly suberized walls alternate with layers of pheloid, i.e., cells with thick lignified shells without suberin. A powerful cork is formed by a velvet tree ( Phellodendron amurensis, from the Rutaceae family), native to the Far East, and especially cork oaks (see below).

The plug can protrude above the surface of branches and young trunks in the form of ribs or wing-like protrusions. These ribs consist of either pheloid (in elm, euonymus) or true cork (in field maple).

In very few plants, periderm is formed on annual non-wintering shoots, mainly on hypocotyls. Some dicotyledons with perennial shoots do not form periderm; such are mistletoe ( Viscum album), cacti.

Crust. In relatively few tree species (beech, aspen, hazel), phellogen, once formed, functions until the end of the life of the trunk or branch, increasing in coverage due to cell division by radial partitions with subsequent proliferation of cells in tangential

Rice. 150. Periderm of elm ( Ulmus suberosa) on a cross section:

pr- cork; f- phellogen; pf- phelloderma.

Rice. 151. Periderm of an annual bird cherry branch ( Radus racemosa) on a cross section:

h- epidermis; pr- cork; f- cork cambium (phellogen); To- collenchyma.

direction. At the periphery of the cork, the cells rupture and slough off, and new layers form from the inside. The surface of the organ remains smooth.

In most woody plants, after the first periderm, starting from a certain age of the organ, new, deeper-lying periderms are formed. The initiation of new phellogens and the formation of periderms passes into the phloem. New periderms are formed either in the form of almost continuous concentric rings (in grapes, Fig. 152, prd, clematis), or in the form of thin curved plates, convexly facing the center of the organ and adjacent to the adjacent periderms (in oak, Fig. 152, prd). The tissues located outward from the first periderm are deprived of the supply of water and substances dissolved in it; the tissues lying between the periderms are deprived of access to air. As a result, the older layers of phellogen and previously living areas of permanent tissues die off. A crust forms on the surface of the organ - a complex of dead tissue, including phloem and periderm. From the inside, the crust gains annual growth, and from the surface it collapses, erodes and falls off.

The formation and separation of the crust begins either early (in the grapevine in the second year of the life of the stem), or at a more or less later age of the trunk and branches (in apple and pear trees - in the 6-8th year, in fir, hornbeam - at the age of less than 50 years old). In hornbeam, the crust appears only on the lower part of the trunk.

On the left - scaly oak bark ( Quercas); on the right is the ring-shaped crust of a grapevine ( Vitis vinifera); Krk- crust: d. forehead. - active bast; etc.- wood; prd- periderm; kcl- stony cells; BGN- bast fibers: cl- medullary rays; KMB- cambium; With- wood vessels; sc- core; ggk- boundary of the annual ring.

Based on the nature of separation from the trunk, the crust is distinguished between ringed and scaly. An annular crust is formed with concentric circular periderms. When separated from the trunk, the crust layer usually splits lengthwise into strips (in grapevines, cypress trees). A scaly crust is formed in periderms that have the outline of plates. In this case, the crust separates and falls off in the form of scales or plates (in plane trees). Shedding of the crust is favored by the differentiation of the plug in the periderm into thin-walled and thick-walled cell layers. In some species (birch, pine), the crust on older trunks no longer peels off: it becomes a thickening tissue mass with a network of cracks, expanding towards the free surface of the crust.

The value of the bark for plants is similar to the value of the periderm, but is greater: the bark protects trees, among other things, from burns and overheating.

Cork oak phellogen can function for a very long time. At the same time, the outer, older layers of cork become rougher and crack. When using cork oaks, the entire cork along with phellogen and phelloderm is cut off from trunks that are about 30 years old. After this, a new phellogen is laid deeper: the plug it generates, soft and elastic, is removed for use every 8-10 years, until about 200 years of age of the tree.

Lentils. Lentils are a ventilation system for perennial plants whose stems are covered with cork. At

Rice. 153. Part of a cross section through a young lilac branch ( Syringa vulgaris) with laying lentils.

Below the stomata at from the cells of the primary cortex, performing cells were formed (by increasing their volume, dividing and rounding); There is no phellogen yet.

With the death of the skin and the formation of the periderm, lentils are formed to replace the stomata. A brownish or grayish tubercle appears on the surface of the shoot. The skin breaks above its central part, then a depression forms in the form of a crater surrounded by a ridge. Over time, the lentil increases in size and changes shape. In aspens, for example, lentils become rhombic in outline, in birches they take on the appearance of long, up to 15 cm, narrow transverse stripes. The appearance of lentils usually begins with the proliferation and division of chlorophyll-bearing parenchyma cells under the stomata. The resulting cells differentiate into filling, or fulfilling, cells - round, thin-walled, chlorophyll-free cells, with large intercellular spaces in between. The filling cells lift the skin and tear it apart. Then, somewhat deeper in the primary cortex, due to tangential divisions of parenchyma cells, the lentil phellogen is laid down. Later, areas of lentil phellogen merge with the periderm phellogen. Newly formed cells quickly lose connection with each other, become suberized, rounded, intercellular spaces are formed - filling tissue appears.

The phellogen of lentils is formed when the stomata are sparsely located under each of them (in lilac, Fig. 153, in ash), when they are arranged in groups (in some types of poplar) - under each of the groups, when they are evenly and frequently distributed (in viburnum) - under some of the stomata.

The lentil phellogen contains narrow radial intercellular spaces. The lentil phellogen generates phelloderm inward, and outward - a loose mass of filling cells. This mass is usually homogeneous and consists of cells with thin walls. In most cases, the filling cells soon after formation are rounded and form a loose mass with a highly developed system of intercellular spaces (Fig. 154). From time to time, in lentils of this type, a closing layer is formed - a plate of one or several rows of polyhedral cells with corky shells; the trailing layer is penetrated by narrow radial intercellular spaces. After the formation of a new mass of filling cells, the trailing layer breaks, and after some time a new one is formed. Closing layers are formed once a year (in willows) or repeatedly; By winter, the lentil is clogged with a closing layer, and in the spring it breaks.

Populus tremuloides), the crust appears after lichens and fungi settle on the trunk.

The resulting product is hard, heterogeneous, little elastic and therefore of little value.