The roots constantly grow due to the division of cells of the apical educational tissue. The root cap facilitates the advancement of the root in the soil and protects the educational tissue. The epidermis protects the root and allows the absorption of water and minerals from the soil using root hairs. Wood conducts substances absorbed from the soil into the stem. The bast ensures the transport of organic substances from the leaves to the root cells. Mechanical tissues give strength to the root.

All roots (main, lateral, adventitious) are structured the same. They can branch, but leaves never form on them.

Bast root

Next to the wood there are bast cells, through which organic substances formed in the leaves and stems enter the root.

Mechanical root tissue

The strength and elasticity of the root is provided by mechanical tissue.

Root cambium (formative tissue)

With age, a lateral educational tissue, the cambium, appears between the wood and the bast. Thanks to the division of cambium cells, new elements of wood, bast, and mechanical tissue are formed. This ensures the root grows thicker. At the same time, the root acquires additional functions - support and storage.

The structure of the root of a plant is studied by the science of botany. Studying this material will help you learn the characteristics of this part of the plant.

What is a root

The root is a constantly growing and developing organ. Its most important function is to carry out the growth and vital activity of the plant. This includes nutrition and respiratory function. Its length and shape constantly changes as the stem grows.

Inside this organ are all the vitamins and substances that are obtained and formed through synthesis.

Root zones

Detailed tables describing the zones of the root system can be found in textbooks on botany. We will tell you the main points.

In the structure of the root system, important zones are distinguished from the top to the tail. The root cap serves as a cover for the tail part and protects the end from damage. With each growth of the end of the root, one can observe the resulting wrinkling of the cap and the appearance of new cells.

Below the cover there is a division zone. This is where cell reproduction occurs. The length of this zone is usually only a few millimeters. Above it is a growth zone in which these cells elongate.

Next comes the suction zone. Its length is about one centimeter. This is where seedlings form. They are called root hairs. All of them are clearly visible to the naked eye, and together they form a thin white fluff on the spine. Root hairs consist of a nucleus, a membrane, leukocytes and cytoplasm.

The suction zone provides fluid and mineral nutrition. Root hairs penetrate between soil cells and absorb nutrition. Next, the nutrients move through the internal cells of the root to the conduction zone. This zone carries out the transition of the necessary important nutrients to the cells of the stem.

There is a continuous relationship between the root and the stem. From the stem, all the organic nutrients necessary for its growth enter the root. The conduction system zone is also located at the root tip. With the help of fibers, interaction occurs between the elements of the root.

Root modifications

To survive in different conditions, plants can have completely different types of roots. The characteristics of the ivy plant help it climb any height with the help of roots-trailers.

Roots found in rutabaga, turnips, and carrots. These are mainly biennial plants. If a person needs to get seeds, then the fruit is left for next year. But mostly they eat root vegetables.

Root tubers found in lilies, dahlias and other flowers. They accumulate all the nutrients needed for nutrition. They are formed from lateral or adventitious roots.

Support roots found in many tropical trees. They protrude from the soil, creating columnar supports for plants. For example, the banyan plant, some types of ficus.

Aerial roots have orchids and other tropical flowers. The growth and life of a plant occurs when the hanging roots draw in water and nutrition from the air sphere.

Sucker roots found in many poisonous plants. With their help, they attach themselves to other plants, sucking nutrients and moisture from them.

Types of roots

In biology there are three types of roots:

1. Subordinate clauses are called shoots directed horizontally, parallel to the soil. They originate from various organs of the plant: on stems, leaves, and the main root.
2. main root usually the largest, goes down into the ground, grows vertically downwards. It grows from an embryonic seed.
3. Lateral can grow on both adventitious roots and the main root.

Types of root systems

There are two types of root systems: fibrous And core. The taproot type structure consists of a basic tap root. He is strong and well developed.

The fibrous type consists of several identical processes that intertwine with each other and are shaped like a nest or a bundle.

Internal structure of the root

Let's examine the microscopic structure of the root system in a cross section using a drawing with captions. A longitudinal section can show how the root is arranged inside.

The root has several layers:

• peel;
• primary cortex;
• tissue forming the outer layer;
• conductive fabrics;
• vessels through which nutrients, minerals and water move;
• tissue that stores nutrients.

Conclusion

We figured out what roots come in shape and type, what they serve for plants, and what important role they play. By studying the anatomical structure of the root system, you can find out its meaning and function.

Different parts of the root perform different functions and are characterized by certain morphological features. These parts are called root zones(Fig. 5.3.):

–division zone – apical meristem of the root (from 1 to 5 mm), as a result of intensive division of its cells, all other zones and tissues of the root are formed; protected from damage root cap - a constantly renewed formation at the apex of a growing root - represented by a special parenchymal tissue that protects the apical meristem from friction with soil particles and promotes the advancement of the root due to the secretion of mucus; aquatic plants, as a rule, do not have a root cap (instead, a cap-like formation is formed - root pocket);

–

Rice. 5.3. General view (A) and longitudinal view

cut (diagram B) of a young root:

I – root cap covering the division zone; II – growth zone; III – suction zone; IV – holding area;

1 – root cap, 2 – root apex, 3 – calyptrogen, 4 – root hairs, 5, 6 – lateral roots.

growth zone, or stretching – the cell growth zone (several mm), stretching in the longitudinal direction, pushes the root end deep into the soil; cells of the zone are characterized by high turgor; cell differentiation begins in this zone;

– suction zone(from several mm to several cm) is responsible for the absorption of water and minerals with the help of root hairs - cell outgrowths epiblems(rhizoderms) lifespan of root hairs – 10–20 days;

One plant rye approximately 14 billion root hairs with a total length of more than 10,000 km.

– venue area has well-developed conductive tissue, transmits soil solutions to the overlying parts of the plant; root hairs along with rhizoderm cells die, and integumentary tissue is formed that protects living root tissues; lateral roots appear here (hence the second name of the zone - branching zone); makes up the bulk of the root.

There are no sharp boundaries between root zones.

The place where the root meets the stem is called root collar.

4. Internal (primary and secondary) structure of the root

The outside of the young root endings are covered epiblema(rhizoderma) - a single-layer primary integumentary tissue of the root (formed from dermatogen – outer layer of the apical meristem of the root tip) (Fig. 5.4.). In the absorption zone, epiblema cells form root hairs, and in the transmission zone they slough off quite quickly. Penetration of water and salts into root hairs and further into the cells cortex and central cylinder occurs by osmosis, diffusion and active transport.

P od epiblema located primary cortex (differentiated from peribles – peripheral part of the apical meristem, lying deeper dermatogen).

External cells primary cortex, lying directly under epiblem, are called exodermis. It can be single-layer or multi-layer (2 – 3 layers). In the conduction zone, after desquamation of the epiblema, the exodermis appears outside, can suberize and performs the function of a protective covering tissue.

ABOUT the main mass of the primary crust is mesoderm– formed by parenchyma cells: multilayered, loose, with intercellular spaces. Radial (short-range) transport of water with minerals from the epiblema to the central cylinder passes through it; Here, active synthesis of metabolites takes place and reserve nutrients are deposited.

The innermost layer of the cortex is endoderm, which acts as a barrier - controls the movement of substances from the cortex to the axial cylinder and back (Fig. 5.5.). In the early stages of development endoderm consists of living, thin-walled cells arranged tightly, without intercellular spaces. Later, its cells acquire some characteristic structural features: on the radial walls of the cells endoderm special thickenings appear (as a result of suberinization and lignification) – Casparian belts, with the help of which the movement of solutions along the cell walls is blocked ( apoplastic pathway). As a result, all substances in central cylinder and can penetrate from it only through living protoplasts of endodermal cells ( symplastic pathway) and under their control (selective permeability, protection against the penetration of pathogenic microorganisms). In monocots in cells endoderm further changes may occur: deposits on the inner surface of the primary cell membranes suberin and then the secondary cellulose shell, which becomes lignified over time, thus blocking the second route of movement of substances - symplastic(through the cytoplasm of cells). On some cells this does not happen and they remain only with Casparian belts, these are the so-called access cells - at monocots, only through them is the physiological connection between the primary cortex and the axial cylinder realized. Pass cells V endoderm small, and its diameter is much smaller than the outer diameter of the root in the area epiblems, so around endoderm an increased amount of water is formed compared to other tissues. As a result, water penetrates through access cells into vessels xylem with a certain pressure, which is called root pressure(Fig. 5.6.) .

Rice. 5.6. Diagram of water movement in the root.

Central (axial) cylinder(formed from pleroma – inner part of the apical meristem) begins to differentiate in the growth zone, close to the division zone. Its outer layer is pericycle It is a single-layer educational tissue consisting of living parenchyma cells. IN pericycle lateral roots are laid, and in some plants the rudiments of adventitious buds appear. In dicotyledonous plants, it participates in secondary thickening of the root, partly forming the cambium and phellogen.

The central part of the cylinder is occupied by fibrovascular bundle, consisting of primary xylem And primary phloem(conductive tissues are formed from procambia, which is laid under pericycle). Elements phloem And xylem are laid in a circle, alternating with each other, and develop centripetally (towards the center of the root), however xylem grows faster and occupies the center of the root - the formed structure of conductive tissue is called radial conductive beam.

The pith is not typical for a root, but sometimes (for example, in corn) is noticeable in the center as a small area of ​​mechanical tissue or thin-walled cells arising from the procambium.

This primary the structure of the root is preserved until the end of life horsetails, mosses, ferns And monocots, and for the rest - only in the suction zone.

Gymnosperms and dicotyledonous plants are characterized by secondary changes in the structure of the root, ensuring its growth in thickness. Secondary changes occur due to secondary meristems – cambium And phellogen(Fig. 5.7.) .

IN beginning cambium appears from the parenchyma cells of the central cylinder (procambium) between the vessels of the primary xylem and primary phloem (from the inside). Sites cambium gradually grow, go around the phloem and come into contact with the pericycle. Cells cambium of procambial origin divide and differentiate: deposited towards the center secondary xylem, to the outside - secondary phloem. In places where blood vessels primary xylem come into contact with pericycle, the cells of the latter also turn into cambium(pericyclic origin), but it is differentiated only in parenchyma, which forms radial rays opposite the primary xylem. A cambial ring is formed.

Due to the rapid growth of secondary tissues from within, causing a strong thickening of the root, the primary cortex is often torn.

Pericycle also becomes meristematically active: it divides and deposits the cork cambium in a centrifugal direction - phellogen. Phellogen divides and puts aside traffic jam(phellema) - secondary integumentary tissue of the root. Cork isolates primary cortex from conducting tissues, it loses connection with living cells central cylinder, dies and sloughs off. Inside phellogen postpones phelloderma, which then turns into parenchymal tissue and forms, together with pericycle the secondary crust. On the outside, the roots of dicotyledonous plants, which have a secondary structure, are covered periderma. Crust It is rarely formed, only on old tree roots.

Perennial roots of woody plants often become very thick as a result of prolonged cambial activity. Secondary xylem in such roots it merges into a solid cylinder, surrounded on the outside by a ring of cambium and a continuous ring of secondary phloem.

Thus, the stages of root transition from primary buildings to secondary the following:

1. Appearance cambium between the xylem and phloem rays and the formation of the cambial ring;

2. Education phellogen pericycle, emergence of the secondary cortex;

3. Reset primary cortex;

4. Change radial arrangement of xylem and phloem tissues collateral.

Introduction

The root is of great interest in terms of study. The fact is that plant roots, in comparison with shoots, exist in a more inert, less plastic environment - in the soil, and therefore have a simpler structure; while the escape develops in an unstable, dynamic air environment.

On the other hand, we know much less about the structure and functions of the root and its various modifications than about the stem and leaf, and this is primarily due to the technical difficulties that arise when studying underground organs.

A typical root is an underground organ common to all higher plants (except mosses). The root serves to anchor the plant in the soil, absorb water from the soil with salts dissolved in it, reserve products are often deposited in the root, the root participates in the synthesis of organic substances, and serves for vegetative propagation. The root never bears leaves, so compared to the internal structure of the stem at the root, it is relatively simple.

The topic of our work is interesting and relevant. The purpose of the work is to study the importance of roots in plant life. To achieve this goal, it is necessary to solve a number of problems:

Study the structure of the root.

Consider the main metamorphoses of roots.

Determine the functions of the root.

Draw conclusions on the topic of the work.

Place of the root in the plant organ system

The basic plan of the plant body structure in morphology has been interpreted in different ways. Previously, it was accepted that the body of a plant consists of several “main parts” or organs: root, stem, leaf, flower, ovules, hairs. Later, the number of these main organs was reduced to three (the so-called “iron triad” of organs (by the way, it was included in all school textbooks): root, stem and leaf.

Currently, the stem and its accessory organs are considered as a single whole - a shoot.

The question of the evolutionary origin of plant organs has been resolved for a long time. Some scientists considered the stem to be primary for above-ground organs, others - the leaf. And only the discovery of psilophytes made it possible to state quite unambiguously that plants have two main vegetative organs: the root and the shoot.

Rice. 1.

Root structure

The root is an axial, underground vegetative organ of higher plants, possessing unlimited growth in length and positive geotropism. The root has no leaves or chloroplasts.

In addition to the main root, many plants have numerous adventitious roots. The totality of all the roots of a plant is called the root system. In the case when the main root is slightly expressed, and the adventitious roots are significantly expressed, the root system is called fibrous. If the main root is significantly expressed, the root system is called tap root.

The collection of roots of one plant is called the root system.

Root systems include roots of various natures. There are main roots, lateral roots and subordinate roots. The main root develops from the embryonic root. Lateral roots occur on any root as a side branch. Adventitious roots are formed by the shoot and its parts.

In the taproot system, the main root is highly developed and clearly visible among other roots (characteristic of dicotyledons). In the fibrous root system, at the early stages of development, the main root, formed by the embryonic root, dies, and the root system is composed of adventitious roots (typical of monocots). The tap root system usually penetrates deeper into the soil than the fibrous root system, but the fibrous root system weaves better around adjacent soil particles. Especially in its upper fertile layer.

Different parts of the root perform different functions and differ in appearance. These parts are called zones.

The outside tip of the root is always covered with a root cap, which protects the delicate cells of the meristem. The cap consists of living cells that are constantly renewed. The cells of the root cap secrete mucus, which covers the surface of the young root. Thanks to mucus, friction with the soil is reduced; its particles easily stick to the root ends and root hairs. In rare cases, the roots lack a root cap (aquatic plants). Under the cap there is a division zone, represented by educational tissue - the meristem.

The cells of the division zone are thin-walled and filled with cytoplasm; there are no vacuoles. The division zone can be distinguished on a living root by its yellowish color; its length is about 1 mm. Following the division zone is a stretch zone. It is also small in length, only a few millimeters, stands out with a light color and is seemingly transparent. The cells of the growth zone no longer divide, but are able to stretch in the longitudinal direction, pushing the root end deeper into the soil. Within the growth zone, cells are divided into tissues.

The end of the growth zone is clearly visible by the appearance of numerous root hairs. Root hairs are located in the suction zone, the function of which is clear from its name. Its length ranges from several millimeters to several centimeters. Unlike the growth zone, sections of this zone no longer shift relative to the soil particles. Young roots absorb the bulk of water and nutrients using root hairs.

Root hairs appear in the form of small papillae - cell outgrowths. After a certain time, the root hair dies off. Its lifespan does not exceed 10-20 days.

Above the absorption zone, where the root hairs disappear, the conduction zone begins. Through this part of the root, water and solutions of mineral salts absorbed by root hairs are transported to the higher lying parts of the plant.

In the growth zone, cells begin to differentiate into tissues, and in the absorption and conduction zone, conductive tissues are formed, ensuring the rise of nutrient solutions to the above-ground part of the plant.

Already at the very beginning of the root growth zone, the mass of cells differentiates into three zones: rhizoderm, cortex and axial cylinder.

Rhizoderm is the integumentary tissue that covers the outside of young root endings. It contains root hairs and is involved in absorption processes. In the absorption zone, the rhizoderm passively or actively absorbs elements of mineral nutrition, expending energy in the latter case. In this regard, rhizoderm cells are rich in mitochondria.

The cortex is formed by parenchyma, usually differentiated at the level of the stretch zone. It is loose and has a system of intercellular spaces through which gases necessary for respiration and maintaining metabolism circulate along the root axis. In marsh and aquatic plants, the intercellular spaces of the bark are especially extensive. The cortex is that part of the root through which radial (short-range) transport of water and dissolved salts from the rhizoderm to the axial cylinder actively passes. In the tissues of the cortex, active synthesis of metabolites occurs and reserve nutrients are deposited.

The axial cylinder is a complex complex of conductive, educational and basic tissues.

Primary structure of the root. It is characteristic of young roots of all plants. In mosses, horsetails, ferns and monocots, it persists throughout life. The primary structure arises as a result of differentiation of the growth cone meristem. On a cross section of the root in the absorption zone, three parts can be distinguished: the epiblema, the primary cortex and the central axial cylinder (stele).

Epiblema (rhizoderm), or peel – primary covering tissue of the root. It consists of one row of tightly closed cells with outgrowths - root hairs.

Primary cortex consists of living thin-walled cells in the peripheral part of the root. It is represented by three clearly distinct layers: exoderm, mesoderm and endoderm.

Exodermis located directly under the epiblema, being the outer part of the primary cortex. Its cells are polygonal, tightly closed, arranged in one or several rows. As the root hairs die, the exodermis appears on the surface of the root and acts as a covering tissue, while the cell membranes thicken and suberize and the cell contents die.

Mesoderm, or main parenchyma, is located outside the endoderm. It consists of loosely arranged cells with a system of intercellular spaces through which intense gas exchange occurs. Here the synthesis and movement of plastic substances into other tissues occurs, nutrients accumulate, and mycorrhiza is located.

Endoderm – the innermost layer of bark immediately adjacent to the stele. In dicotyledonous plants it consists of one row of cells with thickenings on the radial walls - Casparian belts, impervious to water. In monocotyledonous plants, horseshoe-shaped thickenings of cell walls are formed. The endoderm contains living thin-walled cells called access cells. These cells also have Casparian belts. Endodermal cells control the flow of water and minerals dissolved in it from the cortex to the central cylinder and back.

Central cylinder, or axial cylinder, or stele, occupies the central part of the root. The outer layer of the stele, adjacent to the endodermis, is called pericycle. Its cells retain the ability to divide for a long time. This is where the side roots are laid. In the central part of the axial cylinder there is a vascular-fibrous bundle. The roots are characterized by alternating sections in the stele primary xylem And primary phloem. The xylem forms a star, and between its rays is the phloem. The number of xylem rays varies - from two to several dozen, in dicotyledons - up to five, in monocotyledons - more than five. In the very center of the cylinder there may be elements of xylem, sclerenchyma or thin-walled parenchyma.

Secondary structure of the root. In dicotyledonous and gymnosperm plants, the primary structure of the root is not retained for long. Approximately 10 days after seed germination, changes occur, resulting in a secondary root structure.

The process of secondary changes begins with the appearance of layers of cambium under areas of the primary phloem, inward from it. The cambium arises from the poorly differentiated parenchyma of the central cylinder. He puts elements inside secondary xylem (wood), outward – elements secondary phloem (bast). At first, the cambium layers are separated, then they close together, forming a continuous layer. This occurs due to the division of pericycle cells opposite the xylem rays. The cambial regions arising from the pericycle form only the parenchyma cells of the medullary rays; the remaining cambium cells form the conducting elements - xylem and phloem. When cambium cells divide, the radial symmetry characteristic of the primary structure of the root disappears.

The cork cambium (phellogen) also appears in the pericycle. It lays out layers of cells of secondary integumentary tissue - cork. In this case, the primary cortex dies.

Root systems

Root system – This is the totality of all the roots of a plant. The formation of the root system involves the main root, lateral and adventitious roots. Based on their shape, there are two main types of root systems:

Tap root system(A) has a well-defined main root. It is characteristic of dicotyledonous plants.

Fibrous root system(B) formed by lateral and adventitious roots. The main root grows weakly and stops growing early. It is typical for monocotyledonous plants.

The soil

For normal growth and development of plants, water and nutrients are needed, the source of which is the soil. Soil called the upper root-inhabited, fertile layer of the earth's crust in which the roots of plants are located.

Any soil consists of three main components:

Solid phase – finely crushed simple and complex minerals, organic substances;

Liquid phase – soil solution;

Gaseous phase – soil air.

Solid phase consists of 90% or more minerals and approximately 10% organic matter – humus formed by the remains of plant and animal origin. The amount of humus in the soil determines its fertility. Humus content can be determined by the color of the soil: the more humus in the soil, the darker it is.

Liquid phase is an aqueous solution of various mineral salts, carbon dioxide, mineral and organic acids. It serves as a direct source of nutrients for plants.

Gaseous phase serves as a source of oxygen for root respiration.

The classification of soils is based on the particle size of the solid phase - from coarse gravel (over 2 mm in diameter) to clay (particle diameter less than 0.002 mm). There are rocky, sandy, loamy (50% sand, 25% dust and 25% clay) and podzolic soils. The most favorable for plant growth are chernozems - soils rich in humus. Its moisture and air capacity depends on the mechanical composition of the soil.
In addition to humus, the soil contains a large number of bacteria and fungi that take part in the decomposition of organic residues.

Fertilizers
To improve plant growth, minerals and organic compounds - fertilizers - are added to the soil. Fertilizer are organic or mineral substances used to improve the nutritional conditions of plants.
Fertilizers are divided into two groups:

organic(manure, peat, slurry, bird droppings, feces, composts, green manure);

mineral- nitrogen, phosphorus, potassium and other industrial fertilizers, and their local fertilizers - ash.

Mineral fertilizers. Industrial fertilizers, depending on the content of basic nutrients, are divided into:

simple, or unilateral- fertilizers containing only one of the three most important nutrients (N, P or K) - nitrogen, phosphorus, potassium;

complex, or combined- fertilizers containing two or three elements: nitrogen-potassium, nitrogen-phosphorus, nitrogen-phosphorus-potassium (nitrophoska).
The most important fertilizers include:

nitrogen- ammonium nitrate, urea (synthetic urea), ammonium sulfate, ammonium chloride, sodium nitrate, calcium nitrate (increase the growth of stems and leaves);

phosphorus- simple superphosphate, double superphosphate, phosphate rock, bone meal (prolong flowering, accelerate fruit ripening);

potassium: potassium chloride, potassium sulfate, potassium carbonate, potassium sulfate (enhance the growth of roots, bulbs, tubers);

complex fertilizers: sulfate nitrophoska, sulphate nitrophoska, nitroammophoska (N, P, K), ammophos, diammophos (N, P), potassium polyphosphate, potassium metaphosphate (P, K).

In addition to N, P, K, which plants require in significant quantities, plants also need some other elements, such as boron, manganese, copper, molybdenum, zinc and others. These elements are not required by all crops and not in all soils in small quantities. They are necessary to obtain high yields. Such elements are called microelements, and fertilizers containing them are called microfertilizers. Microfertilizers can be industrial waste or specially produced compounds.

Organic fertilizers. The advantage of organic fertilizers is, first of all, their complexity. They combine both mineral salts and organic substances, which during decomposition form not only mineral compounds, but also a lot of carbon dioxide, that is, they improve both root and air nutrition of plants.
One of the main organic fertilizers is manure - livestock waste, consisting of animal excretions and litter. Organic matter in manure becomes available to plants only after mineralization. This process proceeds slowly, so over several years the plants are provided with the substances they need.
Together with manure, not only countless microbes are introduced into the soil, but also an important source of their food, which enhances the energy of biological processes in it.
The use of manure simultaneously improves root and aerial nutrition of crops. But that is not all. Organic matter from manure helps increase the humus content in the soil.

Application of fertilizers. The highest yield increases are obtained with the right combination of organic and mineral fertilizers, since they complement each other in a number of respects.
The benefits of joint use or combination of organic and mineral fertilizers are that:

• organic fertilizers act slowly, mineral fertilizers quickly; better nutritional conditions are created for plants when both groups of fertilizers are applied;
• organic substances absorb excess mineral fertilizers and then gradually release them;
• organic fertilizers deliver food to beneficial microbes, which convert it into the salts plants need;
• organic fertilizers improve the structure and properties of the soil.

The effect of fertilizers on plants depends not only on their type, composition, solubility, but also on the method of application to the soil. There are three ways to apply fertilizers:

· Basic fertilizer applied before plowing and incorporated into the soil (manure, peat and at least two-thirds of mineral fertilizers intended for the crop). The plant's main fertilizer is used for nutrition during most of the growing season.

· Pre-sowing fertilizer applied in small quantities when sowing seeds, planting tubers, roots, seedlings. It supplies plants with readily available food at the beginning of growth, when the root system is still underdeveloped. Therefore, substances that are easily soluble in water and quickly absorbed by plants are used as pre-sowing fertilizer.

· Top dressing- application of easily digestible fertilizers in dry or dissolved form during plant growth. When feeding, the substances that are most necessary for the plant at a given period of its life are usually added.
To apply fertilizers correctly, you need to know the composition of the soil and the nutrient requirements of a particular plant type.

Physiology of the root

Root growth. The root has unlimited growth. It grows from the apex, on which the apical meristem is located.
Take 3-4 day old bean seedlings, apply thin marks on the developing root with ink at a distance of 1 mm from each other and place them in a humid chamber. After a few days, you can find that the distance between the marks at the root tip has increased, while in higher areas of the root it does not change. This experience proves the apical growth of the root (Fig. 2).
This fact is used in human practice. When transplanting seedlings of cultivated plants, picking- removal of the root tip. This leads to the cessation of growth of the main root and causes increased development of lateral roots (Fig. 3). As a result, the suction area of ​​the root system increases significantly; all roots are located in the upper most fertile layers of the soil, which leads to an increase in plant productivity.

Root absorption and transport of water and minerals. Absorption of water and minerals from the soil and movement to ground organs is one of the most important functions of the root. This function arose in plants in connection with their access to land. The structure of the root is adapted to absorb water and nutrients from the soil. Water enters the plant body through the rhizoderm, the surface of which is greatly increased due to the presence of root hairs. In this root zone, the root conducting system, the xylem, is formed, which is necessary to ensure the upward flow of water and minerals.

Absorption of water and minerals.

The absorption of water and minerals by the plant occurs independently of each other, since these processes are based on different mechanisms of action. Water passes into the root cells passively, and minerals enter the root cells mainly as a result of active transport, which involves energy expenditure.
Water enters the plant mainly according to the law osmosis. Root hairs have a huge vacuole with a large osmotic potential, which ensures the flow of water from the soil solution into the root hair.

Horizontal transport of substances.

The absorption of minerals is also facilitated by the release of various organic acids by the roots, which convert inorganic compounds into a form accessible for absorption by the roots.
In the root, the transverse movement of water and minerals occurs in the following order: root hair, cortical parenchyma cells, endodermis, pericycle, parenchyma of the axial cylinder, root vessels. Horizontal transport of water and minerals occurs along three routes (Fig. 4):

In the root, water moves through the apoplast to the endodermis. Here, its further advancement is hampered by waterproof cell walls impregnated with suberin (Caspari's belts). Therefore, water enters the stele along the symplast through passage cells (water passes through the plasma membrane under the control of the cytoplasm of passage cells of the endodermis). Thanks to this, the movement of water and minerals from the soil into the xylem is regulated. In the stele, water no longer encounters resistance and enters the conducting elements of the xylem.

Vertical transport of substances.

Roots not only absorb water and minerals from the soil, but also supply them to above-ground organs. Vertical movement of water occurs along dead cells that are unable to push water to the leaves. Vertical transport of water and solutes is ensured by the activity of the roots and leaves themselves. The root is a lower end motor that supplies water to the vessels of the stem under pressure called root. Under root pressure understand the force with which the root pumps water into the stem. Root pressure arises mainly as a result of an increase in osmotic pressure in the root vessels above the osmotic pressure of the soil solution. It is a consequence of the active release of mineral and organic substances into the vessels by root cells. The value of root pressure is usually 1-3 atm.
Proof of the presence of root pressure is “plant crying” and guttation.
“Plant crying” is the release of liquid from a cut stem. This liquid is called pasokoy.
Guttation - This is the release of water from an intact plant through the tips of its leaves when it is in a humid atmosphere or when it intensively absorbs water and minerals from the soil.
The upper end motor provides vertical water transport - the suction force of the leaves. It arises as a result transpiration- evaporation of water from the surface of leaves. The continuous evaporation of water creates the opportunity for a new influx of water to the leaves. The sucking force of tree leaves can reach 15-20 atm.
In xylem vessels, water moves in the form of continuous water filaments. As they move upward, the water molecules stick together (cohesion), which causes them to move one after another. In addition, water molecules are able to stick to the walls of blood vessels (adhesion). Thus, the rise of water throughout the plant is carried out thanks to the upper and lower motors of water flow and the adhesion forces of water molecules in the vessels. The main driving force is transpiration.

Storage roots. Often the root performs the function of accumulating a supply of nutrients. Such roots are called storage roots. They differ from typical roots in the strong development of storage parenchyma, which can be located in the primary (in monocots) or secondary bark, as well as in the wood or core (in dicots). Among the storage roots, root tubers and root vegetables are distinguished.

• The horizontal dotted line shows the border between the stem and the root; the xylem is indicated in black.
  Root tubers are characteristic of both dicotyledonous and monocotyledonous plants, and are formed as a result of modification of lateral or adventitious roots (chistyak, orchis, lyubka). Due to limited growth in length, they can have an oval, spindle-shaped shape and do not branch. In most species of dicotyledons and monocotyledons, the tuber is only part of the root, and throughout the rest of the length the root has a typical structure and branches (sweet potato, dahlia, daylily).
• The root crop is formed mainly as a result of thickening of the main root, but the stem also takes part in its formation (Fig. 5).

Root crops are characteristic of many cultivated vegetable, fodder and technical biennial plants, and of wild herbaceous perennial plants (chicory, dandelion, scorzonera, ginseng, oriental poppy).
Most often, root vegetables are formed as a result of secondary thickening of the roots (carrots, parsnips, parsley, celery, turnips, radishes, radishes). In this case, storage tissue can develop both in the xylem and in the phloem. The pericycle can also take part in the thickening of the main root, forming additional cambial rings (in beets).