Conductive fabric
Conductive tissue transports dissolved substances nutrients by plant. For many higher plants it is represented by conducting elements (vessels, tracheids and sieve tubes). The walls of the conductive elements have pores and through holes that facilitate the movement of substances from cell to cell. Conductive tissue forms a continuous branched network in the plant body, connecting all its organs into a single system - from the thinnest roots to young shoots, buds and leaf tips.
Origin
Scientists believe that the emergence of tissues is associated in the history of the Earth with the emergence of plants on land. When part of the plant is in air environment, and the other part (root) is in the soil, there is a need to deliver water and mineral salts from the roots to the leaves, and organic substances from the leaves to the roots. So in the course of evolution flora Two types of conductive fabrics arose - wood and bast. Through the wood (through tracheids and vessels), water with dissolved minerals rises from the roots to the leaves - this is a water-conducting, or ascending, current. By bast (by sieve tubes) organic substances formed in green leaves flow to the roots and other organs of the plant - this is a downward current.
Meaning
The conductive tissues of plants are xylem (wood) and phloem (bast). Along the xylem (from the root to the stem) there is an upward flow of water with mineral salts dissolved in it. Along the phloem there is a weaker and slower flow of water and organic matter.
Meaning of wood
The xylem, through which there is a strong and rapid upward current, is formed by dead cells of different sizes. There is no cytoplasm in them, the walls are lignified and equipped with numerous pores. They are chains of long dead water-conducting cells adjacent to each other. At the points of contact they have pores, through which they move from cell to cell towards the leaves. This is how tracheids are arranged. Flowering plants also develop more advanced vascular tissues. In vessels, the transverse walls of the cells are destroyed to a greater or lesser extent, and appear as hollow tubes. Thus, vessels are connections of many dead tubular cells called segments. Located above each other, they form a tube. Through such vessels, solutions move even faster. Apart from flowering plants, other higher plants have only tracheids.
Luba meaning
Because the downward current is weaker, phloem cells can remain alive. They form sieve tubes - their transverse walls are densely pierced with holes. There are no nuclei in such cells, but they retain living cytoplasm. Sieve tubes do not remain alive for long, usually 2-3 years, occasionally - 10-15 years. New ones are constantly being formed to replace them.
| Biological tissues | |
|---|---|
| Cell | |
| Animals | Epithelial Connective (bone, cartilage, fat, blood and lymph) Nervous Muscular Integument |
| Plants | Educational (meristem) Integumentary Mechanical Adsorption Assimilation Conductive Secretory Aerenchyma |
| see also | Histology Intercellular substance |
| Organ | |
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See what “Conductive fabric” is in other dictionaries:
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Great importance in life land plants mechanical and conductive tissues play.
Mechanical fabrics
Everyone watched how a thin straw, supporting a heavy ear, swayed in the wind, but did not break.
Mechanical tissues give the plant strength. They serve as support for the organs in which they are located. Mechanical tissue cells have thickened membranes.
In leaves and other organs of young plants, cells mechanical fabric alive. This tissue is located in separate strands under the stem and petioles of leaves, bordering the veins of the leaves. Cells of living mechanical tissue are easily extensible and do not interfere with the growth of the part of the plant in which they are located. Thanks to this, plant organs act like springs. They are able to return to their original state after removing the load. Everyone has seen the grass rise again after a person has walked across it.
Mechanical tissue also serves as support for parts of the plant whose growth is complete, but the mature cells of this dead tissue. These include bast and wood cells - long thin cells collected in strands or bundles. The fibers give strength to the stem. Short dead cells of mechanical tissue (they are called stony cells) form the seed coat, nut shells, fruit seeds, and give the pear pulp its grainy character.
Conductive fabrics
All parts of the plant contain conductive tissues. They ensure the transport of water and substances dissolved in it.
Conductive tissues were formed in plants as a result of adaptation to life on land. The body of terrestrial plants is located in two environments of life - ground-air and soil. In this regard, two conductive fabrics arose - wood and bast. Water and mineral salts dissolved in it rise along the wood from bottom to top (from roots to). That's why wood is called a water-conducting fabric. Lub is inner part bark. Organic substances move along the bast from top to bottom (from leaves to roots). Wood and bast form a continuous branched system in the body of the plant, connecting all its parts.
The main conductive elements of wood are vessels. They are long tubes formed by the walls dead cells. At first, the cells were alive and had thin extensible walls. Then the cell walls became lignified and the living contents died. The transverse partitions between the cells collapsed, and long tubes formed. They consist of individual elements and are similar to bon din barrels and lids. Water with dissolved substances passes freely through the vessels of wood.
The conducting elements of the phloem are living elongated cells. They are connected at their ends and form long rows of cells - tubes. There are small holes (pores) in the transverse walls of the phloem cells. Such walls are similar to a sieve, which is why the tubes are called sieve-shaped. Solutions of organic substances move through them from the leaves to all organs of the plant.
25 ..CONDUCTIVE FABRICS.
Conductive tissues serve to move nutrients dissolved in water throughout the plant.
Rice. 43 Wood fibers of the meadow geranium leaf (transverse - A, B and longitudinal - C section of fiber groups):
1 - cell wall, 2 - simple pores, 3 - cell cavity
Like integumentary tissues, they arose as a consequence of the plant’s adaptation to life in two environments: soil and air. In this regard, it became necessary to transport nutrients in two directions.
An ascending, or transpiration, current of aqueous solutions of salts moves from the root to the leaves. The assimilation, downward flow of organic substances is directed from the leaves to the roots. The ascending current is carried out almost exclusively through the tracheal
Rice. 44 Sclereids of the stone of ripening cherry plum fruits with living contents: 1 - cytoplasm, 2 - thickened cell wall, 3-pore tubules
elements of xylem, a. descending - along the sieve elements of the phloem.
A highly branched network of conducting tissues carries water-soluble substances and photosynthetic products to all plant organs, from the thinnest root endings to the youngest shoots. Conductive tissues unite all plant organs. In addition to long-distance, i.e. axial, transport of nutrients, short-range radial transport is also carried out through conducting tissues.
All conductive tissues are complex, or complex, that is, they consist of morphologically and functionally heterogeneous elements. Forming from the same meristem, two types of conducting tissues - xylem and phloem - are located nearby. In many plant organs, xylem is combined with phloem in the form of strands called vascular bundles.
There are primary and secondary conducting tissues. Primary tissues are formed in leaves, young shoots and roots. They differentiate from procambium cells. Secondary conducting tissues, usually more powerful, arise from the cambium.
Xylem (wood). Water and dissolved minerals move through the xylem from the root to the leaves. Primary and secondary xylem contain the same types of cells. However, the primary xylem does not have medullary rays, differing in this from the secondary.
The composition of xylem includes morphologically different elements that perform the functions of both conducting and storing reserve substances, as well as purely supporting functions. Long-distance transport is carried out through the tracheal elements of xylem: tracheids and vessels, short-distance transport is carried out through parenchymal elements. Supporting and sometimes storage functions are performed by part of the tracheids and fibers of the mechanical tissue of the libriform, which are also part of the xylem.
Tracheids in a mature state are dead prosenchymal cells, narrowed at the ends and devoid of protoplast. The length of tracheids is on average 1-4 mm, while the diameter does not exceed tenths or even hundredths of a millimeter. The walls of the tracheids become lignified, thicken and bear simple or bordered pores through which solutions are filtered. Most of the bordered pores are located near the ends of the cells, that is, where solutions leak from one tracheid to another. Tracheids are present in sporophytes of all higher plants, and in most horsetails, lycophytes, pteridophytes and gymnosperms they are the only conducting elements of the xylem.
Vessels are hollow tubes consisting of individual segments located one above the other.
Between the segments of the same vessel located one above the other there are different types through holes - perforations. Thanks to the perforations along the entire vessel, liquid flows freely. Evolutionarily, vessels apparently originated from tracheids by destruction of the closing films of the pores and their subsequent fusion into one or more perforations. The ends of the tracheids, initially strongly beveled, took a horizontal position, and the tracheids themselves became shorter and turned into segments of blood vessels (Fig. 45).
Vessels appeared independently in different evolutionary lines of land plants. However, they reach their greatest development in angiosperms, where they are the main water-conducting elements of the xylem. The appearance of vessels is an important evidence of the evolutionary progress of this taxon, since they significantly facilitate the transpiration flow along the plant body.
In addition to the primary shell, vessels and tracheids in most cases have secondary thickenings. In the youngest tracheal elements, the secondary membrane may take the form of rings not connected to each other (ringed tracheids and vessels). Later, tracheal elements with spiral thickenings appear. These are followed by vessels and tracheids with thickenings, which can be characterized as spirals, the turns of which are interconnected (scalene thickenings). Ultimately, the secondary shell merges into a more or less continuous cylinder, forming inward from the primary shell. This cylinder is interrupted in certain areas by pores. Vessels and tracheids with relatively small rounded areas of the primary cell membrane, not covered from the inside by the secondary membrane, are often called porous. In cases where the pores in the secondary membrane form something like a mesh or ladder, they speak of reticulate or scalariform tracheal elements (scalene vessels and tracheids ).
Rice. 45 Changes in the structure of tracheal xylem elements during their evolution (the direction is indicated by an arrow):
1,2 - tracheids with rounded bordered pores, 3 - tracheids with elongated bordered pores, 4 - a vessel segment of a primitive type and its perforation formed by close pores, 5 - 7 - successive stages of specialization of vessel segments and the formation of a simple perforation
The secondary, and sometimes the primary shell, as a rule, is lignified, that is, impregnated with lignin, this gives additional strength, but limits the possibility of their further growth in length.
Tracheal elements, i.e. tracheids and vessels, are distributed in the xylem in different ways. Sometimes on a cross section they form well-defined rings (ring-vascular wood). In other cases, the vessels are scattered more or less evenly throughout the entire mass of xylem (disseminated vascular wood). Features of the distribution of tracheal elements in the xylem are used to identify wood of various tree species.
In addition to the tracheal elements, the xylem includes ray elements, i.e., cells that form the medullary rays (Fig. 46), most often formed by thin-walled parenchyma cells (radial parenchyma). Ray tracheids are less common in the rays of conifers. The medullary rays carry out short-range transport of substances in the horizontal direction. In addition to conducting elements, the xylem of angiosperms also contains thin-walled, non-lignified living parenchyma cells called wood parenchyma. Along with the core rays, short-range transport is partially carried out along them. In addition, the wood parenchyma serves as a storage site for reserve substances. Elements
medullary rays and wood parenchyma, like tracheal elements, arise from the cambium.
CONDUCTIVE FABRICS
Conductive tissues transport nutrients in two directions. Ascending (transpiration) current liquids (aqueous solutions and salts) goes through vessels And tracheids xylem (Fig. 32) from the roots up the stem to the leaves and other plant organs. Downward current(assimilation) organic matter is carried from the leaves along the stem to the underground organs of the plant through
special sieve tubes phloem (Fig. 33). The conducting tissue of the plant is somewhat reminiscent of the human circulatory system, since it has an axial and radial highly branched network; nutrients enter every cell of a living plant. In each plant organ, xylem and phloem are located side by side and are presented in the form of strands - conducting bundles.
There are primary and secondary conducting tissues. Primary ones differentiate from procambium and are formed in young plant organs; secondary conducting tissues are more powerful and are formed from cambium.
Xylem (wood) presented tracheids And trachea, or vessels.
Tracheids- elongated closed cells with obliquely cut jagged ends, in a mature state they are represented by dead prosenchymal cells. The length of the cells is on average 1 - 4 mm. Communication with neighboring tracheids occurs through simple or bordered pores. The walls are unevenly thickened; according to the nature of the thickening of the walls, tracheids are distinguished as annular, spiral, scalariform, reticulated and porous (Fig. 34). Porous tracheids always have bordered pores (Fig. 35). Sporophytes of all higher plants have tracheids, and in most horsetails, lycophytes, pteridophytes and gymnosperms they serve as the only conducting elements of the xylem. Tracheids
perform two main functions: conduction of water and mechanical strengthening of the organ.
Trachea, or vessels, are the main water-conducting elements of the xylem of angiosperms. Tracheas are hollow tubes consisting of individual segments; in the partitions between the segments there are holes - perforation, thanks to which the fluid flow is carried out. Tracheas, like tracheids, are a closed system: the ends of each trachea have beveled transverse walls with bordered pores. The tracheal segments are larger than the tracheids: in diameter they are about different types plants from 0.1 - 0.15 to 0.3 - 0.7 mm. The length of the trachea ranges from several meters to several tens of meters (for lianas). The trachea consists of dead cells, although in the initial stages of formation they are alive. It is believed that tracheae arose from tracheids in the process of evolution.
In addition to the primary shell, most vessels and tracheids have secondary thickenings in the form of rings, spirals, ladders, etc. Secondary thickenings form on the inner wall of the vessels (see Fig. 34). Thus, in an annular vessel, the internal thickenings of the walls are in the form of rings located at a distance from each other. The rings are located across the vessel and slightly oblique. In a spiral vessel, the secondary membrane is layered from the inside of the cell in the form of a spiral; in a mesh vessel, the non-thickened areas of the shell look like slits, reminiscent of mesh cells; in the scalene vessel, thickened places alternate with non-thickened ones, forming a semblance of a ladder.
Tracheids and vessels - tracheal elements - are distributed in the xylem in different ways: in a cross section in continuous rings, forming ring-vascular wood, or scattered more or less evenly throughout the xylem, forming scattered vascular wood. The secondary shell is usually impregnated with lignin, giving the plant additional strength, but at the same time limiting its growth in length.
In addition to vessels and tracheids, xylem includes beam elements, consisting of cells forming the medullary rays. The medullary rays consist of thin-walled living parenchyma cells through which nutrients flow horizontally. The xylem also contains living wood parenchyma cells, which function as short-range transport and serve as a storage site for reserve substances. All xylem elements come from the cambium.
Phloem- conductive tissue through which glucose and other organic substances are transported - products of photosynthesis from leaves to places of their use and deposition (to growth cones, tubers, bulbs, rhizomes, roots, fruits, seeds, etc.). Phloem is also primary and secondary.
Primary phloem is formed from procambium, secondary (phloem) - from cambium. Primary phloem lacks pith rays and has a less powerful system sieve elements than in tracheids. During the formation of the sieve tube, mucus bodies appear in the protoplast of the cells - segments of the sieve tube, which take part in the formation of the mucus cord near the sieve plates (Fig. 36). This completes the formation of the sieve tube segment. Sieve tubes function in most herbaceous plants one growing season and up to 3-4 years for trees and shrubs. Sieve tubes consist of a number of elongated cells communicating with each other through perforated septa - strainer. The shells of functioning sieve tubes do not become lignified and remain alive. Old cells become clogged with the so-called corpus callosum, and then die and are flattened under the pressure of younger functioning cells on them.
Refers to phloem bast parenchyma, consisting of thin-walled cells in which reserve nutrients are deposited. By medullary rays Secondary phloem also carries out short-range transportation of organic nutrients - products of photosynthesis.
Conductive bundles- strands formed, as a rule, by xylem and phloem. If cords are adjacent to the conductive bundles
mechanical tissue (usually sclerenchyma), then such bundles are called vascular-fibrous. Other tissues may also be included in the vascular bundles - living parenchyma, laticifers, etc. The vascular bundles can be complete, when both xylem and phloem are present, and incomplete, consisting only of xylem (xylem, or woody, vascular bundle) or phloem (phloem , or bast, conductive bundle).
The vascular bundles were originally formed from procambium. There are several types of conductive bundles (Fig. 37). Part of the procambium can be preserved and then turn into cambium, then the bundle is capable of secondary thickening. This open bundles (Fig. 38). Such vascular bundles predominate in most dicotyledons and gymnosperms. Plants with open bunches are able to grow in thickness due to the activity of the cambium, and the woody areas (Fig. 39, 5) are approximately three times larger than the bast areas (Fig. 39, 5). 2) . If, during differentiation of the vascular bundle from the procambial cord, the entire educational fabric is completely spent on the formation of permanent tissues, then the bundle is called closed(Fig. 40). Closed
vascular bundles are found in the stems of monocots. Wood and bast in bundles may have different mutual arrangement. In this regard, several types of vascular bundles are distinguished: collateral, bicollateral (Fig. 41), concentric and radial. Collateral, or side-by-side, - bundles in which xylem and phloem are adjacent to each other. Bicollateral, or double-sided, - bundles in which two strands of phloem adjoin the xylem side by side. IN concentric in bundles, xylem tissue completely surrounds phloem tissue or vice versa (Fig. 42). In the first case, such a bundle is called centrifloem. Centrophloem bundles are present in the stems and rhizomes of some dicotyledonous and monocotyledonous plants (begonia, sorrel, iris, many sedges and lilies). Ferns have them. There are also
intermediate vascular bundles between closed collateral and centrifloem ones. Found in the roots radial bundles in which the central part and rays along the radii are left by wood, and each ray of wood consists of central larger vessels, gradually decreasing along the radii (Fig. 43). Number of rays different plants not the same. Between the wood rays there are bast areas. The types of conductive bundles are shown schematically in Fig. 37. Vascular bundles stretch along the entire plant in the form of cords, which begin in the roots and run along the entire plant along the stem to the leaves and other organs. In leaves they are called veins. Their main function is to conduct descending and ascending currents of water and nutrients.
The function of conductive tissues is to conduct water with nutrients dissolved in it through the plant. Therefore, the cells that make up the conducting tissues have an elongated tubular shape, the transverse partitions between them are either completely destroyed or penetrated by numerous holes.
The movement of nutrients in a plant occurs in two main directions. Water and minerals rise from the roots to the leaves, which plants obtain from the soil through the root system. Organic substances produced during photosynthesis move from the leaves to the underground organs of plants.
Classification. Mineral and organic substances dissolved in water, as a rule, move along various elements conductive tissues, which, depending on the structure and physiological function performed, are divided into vessels (tracheas), tracheids and sieve tubes. Water rises through vessels and tracheids from minerals, through sieve tubes - various products of photosynthesis. However, organic substances move throughout the plant not only in a downward direction. They can rise up through the vessels, coming from underground organs to the above-ground parts of plants.
It is possible to move organic substances in an upward direction and through sieve tubes - from leaves to growing points, flowers and other organs located in the upper part of the plant.
Vessels and tracheids. The vessels consist of a vertical row of cells located one above the other, between which transverse partitions are destroyed. Individual cells are called vessel segments. Their shell becomes woody and thickens, the living contents in each segment die off. Depending on the nature of the thickening, several types of vessels are distinguished: annular, spiral, reticular, scalariform and porous (Fig. 42).
Ringed vessels have ring-shaped woody thickenings in the walls, but most of the wall remains cellulose. Spiral vessels have thickenings in the form of a spiral. Ringed and spiral vessels are characteristic of young plant organs, since, due to their structural features, they do not interfere with their growth. Later, reticular, scalariform and porous vessels are formed, with a stronger thickening and lignification of the membrane. The greatest thickening of the membrane is observed in porous vessels. The walls of all vessels are equipped with numerous pores, some of these pores have through holes - perforations. When vessels age, their cavity is often clogged with tills, which are formed as a result of neighboring parenchyma cells invaginating through the pores into the vessels and having the appearance of a bubble. The vessels in whose cavities tills appear cease to function and are replaced by younger ones. The formed vessel is a thin capillary tube (0.1...0.15 mm in diameter) and sometimes reaches a length of several tens of meters (some vines). Most often, the length of the vessels varies from 10 to 20 cm in different plants. The articulation between the segments of the vessels can be horizontal or oblique.
Tracheids differ from vessels in that they are individual closed cells with pointed ends. The movement of water and minerals occurs through various pores located in the shell of the tracheids, and therefore has a lower speed compared to the movement of substances through the vessels. Tracheids are similar in structure to vessels (thickening and lignification of the shell, death of the protoplast), but are a more ancient and primitive water-conducting element than vessels. The length of tracheids ranges from tenths of a millimeter to several centimeters.
Thanks to the thickening and lignification of the walls, vessels and tracheids perform not only the function of conducting water and minerals, but also mechanically, giving plant organs strength. The thickenings protect the water-conducting elements from being compressed by neighboring tissues.
In the walls of blood vessels and tracheids are formed various types pores - simple, bordered and semi-margined. Simple pores most often have a cross-section rounded shape and are a tubule passing through the thickness of the secondary membrane and coinciding with the pore tubule of the neighboring cell. Bordered pores are usually observed in the lateral walls of tracheids. They look like a dome rising above the wall of the water-conducting cage with a hole at the top. The dome is formed by the secondary membrane and its base borders on the thin primary cell membrane.
U coniferous plants in the thickness of the primary shell, directly below the opening of the bordered pore, there is a thickening - the torus, which plays the role of a two-way valve and regulates the flow of water into the cell. The torus is usually pierced with tiny holes. The bordered pores of adjacent vessels or tracheids, as a rule, coincide. If a vessel or tracheid borders on parenchyma cells, semi-bordered pores are obtained, since the border is formed only on the side of water-conducting cells (see Fig. 21).
In the process of evolution, there was a gradual improvement in the water-conducting elements of plants. Tracheids, as a primitive type of conducting tissue, are characteristic of more ancient representatives of the plant world (mosses, gymnosperms), although they are sometimes found in highly organized plants.
The initial type should be considered ring-shaped vessels, from which further development proceeded to the most advanced vessels - porous. There was a gradual shortening of the vascular segments with a simultaneous increase in their diameter. The transverse partitions between them acquired a horizontal position and were pierced with holes, which ensured better movement of water. Subsequently, the complete destruction of the partitions occurred, from which a small ridge sometimes remains in the cavity of the vessel.
Vessels and tracheids, in addition to water with minerals dissolved in it, sometimes also carry organic substances, the so-called sap. This is usually observed in the spring, when fermented organic substances are directed from the places of their deposition - roots, rhizomes and other underground parts of plants - to above-ground organs - stems and leaves.
Sieve tubes. Organic substances dissolved in water are transported through sieve tubes. They consist of a vertical row of living cells and contain well-defined cytoplasm. The nuclei are very small and are usually destroyed during the formation of the sieve tube. There are also leucoplasts. The transverse partitions between the cells of the sieve tubes are equipped with numerous openings and are called sieve plates. Plasmodesmata extend through the holes. The shells of the sieve tubes are thin, cellulose, and have simple pores on the side walls. In most plants, during the development of sieve tubes, satellite cells adjacent to them are formed, with which they are connected by numerous plasmodesmata (Fig. 43). Companion cells contain dense cytoplasm and a well-defined nucleus. Companion cells were not found in conifers, mosses and ferns.
The length of the sieve tubes is significantly shorter than that of the vessels, and ranges from fractions of a millimeter to 2 mm with a very small diameter, not exceeding hundredths of a millimeter.
Sieve tubes usually function for one growing season. In autumn, the pores of the sieve plates become clogged, and a corpus callosum is formed on them, consisting of a special substance - calloses. In some plants, such as linden, the corpus callosum resolves and the sieve tubes resume their activity, but in most cases they die off and are replaced by new sieve tubes.
Living sieve tubes resist the pressure of neighboring tissues due to the turgor of their cells, and after dying they flatten and dissolve.
Lacteal vessels (lacteals). Lactifers, found in many flowering plants, can be classified as both conducting and excretory tissues, since they perform diverse functions - conducting, excreting and accumulating various substances. Lacteal vessels contain cell sap of a special composition, called milky sap, or latex. They are formed by one or more living cells that have a cellulose membrane, wall layers of cytoplasm, a nucleus, leukoplasts and a large central vacuole with milky juice, which occupies almost the entire cell cavity. There are 2 types of laticifers - articulated and non-articulated (Fig. 44).
Articulated lacticifers, like vessels and sieve tubes, consist of a longitudinal row of elongated cells. Sometimes the transverse partitions between them dissolve, and continuous thin tubes are formed, from which numerous lateral outgrowths extend, connecting individual laticifers with each other. Articulated laticifers include plants from the families Compositae (Asteraceae), Poppy, Campanaceae, etc.
Unsegmented lacticifers consist of a single cell, which grows as the plant grows. Branching out, they permeate the entire body of the plant, but the individual laticifers never connect. Their length can reach several meters. Unsegmented lacticifers are observed in plants of the nettle, euphorbia, kutraceae, and other families.
Milktails are usually short-lived and, having reached a certain age, die off and flatten. At the same time, rubber plants the latex coagulates, resulting in a mass of hardened rubber.
Excretory tissues (excretory system)
Functions and structural features. Excretory tissues serve to accumulate or secrete final metabolic products (catabolites) that are not involved in further metabolism and are sometimes harmful to plants. Their accumulation can occur both in the cavity of the cell itself and in the intercellular spaces. The elements of excretory tissues are very diverse - specialized cells, canals, glands, hairs, etc. The combination of these elements represents the excretory system of plants.
Classification. Distinguish excretory tissues internal secretion and excretory tissues of external secretion.
Excretory tissues of internal secretion. These include various secretion containers in which metabolic products such as essential oils, resins, tannins, and rubber accumulate. However, in some plants, resins can also be released outside.
Essential oils most often accumulate in the receptacles of secretions. These receptacles are usually located among the cells of the main tissue near the surface of the organ. According to their origin, secretion receptacles are divided into schizogenic and lysigenic (Fig. 45). Schizogenic spaces arise as a result of the accumulation of substances in the intercellular space and the subsequent separation and death of neighboring cells. Similar channel-shaped excretory passages containing essential oil are characteristic of the fruits of plants of the umbelliferous (celery) family - dill, coriander, anise, etc. Resin passages in the leaves and stems of coniferous plants can serve as an example of containers of schizogenic origin.
Lysigenic receptacles arise as a result of the accumulation of the excretory product inside the cells, after which the dissolution of the cell membranes occurs. Lysigenic receptacles are widely known essential oils in citrus fruits and leaves.
Excretory tissues of external secretion. They are less diverse than endocrine tissues.
Of these, the most common are glandular hairs and glands, adapted to secrete essential oils, resinous substances, nectar and water. The glands that secrete nectar are called nectaries. They have a varied shape and structure and are mainly found in flowers, but are sometimes formed on other plant organs. The glands that secrete water play the role of hydathodes. The process of releasing water in a drop-liquid state is called guttation. Guttation occurs under conditions high humidity air that prevents transpiration.
