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 with radial symmetry and growing in length indefinitely due to the activity of the apical meristem. It differs from the shoot morphologically 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 take the shoots up;

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

3) reserve substances can be deposited in the roots;

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

The set of roots of one individual forms a single morphological and physiological root system.

Root systems include roots of various morphological nature - mainroot, lateraland clauses roots.

Main root develops from the embryonic 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 apex. Lateral roots are laid endogenously, i.e. in the internal tissues of the maternal root. If branching took place in the apex itself, it would make it difficult for the root to advance in the soil. Adventitious rootscan occur on stems, leaves, and roots. In the latter case, they differ from lateral roots in that they do not exhibit a strict order of origin near the apex of the maternal root and can arise in old root areas.

By origin, the following types of root systems are distinguished ( fig. 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 systemdevelops on stems, leaves; found in most monocotyledonous plants and many dicotyledonous plants propagating vegetatively;

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

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

Distinguish in form pivotal and fibrous root systems.

IN pivotalroot system, the main root is highly developed and clearly visible among the rest of the roots. IN fibrous root system, the main root is invisible or not, and the root system is composed of numerous adventitious roots ( fig. 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 extend beyond the radius of the crowns. The root system of maize extends to a depth of about 1.5 m and about 1 m in all directions from the plant. A record depth of root penetration into the soil was noted in the desert mesquite shrub - more than 53 m.

One rye bush grown in a greenhouse had a total root length of 623 km. The total growth of all roots in one day was approximately 5 km. The total area of \u200b\u200ball roots in this plant was 237 m 2 and was 130 times larger than the surface of the aboveground organs.

Young root zones -these are parts of a young root different in length, performing different functions and characterized by certain morphological and anatomical features ( fig. 4.2).

The root tip is always covered outside root capprotecting the apical meristem. The cap consists of living cells and is constantly renewed: as old cells slough off from its surface, the apical meristem forms new young cells to replace them from the inside. The outer cells of the root cap peel off while still living, they produce abundant mucus, which facilitates the movement of the root among the solid particles of the soil. The cells of the central part of the cap contain many starch grains. Apparently, these grains serve statoliths, that is, 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 division zone, represented by the apical meristem, as a result of the activity of which all other zones and root tissues are formed. The division zone is about 1 mm in size. The cells of the apical meristem are relatively small, multifaceted, with dense cytoplasm and a large nucleus.

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

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

Next comes absorption zone, or suction zone... In this zone, the integumentary tissue is rhizoderm(epible), whose cells carry numerous root hairs... Root stretching stops, root hairs tightly cover 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 zone is also called zone of differentiationbecause this is where the formation of permanent primary tissues occurs.

The lifespan of the root hair does not exceed 10-20 days. Above the suction zone, where root hairs disappear, zone... 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 area (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 end grows. Young cells from the side of the stretch zone are constantly included in the absorption zone, and at the same time aging cells are excluded, passing into the conduction zone. Thus, the root suction apparatus is a mobile formation continuously moving in the soil.

In the same way consistently and naturally in the root end, internal tissues arise.

Primary root structure.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 taxonomic groups. Derivatives of initials already near the apical meristem differentiate into primary meristems - 1) protoderm, 2) main meristem and 3) procambium(fig. 4.3). Three tissue systems are formed from these primary meristems in the absorption zone: 1) rhizoderm, 2) primary cortex and 3) axial (central) cylinder, or stele.

Figure: 4.3. Longitudinal section of the tip of the onion root.

Rhizoderma (epible, root epidermis) is a suction tissue formed from protoderm, the outer layer of the primary root meristem. Functionally, 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, substances that help soil nutrition are released from the root into the soil through the rhizoderm. The absorbing surface of the rhizoderm is greatly increased 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). One four-month-old rye plant had approximately 14 billion root hairs with an absorption area of \u200b\u200b401 m2 and a total length of over 10,000 km. Have aquatic plants root hairs may be missing.

The hair wall is very thin and consists of cellulose and pectin substances. Its outer layers contain mucus, which contributes to the establishment of 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 desiccation. Physiologically, 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 characteristic of cells with high level metabolism.

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

Of main meristem formed primary cortex... The primary root bark is differentiated into: 1) exoderm - the outer part, lying directly behind the rhizoderma, 2) the middle part - mesoderm and 3) the innermost layer - endoderm (fig. 4.4). The bulk of the primary crust is mesodermformed by living parenchymal cells with thin walls. The cells of the mesoderm are loosely located; gases necessary for cell respiration circulate along the intercellular system along the root axis. In marsh and aquatic plants, the roots of which lack oxygen, the mesoderm is often represented by aerenchyma. Also, mechanical and excretory tissues may 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, and spare parts are often deposited in the cells of the cortex. nutrientssuch 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 rhizoderm dies off above the absorption zone, it appears on the surface of the root and turns into a protective integumentary tissue. The exoderm is formed as a single layer (less often several layers) and consists of living parenchymal cells tightly interconnected. As the root hairs die off, the walls of the exoderm cells are covered from the inside with a layer of suberin. In this respect, the exoderm is similar to a cork, but in contrast to it, it is primary in origin, and the cells of the exoderm remain alive. Sometimes in the exoderm, passage cells with thin non-corked walls are preserved, through which selective absorption of substances occurs.

The innermost layer of the primary cortex - 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 are tightly adjacent to each other and have thin primary walls. On their radial and transverse walls, thickenings in the form of frames are formed - caspari belts (fig. 4.5). The belts of neighboring cells are closely connected with each other, so that their continuous system is created around the stele. Suberin and lignin are deposited in the Caspari belts, which makes them impermeable to solutions. Therefore, substances from the cortex to the stele and from the stele to the cortex can only pass through the symplast, that is, through the living protoplasts of the endoderm cells and under their control.

Figure: 4.5. Endoderm at the first stage of development (diagram).

At the second stage of development, suberin is deposited along the entire inner surface of endoderm cells. At the same time, some cells retain their primary structure. it passage 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 ( fig. 4.7). The passage cells are also preserved in the tertiary endoderm.

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

There are cells behind the pericycle procambiathat differentiate into primary conductive tissues. Phloem and xylem elements are laid in a circle, alternating with each other, and develop centripetally. However, xylem usually overtakes phloem in its development and occupies the center of the root. In the cross section, the primary xylem forms a star, between the rays of which there are phloem areas ( fig. 4.4). This structure is called radial conductive beam.

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

Figure: 4.6. Types of structure of the axial cylinder of the root (diagram): A - diarchic; B - triarchic; B - tetrarch; G - polyarchic: 1 - xylem; 2 - phloem.

The spatial separation of the strands of the primary phloem and xylem located at different radii, and their centripetal origins, 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 solutions coming from the bark penetrate into them more easily, bypassing the phloem.

Figure: 4.7. Monocotyledon root cross section : 1 - the remains of the rhizoderm; 2 - exoderm; 3 - mesoderm; 4 - endoderm; 5 - access cells; 6 - pericycle; 7 - xylem; 8 - phloem.

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

Figure: 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 remains throughout life.

Secondary root structure.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 - cambia and phellogena.

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

Figure: 4.9. Establishment and initiation of cambium activity at the root of a pumpkin seedling: 1 - primary xylem; 2 - secondary xylem; 3 - cambium; 4 - secondary phloem; 5 - primary phloem; 6 - pericycle; 7 - endoderm.

The sections of the cambium arising from the pericycle consist of parenchymal cells and are not capable of depositing elements of conducting tissues. They form primary pith rays, which are wide areas of the parenchyma between secondary conductive tissues ( fig. 4.10). Secondary core, or bast-wood beams occur additionally with prolonged root thickening, they are usually narrower than the primary ones. The pith rays provide a connection between the xylem and the phloem of the root; radial transport of various compounds occurs along them.

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

Figure: 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 a secondary integumentary tissue - periderm, which can stretch on the surface of the thickening root due to the work of phellogen. Phellogenis laid in the pericycle and begins to lay out plug, and inside - phelloderm... The primary cortex, cut off by a cork from internal living tissues, dies off and is discarded ( fig. 4.11).

Phelloderm cells and parenchyma, formed by division of pericycle cells, form parenchyma of the secondary cortexsurrounding conductive tissue (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, cambiums often thicken strongly. The secondary xylem in such roots merges into a solid cylinder surrounded by a cambium ring and a solid ring of secondary phloem ( fig. 4.11). Compared with the stem, the boundaries of the annual rings in the root wood are much less pronounced, the bast is more developed, the core rays are, as a rule, wider.

Figure: 4.11. A cross-section of a willow root at the end of the first growing season.

Root specialization and metamorphosis.Most plants in the same root system clearly differ growth and suckingendings. Growth ends are usually more powerful, quickly lengthen and move deeper into the soil. The stretch zone is well expressed, and the apical meristems work vigorously. Sucking endings arising in a large number on growth roots, elongate slowly, and their apical meristems almost stop working. The sucking ends seem to stop in the soil and intensively "suck" it.

In woody plants, thick skeletal and semi-skeletalroots on which short-lived root lobes... The root lobes, which are continuously replacing each other, include growth and sucking ends.

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

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

Special formations arise on the roots of legumes - nodulesin which bacteria from the genus Rhizobium settle. These microorganisms are able to assimilate atmospheric molecular nitrogen, converting it into a bound state. Some of the substances synthesized in nodules are assimilated by plants, bacteria, in turn, use 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 feed products and enrich the soil with nitrogenous substances.

Very widespread storing roots. They are usually thickened and heavily parenchyma. Strongly thickened adventitious roots called root cones, or root tubers(dahlia, some orchids). Many, more often biennial, plants with a taproot system develop a formation called root vegetable... Both the main root and the lower part of the stem are involved in the formation of the root crop. In carrots, almost the entire root crop is made up of the root, in turnips, the root forms only the lowest part of the root crop ( fig. 4.12).

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

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

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

Figure: 4.13. Root metamorphosis : 1 - corms of gladiolus with retracting roots thickened at the base; 2 - respiratory roots with pneumatophores in Avicennia ( etc- tide zone); 3 - orchid aerial roots.

Figure: 4.14. Part of a cross-section of an aerial root of an orchid : 1 - velamen; 2 - exoderm; 3 - access cell.

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

In some plants, to maintain shoots in the air, additional supporting roots. They move away 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) ( fig. 4.15, 2). Stilted the roots extend from the lower portions of the stem, giving the stem stability. They are formed in plants of mangroves, plant communities that develop on tropical oceans flooded during high tide ( fig. 4.15, 3), as well as in corn ( fig. 4.15, 1). Ficus rubbery forms board-likeroots. Unlike pillars and stilts, they are not adventitious in origin, but lateral roots.

Figure: 4.15. Support roots : 1 - stilted corn roots; 2 - pillar-like banyan roots; 3 - stilted roots of rhizophora ( etc- tide zone; from - low tide zone; silt- the surface of the muddy bottom).

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

The root is an 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;

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

Storage: some roots can store nutrients.

Types of roots

Distinguish between main, adventitious and lateral roots. When the seed germinates, the embryonic 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. The adventitious roots provide the plant with additional nutrition and perform a mechanical function. They develop when hilling, for example, tomatoes and potatoes.

Root functions:

They suck up 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.

Fix the plant in the soil.

In the roots, nutrients (starch, inulin, etc.) are stored in the reserve.

A symbiosis with soil microorganisms - bacteria and fungi.

Vegetative reproduction of many plants takes place.

Some roots function as a respiratory organ (monstera, philodendron, etc.).

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

The root is capable of metamorphosis (thickening of the main root forms "root crops" in carrots, parsley, etc.; thickening of lateral or adventitious roots form root tubers in dahlias, peanuts, peeling, etc., shortening of roots in bulbous plants). The roots of one plant are the root system. The root system is pivotal and fibrous. In the tap root system, the main root is well developed. Most dicotyledonous plants (beets, carrots) have it. In perennial plants, the main root may 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. There is no main root in it. Monocotyledonous plants such as cereals, onions have such a system. Root systems take up a lot of space in the soil. For example, in rye, the roots spread 1-1.5 m in breadth and penetrate up to 2 m deep. Metamorphoses of the root system associated with habitat conditions: * Aerial roots. * Stilted roots. * Respiratory roots. * Wood-like roots. * Roots - props (columnar). * Roots - attachments.

10. Metamorphoses of the root and the functions they perform. The influence of environmental factors on the formation and development of the root system of plants. Mycorrhiza. Mushroom root. Attaches to plants and is in a state of symbiosis. Root-dwelling mushrooms use carbohydrates from photosynthesis; in turn, they 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, transforming it into a bound state; some of these compounds are assimilated by the higher plant. Thanks 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. Board-like roots. These are large plagiotropic lateral roots, along the entire length of which a flat outgrowth is formed. Such roots are typical for trees in the upper and middle tiers of the tropical rainforest. The process of formation of a board-like outgrowth begins at the oldest part of the root - the basal. Columnar roots. They are typical for 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 out, 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 their function - providing gas exchange of 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 protoderm, and it sucks in water. Storage roots. Root tubers form lateral and adventitious roots as a result of metamorphosis. Root tubers function only as storage organs. These roots combine the functions of storing and absorbing soil solutions. 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, cambium activity 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 can limit their growth and development. For example, with regular cultivation of the soil, with 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, oxygen is most often the limiting factor for aquatic plants. For solar plants, for example, sunflower, this factor is most often sunlight (lighting).
The combination of such factors determines the conditions for the development of plants, their growth and the possibility of existence in a certain area. Although, like all living organisms, they can adapt to living conditions. Let's see how this happens:
Drought, high temperatures
Plants growing in hot, arid climates such as the desert have a strong root system to be able to extract water. For example, shrubs belonging to the genus Juzgun have 30-meter roots that extend deep into the ground. But the roots of cacti are not deep, but they are widely spread under the soil surface. They collect water from large soil surfaces during rare, short rains.
The collected water must be conserved. Therefore, some plants - succulents for a long time preserve the supply of moisture in leaves, branches, trunks.
Among the green desert dwellers, there are those who have learned to survive even in long-term drought. Some, 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 lyes and ferns, can live in a dehydrated state. long timeuntil the occasional rain falls.
Cold, humid tundra conditions
Here the plants adapt to very harsh conditions. Even in summer, the temperature is rarely higher than 10 degrees. Summer lasts less than 2 months. But even during this period there are frosts.
There is little rainfall, so the snow cover protecting the plants is small. A strong gust of wind can strip them completely. 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, a wax coating on them, a cork on the stem.
Since it is a polar day in the tundra in summer, 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 tundra conditions produce seeds that grow once every 100 years. Seeds grow only when the conditions are right - after two warm summers in a row. Many have adapted to vegetative reproduction, such as mosses and lichens.
sunlight
Light is very important to plants. Its amount affects their appearance and internal structure. For example, forest trees that grow tall with enough light 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 to capture as much sunlight as possible. Where the sun is sufficient, 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 the higher plant. The root is an axial organ, usually cylindrical in shape, with radial symmetry, with 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 collection of roots of one 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)

Main rootdevelops from the embryonic root.

Clausescalled the roots developing on the stem of the shoot. Adventitious roots can also grow on leaves.

Lateral roots arise on roots of all types (main, lateral and subordinate

Internal structure root. At the tip of the root are the cells of the educational tissue. They are actively sharing. This root section about 1 mm long is called division zone ... The root division zone is protected from outside by a root cap. The cells of the cap secrete mucus that envelops the root tip, making it easier for it to pass through the soil.

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

Above the growth zone there is a root section with root hairs - these are long outgrowths of cells of the outer root cover. With their help, the root absorbs (sucks) water with dissolved mineral salts from the soil. The hair roots work like small pumps. This is why the root-hair zone is called suction zone or absorption zone The suction zone occupies 2-3 cm at the root. Root hairs live for 10-20 days. The cell of the root hair 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 corky membranes. Endoderm cells do not allow water to pass through. Among them there are living thin-walled cells - throughput. 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 at the root form longitudinal strands, where xylem sections alternate with phloem sections. The xylem elements are located opposite the passage cells. The spaces between the xylem and phloem are filled with living cells of the parenchyma. The conductive tissues form a central or axial cylinder. With age, an educational tissue, cambium, appears between the xylem and phloem. Due to the division of cambium cells, new elements of xylem and phloem, mechanical tissue, are formed, which ensures the growth of the root in thickness. At the same time, the root acquires additional functions - support and storage of nutrients. zone root, along the cells of which water and mineral salts absorbed by the 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. Water with dissolved salts rises through the cells of the conductive tissue to the stem - this is upward current, and from the stem and leaves to the root, organic substances move, necessary for the vital activity of root cells, is downward current.The roots most often take the form: cylindrical (horseradish); conical or conical (for dandelion); threadlike (in rye, wheat, onions).

From the soil, water enters the root hairs by osmosis, passing through their shells. In this case, the cell is filled with water. Part of the water enters the vacuole and dilutes the cell sap. Thus, different densities and pressures are created in neighboring cells. The cell with more concentrated vacuolar juice takes part of the water from the cell with diluted vacuolar juice. This cell, through osmosis, transfers water along a chain to another neighboring cell. In addition, part of the water passes through the intercellular spaces, as through 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 \u200b\u200bthe passage cells of the endoderm is much less area the surface of the root peel, considerable 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. Due to the root pressure, water not only enters the central cylinder, but also rises to a considerable height in the stem.

Root growth:

The root of the plant grows throughout its life. As a result, it constantly grows, going deeper into the soil and moving away from the stem. Although the roots have unlimited opportunity growth, they almost never have the opportunity to fully exploit it. In the soil, the roots of the plant are interfered with by the roots of other plants, there may be insufficient water and nutrients. However, if a plant is grown artificially in very favorable conditions for it, then it is capable of developing roots of a huge mass.

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

The root always grows downward. Regardless of which side you turn the seed, the seedling root will begin to grow downward. Absorption by the roots of water from the soil: 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 undeveloped stem with leaves and buds located on it - the rudiments of new shoots that arise in a certain order. These rudiments of new shoots provide 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, provides 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-the growth is due to the apical kidney

Sympodial- shoot growth continues due to the nearest lateral bud

Pseudo-dichotomous- after the apical bud dies off, shoots grow (lilac, maple)

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

Tillering - This is a branching in which large lateral shoots grow from the lowest buds, located at the surface of the earth or even underground. As a result of tillering, a bush is formed. Very dense perennial bushes called turf.

The structure and types of shoots:

Types:

The main shoot is a shoot that has developed from the bud of the seed embryo.

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

Elongated shoot - a shoot with elongated internodes.

Shortened shoot - a shoot with shortened internodes.

A vegetative shoot is a shoot bearing leaves and buds.

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

Branching and growth of shoots:

Branching Is the formation of lateral shoots from axillary buds. A highly branched system of shoots is obtained when lateral shoots grow on one shoot, and the following lateral ones grow on them, and so on. In this way, as much of the 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 adventitious buds

13. Structure, functions and types of kidneys. Variety of buds, bud development. Bud - an embryonic, 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 flower or inflorescence rudiments. A flower bud containing 1 flower is called a bud. Kidney types.

Plants have several types of buds. They are usually divided according to several criteria.

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

2. By location on the shoot: * apical (always axillary) * lateral (can be axillary and adventitious).

3) By the time of action: * summerfunctioning * wintering, i.e. in a state of winter dormancy * sleeping, those. being in a state of long, even long-term rest.

In appearance, these kidneys are well distinguished. In summer buds, the color is light green, the cone of growth 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 leaves stop growing and specialize in protective structures - kidney scales. Their epidermis becomes lignified, and in the mesophyll sclereids and containers with balms and resins are formed. The kidney scales, glued together with resins, hermetically close the air flow into the kidney. In the spring of next year, the wintering bud turns into an active, summer one, and that one into a new shoot. When the hibernating kidney awakens, the meristem cells begin to divide, the internodes lengthen, as a result, the kidney scales fall off, leaving leaf scars on the stem, the combination of which forms a kidney ring (a trace from a hibernating or dormant kidney). The age of the shoot can be determined from these rings. Part of the axillary buds remains at rest. These are living buds, they receive nourishment, but they 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 when forming external appearance plants

14. Anatomical structure of the stem of herbaceous dicotyledonous and monocotyledonous plants. The structure of the stem of a monocotyledonous plant.Of the most important monocotyledonous plants are cereals, the stem of which is called a straw. With an insignificant straw thickness, it has significant strength. It consists of nodes and internodes. The latter are hollow inside and have the greatest length at the top, and the smallest at the bottom. The most delicate parts of the straw are above the knots. There is educational tissue in these places, so cereals grow with their internodes. This growth of cereals is called interstitial growth. In the stems of monocotyledonous plants, the bundle structure is well expressed. Closed fibrous bundles (without cambium) are distributed over the entire thickness of the stem. From the surface, the stem is covered with a single layer of epidermis, which subsequently lignifies, forming a cuticle layer. Located directly under the epidermis, the primary cortex consists of a thin layer of living parenchymal cells with chlorophyll grains. In the interior of the parenchymal cells, there is a central cylinder, which begins from the outside with a mechanical tissue of sclerenchyma of pericyclic origin. Sclerenchyma gives the stem strength. The main part of the central cylinder consists of large cells of the parenchyma with intercellular spaces and randomly located vascular fibrous bundles. The shape of the beams 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 fibrovascular bundle, and the stem cannot thicken. Each tuft is surrounded on the outside by mechanical tissue. The maximum amount of mechanical tissue is concentrated around the bundles near the surface of the stem.

Anatomical structure of the stems of dicotyledonous plants already in early age differs from the structure of monocots (Fig. 1). The vascular bundles are located in one circle here. Between them is the main parenchymal tissue, which forms the medullary rays. The main parenchyma is also located inward from 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 cluster cambium, consisting of several regular rows of lower dividing cells; cells inward from which secondary wood is formed, and outward - cells from which secondary bast (phloem) is formed... Parenchymal cells of the underlying tissue surrounding the bundle, often filled with storage substances; various vessels conducting water; cambial cells, from which new elements of the bundle arise; sieve tubes, conducting organic substances, and mechanical cells (bast fibers), which give strength to the bundle. The dead elements are water-conducting vessels and mechanical tissues, and all the rest are living cells with a protoplast inside... From the division of cambium cells in the radial direction (that is, perpendicular to the stem surface) the cambial ring lengthens, and from their division in the tangential direction (that is, parallel to the stem surface) the stem thickens. In the direction of the wood, 10-20 times and more cells are deposited than in the direction of the bast, and therefore the wood grows much faster than the bast.
Classes Dicotyledons and Monocots 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 peculiarities 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 lignify 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 inside. These three integumentary tissues form the integumentary complex of the periderm. within 2-3 years they slough off and die off. Under the periderm there is a primary cortex. The outer layers are represented by cells of lamellar chlorophyll-bearing collenchism, then there is a chlorophyll-bearing parenchyma and a weakly expressed endoderm.

Most of the stem is made up of tissues cut off by the activity of yucambium. The boundaries of the bark and wood passes along the cambium. All tissues lying outward from the cambium are called bark. The bark is primary and secondary. The primary one has already been described, the secondary cortex is made up of phloem, illub, and heart-shaped trapezium. Phloid form. and the medullary rays are presented in the form of triangles, the vertices of which converge to the center of the stem to the pith.

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

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

To the center of the stem, inward from the cambium, wood is formed, consisting of vessels (trachea), tracheids, woody parenchyma and wood of sclerenchyma (libriform). Libriform is a collection of narrow thick-walled and lignified cells of mechanical tissue. Wood is deposited in the form of annual rings (a combination of spring and autumn 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 by the number of annual rings, you can determine the relative age of the tree. 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. Outside the sheet is covered skin... 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 cleft between them call stomata ... Moving apart and closing, these two cells open and close the stomata. Gas exchange occurs through the stomata and moisture evaporates.

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

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

FunctionsWater 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 from photosynthesis. This process is called gas exchange.

Parts of the sheet

External structure sheet. In most plants, the leaf consists of a blade and a petiole. A leaf blade is an expanded lamellar part of a leaf, hence its name. The leaf blade performs the basic functions of a leaf. At the bottom, it passes into a petiole - a 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 is in the most favorable lighting conditions. In the petiole there are conducting bundles that connect the vessels of the stem with the vessels of the leaf blade. Due to the elasticity of the petiole, the leaf blade withstands blows on the leaf of rain drops, hail, gusts of wind more easily. In some plants, at the base of the petiole there are stipules in the form of films, scales, small leaves (willow, rosehip, hawthorn, white acacia, peas, clover, etc.). The main function of stipules is to protect young developing leaves. Stipules can be green, in which case they are similar to a leaf blade, but usually much smaller in size. In peas, meadow ranches, and many other plants, stipules persist throughout the life of the leaf and perform the function of photosynthesis. In linden, birch, oak, scarious stipules fall off in the young leaf stage. In some plants - tree 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 kept there throughout life cycleand is also provided with water, minerals and nutrients contained in it. There are different types and types of roots. Each of them has its own distinctive characteristics... In this article we will look at the existing types of roots, types of root systems. We will also get acquainted with their characteristic features.

What types of roots are there?

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 embryonic root of the seed. The main root is always the same (other types of plant roots are usually present in plural). It is stored in a plant throughout its entire life cycle.

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

Adventitious roots

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

There are also leafy 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 air (or support).

The appearance of adventitious roots determines the plant's ability to vegetative propagation.

Lateral roots

Lateral roots are called roots that arise as a lateral branch. They can form both on the main and on the adventitious roots. In addition, they can also 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 called the root system?

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

Types of root systems

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

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

If the adventitious roots, which develop in large numbers, are more pronounced, 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 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 shrubs and rhizome grasses, which form an abundant amount of fibrous thin roots, are widely used to anchor ravines, soils on slopes, etc. The best grasses include awnless fire, 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 storage includes 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 fabric. Examples of root vegetables include parsley, radishes, carrots, beets, etc.

If the lateral and adventitious roots are the thickened storage 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. Present in a number of tropical plants. Water and oxygen are absorbed from the air. They are found in tropical plants growing in conditions of a lack of minerals.

Respiratory roots

This is a type 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-like) roots

These types of tree roots are typical for large species (beech, elm, poplar, tropical, etc.). They are triangular vertical outgrowths formed by lateral roots and extending near or above the soil surface. They are also called planks because they resemble planks 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 are able to attach to a certain support and climb (weave) up. Such roots are available, for example, in the tenacious ficus, ivy, etc.

Retractable (contractile) roots

Typical for plants, the root of which is sharply reduced in the longitudinal direction at the base. An example is plants that have bulbs. Retractable roots provide bulbs and root crops with some indentation into the soil. In addition, their presence determines the tight fit of the 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 called symbiosis (mutually beneficial cohabitation) of the roots of higher plants with fungal hyphae, which braid them, performing the functions of root hairs. Mushrooms provide plants with water and nutrients dissolved in it. Plants, in turn, provide the fungi with the organic substances necessary for their life.

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. This mutually beneficial cohabitation allows plants to receive nitrogen, which bacteria transfer from the air into a form accessible to them. Bacteria are provided with 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 for plants of the legume family are characteristic, which are widely used as ameliorants in crop rotations in order to enrich the soil with nitrogen. The best nitrogen-fixing plants are tap-root legumes, such as blue and yellow alfalfa, red and sainfoin, hornbeam, etc.

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

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

They suck up 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.

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

1. When water, ions of mineral salts and products of photosynthesis interact, the products of primary and secondary metabolism are synthesized.
2. 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.
3. In the roots, nutrients (starch, inulin, etc.) are stored in the reserve.
4. In the roots, the biosynthesis of secondary metabolites (alkaloids, hormones and other biologically active substances) is carried out.
5. The growth substances synthesized in the meristematic zones of the roots (gibberellins, etc.) are necessary for the growth and development of the aboveground parts of the plant.
6. Due to the roots, symbiosis with soil microorganisms - bacteria and fungi - is carried out.
7. Many plants propagate vegetatively with the help of roots.

10. Some roots function as 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 metamorphosis (thickening of the main root form "root crops" in carrots, parsley, etc.; thickening of lateral or adventitious roots form root tubers in dahlias, peanuts, peel, etc., shortening of roots in bulbous plants).

The root is an axial organ, usually cylindrical in shape, with radial symmetry, with 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 collection of roots of one plant. The nature of the root system depends on the ratio of the growth of the main, lateral and adventitious roots.

^ Types of roots and root systems.In the embryo of the seed, all the organs of the plant are in their infancy. The main, or first, root develops from embryonic root.The main root is located at the center of the entire root system, the stem serves as an extension 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 thickness of the stem and root: the stem is thicker than the root. The section of the stem from the root collar to the first germinal leaves - the cotyledons are called subcotyledonous kneeor hypocotyl... From the main root, lateral roots of successive orders extend to the sides. Such a root system is called pivotal, in many dicotyledonous plants, it is capable of branching. 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 apex and are formed endogenously - in the internal tissues of the parent root of the previous order due to the activity of the pericycle. The more the lateral roots move away from the main root, the larger the plant nutrition area, therefore there are special agronomic techniques that enhance the ability of the main root to form lateral, for example, pinching or divethe main root by l / 3 of its length. After diving for a while, 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 monocotyledons, the embryonic root dies off quickly, the main root does not develop, and form from the base of the shoot clausesroots that also branch off the first, second, etc. orders. Such a root system is called fibrous.The adventitious roots, like the lateral ones, are laid endogenously. They can form on stems and leaves. The ability of plants to develop adventitious roots is widely used in plant growing during vegetative propagation of plants (propagation by stem and leaf cuttings). Aboveground stem cuttings propagate willow, poplar, maple, black currant, etc .; leafy cuttings - uzambara violet, or saintpaulia, some types of begonias. Underground cuttings of modified shoots (rhizomes) are propagated by many medicinal plants, for example, May lily of the valley, medicinal kupenu, etc. Some plants form many adventitious roots when hilling the lower part of the stem (potatoes, cabbage, corn, etc.), thereby creating additional nutrition.

In higher spore plants (lyes, horsetails, ferns), the main root does not arise at all, they only form adventitious roots extending from the rhizome. In many dicotyledonous herbaceous rhizome plants, the main root often dies off and a system of adventitious roots extending from the rhizomes prevails (runny, nettle, creeping buttercup, etc.).

In terms of the depth of penetration into the soil, the first place belongs to the tap root system: the record depth of penetration of roots, according to some information, reaches 120 m! However, the fibrous root system, having mainly superficial 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 or 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 roots of the first, second and third orders is over 180 km, and with the addition of roots of the fourth order - 623 km. Despite the fact that 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 the sandy deserts, where deep groundwater, the roots of some plants go to a depth of 40 m or more (Selin cereal, acupressure prosopis from the Legume family, etc.). Semi-desert ephemeral plants have superficialthe root system, which is adapted to the rapid absorption of early spring moisture, which is sufficient for the rapid passage of all phases of the vegetation of plants. On clayey, poorly aerated podzols of the taiga forest zone, the root system of plants is 90% concentrated in the surface soil layer (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 is towards higher 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 type of plant.

^ Zones of young root.In a young root, there are: 1) a division zone covered by a root cap; 2) a zone of cell stretching, or a growth zone; 3) the zone of suction, or the zone of root hairs; 4) conductive zone.

^ Division zonerepresents the tip of the root, covered on the outside root cap,protecting the apical, or apical, meristem. The young root tip is slippery to the touch due to 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 geotropismthe root itself, that is, it promotes the growth of the root and its penetration into the depths of the soil. The root cap consists of living parenchymal cells, which contain starch grains. There is a division zone under the cover, or root cone,represented by the primary educational tissue (meristem). As a result of active division of the root apical meristem, all other root zones and tissues 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,with a length of several millimeters, it is outwardly transparent, consists of cells that are practically non-dividing, but stretching in the longitudinal direction. The cells increase in size, vacuoles appear in them. The cells are characterized by high turgor. In the stretch zone, differentiation of primary conductive tissues occurs and permanent root tissues begin to form.

Above the stretch zone is located suction zone.Its length is 5 - 20 mm. The suction 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 larger the suction 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 off. Length of root hairs at different plants from 0.5 - 1.0 cm.Young root hairs are formed above the stretch zone, and die off above the suction zone, so the zone of root hairs 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 the zone of conduction, or the zone of lateral roots.The water and salt solutions absorbed by the root are transported through the vessels of the wood up to the aerial parts of the plant.

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

6. Metamorphosis of the root. Their biological significance. Mycorrhiza.Most plants in the same root system clearly differ growth and suckingendings. Growth ends are usually more powerful, quickly lengthen and move deeper into the soil. The stretch zone in them is well defined, and the apical meristems work vigorously. Sucking endings, which appear in large numbers on the growth roots, lengthen slowly, and their apical meristems almost stop working. The sucking ends seem to stop in the soil and intensively "suck" it.

In woody plants, thick skeletal and semi-skeletalroots on which short-lived root lobes... The root lobes, which are continuously replacing each other, include growth and sucking ends.

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

The roots of many plants form a symbiosis with the hyphae of soil fungi, called mycorrhiza("Mushroom root"). Mycorrhiza forms on sucking roots in the absorption zone. The fungal component makes it easier for the roots to get water and mineral elements from the soil, often fungal hyphae replace root hairs. In turn, the fungus receives carbohydrates and other nutrients from the plant. There are two main types of mycorrhiza. Hyphae ectotrophicmycorrhiza form a cover that envelops the root from the outside. Ectomycorrhiza is widespread in trees and shrubs. Endotrophicmycorrhiza occurs mainly in herbaceous plants. Endomycorrhiza is located inside the root, hyphae are introduced into the cells of the core parenchyma. Mycotrophic nutrition is very widespread. Some plants, for example orchids, cannot exist at all without symbiosis with fungi.

Special formations arise on the roots of legumes - nodulesin which bacteria from the genus Rhizobium settle. These microorganisms are able to assimilate atmospheric molecular nitrogen, converting it into a bound state. Some of the substances synthesized in the nodules are assimilated by plants; bacteria, in turn, use the substances in the roots. This symbiosis is of great importance to agriculture. Legumes are rich in protein due to their additional nitrogen source. They provide valuable food and feed products and enrich the soil with nitrogenous substances.

Very widespread storing roots. They are usually thickened and heavily parenchyma. Strongly thickened adventitious roots are called root cones, or root tubers(dahlia, some orchids). Many, more often biennial, plants with a taproot system develop a formation called root vegetable... Both the main root and the lower part of the stem are involved in the formation of the root crop. In carrots, almost the entire root crop is made up of the root, in turnips, the root forms only the lowest part of the root crop ( fig. 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 umbrella parenchyma, the parenchyma is strongly developed in the phloem; in turnips, radishes and other cruciferous plants - in the xylem. In beets, reserve substances are deposited in the parenchyma formed by the activity of several additional layers of cambium ( fig. 4.12).

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

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

In some plants, to maintain shoots in the air, additional supporting roots. They move away 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 ( columnarbanyan roots) ( fig. 4.15, 2). Stilted the roots extend from the lower portions of the stem, giving the stem stability. They are formed in plants of mangroves, plant communities that develop on tropical oceans flooded during high tide ( fig. 4.15, 3), as well as in corn ( fig. 4.15, 1). Ficus rubbery forms board-likeroots. Unlike pillars and stilts, they are not adventitious in origin, but lateral roots.

Figure: 4.15. ^ Supporting roots : 1 - stilted corn roots; 2 - pillar-like banyan roots; 3 - stilted roots of rhizophora ( etc- tide zone; from - low tide zone; silt- the surface of the muddy bottom).

Escape concept. Morphological dissection of the shoot. Nodes and interzillas. Apical shoot growth. The structure and activity of the cone is growing. A shoot is a stem with leaves and buds located on it.

Areas of the stem where leaves develop called nodes.
Stem sections between the two nearest nodes called internodes.
The angle between the sheet and the above internode called the leaf axil.
An axillary bud is formed in the leaf axil. Escape consists of repeating sections - metamers.
One metamere includes internode, node, leaf, and 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 the kidney. The bud consists of an embryonic stem - an epicotyl, an apical meristem, and one or more leaf primordia (leaf primordia). When the seed germinates, the stalk lengthens. New leaf primordia develop from the apical meristem, from leaf primordia leaves develop, and in leaf axils kidney primordia are formed. This development algorithm can be repeated many times during the formation of the plant shoot system.

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

The buds are also part of the shoot. This is, first of all, the apical bud, which represents the growth cone of the shoot. IN leaf axils in seed plants, axillary or lateral buds are formed. If they develop one above the other (honeysuckle, walnut, robinia, etc.), then they are called serial. If the buds develop in the leaf axils next to each other (plum, cereals, etc.), then they are called collateral. The kidneys can form endogenously in the internode region. These kidneys are called adventitious kidneys.

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

Overwintering, or dormant 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 buds are called renewal buds. From them aerial shoots develop in spring.

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

From a kidney that does not have renal primordia, a simple or unbranched the escape... From a bud with renal primordia, a branched 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 in appearance. In addition to the apex, rudimentary internodes and rudimentary nodes, such buds have primordia, which give rise to parts of a flower or parts of cones. At the buds that give rise to inflorescences, flowering primordia are formed.

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

The morphological characteristics 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 at the node, but it can be opposite or whorled. Specific type leaf arrangement forms a leaf mosaic, which makes the best use of space to ensure uniform illumination of the leaf.

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, the middle leaves are usually described, but a complete morphological description requires separate description all categories of leaves, because even middle leaves on one shoot have differences. This phenomenon is called heterophyllia or variegation.

Apical shoot growth - the growth of the shoot in length due to the modification of the growth cone, 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 growth cone (rudimentary stem) and leaf primordia (rudimentary leaves), that is, from a series of rudimentary metameres. The differentiated leaves located below cover the growth cone and primordia. This is how the vegetative kidney works. In a vegetative-reproductive bud, the growth cone has been transformed into a rudimentary flower or rudimentary inflorescence. Reproductive (flower) buds consist only of a rudimentary flower or inflorescence and do not have photosynthetic leaf rudiments.

13. Metamorphosed shoots.

Their appearance is often associated with the performance of the functions of a container for spare products, transferring adverse conditions of the year, vegetative propagation.

Rhizome - This is a perennial underground shoot with a horizontal, ascending or vertical direction of growth, performing the functions of accumulation of spare 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 normal 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. Aerial buds are formed annually from the apical and axillary buds. annual shoots... The old parts of the rhizome gradually die off. Plants with horizontal long rhizomes forming many aerial 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 sands (spikelet, aristida). In meadow growing, cereals with long horizontal rhizomes are called rhizome (bent grass, bluegrass), and with short ones - bushy (timothy, whiteus). Rhizomes are found mainly in perennial herbaceous plants, but sometimes in shrubs (euonymus) and shrubs (lingonberry, blueberry).

Tuber - This is a thickened part of the shoot, a container for spare products. Tubers are aboveground and underground.

Aerial tuber is a thickening of the main (kohlrabi) or lateral (tropical orchid) shoot and bears normal leaves.

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

Overground stolon - This is a short-lived creeping shoot, serving for distribution (seizure of territory) and vegetative reproduction. It has long internodes and green leaves. Adventitious roots are formed on the nodes, and a shortened shoot (rosette) from the apical bud is formed, which, after the stolon dies off, continues to exist independently. The overground stolon is growing for sympodialia. Aerial stolons that have lost the function of photosynthesis and perform mainly the function of vegetative reproduction are sometimes called whiskers (strawberries).

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

Corm outwardly similar to an onion, but all of its leaf scales are dry, and spare products are deposited in the stem part (saffron, gladiolus).

Thorns have different origins - from the shoot (apple, pear, blackthorn, hawthorn, gleditsia, citrus), leaf (barberry) or parts of it: rachis (astragalus), stipules (white acacia), part of the plate (Compositae). Spines are characteristic of plants in hot, dry habitats.

Antennae are formed from a shoot (grapes), a leaf or its parts: rachis and several leaves (peas), a plate (rank.), stipules (sarsaparilla). They are used to attach to the support.

Phylocladia are flat, leaf-shaped shoots located in the axils of reduced leaves. Flowers are formed on them. They are found in plants mainly in arid habitats (butcher, phyllanthus). Fishing apparatus - modified leaves characteristic of insectivorous plants (sundew, flycatcher). They are in the form of jugs, urns, bubbles, or slamming and folding plates. Small insects, getting 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 no leaves or buds arranged in a certain order. It is characterized by apical growth in length, its lateral ramifications arise from internal tissues, the growth point is covered with a root cap. The root system is formed throughout the life of a plant organism. Sometimes the root can serve as a place of deposition in the supply of nutrients. In this case, it is modified.

Types of roots

The main root is formed from the embryonic root during seed germination. Lateral roots extend from it.

Adventitious roots develop on stems and leaves.

Lateral roots are branches of any root.

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

Types of root systems

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

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

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

This is many times the area of \u200b\u200bthe aboveground mass.

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

The external structure of the root. Internal structure of the root

Root zones

Root cap

The root grows in length at its tip, where young cells of the educational tissue are located. The growing part is covered with a root cap that protects the root tip from damage and makes it easier for the root to move through 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 alive and often contain starch grains. The cap cells are constantly renewed due to division. Participates in positive geotropic 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 is not the same in different species and in different roots of the same plant.

A stretch zone (growth zone) is located behind the division zone. The length of this zone does not exceed a few millimeters.

As the 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.

Root hair structure

Root hairs are highly elongated outgrowths of the outer cells that cover the root. The number of root hairs is very large (per 1 mm 2 from 200 to 300 hairs). Their length reaches 10 mm. Hair is formed very quickly (in young apple seedlings in 30-40 hours). Root hairs are short-lived. They die off after 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 grows continuously, forming more and more new areas of root hairs. The hairs can not only absorb ready-made solutions of substances, but also help dissolve some soil substances, and then suck them in. The area of \u200b\u200bthe root, where the root hairs have died off, is able to absorb water for some time, but then it becomes covered with a cork and loses this ability.

The hair sheath 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 adhesion of root hairs with soil particles, which improves their contact and increases the hydrophilicity of the system. The absorption is promoted by the release of acids (carbonic, malic, citric) by the root hairs, which dissolve mineral salts.

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

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

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

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 sections of the phloem (along which substances move to the root) and xylem (along which substances move from the root). The main conducting elements of phloem are sieve tubes, xylems are trachea (vessels) and tracheids.

Root vital processes

Root water transport

Absorption of water by root hairs from the soil nutrient solution and carrying it in the radial direction along the cells of the primary cortex through the passage cells in the endoderm to the xylem of the radial conducting bundle. The intensity of water absorption by the root hairs is called the suction force (S), it is equal to the difference between osmotic (P) and turgor (T) pressure: S \u003d P-T.

When the osmotic pressure is equal to the turgor pressure (P \u003d T), then S \u003d 0, water stops flowing into the cell of the root hair. If the concentration of substances in the soil nutrient solution is higher than inside the cell, then the water will leave the cells and plasmolysis will occur - the plants will wither. This phenomenon is observed under conditions of dry soil, as well as with excessive application of mineral fertilizers. Inside the root cells, the sucking force of the root increases from the rhizoderm towards the central cylinder, so the water moves along the concentration gradient (i.e., from a place with its higher concentration to a place with a lower concentration) and creates root pressure, which raises the water column along the xylem vessels forming an upward current. This can be found on leafless spring trunks when harvesting "sap", or on cut tree stumps. The outflow of water from wood, fresh stumps, leaves is called the "cry" 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. The root pressure is the lower motor of the water current, and the sucking force of the leaves is the upper one. This can be confirmed with the help of simple experiments.

Absorption of water by roots

Goal: figure out the basic function of the root.

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

What we observe: in a day or two, the water in the container 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 to prove the absorption of nutrients by the root.

What we do: cut off the stem of the plant, leaving a stump 2-3 cm high.Place 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 water temperature affect the rate of water absorption by the root?

Goal: find out how temperature affects the work of the root.

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

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

Result: this is proof that temperature has a profound 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 important. 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; serve as catalysts for biochemical reactions; affect cell turgor and protoplasm permeability; are centers of electrical and radioactive phenomena in plant organisms.

It has been established that the normal development of plants is possible only if the nutrient solution contains three non-metals - 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 present 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 all the necessary nutrients are contained in the environment surrounding the roots. Soil is such a medium for most plants.

Breathing roots

For normal growth and development of the plant, it is necessary that the root is supplied fresh air... Let's check if this is so?

Goal: does the root need air?

What we do: take two identical vessels with water. We place developing seedlings in each vessel. We saturate the water in one of the vessels with air every day using a spray bottle. Pour a thin layer of vegetable oil on the surface of the water in the second vessel, since 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

Some plants store reserve nutrients 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 storage 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 mainly biennials. In the first year of life, they do not bloom and accumulate many nutrients in the roots. On the second, they bloom quickly, using accumulated nutrients and form fruits and seeds.

Root tubers

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

Bacterial nodules

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

Stilted

A ramp growing in an ebb-tide zone develops stilted roots. They hold large leafy shoots high above the water on unsteady muddy ground.

Air

Tropical plants living 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.

Retracting

In bulbous and corms, such as crocuses, among the numerous filamentous roots there are several thicker, so-called retracting roots. Shrinking, such roots pull the corms deeper into the soil.

Columnar

The ficus develops columnar aerial roots, or support roots.

Soil as a habitat for roots

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

Soil particles compete with the roots for moisture, retaining it on their surface. This is the so-called bound water, which is subdivided into hygroscopic and film water. 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 relationships 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 absorption capacity of the soil - the ability to retain or bind chemical compounds.

Soil microflora decomposes organic matter to simpler compounds, participates in the formation of the 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 the totality of biological and chemical processes in the soil, a complex complex of organic substances is formed, which is united by the term "humus".

Aquatic culture method

What salts the plant needs, and what effect they have on its growth and development, was established by experiment with aquatic crops. 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 an individual salt from the solution, reduce or increase its content. It was found that fertilizers containing nitrogen contribute to the growth of plants containing phosphorus - the early ripening of fruits, and those containing potassium - the fastest outflow of organic matter from the leaves to the 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 aquatic cultures, it was possible to establish not only the plant's need for macronutrients, but also to clarify the role of various trace elements.

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

Hydroponics - growing plants in containers filled with gravel. The nutrient solution containing the necessary elements is fed into the vessels from the bottom.

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