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

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 roots.

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

Types of root systems

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

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

• the total length of winter rye roots reaches 600 km;
• length of root hairs - 10,000 km;
• the total root surface is 200 m2.

This is many times the area of ​​the aboveground mass.

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

External structure of the root. Internal structure of the root

Root zones

Root cap

The root grows in length from its apex, where the young cells of the educational tissue are located. The growing part is covered with a root cap, which protects the root tip from damage and facilitates the movement of the root in the soil during growth. The latter function is carried out due to the property of the outer walls of the root cap being covered with mucus, which reduces friction between the root and soil particles. They can even push soil particles apart. The cells of the root cap are living and often contain starch grains. The cells of the cap 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 extent of this zone varies in different species and in different roots of the same plant.

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

As linear growth completes, the third stage of root formation begins—its differentiation; a zone of cell differentiation and specialization (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 covering the root. The number of root hairs is very large (per 1 mm2 from 200 to 300 hairs). Their length reaches 10 mm. Hairs form very quickly (in young apple tree 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 roots. The root continuously grows, forming more and more new areas of root hairs. Hairs can not only absorb ready-made solutions of substances, but also contribute to the dissolution of certain soil substances and then absorb them. The area of ​​the root where the root hairs have died is able to absorb water for a while, but then becomes covered with a plug and loses this ability.

The hair shell 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 the gluing of root hairs to soil particles, which improves their contact and increases the hydrophilicity of the system. Absorption is facilitated by the secretion of acids (carbonic, malic, citric) by root hairs, which dissolve mineral salts.

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

Under a microscope, a cross section of the root in the absorption zone shows its structure at the cellular and tissue levels. On the surface of the root there is rhizoderm, under it there is bark. The outer layer of the cortex is the exodermis, inward from it is the main parenchyma. Its thin-walled living cells perform a storage function, conducting nutrient solutions in a radial direction - from the suction tissue to the vessels of the wood. They also contain the synthesis of a number of organic substances vital for the plant. The inner layer of the cortex is the endodermis. Nutrient solutions entering the central cylinder from the cortex through endodermal cells pass only through the protoplast of cells.

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

The root vascular system 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 (through which substances move to the root) and xylem (through which substances move from the root). The main conducting elements of phloem are sieve tubes, xylem is trachea (vessels) and tracheids.

Root life processes

Transport of water in the root

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

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

Absorption of water by roots

Target: find out the basic function of the root.

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

What we see: After a day or two, the water in the container dropped below the mark.

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

You can also do one more experiment 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. We put a rubber tube 3 cm long on the stump, and on the upper end we put a curved glass tube 20-25 cm high.

What we see: 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 water temperature affect the intensity of water absorption by roots?

Target: find out how temperature affects root function.

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

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

Result: this is proof that temperature greatly influences root function.

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

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

Mineral nutrition

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

It has been established that normal plant development is possible only if there are three non-metals in the nutrient solution - nitrogen, phosphorus and sulfur and four metals - potassium, magnesium, calcium and iron. Each of these elements has an individual meaning and cannot be replaced by another. These are macroelements, their concentration in the plant is 10 -2 -10%. For normal plant development, 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 added to the soil.

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

Breathing of roots

For normal growth and development of the plant, fresh air must be supplied to the roots. Let's check if this is true?

Target: Does the root need air?

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

What we see: After some time, the plant in the second vessel will stop growing, wither, and eventually die.

Result: The death of the plant occurs due to a lack of air necessary for the root to breathe.

Root modifications

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

Roots

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

Root tubers

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

Bacterial nodules

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

Stilates

Ramp, which grows in the intertidal zone, develops stilted roots. They hold large leafy shoots on unstable muddy soil high above the water.

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 without reaching the ground and absorb moisture from rain or dew that falls on them.

Retractors

In bulbous and corm plants, such as crocuses, among the numerous thread-like roots there are several thicker, so-called retractor roots. By contracting, such roots pull the corm deeper into the soil.

Columnar

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

Soil as a habitat for roots

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 parent rock, the activity of organisms, the life activity of the plants themselves, and the type of soil.

Soil particles compete with roots for moisture, retaining it on their surface. This is the so-called bound water, which is divided into hygroscopic and film water. It is held in place 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.

An antagonistic relationship develops between moisture and the air phase of the soil. The more large pores there are in the soil, the better the gas regime of these soils, the less moisture the soil retains. The most favorable water-air regime is maintained in structural soils, where water and air exist simultaneously and do not interfere with each other - water fills the capillaries inside the structural units, and air fills the large pores between them.

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

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

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

Water culture method

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

Using the water culture method, it was possible to establish not only the plant’s need for macroelements, but also to clarify the role of various microelements.

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

Hydroponics is the growing of plants in containers filled with gravel. A nutrient solution containing the necessary elements is fed into the vessels from below.

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

Test on the topic: “Root”

Option 1

Exercise 1.

1. Dandelion has a tap root system.
2. The main root develops from the radicle of the embryo.
3. The dark color of the soil depends on the presence of humus in it.
4. Adventitious roots are formed not only on the stems, but also on the leaves of some plants.
5. The root cap covers the entire growth zone.

Task 2. Complete the sentences.

1. Through the root, the plant receives from the soil... and....
2. If the main root does not develop or does not differ from numerous other roots, then the root system is called....
3. Soil differs from rocks in the presence of... .
4. The root grows in length... .
5. Under the cover there is... .

Task 3.

1. Water and mineral salts enter the plant from the soil:

a) through the roots;
b) through the roots and the lower part of the stem;
c) through the roots and other organs of the plant in contact with the soil.

2. Lateral roots develop:

a) only on the main root;

c) both on the main and adventitious roots.

3. The main root develops:

a) in annual plants;
b) in biennials and perennials;
c) in dicotyledonous plants grown from seeds.

4. Cell division zone:

a) small, loosely located;
b) small, tightly adjacent to each other;
c) large, round.

5. As a result of thickening of the lateral and adventitious roots, the following develop:

a) tubers;
b) root “cones” or root tubers;
c) lateral and adventitious roots do not grow.

Task 4. Explain the terms.

1. Root.
2. Lobed root system.
3. Division zone.
4. Rhizoderm.
5. Superphosphate.

Option 2

Exercise 1. Decide whether a statement is true or false. Write down the numbers of the correct statements.

1. Wheat has a fibrous root system.
2. Onions and tulips have a clearly visible main root.
3. Humus is dead and rotting roots, plant leaves, dead insects, and microorganisms.
4. All that a plant has in the soil are its roots.
5. The cells of the root cap are short-lived: some are destroyed, while others are formed.

Task 2. Complete the sentences.

1. All the roots of a plant make it up... .
2. On the main root and adventitious roots... develop.
3. During respiration, root cells absorb... and release....
4. Long, dead, hollow cells with thick membranes without transverse partitions are called....
5. The flow of water from the root to the stem is facilitated by....

Task 3. From the information provided for each question, select those letter designations after which the correct answers are given.

1. Most monocotyledonous plants have a root system:

a) rod;
b) fibrous;
c) mixed.

2. Adventitious roots are formed:

a) only on the main root;
b) only on the lower part of the stem;
c) both on the stem and on the leaves.

3. The main root is clearly visible in the root system:

a) beans;
b) wheat;
c) currants grown from cuttings.

4. It is better to water cultivated plants in gardens and vegetable gardens:

a) in the morning;
b) in the evening;
c) during the day.

a) covering tissue;
b) conductive fabric;
c) mechanical fabric.

Task 4. Explain the terms.

1. Main root.
2. Soil.
3. Suction zone.
4. Root pressure.
5. Root tubers.

Option 3

Exercise 1. Decide whether a given statement is correct or incorrect. Write down the numbers of the correct judgments.

1. The suction zone is located between the growth zone and the conductive zone of the root.
2. Lateral roots develop at the bottom of the stem.
3. The carrot root crop is formed by a main root that has grown in length and thickness.
4. If there were no microorganisms in the soil, then there would be no humus.
5. Root hairs are found throughout the root.

Task 2. Complete the sentences.

1. In the root system of the dandelion it is well expressed... .
2. The root tip is covered... .
3. The root division zone is formed by tissue called....
4. In dahlia and chisyak, some adventitious roots are transformed into... .
5. When a seed germinates, the first thing to appear is... .

Task 3. From the information provided for each question, select those letter designations after which the correct answers are given.

1. Carrots, beets, and turnips develop:

a) all types of roots;
b) only the main root;
c) main and lateral roots.

2. On cuttings of willow and poplar placed in water, the following develop:

a) main roots;
b) lateral roots;
c) adventitious ones, and on them are lateral roots.

3. The root cap can be seen:

a) with the naked eye;
b) using a magnifying glass;
c) only using a microscope.

4. Root hairs live:

a) about a month;
b) several days;
c) about a day.

5. Garden plants need to be watered:

a) rarely and little by little;
b) rarely, but abundantly;
c) often and abundantly.

Task 4. Explain the terms.

1. Adventitious roots.
2. Root cap.
3. Root hair.
4. Fertilizers.
5. Picking.

Option 4

Exercise 1. Decide whether a given statement is true or false. Write down the numbers of the correct judgments.

1. Adventitious roots develop on a poplar cutting placed in water.
2. In soil with a high sand content, water and mineral salts are retained better than in clay soil.
3. Lateral roots, unlike the main one, do not branch.
4. Root hairs are long outgrowths of rhizoderm cells.
5. The entry of water and mineral salts into the root occurs only in the suction zone.

Task 2. Complete the sentences.

1. The root system of a dandelion is called... .
2. The top fertile layer of the earth is called... .
3. Soil has a special property called... .
4. Under the cover there is an area... .
5. Tissue develops in the root area... .

Task 3. From the information provided for each question, select those letter designations after which the correct answers are given.

1. Lateral roots develop:

a) only on the main root;
b) only on adventitious roots;
c) both on the main and adventitious roots.

2. The root grows in length:

a) only the top;
b) a section extending from the stem;
c) the apex and all other areas.

3. Cells of the root cap:

a) alive;
b) dead, with thick shells;
c) along with the living there are also the dead.

4. Root hairs are usually no longer:

a) 10 mm;
b) 20 mm;
c) 30 mm.

5. The strength and elasticity of the root is ensured by:

a) covering tissue;
b) conductive fabric;
c) mechanical fabric.

Task 4. Explain the terms.

1. Tap root system.
2. Growth zone.
3. Venue area.
4. Root vegetables.
5. Feeding.

Answers

Option 1

Exercise 1.

Task 2.

1 – water and mineral salts;
2 – fibrous;
3 – humus (humus);
4 – apex;
5 – division zone.

Task 3.

1–a; 2–c; 3–c; 4–b; 5 B.

Task 4.

1 – axial vegetative organ of the plant, which has unlimited growth, positive geotropism, and serves to hold plants in the soil;
2 – root system, consisting of adventitious and lateral roots;
3 – zone located between the root cap and the growth zone, consisting of dividing cells;
4 – covering tissue in the suction zone;
5 – mineral fertilizer containing phosphorus.

Option 2

Exercise 1.

Task 2.

1 – root system;
2 – lateral roots;
3 – oxygen, carbon dioxide;
4 – vessels;
5 – root pressure.

Task 3.

1– b; 2– in; Behind; 4– b; 5th century

Task 4.

1 – root developing from the radicle of the embryo;
2 – top fertile layer of soil;
3 – zone located between the growth zone and the conduction zone;
4 – pressure, due to which water and mineral salts rise up the stem;
5 – overgrown lateral or adventitious roots.

Option 3

Exercise 1.

Task 2.

1 – main root;
2 – root cap;
3 – meristematic (educational);
4 – root tubers;
5 – embryonic root (main root).

Task 3.

1–b; 2–c; 3–a; 4–a; 5 B.

Task 4.

1 – roots growing from stems or leaves;
2 – a cap of cells that protects the division zone;
3 – long outgrowth of the outer root cell in the suction zone;
4 – substances that increase soil fertility;
5 – pinching off the root tip when planting young plants.

Option 4

Exercise 1.

Task 2.

1 – rod;
2 – soil;
3 – fertility;
4 – divisions;
5 – conductive.

Task 3.

1–c; 2–a; 3–c; 4–a; 5–c.

Task 4.

1 – system formed by main and lateral roots;
2 – the zone in which cells increase in size is located between the division zone and the absorption zone;
3 – the zone in which the vessels and sieve tubes are located is located above the suction zone;
4 – overgrown main root;
5 – application of fertilizers during plant growth and development.

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101-01. Are the following statements about plant growth processes true?
1. Dicotyledonous plants grown from cuttings develop a fibrous root system.
2. Adventitious roots grow from the main root of plants.
A) only 1 is correct
B) only 2 is correct
C) both statements are correct
D) both judgments are incorrect

Answer

101-02. Which root is called the main root?
A) highly branched
B) developing from the root of the embryo
B) growing from the stem
D) the longest in the root system

Answer

101-03. What roots are called adventitious?
A) growing from the stem
B) growing from the main root
B) developing from the root of the embryo
D) developing on the main root

Answer

101-04. A cut poplar branch placed in water will develop roots
A) air
B) main
B) lateral
D) subordinate clauses

Answer

101-05. Determine the correct designation of the types of roots.

A) 1 – adventitious root, 2 – lateral root, 3 – main root
B) 1 – main root, 2 – adventitious root, 3 – lateral root
B) 1 – main root, 2 – lateral root, 3 – adventitious root
D) 1 – lateral root, 2 – adventitious root, 3 – main root

Answer

101-06. The main root develops from
A) lateral roots
B) germinal root
B) adventitious root
D) dormant kidneys

Answer

101-07. In which zone of the root are root hairs found?
A) divisions
B) growth
B) suction
D) carrying out

Answer

101-08. The correct sequence of location of root zones upward from the root cap:
A) division > stretching > suction > conduction
B) stretching > division > root hairs > suction
B) carrying out > stretching > dividing > root hairs
D) absorption > conduction > division > growth

Answer

101-09. What characterizes a fibrous root system?
A) the development of numerous adventitious roots
B) the presence of several main roots
B) absence of root hairs
D) development of a conducting zone in the lateral roots

Answer

101-10. In the table below, there is a relationship between the positions in the first and second columns.

Answer

101-11. In the table below, there is a relationship between the positions in the first and second columns.

Answer

101-12. Look at the drawing. What is shown in the picture under number 1?

Answer

101-13. Consider the internal structure of the root. Which letter in the figure indicates the structure through which water moves into the stem?

Answer

101-14. Look at the picture showing the structure of the root. What number on it indicates the division zone?

The totality of all the roots of a plant is called 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 core .

Some plants deposit reserve nutrients in the roots, such formations are called root vegetables .

Encyclopedic YouTube

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  In many plants, the roots perform special functions (aerial roots, sucker roots).

  Origin of the root

  The body of the first plants that came onto land was not yet divided into shoots and roots. It consisted of branches, some of which rose vertically, while others pressed against the soil and absorbed water and nutrients. Despite their primitive structure, these plants were provided with water and nutrients, since they were small in size and lived near water.

  In the course of further evolution, some branches began to go deeper into the soil and gave rise to roots adapted to more advanced soil nutrition. This was accompanied by a profound restructuring of their structure and the appearance of specialized tissues. Root formation was a major evolutionary advance that enabled plants to colonize drier soils and produce large shoots that rose upward toward the light. For example, bryophytes do not have real roots, their vegetative body is small in size - up to 30 cm, and mosses live in damp places. Fern-like plants develop true roots, which leads to an increase in the size of the vegetative body and to the flowering of this group during the Carboniferous period.

  Features of the structure of roots

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

  Root systems include roots of various natures.

  There are:

  • main root,
  • lateral roots,
  • adventitious roots.

  The main root develops from the germinal root. Lateral roots occur on any root as a side branch. Adventitious roots are formed by the shoot and its parts.

  Root parts

  • Root cap, or calyptra. Living thimble from cells that live 5-9 days. The outer cells exfoliate while still alive and secrete abundant mucus, which facilitates the passage of the root between the soil particles. To replace them, from the inside, the apical meristem produces new cells. In the cells of the axial part of the cap, the so-called columella, there are mobile starch grains that have the properties of crystals. They play the role of statoliths and determine the geotropic bends of the roots.
  • Division zone. About 1 mm, covered from the outside with a cover. It is darker or yellowish in color, consists of small multifaceted, constantly dividing cells with dense cytoplasm and a large nucleus. The division zone includes the root apex with its initials and their derivatives.
  • Growth zone, or stretch zone. It is several millimeters, lighter, more transparent. Cells, until their cell walls become rigid, stretch in length when water is absorbed. This stretch pushes the root tip further into the soil.
  • Suction zone, or zone of absorption and differentiation. Up to several centimeters. It stands out well due to the development of rhizoderm, surface tissue, some of the cells of which give rise to long thin outgrowths - root hairs. They absorb soil solutions within a few days, and new hairs form below them.
  • Venue area. The old rhizoderm dies and sloughs off. At the same time, the root thins out a little and becomes covered with an outer layer of the primary cortex - exodermis, which performs the function of integumentary tissue. The transition from one zone to another is gradual and conditional.

  Young root ending zones

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

  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: it is only a few millimeters, stands out in light color and is, as it were, transparent. The cells of the elongation zone no longer divide, but are capable of stretching 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 elongation 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 with the help of root hairs - outgrowths of surface tissue cells. They increase the absorption surface of the root and release metabolic products; located just above the root cap. Together they create the impression of white fluff around the root. In a plant that has just been removed from the soil, you can always see lumps of soil stuck to the root hairs. They contain a layer of protoplasm, a nucleus, and a large vacuole; their thin shells, easily permeable to water, stick tightly to lumps of soil. Root hairs release various substances into the soil. The length varies among different plant species from 0.06 to 10 mm. As soil moisture increases, formation slows down; They do not form in very dry soil. 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 overlying parts of the plant.

  Anatomical structure of the root

  In the growth zone, cells begin to differentiate into tissues, and conductive tissues are formed in the absorption and conduction zone, 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.

  Root modifications:

  • Root vegetable- thickened main root. The main root and the lower part of the stem are involved in the formation of the root crop. Most root plants are biennial. Root vegetables consist mainly of storage tissue (turnips, carrots, parsley).
  • Pip(root cones) are formed as a result of thickening of the lateral and adventitious roots. With their help, the plant blooms faster.
  • Roots-holds- peculiar adventitious roots. With the help of these roots, the plant “glues” to any support.
  • Stilt roots- adventitious roots extending from the trunk at an angle, which, having reached the soil, grow into it. Sometimes, over time, the bases of the trunks rot and the trees stand only on these roots, as if on stilts. Act as a support. The stilted roots of mangrove trees serve not only for support, but also for additional air supply.
  • Board-shaped roots They are lateral roots passing near or above the soil surface, forming triangular vertical outgrowths adjacent to the trunk. Characteristic of large trees of the tropical rain forest.
  • Aerial roots, or Breathing roots- perform the function of additional respiration, grow in the aerial part. Absorb rainwater and oxygen from the air. They are formed in many tropical plants, especially in mangrove plants, under conditions of a lack of mineral salts in the soil of the tropical forest. They are also found in plants of the temperate zone. They can have a variety of shapes: serpentine, cranked, asparagus-shaped (pneumatophores growing vertically upward). The main way gases move in respiratory roots is diffusion through the lentils and aerenchyma. In mangroves, it also helps to increase water pressure at high tide, at which the roots are compressed and some of the air is squeezed out, and to decrease water pressure at low tide, at which air is sucked into the roots. This can be compared to inhalation and exhalation in vertebrates.
  • Mycorrhiza- cohabitation of the roots of higher plants with fungal hyphae. With such mutually beneficial cohabitation, called symbiosis, the plant receives water with nutrients dissolved in it from the fungus, and the fungus receives organic substances. Mycorrhiza is characteristic of the roots of many higher plants, especially woody ones. Fungal hyphae, entwining thick lignified roots of trees and shrubs, perform the functions of root hairs.
  • Bacterial nodules on the roots of higher plants- cohabitation of higher plants with nitrogen-fixing bacteria - they are modified lateral roots adapted to symbiosis with bacteria. Bacteria penetrate through the root hairs into young roots and cause them to form nodules. With such symbiotic cohabitation, bacteria convert nitrogen contained in the air into a mineral form available to plants. And plants, in turn, provide bacteria with a special habitat in which there is no competition with other types of soil bacteria. Bacteria also use substances found in the roots of higher plants. More often than others, bacterial nodules form on the roots of plants of the legume family. Due to this feature, legume seeds are rich in protein, and members of the family are widely used in crop rotation to enrich the soil with nitrogen.
  • Support roots (columnar roots)- adventitious roots of some tropical plants, growing on trunks and branches and reaching the ground.

  see also

  • Cornoplasty - a type of decorative and applied art

  Notes

  1. // Small Encyclopedic Dictionary of Brockhaus and Efron: in 4 volumes - St. Petersburg. , 1907-1909.
  2. Pneumatophores // Great Soviet encyclopedia: [in 30 volumes] / ch. ed. A. M. Prokhorov. - 3rd ed. - M.: Soviet Encyclopedia, 1969-1978.
  3. Mangroves // Geography: Modern illustrated encyclopedia / Ch. ed.