Root and root system. Root functions

Root and root systems

Root- the main vegetative organ of a plant, which in a typical case performs the function of soil nutrition. The root is an axial organ that has radial symmetry and grows in length indefinitely due to the activity of the apical meristem. It differs morphologically from the shoot in that leaves never form on it, and the apical meristem is always covered by a root cap.

In addition to the main function of absorbing substances from the soil, the roots also perform other functions:

1) the roots strengthen (“anchor”) the plants in the soil, make it possible to grow vertically and shoot up;

2) various substances are synthesized in the roots, which then move to other organs of the plant;

3) reserve substances can be deposited in the roots;

4) roots interact with the roots of other plants, microorganisms, fungi that live in the soil.

The totality of the roots of one individual forms a single morphological and physiological relation root system.

The composition of root systems includes roots of various morphological nature - main root, lateral and adnexal roots.

main root develops from the germinal root. Lateral roots are formed on the root (main, lateral, subordinate), which in relation to them is designated as maternal. They arise at some distance from the apex, in the direction from the base of the root to its top. Lateral roots are laid endogenously, i.e. in the internal tissues of the maternal root. If branching occurred at the apex itself, it would make it difficult for the root to move through the soil. adventitious roots can occur on stems, and on leaves, and on roots. In the latter case, they differ from lateral roots in that they do not show a strict order of initiation near the apex of the maternal root and may appear in old root areas.

By origin, the following types of root systems are distinguished ( rice. 4.1):

1) main root system represented by the main root (first order) with lateral roots of the second and subsequent orders (in many shrubs and trees, most dicotyledonous plants);

2) adventitious root system develops on stems, leaves; found in most monocotyledonous plants and many dicotyledons that reproduce vegetatively;

3) mixed root system formed by the main and adventitious roots with their lateral branches (many herbaceous dicots).

Rice. 4.1. Types of root systems: A - main root system; B - system of adventitious roots; C - mixed root system (A and C - tap root systems; B - fibrous root system).

Distinguished by shape rod and fibrous root systems.

AT pivotal In the root system, the main root is strongly developed and is clearly visible among the other roots. AT fibrous root system, the main root is invisible or absent, and the root system is composed of numerous adventitious roots ( rice. 4.1).

The root has potentially unlimited growth. However, under natural conditions, the growth and branching of roots is limited by the influence of other roots and soil environmental factors. The bulk of the roots is located in the upper soil layer (15 cm), the richest in organic matter. The roots of trees deepen on average by 10-15 m, and in width they usually spread beyond the radius of the crowns. The root system of corn goes to a depth of about 1.5 m and about 1 m in all directions from the plant. The record depth of root penetration into the soil was noted in the desert mesquite shrub - more than 53 m.

In one rye bush grown in a greenhouse, the total length of all roots was 623 km. The total growth of all roots in one day was approximately 5 km. The total surface of all the roots of this plant was 237 m 2 and was 130 times larger than the surface of the above-ground organs.

Zones of the young root ending - these are parts of a young root that are different in length, perform different functions and are characterized by certain morphological and anatomical features ( rice. 4.2).

The tip of the root is always covered from the outside root cap protecting the apical meristem. The sheath consists of living cells and is constantly updated: as old cells are shed from its surface, the apical meristem forms new young cells to replace them from the inside. The outer cells of the root cap flake off while still alive, producing a copious mucus which facilitates the root to move through the hard soil particles. The cells of the central part of the cap contain many starch grains. Apparently, these grains serve statoliths, i.e., they are able to move in the cell when the position of the root tip in space changes, due to which the root always grows in the direction of gravity ( positive geotropism).

Under the cover is dividing zone, represented by the apical meristem, as a result of which all other zones and tissues of the root are formed. The division zone has dimensions of about 1 mm. The cells of the apical meristem are relatively small, multifaceted, with a dense cytoplasm and a large nucleus.

Following the division zone is located stretch zone, or growth zone. In this zone, cells almost do not divide, but strongly stretch (grow) in the longitudinal direction, along the axis of the root. The volume of cells increases due to the absorption of water and the formation of large vacuoles, while high turgor pressure pushes the growing root between the soil particles. The stretch zone is usually small and does not exceed a few millimeters.

Rice. 4.2. General view (A) and longitudinal section (B) of the root end (scheme): I - root cap; II - zones of division and stretching; III - suction zone; IV - beginning of the conduction zone: 1 - growing lateral root; 2 - root hairs; 3 - rhizoderma; 3a - exoderm; 4 - primary bark; 5 - endoderm; 6 - pericycle; 7 - axial cylinder.

Next comes absorption zone, or suction zone. In this zone, the integumentary tissue is rhizoderma(epiblema), the cells of which bear numerous root hairs. The stretching of the root stops, the root hairs tightly cover the soil particles and, as it were, grow together with them, absorbing water and mineral salts dissolved in it. The absorption zone extends up to several centimeters. This area is also called zone of differentiation, since it is here that the formation of permanent primary tissues occurs.

The life span of the root hair does not exceed 10-20 days. Above the suction zone, where the root hairs disappear, begins holding area. Through this part of the root, water and salt solutions absorbed by the root hairs are transported to the overlying organs of the plant. Lateral roots are formed in the conduction zone (Fig. 4.2).

The cells of the suction and conduction zones occupy a fixed position and cannot move relative to the soil areas. However, the zones themselves, due to constant apical growth, continuously move along the root as the root ending grows. Young cells are constantly included in the absorption zone from the side of the stretching zone and at the same time aging cells are excluded, passing into the composition of the conduction zone. Thus, the suction apparatus of the root is a mobile formation that continuously moves in the soil.

In the same way, internal tissues appear consistently and naturally in the root ending.

The primary structure of the root. The primary structure of the root is formed as a result of the activity of the apical meristem. The root differs from the shoot in that its apical meristem deposits cells not only inward, but also outward, replenishing the cap. The number and location of initial cells in the root apexes vary considerably in plants belonging to different systematic groups. Derivatives of initials already near the apical meristem differentiate into primary meristems - 1) protodermis, 2) main meristem and 3) procambium(rice. 4.3). From these primary meristems, three tissue systems are formed in the suction zone: 1) rhizoderma, 2) primary cortex and 3) axial (central) cylinder, or stele.

Rice. 4.3. Longitudinal section of the tip of an onion root.

rhizoderma (epiblema, root epidermis) - absorbent tissue formed from protoderms, the outer layer of the primary root meristem. In functional terms, the rhizoderm is one of the most important plant tissues. Through it, water and mineral salts are absorbed, it interacts with the living population of the soil, and through the rhizoderm, substances that help soil nutrition are released from the root into the soil. The absorbing surface of the rhizodermis is greatly enlarged due to the presence of tubular outgrowths in some of the cells - root hairs(Fig. 4.4). The hairs are 1-2 mm long (up to 3 mm). In one four-month-old rye plant, approximately 14 billion root hairs were found with a absorption area of 401 m 2 and a total length of more than 10,000 km. At aquatic plants root hairs may be absent.

The wall of the hair is very thin and consists of cellulose and pectin. Its outer layers contain mucus, which helps to establish closer contact with soil particles. Slime creates favorable conditions for the settlement of beneficial bacteria, affects the availability of soil ions and protects the root from drying out. Physiologically, the rhizoderm is highly active. It absorbs mineral ions with the expenditure of energy. The hyaloplasm contains a large number of ribosomes and mitochondria, which is typical for cells with high level metabolism.

Rice. 4.4. Cross section of the root in the suction zone: 1 - rhizoderma; 2 - exoderm; 3 - mesoderm; 4 - endoderm; 5 - xylem; 6 - phloem; 7 - pericycle.

From main meristem formed primary cortex. The primary cortex of the root is differentiated into: 1) exoderm- the outer part, lying directly behind the rhizoderm, 2) the middle part - mesoderm and 3) the innermost layer - endoderm (rice. 4.4). The bulk of the primary cortex is mesoderm, formed by living parenchymal cells with thin walls. The cells of the mesoderm are located loosely, the gases necessary for cell respiration circulate along the system of intercellular spaces along the axis of the root. In marsh and aquatic plants, the roots of which lack oxygen, the mesoderm is often represented by aerenchyma. Mechanical and excretory tissues may also be present in the mesoderm. The parenchyma of the primary cortex performs a number of important functions: it participates in the absorption and conduction of substances, synthesizes various compounds, spare parts are often deposited in the cells of the cortex. nutrients such as starch.

The outer layers of the primary cortex, underlying the rhizoderm, form exoderm. The exoderm arises as a tissue that regulates the passage of substances from the rhizoderm to the cortex, but after the death of the rhizoderm above the absorption zone, it appears on the root surface and turns into a protective integumentary tissue. The exoderm is formed as a single layer (rarely several layers) and consists of living parenchymal cells tightly closed together. As the root hairs die, the walls of the exoderm cells are covered on the inside with a layer of suberin. In this respect, the exoderm is similar to the cork, but unlike it, it is primary in origin, and the cells of the exoderm remain alive. Sometimes in the exoderm, pass cells with thin, non-corked walls are preserved, through which selective absorption of substances occurs.

The innermost layer of the primary cortex is endoderm. It surrounds the stele in the form of a continuous cylinder. Endoderm in its development can go through three stages. At the first stage, its cells fit tightly to each other and have thin primary walls. Thickenings in the form of frames are formed on their radial and transverse walls - Caspari belts (rice. 4.5). The belts of neighboring cells are closely connected with each other, so that a continuous system of them is created around the stele. Suberin and lignin are deposited in Caspari bands, which makes them impermeable to solutions. Therefore, substances from the cortex to the stele and from the stele to the cortex can pass only along the symplast, i.e., through the living protoplasts of endoderm cells and under their control.

Rice. 4.5. Endoderm at the first stage of development (scheme).

At the second stage of development, suberin is deposited over the entire inner surface of endoderm cells. However, some cells retain their original structure. This is check cells, they remain alive, and through them the connection between the primary cortex and the central cylinder is carried out. As a rule, they are located opposite the rays of the primary xylem. In roots that do not have secondary thickening, the endoderm can acquire a tertiary structure. It is characterized by a strong thickening and lignification of all walls, or more often the walls facing outward remain relatively thin ( rice. 4.7). Passage cells are also preserved in the tertiary endoderm.

Central(axial) cylinder, or stele formed in the center of the root. Already close to the division zone, the outermost layer of the stele forms pericycle, the cells of which retain the character of the meristem and the ability for neoplasms for a long time. In a young root, the pericycle consists of a single row of thin-walled living parenchymal cells ( rice. 4.4). The pericycle performs several important functions. In most seed plants, lateral roots are laid in it. In species with secondary growth, it participates in the formation of the cambium and gives rise to the first layer of the phellogen. In the pericycle, the formation of new cells often occurs, which are then included in its composition. In some plants, the adventitious buds also appear in the pericycle. In old roots of monocots, the cells of the pericycle are often sclerified.

Cells behind the pericycle procambia, which differentiate into primary conductive tissues. Phloem and xylem elements are laid in a circle, alternating with each other, and develop centripetally. However, the xylem in its development usually overtakes the phloem and occupies the center of the root. On a transverse section, the primary xylem forms a star, between the rays of which there are sections of phloem ( rice. 4.4). This structure is called radial conducting beam.

The xylem star may have different number rays - from two to many. If there are two, the root is called diarchic if three - triarchal, four - tetrarch, and if a lot - polyarchal (rice. 4.6). The number of xylem rays usually depends on the thickness of the root. In the thick roots of monocot plants, it can reach 20-30 ( rice. 4.7). In the roots of the same plant, the number of xylem rays can be different; in thinner branches, it is reduced to two.

Rice. 4.6. Types of structure of the axial cylinder of the root (scheme): A - diarch; B - triarch; B - tetrarch; G - polyarchy: 1 - xylem; 2 - phloem.

Spatial separation of strands of primary phloem and xylem, located at different radii, and their centripetal laying are characteristics structures of the central cylinder of the root and are of great biological importance. The elements of the xylem are as close as possible to the surface of the stele, and it is easier for them, bypassing the phloem, to penetrate the solutions coming from the bark.

Rice. 4.7. Cross section of the root of a monocot plant: 1 - remains of rhizoderm; 2 - exoderm; 3 - mesoderm; 4 - endoderm; 5 - checkpoints; 6 - pericycle; 7 - xylem; 8 - phloem.

The central part of the root is usually occupied by one or more large xylem vessels. The presence of a core is generally atypical for a root, however, in the roots of some monocots in the middle is small plot mechanical tissue ( rice. 4.7) or thin-walled cells arising from procambium (Fig. 4.8).

Rice. 4.8. Cross section of a corn root.

The primary root structure is characteristic of young roots of all plant groups. In spore and monocotyledonous plants, the primary structure of the root is preserved throughout life.

Secondary structure of the root. In gymnosperms and dicotyledonous plants, the primary structure does not last long and above the absorption zone is replaced by a secondary one. Secondary root thickening occurs due to the activity of secondary lateral meristems - cambium and phellogen.

Cambium arises in the roots from meristematic procambial cells in the form of a layer between the primary xylem and phloem ( rice. 4.9). Depending on the number of phloem cords, two or more zones of cambial activity are formed simultaneously. At first, the cambial layers are separated from each other, but soon the cells of the pericycle, lying opposite the rays of the xylem, divide tangentially and connect the cambium into a continuous layer surrounding the primary xylem. The cambium lays down layers secondary xylem (wood) and out secondary phloem (bast). If this process lasts a long time, then the roots reach a considerable thickness.

Rice. 4.9. The establishment and beginning of the activity of the cambium in the root of the pumpkin seedling: 1 - primary xylem; 2 - secondary xylem; 3 - cambium; 4 - secondary phloem; 5 - primary phloem; 6 - pericycle; 7 - endoderm.

The areas of the cambium that have arisen from the pericycle consist of parenchymal cells and are not capable of depositing elements of conducting tissues. They form primary core rays, which are wide areas of the parenchyma between the secondary conductive tissues ( rice. 4.10). Secondary core, or beams of wood appear additionally with prolonged thickening of the root, they are usually narrower than the primary ones. The core rays provide a link between the xylem and phloem of the root, and radial transport of various compounds occurs along them.

As a result of the activity of the cambium, the primary phloem is pushed outward and squeezed. The primary xylem star remains in the center of the root, its rays can persist for a long time ( rice. 4.10), but more often the center of the root is filled with secondary xylem, and the primary xylem becomes invisible.

Rice. 4.10. Cross section of pumpkin root (secondary structure): 1 - primary xylem; 2 - secondary xylem; 3 - cambium; 4 - secondary phloem; 5 - primary core beam; 6 - cork; 7 - parenchyma of the secondary cortex.

The tissues of the primary cortex cannot follow the secondary thickening and are doomed to death. They are replaced by secondary integumentary tissue - periderm, which can be stretched on the surface of a thickening root due to the work of phellogen. fellogen is laid in the pericycle and begins to lay out cork, and inside phelloderma. The primary bark, cut off by a cork from the internal living tissues, dies and is discarded ( rice. 4.11).

Phelloderm cells and parenchyma, formed by cell division of the pericycle, form parenchyma of the secondary cortex surrounding conductive tissues (Fig. 4.10). Outside, the roots of the secondary structure are covered with periderm. The crust is rarely formed, only on old tree roots.

perennial roots woody plants as a result of prolonged activity, the cambium often thickens greatly. The secondary xylem of such roots merges into a solid cylinder, surrounded on the outside by a cambium ring and a continuous ring of secondary phloem ( rice. 4.11). Compared with the stem, the boundaries of annual rings in the wood of the root are much less pronounced, the bast is more developed, and the medullary rays are, as a rule, wider.

Rice. 4.11. Cross section of a willow root at the end of the first growing season.

Specialization and metamorphoses of roots. Most plants in the same root system have distinctly different growth and sucking endings. Growth endings are usually more powerful, quickly elongate and move deep into the soil. Their elongation zone is well defined, and the apical meristems work vigorously. Sucking endings arising in in large numbers on growth roots, elongate slowly, and their apical meristems almost stop working. The sucking endings, as it were, stop in the soil and intensively “suck” it.

Woody plants have thick skeletal and semi-skeletal roots on which short-lived root lobes. The composition of the root lobes, continuously replacing each other, includes growth and sucking endings.

If the roots perform special functions, their structure changes. A sharp, hereditarily fixed modification of an organ, caused by a change in functions, is called metamorphosis. Root modifications are very diverse.

The roots of many plants form a symbiosis with hyphae of soil fungi, called mycorrhiza("mushroom root"). Mycorrhiza is formed on sucking roots in the absorption zone. The fungal component makes it easier for the roots to obtain water and mineral elements from the soil; fungal hyphae often replace root hairs. In turn, the fungus receives carbohydrates and other nutrients from the plant. There are two main types of mycorrhiza. gifs ectotrophic mycorrhiza form a sheath that envelops the root from the outside. Ectomycorrhiza is widespread in trees and shrubs. Endotrophic mycorrhiza is found mainly in herbaceous plants. Endomycorrhiza is located inside the root, hyphae are introduced into the cells of the bovine parenchyma. Mycotrophic nutrition is very widespread. Some plants, such as orchids, cannot exist at all without symbiosis with fungi.

On the roots of legumes, special formations appear - nodules in which bacteria from the genus Rhizobium settle. These microorganisms are able to assimilate atmospheric molecular nitrogen, converting it into a bound state. Part of the substances synthesized in the nodules are absorbed by plants, bacteria, in turn, use the substances found in the roots. This symbiosis is of great importance for Agriculture. leguminous plants thanks to an additional source of nitrogen, they are rich in proteins. They provide valuable food and fodder products and enrich the soil with nitrogenous substances.

Very widespread hoarding roots. They are usually thickened and strongly parenchymatized. Strongly thickened adventitious roots called root cones, or root tubers(dahlia, some orchids). Many, more often biennial, plants with a tap root system develop a formation called root crop. Both the main root and the lower part of the stem take part in the formation of the root crop. In carrots, almost the entire root crop is composed of a root; in turnips, the root forms only the lowest part of the root crop ( rice. 4.12).

Fig.4.12. Root vegetables of carrots (1, 2), turnips (3, 4) and beets (5, 6, 7) ( xylem black on transverse sections; the horizontal dotted line shows the border of the stem and root).

Roots cultivated plants arose as a result of long-term selection. In root crops, the storage parenchyma is highly developed and mechanical tissues have disappeared. In carrots, parsley, and other umbellifers, the parenchyma is strongly developed in the phloem; in turnips, radishes and other cruciferous plants - in xylem. In beets, reserve substances are deposited in the parenchyma formed by the activity of several additional layers of cambium ( rice. 4.12).

Many bulbous and rhizomatous plants form retractors, or contractile roots ( rice. 4.13, 1). They can shorten and draw the shoot into the soil to the optimum depth during the summer drought or winter frosts. Retracting roots have thickened bases with transverse wrinkling.

Rice. 4.13. root metamorphoses: 1 - corm of gladiolus with retracting roots thickened at the base; 2 - respiratory roots with pneumatophores in Avicenna ( etc- tidal zone); 3 - aerial roots of an orchid.

Rice. 4.14. Part of a cross section of an aerial root of an orchid: 1 - velamen; 2 - exoderm; 3 - checkpoint.

Respiratory roots, or pneumatophores (rice. 4.13, 2) are formed in some tropical woody plants living in conditions of lack of oxygen (taxodium, or swamp cypress; mangrove plants that live along the swampy shores of ocean coasts). Pneumatophores grow vertically upwards and protrude above the soil surface. Through a system of holes in these roots, connected with the aerenchyma, air enters the underwater organs.

In some plants, to maintain shoots in the air, additional support roots. They depart from the horizontal branches of the crown and, having reached the soil surface, branch intensively, turning into columnar formations that support the crown of the tree ( columnar banyan roots) ( rice. 4.15, 2). stilted roots extend from the lower parts of the stem, giving the stem stability. They form in mangrove plants, plant communities that develop on tropical ocean shores flooded at high tide ( rice. 4.15, 3), as well as in corn ( rice. 4.15, 1). Ficus rubbery are formed plank-shaped roots. Unlike columnar and stilted, they are by origin not adventitious, but lateral roots.

Rice. 4.15. supporting roots: 1 - stilted corn roots; 2 - columnar banyan roots; 3 - stilted roots of rhizophora ( etc- tidal zone; from- low tide zone; silt- the surface of the muddy bottom).

The root, its functions. Types of roots and root systems.

The root is the underground organ of the plant. The main functions of the root are:

Supporting: the roots fix the plant in the soil and hold it throughout its life;

Nutritious: through the roots, the plant receives water with dissolved mineral and organic substances;

Storage: some roots can accumulate nutrients.

Root types

There are main, adventitious and lateral roots. When the seed germinates, the germinal root appears first, which turns into the main one. Adventitious roots may appear on the stems. Lateral roots extend from the main and adventitious roots. Adventitious roots provide the plant with additional nutrition and perform a mechanical function. Develop when hilling, for example, tomatoes and potatoes.

Root functions:

They absorb water and mineral salts dissolved in it from the soil, transport them up the stem, leaves and reproductive organs. The suction function is performed by root hairs (or mycorrhiza) located in the suction zone.

Anchor the plant in the soil.

Nutrients (starch, inulin, etc.) are stored in the roots.

Symbiosis is carried out with soil microorganisms - bacteria and fungi.

Many plants reproduce vegetatively.

Some roots perform the function of a respiratory organ (monstera, philodendron, etc.).

The roots of a number of plants perform the function of "stilted" roots (ficus banyan, pandanus, etc.).

The root is capable of metamorphoses (thickenings of the main root form "root crops" in carrots, parsley, etc.; thickenings of lateral or adventitious roots form root tubers in dahlias, peanuts, chistyak, etc., shortening of roots in bulbous plants). The roots of one plant are the root system. The root system is rod and fibrous. In the tap root system, the main root is well developed. It has most dicotyledonous plants (beets, carrots). In perennial plants, the main root can die off, and nutrition occurs due to lateral roots, so the main root can only be traced in young plants. The fibrous root system is formed only by adventitious and lateral roots. It has no main root. Monocotyledonous plants, for example, cereals, onions, have such a system. Root systems take up a lot of space in the soil. For example, in rye, the roots spread in breadth by 1-1.5 m and penetrate deep into 2 m. Metamorphoses of the root system associated with habitat conditions: * Aerial roots. * Stilted roots. * Respiratory roots. (columnar). * Roots - trailers.

10. Root metamorphoses and their functions. Influence of environmental factors on the formation and development of the root system of plants. Mycorrhiza. Mushroom root. Attached to plants and are in a state of symbiosis. Mushrooms living on roots use carbohydrates, which are formed as a result of photosynthesis; in turn deliver water and minerals.

Nodules. The roots of leguminous plants thicken, forming outgrowths, due to bacteria from the genus Rhizobium. Bacteria are able to fix atmospheric nitrogen, converting it into a bound state, some of these compounds are absorbed by a higher plant. Due to this, the soil is enriched with nitrogenous substances. Retracting (contractile) roots. Such roots are able to draw the organs of renewal into the soil to a certain depth. Retraction (geophilia) occurs due to the reduction of typical (main, lateral, adventitious roots) or only specialized contractile roots. Plank roots. These are large plagiotropic lateral roots, along the entire length of which a flat outgrowth is formed. Such roots are characteristic of the trees of the upper and middle tiers of the tropical rainforest. The process of formation of a board-shaped outgrowth begins at the oldest part of the root - the basal. Columnar roots. They are characteristic of tropical Bengal ficus, sacred ficus, etc. Some of the aerial roots hanging down show positive geotropism - they reach the soil, penetrate into it and branch, forming an underground root system. Subsequently, they turn into powerful pillar-like supports. Stilted and respiratory roots. Mangrove plants that develop stilted roots are rhizophores. Stilted roots are metamorphosed adventitious roots. They are formed in seedlings on the hypocotyl, and then on the stem of the main shoot. Respiratory roots. The main adaptation to life on unsteady silty soils in conditions of oxygen deficiency is a highly branched root system with respiratory roots - pneumatophores. The structure of pneumatophores is associated with the function they perform - ensuring the gas exchange of the roots and supplying their internal tissues with oxygen. Aerial roots are formed in many tropical herbaceous epiphytes. Their aerial roots hang freely in the air and are adapted to absorb moisture in the form of rain. For this, velamen is formed from the protodermis, and it absorbs water. storage roots. Root tubers form as a result of metamorphosis of lateral and adventitious roots. Root tubers function only as storage organs. These roots combine the functions of storage and absorption of soil solutions. A root crop is an axial orthotropic structure formed by a thickened hypocotyl (neck), the basal part of the main root and the vegetative part of the main shoot. However, the activity of the cambium is limited. Further thickening of the root continues due to the pericycle. Cambium is added and a ring of meristematic tissue is formed.

The environmental factor may limit their growth and development. For example, with regular cultivation of the soil, the annual cultivation of any crop on it, the supply of mineral salts is depleted, so the growth of plants in this place stops or is limited. Even if all other conditions necessary for their growth and development are present. This factor is designated as limiting.
For example, the limiting factor for aquatic plants is most often oxygen. For solar plants, for example, sunflower, such a factor most often becomes sunlight (lighting).
The combination of such factors determines the conditions for the development of plants, their growth and the possibility of existence in a particular area. Although, like all living organisms, they can adapt to living conditions. Let's see how this happens:
Drought, high temperatures
Plants that grow in hot, arid climates, such as the desert, have strong root systems to get water. For example, shrubs belonging to the genus Juzgun have 30-meter roots that go deep into the ground. But the roots of cacti are not deep, but spread widely under the surface of the soil. They collect water from a large surface of the soil during rare, short rains.
The collected water must be saved. Therefore, some plants - succulents for a long time save a supply of moisture in the leaves, branches, trunks.
Among the green inhabitants of the desert, there are those who have learned to survive even with many years of drought. Some, which are called ephemera, live only a few days. Their seeds germinate, bloom and bear fruit as soon as the rain passes. At this time, the desert looks very beautiful - it blooms.
But lichens, some club mosses and ferns, can live in a dehydrated state. long time until the occasional rain falls.
Cold, wet tundra conditions
Here the plants adapt to very harsh conditions. Even in summer it is rarely above 10 degrees Celsius. Summer lasts less than 2 months. But even during this period there are frosts.
There is little rainfall, so the snow cover that protects the plants is small. A strong gust of wind can completely expose them. But permafrost retains moisture and there is no shortage of it. Therefore, the roots of plants growing in such conditions are superficial. The plants are protected from the cold by the thick skin of the leaves, the wax coating on them, and the cork on the stem.
Due to the polar day in the summer in the tundra, photosynthesis in the leaves continues around the clock. Therefore, during this time they manage to accumulate a sufficient, durable supply of necessary substances.
Interestingly, trees growing in the tundra produce seeds that grow once every 100 years. Seeds grow only when the right conditions come - after two warm summer seasons in a row. Many have adapted to reproduce vegetatively, such as mosses and lichens.
sunlight
Light is very important for plants. Its quantity affects their appearance and internal structure. For example, forest trees that have enough light to grow tall have a less spreading crown. Those who are in their shadow develop worse, are more oppressed. Their crowns are more spreading, and the leaves are arranged horizontally. This is necessary in order to capture as much sunlight as possible. Where there is enough sun, the leaves are arranged vertically to avoid overheating.

11. External and internal structure of the root. Root growth. Absorption of water from soil by roots. The root is the main organ of a higher plant. Root - an axial organ, usually cylindrical in shape, with radial symmetry, possessing geotropism. It grows as long as the apical meristem is preserved, covered with a root cap. On the root, unlike the shoot, leaves never form, but, like the shoot, the root branches, forming root system.

The root system is the totality of the roots of a single plant. The nature of the root system depends on the ratio of growth of the main, lateral and adventitious roots. In the root system, the main (1), lateral (2) and adventitious roots (3) are distinguished.

main root develops from the germinal root.

Adnexal called the roots that develop on the stem part of the shoot. Adventitious roots can also grow on leaves.

Lateral roots occur on the roots of all types (main, lateral and adnexal

Internal structure root. At the tip of the root are the cells of the educational tissue. They share actively. This section of the root about 1 mm long is called division zone . The root division zone is protected from damage by a root cap from the outside. The cap cells secrete a mucus that coats the tip of the root, which facilitates its passage through the soil.

Above the division zone there is a smooth section of the root about 3-9 mm long. Here, the cells no longer divide, but strongly elongate (grow) and thus increase the length of the root - this is stretch zone , or growth zone root.

Above the growth zone is a section of the root with root hairs - these are long outgrowths of the cells of the outer cover of the root. With their help, the root absorbs (sucks) water from the soil with dissolved mineral salts. The root hairs work like little pumps. That is why the root zone with root hairs is called suction zone or absorption zone The suction zone takes 2-3 cm on the root. Root hairs live 10-20 days. The root hair cell is surrounded by a thin membrane and contains the cytoplasm, nucleus and vacuole with cell sap. Under the skin there are large rounded cells with thin membranes - the cortex. The inner layer of the cortex (endoderm) is formed by cells with corked membranes. Endoderm cells do not allow water to pass through. Among them there are living thin-walled cells - checkpoints. Through them, water from the bark enters the conductive tissues, which are located in the central part of the stem under the endoderm. Conductive tissues in the root form longitudinal strands, where xylem sections alternate with phloem sections. Xylem elements are located opposite the gate cells. The spaces between xylem and phloem are filled with living parenchyma cells. Conductive tissues form a central or axial cylinder. With age, an educational tissue, the cambium, appears between the xylem and phloem. Thanks to the division of cambial cells, new elements of xylem and phloem, mechanical tissue, are formed, which ensures the growth of the root in thickness. The root thus acquires additional functions- support and storage of nutrients. Above is holding area root, through the cells of which water and mineral salts, absorbed by root hairs, move to the stem. The conduction zone is the longest and strongest part of the root. There is already a well-formed conductive tissue here. Water with dissolved salts rises along the cells of the conductive tissue to the stem - this upward current, and organic substances necessary for the vital activity of root cells move from the stem and leaves to the root - this is downward current.Roots most often take the form: cylindrical (for horseradish); conical or cone-shaped (at a dandelion); filiform (in rye, wheat, onions).

From the soil, water enters the root hairs by osmosis, passing through their membranes. In this case, the cell is filled with water. Part of the water enters the vacuole and dilutes the cell sap. Thus, different density and pressure are created in neighboring cells. A cell with a more concentrated vacuolar sap takes some of the water from a cell with a dilute vacuolar sap. This cell, through osmosis, passes water along the chain to another neighboring cell. In addition, part of the water passes through the intercellular spaces, as through the capillaries between the cells of the cortex. Having reached the endoderm, water rushes through the passage cells into the xylem. Since the surface area of the endoderm throughput cells is much less area surface of the root skin, significant pressure is created at the entrance to the central cylinder, which allows water to penetrate into the xylem vessels. This pressure is called root pressure. Thanks to root pressure, water not only enters the central cylinder, but also rises to a considerable height in the stem.

Root growth:

The root of a plant grows throughout its life. As a result, it constantly increases, deepening into the soil and moving away from the stem. Although the roots are unlimited opportunity growth, they almost never have the opportunity to use it to the fullest. In the soil, the roots of a plant interfere with the roots of other plants, there may be insufficient water and nutrients. However, if the plant is grown artificially in very favorable conditions for it, then it is able to develop roots of a huge mass.

The roots grow from their apical part, which is located at the very bottom of the root. When the top of the root is removed, its growth in length stops. However, the formation of many lateral roots begins.

The root always grows down. No matter which way the seed is turned, the root of the seedling will begin to grow downward. Water Absorption from the Soil by the Roots: Water and minerals are absorbed by the epidermal cells near the root tip. Numerous root hairs, which are outgrowths of epidermal cells, penetrate into cracks between soil particles and greatly increase the absorbing surface of the root.

12. Escape and its functions. The structure and types of shoots. Branching and growth of shoots. The escape- this is an unbranched stem with leaves and buds located on it - the beginnings of new shoots that appear in a certain order. These rudiments of new shoots ensure the growth of the shoot and its branching. Shoots are vegetative and spore-bearing

The functions of vegetative shoots include: the shoot serves to strengthen the leaves on it, ensures the movement of minerals to the leaves and the outflow of organic compounds, serves as a reproductive organ (strawberries, currants, poplar), Serves as a reserve organ (potato tuber) Spore-bearing shoots perform the function of reproduction.

monopodial-growth is due to the apical kidney

Sympodial- shoot growth continues due to the nearest lateral bud

False dichotomous- after the death of the apical bud, shoots grow (lilac, maple)

Dichotomous- from the apical bud, two lateral buds are formed, giving two shoots

tillering– this is a branching in which large side shoots grow from the lowest buds located near the surface of the earth or even underground. As a result of tillering, a bush is formed. Very dense perennial bushes are called turfs.

The structure and types of shoots:

Types:

The main shoot is the shoot that developed from the bud of the seed germ.

Lateral shoot - a shoot that appeared from the lateral axillary bud, due to which the stem branches.

An elongated shoot is a shoot with elongated internodes.

A shortened shoot is a shoot with shortened internodes.

A vegetative shoot is a shoot that bears leaves and buds.

A generative shoot is a shoot that bears reproductive organs - flowers, then fruits and seeds.

Branching and growth of shoots:

branching- this is the formation of lateral shoots from axillary buds. A highly branched system of shoots is obtained when side shoots grow on one shoot, and on them, the next side ones, and so on. In this way, as much air supply medium as possible is captured.

The growth of shoots in length is carried out due to the apical buds, and the formation of lateral shoots occurs due to the lateral (axillary) and adnexal buds

13. Structure, functions and types of kidneys. Diversity of buds, development of shoot from bud. Bud- a rudimentary, not yet unfolded shoot, at the top of which there is a growth cone.

Vegetative (leaf bud)- a bud consisting of a shortened stem with rudimentary leaves and a growth cone.

Generative (flower) bud- a bud, represented by a shortened stem with the rudiments of a flower or inflorescence. A flower bud containing 1 flower is called a bud. Kidney types.

There are several types of buds in plants. They are usually divided according to several criteria.

1. By origin:* axillary or exogenous (arise from secondary tubercles), are formed only on the shoot * adnexal or endogenous (arising from the cambium, pericycle, or parenchyma). The axillary bud occurs only on the shoot and can be recognized by the presence of a leaf or leaf scar at its base. An adnexal bud occurs on any organ of the plant, being a reserve for various injuries.

2. By location on the shoot: * apical(always axillary) * side(may be axillary and adnexal).

3) By duration:* summer, functioning* wintering, i.e. in a state of winter dormancy* sleeping, those. in a state of long-term even many years of dormancy.

In appearance, these kidneys are well distinguished. In summer buds, the color is light green, the growth cone is elongated, because. there is an intensive growth of the apical meristem and the formation of leaves. Outside, the summer bud is covered with green young leaves. With the onset of autumn, growth in the summer bud slows down and then stops. The outer leaflets stop growing and specialize in protective structures - kidney scales. Their epidermis becomes lignified, and sclereids and receptacles with balms and resins are formed in the mesophyll. Renal scales, glued together with resins, hermetically close the access of air into the kidney. In the spring of next year, the wintering bud turns into an active, summer bud, and that bud turns into a new shoot. When the overwintering bud awakens, meristem cell division begins, the internodes lengthen, as a result, the bud scales fall off, leaving leaf scars on the stem, the totality of which forms a bud ring (a trace from the overwintering or dormant bud). From these rings, you can determine the age of the shoot. Part of the axillary kidneys remains dormant. These are living kidneys, they receive food, but do not grow, therefore they are called dormant. If the shoots located above them die off, then the dormant buds can “wake up” and give new shoots. This ability is used in agricultural practice and in floriculture in the formation appearance plants

14. Anatomical structure of the stem of herbaceous dicotyledonous and monocotyledonous plants. The structure of the stem of a monocotyledonous plant. The most important monocotyledonous plants are cereals, the stem of which is called straw. With a slight thickness, the straw has significant strength. It consists of nodes and internodes. The latter are hollow inside and have the greatest length in the upper part, and the smallest in the lower. The most tender parts of the straw are above the knots. In these places there is an educational tissue, so cereals grow with their internodes. This growth of cereals is called intercalary growth. In the stems of monocotyledonous plants, a beam structure is well expressed. Vascular-fibrous bundles of a closed type (without cambium) are distributed over the entire thickness of the stem. From the surface, the stem is covered with a single-layered epidermis, which subsequently lignifies, forming a cuticle layer. Located directly below the epidermis, the primary cortex consists of a thin layer of living parenchymal cells with chlorophyll grains. Deep from the parenchymal cells is the central cylinder, which begins on the outside with the mechanical tissue of sclerenchyma of pericyclic origin. Sclerenchyma gives the stem strength. The main part of the central cylinder consists of large parenchyma cells with intercellular spaces and randomly arranged vascular fibrous bundles. The shape of the bundles on the transverse section of the stem is oval; all areas of wood gravitate closer to the center, and bast areas - to the surface of the stem. There is no cambium in the vascular fibrous bundle, and the stem cannot thicken. Each bundle is surrounded by a mechanical tissue on the outside. The maximum amount of mechanical tissue is concentrated around the bundles near the surface of the stem.

The anatomical structure of the stems of dicotyledonous plants already in early age differs from the structure of monocots (Fig. 1). The vascular bundles here are located in one circle. Between them is the main parenchymal tissue that forms the core rays. The main parenchyma is also located inside the bundles, where it forms the core of the stem, which in some plants (buttercup, angelica, etc.) turns into a cavity, in others (sunflower, hemp, etc.) it is well preserved. The structural features of the vascular-fibrous bundles of dicotyledonous plants are that they are open, that is, they have bundled cambium, consisting of several regular rows of lower dividing cells; inside from them cells arise from which secondary wood is formed, and outwards - cells from which secondary bast (phloem) is formed. Parenchymal cells of the main tissue surrounding the bundle, often filled with spare substances; various vessels that conduct water; cambial cells, from which new bundle elements arise; sieve tubes that conduct organic substances, and mechanical cells (bast fibers) that give strength to the bundle. Dead elements are water-conducting vessels and mechanical tissues, and all the rest are living cells that have a protoplast inside.. From the division of cambial cells in the radial direction (that is, perpendicular to the surface of the stem), the cambial ring lengthens, and from their division in the tangential direction (that is, parallel to the surface of the stem), the stem thickens. 10-20 times more cells are deposited in the direction of the wood than in the direction of the bast, and therefore the wood grows much faster than the bast.
Classes Dicotyledonous and Monocotyledons are divided into families. Plants of each family have common features. In flowering plants, the main features are the structure of the flower and fruit, the type of inflorescence, as well as the features of the external and internal structure of the vegetative organs.

15. Anatomical structure of the stem of woody dicotyledonous plants. Annual shoots of linden are covered with epidermis. By autumn, they become woody and the epidermis is replaced by a cork. During the growing season, a cork cambium is laid under the epidermis, which forms a cork to the outside, and phelloderm cells to the inside. These three integumentary tissues form the integumentary complex of the periderm. within 2-3 years, they peel off and die. The primary cortex is located under the periderm.

Most of the stem is made up of tissues formed by the activity of the cambium. The boundaries of the bark and wood run along the cambium. All tissues lying outward from the cambium are called bark. The bark is primary and secondary. and the core rays are presented in the form of triangles, the vertices of which converge towards the center of the stem to the core.

The core rays penetrate through the wood. These are the primary core rays, water and organic substances move along them in a rational direction. The core rays are represented by parenchymal cells, inside which reserve nutrients (starch) are deposited by autumn, consumed in the spring for the growth of young shoots.

In the phloem, layers of hard bast (bast fibers) and soft (living thin-walled elements) alternate. Bast (slerenchyma) bast fibers are represented by dead prosenchymal cells with thick lignified walls. Soft bast consists of sieve tubes with satellite cells (conductive tissue) and bast parenchyma , in which nutrients (carbohydrates, fats, etc.) accumulate. In spring, these substances are spent on the growth of shoots. Organic substances move through sieve tubes. In spring, when the bark is cut, the juice flows out. The cambium is represented by one dense ring of thin-walled rectangular cells with a large nucleus and cytoplasm. In autumn, cambial cells become thick-walled, and its activity is interrupted.

To the center of the stem, wood is formed inward from the cambium, consisting of vessels (tracheas), tracheids, wood parenchyma and sclerenchyma wood (libriform). Libriform is a collection of narrow, thick-walled and lignified cells of mechanical tissue. elements of wood) wider in spring and summer and narrower in autumn, as well as in dry summer. On the cross cut of a tree, the relative age of the tree can be determined by the number of growth rings. In spring, during the period of sap flow, water with dissolved mineral salts rises through the vessels of the wood.

In the central part of the stem there is a core consisting of parenchymal cells and surrounded by small vessels of primary wood.

16. Sheet, its functions, parts of the sheet. Variety of leaves. The outside of the sheet is covered skinned. It is formed by a layer of transparent cells of the integumentary tissue, tightly adjacent to each other. The peel protects the inner tissues of the leaf. The walls of its cells are transparent, which allows light to easily penetrate into the leaf.

On the lower surface of the leaf, among the transparent cells of the skin, there are very small paired green cells, between which there is a gap. Couple guard cells and stomatal opening between them is called stomata . Moving apart and closing, these two cells either open or close the stomata. Through the stomata, gas exchange occurs and moisture evaporates.

With insufficient water supply, the stomata of the plant are closed. When water enters the plant, they open.

A leaf is a lateral flat organ of a plant that performs the functions of photosynthesis, transpiration and gas exchange. In the cells of the leaf there are chloroplasts with chlorophyll, in which the "production" of organic substances - photosynthesis - is carried out in the light from water and carbon dioxide.

Functions The water for photosynthesis comes from the root. Part of the water is evaporated by the leaves to prevent overheating of the plants by the sun's rays. During evaporation, excess heat is consumed and the plant does not overheat. The evaporation of water from leaves is called transpiration.

Leaves absorb carbon dioxide from the air and release oxygen, which is produced during photosynthesis. This process is called gas exchange.

Leaf parts

External structure sheet. In most plants, the leaf consists of a blade and a petiole. The leaf blade is the expanded lamellar part of the leaf, hence its name. The leaf blade performs the main functions of the leaf. At the bottom, it passes into the petiole - the narrowed stem-like part of the leaf.

With the help of the petiole, the leaf is attached to the stem. Such leaves are called petiolate. The petiole can change its position in space, and with it the leaf blade changes its position, which finds itself in the conditions of the most favorable lighting. Conductive bundles pass in the petiole, which connect the vessels of the stem with the vessels of the leaf blade. Due to the elasticity of the petiole, the leaf blade can more easily withstand the impact of raindrops, hail, and gusts of wind on the leaf. In some plants, at the base of the petiole, there are stipules that look like films, scales, small leaves (willow, wild rose, hawthorn, white acacia, peas, clover, etc.). The main function of stipules is to protect young developing leaves. Stipules may be green, in which case they are lamina-like, but usually much smaller. In peas, meadow ranks and many other plants, stipules persist throughout the life of the leaf and perform the function of photosynthesis. In linden, birch, oak membranous stipules fall off in the stage of a young leaf. In some plants - tree-like caragana, white acacia - they are modified into thorns and perform a protective function, protecting plants from damage by animals.

There are plants whose leaves do not have petioles. Such leaves are called sessile. They are attached to the stem by the base of the leaf blade. Sessile leaves of aloe, carnation, flax, tradescantia. In some plants (rye, wheat, etc.), the base of the leaf grows and covers the stem. This overgrown base is called the vagina.

The root is the underground axial element of plants, which is their most important part, their main vegetative organ. Thanks to the root, the plant is fixed in the soil and is held there throughout the whole life cycle, and is also provided with water, minerals and nutrients contained in it. There are different kinds and types of roots. Each of them has its own distinctive characteristics. In this article we will consider the existing types of roots, types of root systems. We will also get acquainted with their characteristic features.

What are the types of roots?

The standard root is characterized by a filiform or narrow-cylindrical shape. In many plants, in addition to the main (main) root, other types of roots are also developed - lateral and adventitious. Let's take a closer look at what they are.

main root

This plant organ develops from the germinal root of the seed. The main root is always one (other types of plant roots are usually present during plural). It remains in the plant throughout the life cycle.

The root is characterized by positive geotropism, that is, due to gravity, it deepens into the substrate vertically down.

adventitious roots

Adventitious called the types of plant roots that are formed on their other organs. These organs can be stems, leaves, shoots, etc. For example, cereals have so-called primary adventitious roots, which are laid down in the stalk of the seed germ. They develop in the process of seed germination almost simultaneously with the main root.

There are also leaf adventitious types of roots (formed as a result of rooting of leaves), stem or nodal (formed from rhizomes, aboveground or underground stem nodes), etc. lower nodes powerful roots are formed, which are called aerial (or supporting).

The appearance of adventitious roots determines the ability of the plant to vegetative reproduction.

Lateral roots

Lateral are called roots that arise as a lateral branch. They can form both on the main and adventitious roots. In addition, they can branch off from the lateral ones, as a result of which lateral roots of higher orders (first, second and third) are formed.

Large lateral organs are characterized by transverse geotropism, that is, their growth occurs in an almost horizontal position or at an angle to the soil surface.

What is the root system?

The root system is called all types and types of roots that one plant has (that is, their totality). Depending on the ratio of growth of the main, lateral and adventitious roots, its type and character is determined.

Types of root systems

If the main root is very well developed and noticeable among the roots of another species, this means that the plant has a rod system. It is found mainly in dicotyledonous plants.

The root system of this type is characterized by deep germination into the soil. So, for example, the roots of some grasses can penetrate to a depth of 10-12 meters (thistle, alfalfa). The depth of penetration of tree roots in some cases can reach 20 m.

If adventitious roots are more pronounced, developing in large numbers, and the main one is characterized by slow growth, then a root system is formed, which is called fibrous.

As a rule, some of the herbaceous plants are also characterized by such a system. Despite the fact that the roots of the fibrous system do not penetrate as deeply as those of the rod system, they better braid the soil particles adjacent to them. Many loose-shrub and rhizomatous grasses, which form abundant fibrous thin roots, are widely used for fixing ravines, soils on slopes, etc. The best turf grasses include awnless bonfire, fescue, and others.

modified roots

In addition to the typical ones described above, there are other types of roots and root systems. They are called modified.

storage roots

The stocks include root crops and root tubers.

A root crop is a thickening of the main root due to the deposition of nutrients in it. Also, the lower part of the stem is involved in the formation of the root crop. Consists mostly of storage base tissue. Examples of root crops are parsley, radishes, carrots, beets, etc.

If the thickened storage roots are lateral and adventitious roots, then they are called root tubers (cones). They are developed in potatoes, sweet potatoes, dahlias, etc.

aerial roots

These are lateral roots growing in the aerial part. Found in a number of tropical plants. Water and oxygen are absorbed from the air. Available in tropical plants growing in conditions of lack of minerals.

respiratory roots

This is a kind of lateral roots that grow upward, rising above the surface of the substrate, water. Such types of roots are formed in plants growing on too moist soils, in swamp conditions. With the help of such roots, vegetation receives the missing oxygen from the air.

Supporting (board-shaped) roots

These types of tree roots are characteristic of large species (beech, elm, poplar, tropical, etc.). They are triangular vertical outgrowths formed by lateral roots and passing near or above the soil surface. They are also called board-shaped, because they resemble boards that are leaning against a tree.

Sucker roots (haustoria)

This is a type of additional adventitious roots developing on the stem. climbing plants. With their help, plants have the ability to attach to a certain support and climb (weave) up. Such roots are available, for example, in tenacious ficus, ivy, etc.

Retractable (contractile) roots

Characteristic of plants, the root of which is sharply reduced in the longitudinal direction at the base. An example would be plants that have bulbs. Retractable roots provide bulbs and root crops with some recess in the soil. In addition, their presence determines the tight fit of rosettes (for example, in a dandelion) to the ground, as well as the underground position of the vertical rhizome and root collar.

Mycorrhiza (fungus root)

Mycorrhiza is a symbiosis (mutually beneficial cohabitation) of the roots of higher plants with fungal hyphae, which braid them, acting as root hairs. Fungi provide plants with water and nutrients dissolved in it. Plants, in turn, provide fungi with organic substances necessary for their vital activity.

Mycorrhiza is inherent in the roots of many higher plants, especially woody ones.

bacterial nodules

These are modified lateral roots that are adapted for symbiotic cohabitation with nitrogen-fixing bacteria. The formation of nodules occurs due to the penetration of young roots into the interior. Such mutually beneficial cohabitation allows plants to receive nitrogen, which bacteria transfer from the air into a form accessible to them. Bacteria, on the other hand, are given a special habitat where they can function without competing with other types of bacteria. In addition, they use substances present in the roots of vegetation.

Bacterial nodules are typical for plants of the legume family, which are widely used as ameliorants in crop rotations in order to enrich soils with nitrogen. Taproot legumes, such as blue and yellow alfalfa, red and sainfoin, horned locust, etc., are considered the best nitrogen-fixing plants.

In addition to the above metamorphoses, there are other types of roots, such as prop roots (help strengthen the stem), stilted roots (help plants not to sink in liquid mud) and root suckers (have adventitious buds and provide vegetative propagation).

Root functions. The root is the main organ of a higher plant. The functions of the roots are as follows:

Due to its high strength, the plant is fixed in the soil.

When water, ions of mineral salts and photosynthesis products interact, products of primary and secondary metabolism are synthesized.
Under the influence of root pressure and transpiration, ions of aqueous solutions of mineral substances and organic substances move along the vessels of the root xylem along the ascending current into the stem and leaves.
Nutrients (starch, inulin, etc.) are stored in the roots.
Biosynthesis of secondary metabolites (alkaloids, hormones and other biologically active substances) is carried out in the roots.
The growth substances synthesized in the meristematic zones of the roots (gibberellins, etc.) are necessary for the growth and development of the aerial parts of the plant.
Due to the roots, symbiosis is carried out with soil microorganisms - bacteria and fungi.
With the help of roots, vegetative propagation of many plants occurs.

10. Some roots perform the function of a respiratory organ (monstera, philodendron, etc.).

11. The roots of a number of plants perform the function of "stilted" roots (ficus banyan, pandanus, etc.).

12. The root is capable of metamorphoses (thickenings of the main root form “root crops” in carrots, parsley, etc.; thickenings of lateral or adventitious roots form root tubers in dahlias, peanuts, chistyak, etc., shortening of roots in bulbous plants).

Root - an axial organ, usually cylindrical in shape, with radial symmetry, possessing geotropism. It grows as long as the apical meristem is preserved, covered with a root cap. On the root, unlike the shoot, leaves never form, but, like the shoot, the root branches, forming root system.

The root system is the totality of the roots of a single plant. The nature of the root system depends on the ratio of growth of the main, lateral and adventitious roots.

^ Types of roots and root systems. In the embryo of the seed, all organs of the plant are in their infancy. The main, or first, root develops from embryonic root. The main root is located in the center of the entire root system, the stem serves as a continuation of the root, and together they form a first-order axis. The area on the border between the main root and the stem is called root collar. This transition from stem to root is noticeable by the different thicknesses of the stem and root: the stem is thicker than the root. The section of the stem from the root neck to the first germinal leaves - cotyledons is called hypocotyl knee or hypocotyl. Lateral roots of the next orders depart from the main root to the sides. This root system is called pivotal, in many dicotyledonous plants it is capable of branching. A branched root system is a type of tap root system. Lateral branching of the root is characterized by the fact that new roots are laid at some distance from the top and are formed endogenously - in the internal tissues of the maternal root of the previous order due to the activity of the pericycle. The more lateral roots depart from the main root, the larger the area of \u200b\u200bplant nutrition, therefore, there are special agricultural practices that enhance the ability of the main root to form lateral roots, for example, pinching or dive main root by l/3 of its length. After diving for some time, the main root stops growing in length, while the lateral roots grow intensively.

In dicotyledonous plants, the main root, as a rule, persists throughout life, in monocots, the germinal root quickly dies off, the main root does not develop, and shoots form from the base adnexal roots, which also have branches of the first, second, etc. orders. This root system is called fibrous. Adventitious roots, like lateral roots, are laid endogenously. They can form on stems and leaves. The ability of plants to develop adventitious roots is widely used in crop production during vegetative propagation of plants (propagation by stem and leaf cuttings). Willow, poplar, maple, blackcurrant, etc. are propagated by elevated stem cuttings; leafy cuttings - uzambar violet, or saintpaulia, some types of begonias. Underground cuttings of modified shoots (rhizomes) propagate many medicinal plants, for example, May lily of the valley, officinalis, etc. Some plants form many adventitious roots when hilling the lower part of the stem (potato, cabbage, corn, etc.), thereby creating additional nutrition.

In higher spore plants (mosses, horsetails, ferns), the main root does not appear at all, they form only adventitious roots extending from the rhizome. In many dicotyledonous herbaceous rhizomatous plants, the main root often dies off and the system of adventitious roots extending from the rhizomes (snotweed, nettle, creeping ranunculus, etc.) predominates.

In terms of depth of penetration into the soil, the first place belongs to the taproot system: the record depth of penetration of the roots, according to some reports, reaches 120 m! However, the fibrous root system, having a mostly superficial location of the roots, contributes to the creation of a sod cover and prevents soil erosion.

The total length of the roots in the root system is different, some roots reach several tens and even hundreds of kilometers. For example, in wheat, the length of all root hairs reaches 20 km, and in winter rye, the total length of the roots of the first, second, and third orders is over 180 km, and with the addition of roots of the fourth order, 623 km. Although the root grows throughout its life, its growth is limited by the influence of the roots of other plants.

The degree of development of root systems on different soils in different natural zones is not the same. So, in sandy deserts, where they lie deep ground water, the roots of some plants go to a depth of 40 m or more (grass Selin, prosopis earring from the legume family, etc.). Ephemeral plants of semi-deserts have superficial root system, which is adapted to the rapid absorption of early spring moisture, which is quite sufficient for the rapid passage of all phases of plant vegetation. On clay, poorly aerated podzols of the taiga forest zone, the root system of plants is 90% concentrated in the surface layer of the soil (10-15 cm), the plants have "nourishing roots" (European spruce). For example, saxaul has roots in different time years use moisture from different horizons.

Highly important factor in the distribution of the root system - moisture. The direction of the roots goes in the direction of greater humidity, however, in water and in waterlogged soil, the roots branch much weaker.

The degree of development of root systems, the depth of root penetration, and other plastic characteristics of the root depend on external conditions and, at the same time, are hereditarily assigned to each plant species.

^ Young root zones. In a young root, there are: 1) a division zone covered with a root cap; 2) cell elongation zone, or growth zone; 3) the zone of absorption, or the zone of root hairs; 4) conductive zone.

^ Division zone represents the tip of the root, covered on the outside root cap, protecting the apical, or apical, meristem. To the touch, the young tip of the root is slippery due to the mucus secreted by the cells. As the root grows in length, the mucus reduces the friction of the root tip against the soil. According to Academician V.L. Komarov, the root cap "digs the ground", it protects the dividing cells of the meristem from mechanical damage, and also controls positive geotropism the root itself, i.e., promotes the growth of the root and its penetration into the depths of the soil. The root cap consists of living parenchymal cells containing starch grains. Under the cover there is a division zone, or root cone, represented by the primary educational tissue (meristem). As a result of active division of the apical meristem of the root, all other zones and tissues of the root are formed. The division zone of a young root is only 1 mm long. Outwardly, it differs from other zones in yellow.

^ Stretch zone, or growth zone, a few millimeters long, it is externally transparent, consists of practically non-dividing, but longitudinally stretching cells. Cells increase in size, vacuoles appear in them. Cells are characterized by high turgor. In the elongation zone, differentiation of the primary conductive tissues occurs and permanent root tissues begin to form.

Above the stretch zone is suction zone. Its length is 5 - 20 mm. The absorption zone is represented by root hairs - outgrowths of epidermal cells. With the help of root hairs, water and salt solutions are absorbed from the soil. The more numerous the root hairs, the greater the absorptive surface of the root. About 400 root hairs can be located per 1 mm at the root surface. Root hairs are short-lived, live 10 - 20 days, after which they die. The length of the root hairs different plants from 0.5 - 1.0 cm. Young root hairs form above the extension zone, and die off above the absorption zone, so the root hair zone constantly moves as the root grows and the plant is able to absorb water and nutrients dissolved in it from different soil horizons .

Above the suction zone begins conduction zone, or zone of lateral roots. The water absorbed by the root and salt solutions are transported through the vessels of the wood upwards to the aerial parts of the plant.

There are no sharp boundaries between the root zones, but a gradual transition is observed.

6. Metamorphoses of the root. their biological significance. Mycorrhiza. Most plants in the same root system have distinctly different growth and sucking endings. Growth endings are usually more powerful, quickly elongate and move deep into the soil. Their elongation zone is well defined, and the apical meristems work vigorously. Sucking endings, which appear in large numbers on growth roots, elongate slowly, and their apical meristems almost stop working. The sucking endings, as it were, stop in the soil and intensively “suck” it.

On the roots of legumes, special formations appear - nodules in which bacteria from the genus Rhizobium settle. These microorganisms are able to assimilate atmospheric molecular nitrogen, converting it into a bound state. Part of the substances synthesized in the nodules are absorbed by plants, bacteria, in turn, use the substances found in the roots. This symbiosis is of great importance for agriculture. Legumes are rich in protein due to the additional source of nitrogen. They provide valuable food and fodder products and enrich the soil with nitrogenous substances.

Very widespread hoarding roots. They are usually thickened and strongly parenchymatized. Strongly thickened adventitious roots are called root cones, or root tubers(dahlia, some orchids). Many, more often biennial, plants with a tap root system develop a formation called root crop. Both the main root and the lower part of the stem take part in the formation of the root crop. In carrots, almost the entire root crop is composed of a root; in turnips, the root forms only the lowest part of the root crop ( rice. 4.12).

Root crops of cultivated plants arose as a result of long-term selection. In root crops, the storage parenchyma is highly developed and mechanical tissues have disappeared. In carrots, parsley, and other umbellifers, the parenchyma is strongly developed in the phloem; in turnips, radishes and other cruciferous plants - in xylem. In beets, reserve substances are deposited in the parenchyma formed by the activity of several additional layers of cambium ( rice. 4.12).

Rice. 4.15. ^ Support roots: 1 - stilted corn roots; 2 - columnar banyan roots; 3 - stilted roots of rhizophora ( etc- tidal zone; from- ebb zone; silt- the surface of the muddy bottom).

Escape concept. Morphological division of the shoot. Knots and internodes. Apical shoot growth. The structure and activity of the cone of growth. A shoot is a stem with leaves and buds located on it.

The parts of the stem where leaves develop are called nodes.
Stem sections between two nearest nodes called internodes.
The angle between the leaf and the internode above called the leaf axil.
An axillary bud forms in the leaf axil. The escape consists of repeating sections - metamers.
One metamere includes an internode, a node, a leaf, and an axillary bud. A shoot is a complex consisting of a stem and leaves. The primary shoot is laid in the embryo, where it is represented by a kidney. The kidney consists of an embryonic stalk - epicotyl, apical meristem and one or more leaf primordia (leaf rudiments). As the seed germinates, the stem lengthens. New leaf primordia develop from the apical meristem. leaf primordia leaves develop and leaf axils kidney primordia are formed. This algorithm of development during the formation of the shoot system of a plant can be repeated many times.

In the formed shoot, nodes are distinguished - the part of the shoot where the leaf is connected to the stem; internodes - part of the shoot between nodes, usually part of the stem; leaf sinuses - the angle between the leaf and the ascending part of the stem.

Part of the escape are the kidneys. This is, first of all, the apical bud, representing the growth cone of the shoot. AT leaf axils in seed plants, axillary, or lateral buds are formed. If they develop one above the other (honeysuckle, walnut, Robinia, etc.), they are called serial. If the buds develop in the axils of the leaves next to each other (plums, cereals, etc.), then they are called collateral. Kidneys can form endogenously in the region of internodes. These kidneys are called accessory.

In trees and shrubs of a cold and temperate climate, wintering or resting buds are formed, which are often called eyes. New shoots develop from these buds the next year. The outer leaves of these buds usually turn into bud scales that protect the inner parts of the bud from damage.

Wintering or resting buds are also formed in perennial grasses, on those organs that do not die off for the winter, i.e. on rhizomes, at the base of stems, etc. These kidneys are called renewal kidneys. Of these, above-ground shoots develop in the spring.

All of the above kidneys are called vegetative. Such kidneys consist of an apex, rudimentary nodes, rudimentary internodes, leaf primordia, above which bud primordia can develop, and rudimentary leaves.

From a kidney that does not have renal primordia, a simple or unbranched the escape. A branched branch develops from a kidney with renal primordia. the escape.

In addition, seed plants also have generative buds. These are flower buds and buds that give rise to gymnosperm cones. They differ from vegetative ones in appearance. In addition to the apex, rudimentary internodes, and rudimentary nodes, such buds have primordia that give rise to parts of a flower or parts of cones. At the buds that give rise to inflorescences, flower primordia are formed.

Finally, there are the so-called mixed buds, from which leafy shoots with flowers are formed.

The morphological characteristic of the shoot implies a description of the structure of nodes, internodes, and buds. The type of leaf arrangement must be indicated. In most plants, it is alternate - there is one leaf per node, but it can be opposite or whorled. Defined type leaf arrangement forms a leaf mosaic, which makes the best use of space to ensure uniform leaf illumination.

The division of leaves into three categories is also associated with the process of growth and development of the shoot: lower leaves, middle leaves, apical, or upper leaves. In the morphological description of leaves, median leaves are usually described, but a complete morphological description requires separate description all categories of leaves, because even middle leaves on one shoot they have differences. This phenomenon is called heterophylly or diversity.

Apical shoot growth - the growth of the shoot in length due to the modification of the cone of growth, the initiation and growth of rudimentary leaves at its base. In the process of modification, the growth cone increases in length, becomes more complex and changes its shape.

Bud. This is a rudimentary escape. It consists of a meristematic axis ending in a cone of growth (rudimentary stem) and leaf primordia (rudimentary leaves), that is, from a series of rudimentary metameres. The differentiated leaves located below cover the cone of growth and primordia. This is how the vegetative bud is arranged. In a vegetative-reproductive bud, the cone of growth is turned into a rudimentary flower or rudimentary inflorescence. Reproductive (flower) buds consist only of a rudimentary flower or inflorescence and do not have rudiments of photosynthetic leaves.

13. Metamorphosed shoots.

Their occurrence is often associated with the performance of the functions of a receptacle for spare products, the transfer of unfavorable conditions of the year, vegetative propagation.

Rhizome- This is a perennial underground shoot with a horizontal, ascending or vertical direction of growth, which performs the functions of accumulating reserve products, renewal, and vegetative reproduction. The rhizome has reduced leaves in the form of scales, buds, adventitious roots. Spare products accumulate in the stem part. Growth and branching occurs in the same way as in a regular shoot. The rhizome is distinguished from the root by the presence of leaves and the absence of a root cap at the top. The rhizome can be long and thin (wheatgrass) or short and thick. Annually from the apical and axillary buds aerial annual shoots. The old parts of the rhizome gradually die off. Plants with horizontal long rhizomes that form many above-ground shoots quickly occupy a large area, and if these are weeds (wheatgrass), then the fight against them is rather difficult. Such plants are used to fix the sands (grass, aristida). In grassland, cereals with long horizontal rhizomes are called rhizomatous (bent grass, bluegrass), and with short ones - bushy (timothy grass, belous). Rhizomes are found mainly in perennial herbaceous plants, but sometimes in shrubs (euonymus) and shrubs (lingonberries, blueberries).

Tuber- this is a thickened part of the shoot, a container of spare products. Tubers are above ground and underground.

elevated tuber is a thickening of the main (kohlrabi) or side (tropical orchids) shoot and bears normal leaves.

underground tuber- thickening of the hypocotyl (cyclamen) or short-lived underground shoot - stolon (potato). The leaves on the underground tuber are reduced, in their axils there are buds called eyes.

Elevated stolon- this is a short-lived creeping shoot that serves to spread (capture the territory) and vegetative propagation. It has long internodes and green leaves. Adventitious roots are formed on the nodes, and a shortened shoot (rosette) is formed from the apical bud, which, after the death of the stolon, continues to exist independently. The aboveground stolon sympodial grows. Aboveground stolons that have lost the function of photosynthesis and perform mainly the function of vegetative reproduction are sometimes called mustaches (strawberries).

Bulb- this is a shortened stem (bottom), bearing numerous, closely spaced leaves and adventitious roots. At the top of the donut is a kidney. In many plants (onion, tulip, hyacinth, etc.), an above-ground shoot is formed from this bud, and a new bulb is formed from the lateral axillary bud. The outer scales in most cases are dry, membranous and perform a protective function, the inner ones are fleshy, filled with spare products. The shape of the bulbs are spherical, ovoid, flattened, etc.

Corm it looks like an onion, but all its leaf scales are dry, and spare products are deposited in the stem part (saffron, gladiolus).

spines have a different origin - from the shoot (apple, pear, blackthorn, hawthorn, honey locust, citrus), leaf (barberry) or its parts: rachis (astragalus), stipules (white acacia), part of the plate (composite). Spines are characteristic of plants in hot, dry habitats.

tendrils are formed from a shoot (grapes), a leaf or its parts: rachis and several leaves (peas), plates (rank.), Stipules (sarsaparilla). Used to attach to a support.

Phyllocladia- These are flat leaf-shaped shoots located in the axils of reduced leaves. Flowers form on them. They are found in plants of predominantly arid habitats (butcher's needle, phyllanthus). trapping devices- modified leaves characteristic of insectivorous plants (dew, flycatcher). They have the form of jugs, urns, bubbles, or slamming and wrapping plates. Small insects, falling into them, die, dissolve with the help of enzymes and are consumed by plants as an additional source of minerals.

Phylogenetically, the root arose later than the stem and leaf - in connection with the transition of plants to life on land and probably originated from root-like underground branches. The root has neither leaves nor buds arranged in a certain order. It is characterized by apical growth in length, its lateral branches arise from internal tissues, the growth point is covered with a root cap. The root system is formed throughout the life of the plant organism. Sometimes the root can serve as a place of deposition in the supply of nutrients. In this case, it is modified.

Root types

The main root is formed from the germinal root during seed germination. It has lateral roots.

Adventitious roots develop on stems and leaves.

Lateral roots are branches of any roots.

Each root (main, lateral, adventitious) has the ability to branch, which significantly increases the surface of the root system, and this contributes to a better strengthening of the plant in the soil and improves its nutrition.

Types of root systems

There are two main types of root systems: taproot, which has a well-developed main root, and fibrous. The fibrous root system consists of a large number of adventitious roots, the same in size. The entire mass of roots consists of lateral or adventitious roots and looks like a lobe.

A highly branched root system forms a huge absorbing surface. For example,

the total length of winter rye roots reaches 600 km;
length of root hairs - 10,000 km;
the total surface of the roots is 200 m 2.

This is many times greater than the area of the above-ground mass.

If the plant has a well-defined main root and adventitious roots develop, then a mixed-type root system (cabbage, tomato) is formed.

External structure of the root. The internal structure of the root

Root zones

root cap

The root grows in length with its tip, where the young cells of the educational tissue are located. The growing part is covered with a root cap that protects the tip of the root from damage and facilitates the movement of the root in the soil during growth. The latter function is carried out due to the property of the outer walls of the root cap to be covered with mucus, which reduces friction between the root and soil particles. They can even push apart soil particles. The cells of the root cap are living, often containing grains of starch. The cells of the cap are constantly updated due to division. Participates in positive geotropical reactions (direction of root growth towards the center of the Earth).

The cells of the division zone are actively dividing, the length of this zone varies in different species and in different roots of the same plant.

Behind the division zone there is an extension zone (growth zone). The length of this zone does not exceed a few millimeters.

As linear growth is completed, the third stage of root formation begins - its differentiation, a zone of differentiation and specialization of cells (or a zone of root hairs and absorption) is formed. In this zone, the outer layer of the epiblema (rhizoderm) with root hairs, the layer of the primary cortex and the central cylinder are already distinguished.

The structure of the root hair

Root hairs are highly elongated outgrowths of the outer cells covering the root. The number of root hairs is very high (from 200 to 300 hairs per 1 mm2). Their length reaches 10 mm. Hairs are formed very quickly (in young seedlings of an apple tree in 30-40 hours). Root hairs are short-lived. They die off in 10-20 days, and new ones grow on the young part of the root. This ensures the development of new soil horizons by the root. The root continuously grows, forming more and more new areas of root hairs. Hairs can not only absorb ready-made solutions of substances, but also contribute to the dissolution of certain soil substances, and then absorb them. The area of the root where the root hairs have died off is able to absorb water for some time, but then becomes covered with cork and loses this ability.

The sheath of the hair is very thin, which facilitates the absorption of nutrients. Almost the entire hair cell is occupied by a vacuole surrounded by a thin layer of cytoplasm. The nucleus is at the top of the cell. A mucous sheath is formed around the cell, which promotes gluing of root hairs with soil particles, which improves their contact and increases the hydrophilicity of the system. Absorption is facilitated by the secretion of acids (carbonic, malic, citric) by root hairs, which dissolve mineral salts.

Root hairs also play a mechanical role - they serve as a support for the top of the root, which passes between the soil particles.

Under a microscope on a cross section of the root in the absorption zone, its structure is visible at the cellular and tissue levels. On the surface of the root is the rhizoderm, below it is the bark. The outer layer of the cortex is the exoderm, inward from it is the main parenchyma. Its thin-walled living cells perform a storage function, conduct nutrient solutions in the radial direction - from the absorbing tissue to the vessels of the wood. They also synthesize a number of vital organic substances for the plant. The inner layer of the cortex is the endoderm. Nutrient solutions coming from the cortex to the central cylinder through the cells of the endoderm pass only through the protoplast of the cells.

The bark surrounds the central cylinder of the root. It borders on a layer of cells that retain the ability to divide for a long time. This is the pericycle. Pericycle cells give rise to lateral roots, adnexal buds, and secondary educational tissues. Inward from the pericycle, in the center of the root, there are conductive tissues: bast and wood. Together they form a radial conducting beam.

The conducting system of the root conducts water and minerals from the root to the stem (upward current) and organic matter from the stem to the root (downward current). It consists of vascular fibrous bundles. The main components of the bundle are the sections of the phloem (through which substances move to the root) and xylem (through which substances move from the root). The main conducting elements of the phloem are sieve tubes, xylems are tracheas (vessels) and tracheids.

Root life processes

Water transport at the root

Absorption of water by root hairs from the soil nutrient solution and its conduction in the radial direction along the cells of the primary cortex through the passage cells in the endodermis to the xylem of the radial vascular bundle. The intensity of water absorption by the root hairs is called the suction force (S), it is equal to the difference between the osmotic (P) and turgor (T) pressure: S=P-T.

When the osmotic pressure is equal to the turgor pressure (P=T), then S=0, water stops flowing into the root hair cell. If the concentration of substances in the soil nutrient solution is higher than inside the cell, then water will leave the cells and plasmolysis will occur - the plants will wither. This phenomenon is observed in conditions of dry soil, as well as with excessive application of mineral fertilizers. Inside the root cells, the sucking power of the root increases from the rhizoderm towards the central cylinder, so water moves along the concentration gradient (i.e., from a place with a higher concentration to a place with a lower concentration) and creates a root pressure that raises a column of water along the xylem vessels , forming an upward current. It can be found on spring leafless trunks when "sap" is harvested, or on cut stumps. The outflow of water from wood, fresh stumps, leaves, is called the "weeping" of plants. When the leaves bloom, they also create a sucking force and attract water to themselves - a continuous column of water is formed in each vessel - capillary tension. Root pressure is the lower motor of the water current, and the sucking power of the leaves is the upper one. You can confirm this with the help of simple experiments.

Absorption of water by roots

Target: find out the main function of the root.

What we do: a plant grown on wet sawdust, shake off its root system and lower its roots into a glass of water. Pour over water to protect it from evaporation thin layer vegetable oil and mark the level.

What we observe: after a day or two, the water in the tank dropped below the mark.

Result: therefore, the roots sucked in the water and brought it up to the leaves.

One more experiment can be done, proving the absorption of nutrients by the root.

What we do: we cut off the stem of the plant, leaving a stump 2-3 cm high. We put a rubber tube 3 cm long on the stump, and put a curved glass tube 20-25 cm high on the upper end.

What we observe: the water in the glass tube rises and flows out.

Result: this proves that the root absorbs water from the soil into the stem.

Does the temperature of the water affect the rate of absorption of water by the root?

Target: find out how temperature affects root operation.

What we do: one glass should be with warm water (+17-18ºС), and the other with cold water (+1-2ºС).

What we observe: in the first case, water is released abundantly, in the second - little, or completely stops.

Result: this is proof that temperature has a strong effect on root performance.

Warm water is actively absorbed by the roots. Root pressure rises.

Cold water is poorly absorbed by the roots. In this case, the root pressure drops.

mineral nutrition

The physiological role of minerals is very great. They are the basis for the synthesis of organic compounds, as well as factors that change the physical state of colloids, i.e. directly affect the metabolism and structure of the protoplast; act as catalysts for biochemical reactions; affect the turgor of the cell and the permeability of the protoplasm; are the centers of electrical and radioactive phenomena in plant organisms.

It has been established that the normal development of plants is possible only in the presence of three non-metals in the nutrient solution - nitrogen, phosphorus and sulfur and - and four metals - potassium, magnesium, calcium and iron. Each of these elements has individual value and cannot be replaced by another. These are macronutrients, their concentration in the plant is 10 -2 -10%. For the normal development of plants, microelements are needed, the concentration of which in the cell is 10 -5 -10 -3%. These are boron, cobalt, copper, zinc, manganese, molybdenum, etc. All these elements are found in the soil, but sometimes in insufficient quantities. Therefore, mineral and organic fertilizers are applied to the soil.

The plant grows and develops normally if the environment surrounding the roots contains all the necessary nutrients. Soil is such an environment for most plants.

Root breath

For normal growth and development of a plant, it is necessary that the root receive Fresh air. Let's check if it is?

Target: do roots need air?

What we do: Let's take two identical vessels with water. We place developing seedlings in each vessel. We saturate the water in one of the vessels every day with air using a spray bottle. On the surface of the water in the second vessel, pour a thin layer of vegetable oil, as it delays the flow of air into the water.

What we observe: after a while, the plant in the second vessel will stop growing, wither, and eventually die.

Result: the death of the plant occurs due to the lack of air necessary for the respiration of the root.

Root modifications

In some plants, reserve nutrients are deposited in the roots. They accumulate carbohydrates, mineral salts, vitamins and other substances. Such roots grow strongly in thickness and acquire an unusual appearance. Both the root and the stem are involved in the formation of root crops.

Roots

If reserve substances accumulate in the main root and at the base of the stem of the main shoot, root crops (carrots) are formed. Root-forming plants are mostly biennials. In the first year of life, they do not bloom and accumulate a lot of nutrients in root crops. On the second, they quickly bloom, using the accumulated nutrients and form fruits and seeds.

root tubers

In dahlia, reserve substances accumulate in adventitious roots, forming root tubers.

bacterial nodules

The lateral roots of clover, lupine, alfalfa are peculiarly changed. Bacteria settle in young lateral roots, which contributes to the absorption of gaseous nitrogen from the soil air. Such roots take the form of nodules. Thanks to these bacteria, these plants are able to live on nitrogen-poor soils and make them more fertile.

stilted

A ramp growing in the intertidal zone develops stilted roots. High above the water, they hold large leafy shoots on unsteady muddy ground.

Air

Tropical plants that live on tree branches develop aerial roots. They are often found in orchids, bromeliads, and some ferns. Aerial roots hang freely in the air, not reaching the ground and absorbing moisture from rain or dew that falls on them.

Retractors

In bulbous and bulbous plants, for example, crocuses, among the numerous filamentous roots, there are several thicker, so-called retracting roots. Reducing, such roots draw the corm deeper into the soil.

Pillar-shaped

Ficus develop columnar above-ground roots, or support roots.

Soil as a habitat for roots

The soil for plants is the environment from which it receives water and nutrients. The amount of minerals in the soil depends on the specific characteristics of the parent soil. rock, the activity of organisms, from the vital activity of the plants themselves, from the type of soil.

Soil particles compete with roots for moisture, holding it on their surface. This is the so-called bound water, which is divided into hygroscopic and film. It is held by the forces of molecular attraction. The moisture available to the plant is represented by capillary water, which is concentrated in the small pores of the soil.

Antagonistic relations develop between the moisture and the air phase of the soil. The more large pores in the soil, the better. gas mode these soils, the less moisture the soil retains. The most favorable water-air regime is maintained in structural soils, where water and air are located simultaneously and do not interfere with each other - water fills the capillaries inside the structural aggregates, and air fills the large pores between them.

The nature of the interaction between the plant and the soil is largely related to the absorptive capacity of the soil - the ability to retain or bind chemical compounds.

Soil microflora decomposes organic matter into simpler compounds, participates in the formation of soil structure. The nature of these processes depends on the type of soil, the chemical composition of plant residues, the physiological properties of microorganisms, and other factors. Soil animals take part in the formation of the soil structure: annelids, insect larvae, etc.

As a result of a combination of biological and chemical processes in the soil, a complex complex of organic substances is formed, which is combined by the term "humus".

Water culture method

What salts a plant needs, and what effect they have on its growth and development, was established by experiment with aquatic cultures. The aquatic culture method is the cultivation of plants not in soil, but in an aqueous solution of mineral salts. Depending on the goal in the experiment, you can exclude a separate salt from the solution, reduce or increase its content. It was found that fertilizers containing nitrogen promote the growth of plants, those containing phosphorus - the earliest ripening of fruits, and those containing potassium - the fastest outflow of organic matter from leaves to roots. In this regard, fertilizers containing nitrogen are recommended to be applied before sowing or in the first half of summer, containing phosphorus and potassium - in the second half of summer.

Using the method of water cultures, it was possible to establish not only the need of the plant for macroelements, but also to find out the role of various microelements.

Currently, there are cases when plants are grown using hydroponics and aeroponics methods.

Hydroponics is the cultivation of plants in pots filled with gravel. The nutrient solution containing the necessary elements is fed into the vessels from below.

Aeroponics is the air culture of plants. With this method, the root system is in the air and automatically (several times within an hour) is sprayed with a weak solution of nutrient salts.

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