Do all plants have roots. Plants. Root system types

The root is one of the main organs of the plant. It performs the function of absorption from the soil with mineral nutrients dissolved in it. The root anchors and holds the plant in the soil. In addition, the roots have metabolic significance. As a result of primary synthesis, amino acids, hormones, etc. are formed in them, which are quickly included in the subsequent biosynthesis that occurs in the stem and leaves of the plant. The roots can store spare nutrients.

The root is an axial organ with a radially symmetrical anatomical structure. The root grows indefinitely in length due to the activity of the apical meristem, the delicate cells of which are almost always covered by a root cap. In contrast to the shoot, the root is characterized by the absence of leaves and, due to this, dissection into nodes and internodes, as well as the presence of a cap. The entire growing part of the root does not exceed 1 cm.

The root cap, about 1 mm long, consists of loose, thin-walled cells, which are constantly replaced by new ones. At a growing root, the cap is almost renewed every day. The exfoliating cells form mucus, which facilitates the movement of the root tip into the soil. The functions of the root cap are to protect the growing point and provide the roots with positive geotropism, which is especially pronounced at the main root.

Adjacent to the cap is a division zone about 1 mm in size, composed of meristem cells. The meristem in the process of mitotic divisions forms a mass of cells, providing root growth and replenishing the cells of the root cap.

The division zone is followed by a stretch zone. Here, the length of the root increases as a result of cell growth and their acquisition of normal shape and size. The stretch zone is several millimeters long.

Behind the stretch zone is the suction, or absorption zone. In this zone, the cells of the primary integumentary root - epiblems - form numerous root hairs that suck in the soil solution of mineral substances. The absorption zone is several centimeters long, it is here that the roots absorb the bulk of water and salts dissolved in it. This zone, like the two previous ones, gradually moves, changing its place in the soil with the growth of the root. Root hairs die as the root grows, the absorption zone appears on the newly growing root area, and the absorption of nutrients occurs from the new volume of soil. In place of the former absorption zone, a conduction zone is formed.

Primary root structure

The primary structure of the root arises from the differentiation of the apex meristem. In the primary structure of the root, near its tip, three layers are distinguished: the outer layer is the epibleme, the middle layer is the primary cortex, and the central axial cylinder is the stele.

Internal tissues naturally and in a certain sequence arise in the division zone in the apical meristem. There is a clear division into two sections. The outer section, originating from the middle layer of the initial cells, is called the Periblem. The inner section comes from the upper layer of the initial cells and is called the pleroma.

The pleroma gives rise to the stele, while some cells turn into vessels and tracheids, others - into sieve tubes, others - into core cells, etc. Periblemal cells turn into the primary root cortex, consisting of parenchymal cells of the main tissue.

From the outer layer of cells - dermatogen - on the surface of the root, the primary integumentary tissue is isolated - epiblema, or rhizoderm. It is a single layer fabric reaching full development in the absorption zone. The formed rhizoderm forms the thinnest numerous outgrowths - root hairs. The root hair is short-lived and only in its growing state actively absorbs water and substances dissolved in it. Hair formation increases the total surface of the suction zone by 10 or more times. Hair length no more than 1 mm. Its shell is very thin and consists of cellulose and pectin substances.

The primary cortex arising from the periblema consists of living thin-walled parenchymal cells and is represented by three distinct layers: endoderm, mesoderm, and exoderm.

The inner layer of the primary cortex, the endoderm, is adjacent to the central cylinder (stele). It consists of a single row of cells with thickenings on the radial walls, the so-called Caspari bands, which are interspersed with thin-walled cells - passage cells. The endoderm controls the flow of substances from the cortex to the central cylinder and vice versa.

Outside the endoderm is the mesoderm - the middle layer of the primary cortex. It consists of loosely located cells with a system of intercellular spaces through which intensive gas exchange takes place. In the mesoderm, the synthesis and movement of plastic substances into other tissues occurs, reserve substances accumulate, and mycorrhiza is located.

The outer part of the primary cortex is called exoderm. It is located directly under the rhizoderm, and as the root hairs die off, it appears on the root surface. In this case, the exoderm can perform the function of the integumentary tissue: there is a thickening and corking of the cell membranes and the death of the cell contents. Among the corked cells, there are non-corked cells through which substances pass.

The outer layer of the stele, adjacent to the endoderm, is called the pericycle. Its cells retain the ability to divide for a long time. In this layer, the lateral roots are laid, therefore the pericycle is called the corneous layer.

The roots are characterized by the alternation of xylem and phloem sections in the stele. Xylem forms a star (with a different number of rays for different plant groups), and phloem is located between its rays. In the very center of the root, there may be xylem, sclerenchyma, or thin-walled parenchyma. The alternation of xylem and phloem along the periphery of the stele is a characteristic feature of the root, which sharply distinguishes it from the stem.

The primary structure of the root described above is characteristic of young roots in all groups of higher plants. In lymphoids, horsetails, ferns and representatives of the class of Monocotyledonous division of Flowering plants, the primary structure of the root is preserved throughout its life.

Secondary root structure

In the roots of gymnosperms and dicotyledonous angiosperms, the primary structure of the root is retained only until the beginning of its thickening as a result of the activity of the secondary lateral meristems - cambium and phellogen (cork cambium). The process of secondary changes begins with the appearance of layers of cambium under the areas of the primary phloem, inward from it. Cambium arises from the poorly differentiated parenchyma of the central cylinder. Inside, it lays down elements of secondary xylem (wood), outside - elements of secondary phloem (bast). At first, the cambium interlayers are separated, but then they close and form a continuous layer. This is due to the division of pericycle cells against the xylem rays. The cambial areas arising from the pericycle are formed only by the parenchymal cells of the medullary rays, the remaining cambial cells form the conducting elements - xylem and phloem. This process can take a long time, and the roots reach a considerable thickness. In the perennial root, in its central part, there remains a clearly pronounced radial primary xylem.

A cork cambium (phellogen) also appears in the pericycle. It lays out the layers of cells of the secondary integumentary tissue - cork. The primary cortex (endoderm, mesoderm, and exoderm), isolated by the cork layer from the inner living tissues, dies off.

Root systems

The collection of all the roots of a plant is called the root system. Its addition involves the main root, lateral and adventitious roots.

The root system is pivotal or fibrous. The core root system is characterized by the predominant development of the main root in length and thickness, and it stands out well from other roots. In the tap root system, in addition to the main and lateral roots, adventitious roots can also arise. Most dicotyledonous plants have a tap root system.

In all monocotyledonous plants and in some dicotyledons, especially those that reproduce vegetatively, the main root dies off early or develops poorly and the root system is formed from adventitious roots arising at the base of the stem. Such a root system is called fibrous.

For the development of the root system, soil properties are of great importance. The soil affects the structure of the root system, the growth of its roots, the depth of penetration and their spatial distribution in the soil.

The secretions of roots create in the soil around it a zone teeming with bacteria, fungi and other microorganisms, which is called the rhizosphere. The formation of surface, deep and other root systems reflects the adaptation of plants to the conditions of soil water supply.

In addition, any root system is constantly undergoing changes associated with the age of plants, the change of seasons, etc.

Specializations and metamorphoses of roots

In addition to the main functions, the roots can perform some others, while the roots are modified, their metamorphoses.

In nature, the phenomenon of symbiosis of the roots of higher plants with soil fungi is widely spread. The endings of the roots, braided from the surface by fungal hyphae or containing them in the root bark, are called mycorrhiza (literally - "fungal root"). Mycorrhiza is external, or ectotrophic, internal, or endotrophic, and externally.

Ectotrophic mycorrhiza replaces the root hairs of the plant, which usually do not develop. External and external mycorrhiza is noted in woody and shrub plants (for example, in oak, maple, birch, hazel, etc.).

Internal mycorrhiza develops in many species of herbaceous and woody plants (for example, in many types of cereals, onions, walnuts, grapes, etc.). Species of such families as Heather, Grushankovye and Orchidaceae cannot exist without mycorrhiza.

The symbiotic relationship between a fungus and an autotrophic plant is manifested in the following. Autotrophic plants provide the fungal symbiont with soluble carbohydrates available to it. In turn, the fungal symbiont supplies the plant with the most important mineral substances (the nitrogen-fixing fungal symbiont delivers nitrogen compounds to the plant, quickly ferments poorly soluble reserve nutrients, bringing them to glucose, the excess of which increases the absorption activity of the roots.

In addition to mycorrhiza (mycosymbiotrophy), in nature, there is a symbiosis of roots with bacteria (bacteriosymbiotrophy), which is not as widespread as the first. Sometimes growths form on the roots, called nodules. There are many nodule bacteria inside the nodules, which have the property of fixing atmospheric nitrogen.

Storage roots

Many plants are capable of depositing reserve nutrients in the roots (starch, inulin, sugar, etc.). Modified roots that perform the storage function are called "root crops" (for example, in beets, carrots, etc.) or root cones (strongly thickened adventitious roots of dahlia, chistyak, lyubka, etc.). There are numerous transitions between root crops and root cones.

Retracting, or contractile roots

In some plants, there is a sharp reduction of the root in the longitudinal direction at its base (for example, in bulbous plants). Retracting roots are widespread in angiosperms. These roots determine the tight fit of the rosettes to the ground (for example, in the plantain, dandelion, etc.), the underground position of the root collar and vertical rhizome, and provide some deepening of the tubers. In this way, the retracting roots help the shoots find the best possible burial depth in the soil. In the Arctic, the retracting roots provide the experience of the unfavorable winter period with flowering buds and renewal buds.

Aerial roots

Aerial roots develop in many tropical epiphytes (from the families Orchid, Aronnikov, and Bromeliad). They have aerenchem and can absorb atmospheric moisture. On swampy soils in the tropics, trees develop respiratory roots (pneumatophores), which rise above the soil surface and supply the underground organs with air through a system of holes.

Trees growing along the shores of tropical seas as part of mangroves in the tidal strip develop stilted roots. Due to the strong branching of these roots, the trees remain stable in shaky ground.

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 instance,

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-expressed 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 membrane forms 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 is visible at the cellular and tissue levels. On the surface of the root is the rhizoderm, under it is the bark. The outer layer of the cortex is the exoderm, inwardly from 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 to the central cylinder through the endoderm cells pass only through the protoplast of the cells.

The bark surrounds the central cylinder of the root. It borders on a layer of cells that retain 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 the "sap" is collected, 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 a thin layer of vegetable oil over the water to protect it from evaporation 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 the centers of electrical and radioactive phenomena in plant organisms.

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

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

Roots

If 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 the 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 promotes 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 parent rock, the activity of organisms, on the life of the plants themselves, on 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 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 are at the same time 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 combination 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, has been 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.

With the help of 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 microelements.

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.

What are plants?
Both plants and animals are made up of cells. Cells produce chemicals that depend on growth and functioning. In addition, both plants and animals use gases, water and minerals for their life processes. Both plants and animals go through life cycles during which they originate, grow, reproduce and die. But plants have one, very significant difference: they are not able to move from place to place, since the roots are fixed in one place. They have the ability to carry out a special process called photosynthesis. For this process, plants use the energy of solar radiation, carbon dioxide in the air, as well as water and minerals from the soil - and from all this they generate food for themselves. Animals cannot do this. To obtain the energy necessary for life, they must search for food, eat plants or other animals.
The waste product of photosynthesis is oxygen, a gas that all animals need to breathe. This means that if there were no plant life, then there would be no animal life on Earth either.

What do plants eat?
This is not to say that plants eat - in the literal sense, meaning, for example, the food of animals. Green plants feed themselves through a chemical process known as photosynthesis, which uses energy from sunlight, carbon dioxide, and water to make substances called monosaccharides. Then these monosaccharides are converted into starches, proteins or fats, and these, in turn, provide the plant with the necessary energy for vital processes to take place and plants to grow. The plant food we buy in stores is a mixture of minerals that plants need to grow. These minerals include nitrogen, phosphorus and potassium. As a rule, the plant is able to extract them from the soil on which it grows: it absorbs them through the roots along with water. But farmers, gardeners and everyone who grows plants add minerals in addition to make the plants stronger and stronger.

Do all plants have roots?
The simplest plants have no roots. For example, unicellular green algae float on the surface of the water. Likewise, many algae, which are algae of larger species, float on the surface of the water. The same algae that attach to the seabed do so with special anchoring structures that are not true roots. Seaweed assimilates water and minerals from the sea using all its parts. Similarly, simple plants such as mosses form a dense, low carpet in low places and absorb the necessary moisture directly from their surroundings. Instead of roots, they have filamentous outgrowths (they are called rhizoids), and with the help of these outgrowths they cling to trees or stones. But all plants of more complex forms - ferns, conifers (coniferous plants) and flowering plants - have stems and roots. The stems and roots are an internal distribution system that is able to carry water and minerals from where the plant takes them to wherever they are needed.

Do all plants have leaves?
The simplest plants such as algae have no leaves. Mosses have some kind of leaves in which photosynthesis takes place, but these are not real leaves,
Plants of more complex types have leaves. Leaf shape is often determined by the environmental conditions in which the plants grow. Typically, where there is plenty of sunlight and water, the leaves are wide and flat, forming a large surface on which photosynthesis can take place. However, in places where it is dry and cold, moisture loss can cause serious problems. For example, the elongated, needle-shaped leaves of conifers (including pines) help retain water. Due to this, such plants are able to live in very dry and cold places, far to the north and at high altitudes.

If plants are cut, do they feel it?
Plants do not have a nervous system and do not sense when they are cut. But plants feel the power of attraction, light and touch.

How are seeds obtained?
Conifers (coniferous plants) and flowering trees have seeds.
Conifers - pine, spruce, fir, cypress, have male and female cones. Male cones have pollen sacs that release millions of tiny particles of pollen - male reproductive cells - into the air. The wind carries them to the female cones, which have reproductive cells in the ovules. The ovules are sticky and pollen sticks to them. When the male and female cells meet, fertilization occurs, and seeds are generated in the scales of the female cone. As the seeds grow, the cone grows in size. When the seeds are ripe (which usually takes a couple of years), the bud opens and releases them. The seeds have a hard shell and a certain amount of food inside for use in the initial stage of growth (if the seed gets to a place suitable for growth); in addition, the seeds are equipped with wings that help them fly in the wind. Seed formation in flowering plants is somewhat more complicated. Male cells develop in stamens and "travel", being enclosed in hard pollen grains. Female cells, ovules, develop deep in the ovary of a flower and are enclosed in a pistil. The top of the pistil (called the stigma) is long and sticky, making it a good target for pollen. After the pollen hits the stigma, a small tube grows from the pollen grain. The male cell passes through this tube and reaches the ovule. Fertilization occurs and seeds begin to develop.
Wind, water, insects and other animals help transfer pollen from one flower to another.

How do seeds become plants?
If the seeds simply fall down into the soil under the parent tree, they will have to struggle to survive - for sunlight, water and minerals. This means that in order to start growing, turning into new plants, most seeds need to look for other places, traveling in the wind, on water, or with the help of insects and animals. Some seeds, such as conifers and maples, have wings. Others, like dandelion seeds, are equipped with parachutes made of delicate hairs. And in fact, and in another case, the seeds can, thanks to these features, fly in the wind over long distances; sometimes they land in places suitable for germination. Other seeds are carried by water: thanks to their hard, waterproof shell, coconuts, for example, can swim miles across the sea before they find a shore with suitable conditions for germination. Animals are excellent seed distributors. They carry seeds to different places in the mouth (as a squirrel does, storing supplies for the winter); sometimes the seeds cling to animal fur or feathers.
Some seeds can wait for years for the right moment to germinate, and some never get this opportunity.

Why do the flowers have bright colors?
The reproduction of many flowering plants depends on whether insects and birds carry pollen from one plant to another, and plants can attract specific animals with their bright or aromatic flowers. Nourishing pollen and flower nectar form an important part of the diet of many creatures. When birds and insects come to the flower to eat, pollen sticks to their legs and bodies. Flying in search of food on flowers of other plants of the same species, insects and birds leave some of the pollen in them, and thus cross-pollination occurs. In plants pollinated by the wind, flowers are usually small, inconspicuous, without bright color (and many do not have nectar), since they do not need to attract the attention of insects and birds to spread their pollen.

Why do flowers differ from one another?
What a flower looks like depends a lot on the way it is pollinated. Flowers that are pollinated by the wind are usually small, inconspicuous, without bright colors, since they do not need to attract the attention of insects and birds to spread their pollen. Flowers, however, that depend on pollen-carrying creatures for pollination should attract insects and birds to help cross-pollinate. And these flowers are often tailored - in terms of color, smell or shape - to specific insects or animals. Many flowers that attract bees have special parts that serve as "landing platforms" so that bees arriving to them can rest on such platforms while feeding. Bees can distinguish most colors (except red) and are attracted to bright flowers. Butterflies love many of the colors that attract bees. Butterflies also have elongated mouthpieces, and butterflies also like to "land" when feeding. However, large wings prevent butterflies from diving deep into the flower. Therefore, butterflies prefer flat, wide flowers and those that grow in clusters. Butterflies are attracted to flowers of all kinds of bright colors. But moths, which look like butterflies, are nocturnal, that is, they are active at night. Therefore, the flowers that attract moths are mainly of a light color or white, that is, one that is clearly visible in the dark. And since moths prefer to flutter in the air rather than “land” on a flower, they don't need “landing platforms” on the flowers they fly to.

Why do some flowers smell like perfume?
Flowers have a scent, so they attract those they need for cross-pollination. Some insects and other animals that get their food from flowers have a keen sense of smell. Bees, for example, have sensitive odor detectors in their antennae. Therefore, most flowers pollinated by bees have a smell: Flowers that open only at night often have a strong smell, which helps those who receive their food from them, such as night moths, to find them in the dark. However, not all flowers have a pleasant smell. Some flowers smell like rotting meat or other decaying substances, thus attracting flies to them. Flowers that smell unpleasant (from a human point of view) also attract bats, which need plants for food.

Why are some plants poisonous?
Plants cannot escape from "predators" - animals that will eat them, so some plants have developed other methods of defense. Many plants have poisonous parts. Rhubarb leaves, for example, are very dangerous to eat, although the stems of these plants are quite safe and tasty. Scientists believe that plants often have one venomous part to ward off predators; other parts remain harmless and safe for pollinating animals.

Why do some plants have thorns?
As mentioned above, plants are deprived of the opportunity to escape from hungry animals, so they develop different forms of protection. In some plants, some parts are poisonous, others have thorns and various sharp outgrowths, with the help of which they protect themselves from animals that want to eat them. The thorns hurt animals that try to get close to such plants, and they try to stay away from them.

How can desert plants live without water?
In a real desert, where it never rains, plants cannot live. But in places where cacti and other desert plants grow, it still sometimes rains - even if it happens once every couple of years. When it rains, desert plants quickly absorb water from their roots, storing it in thick leaves and stems. And this accumulated moisture allows them to wait for the next rain.

Are mushrooms plants?
Mushrooms are not actually plants. They do not have true roots, leaves, and stems, and they lack the chlorophyll that plants use to make their own food (which is why they are not green and do not need sunlight). Mushrooms feed mainly on the dead flesh of plants and animals, thus purifying the environment and enriching the soil.

What is the most dangerous mushroom?
The most dangerous mushroom is the pale toadstool. It is often found near birches and oaks. Even a small piece of this mushroom can lead to death, which occurs in 6-15 hours. The poison of many mushrooms is destroyed by boiling, but the poison of the pale toadstool is not destroyed by heat treatment.

How long do trees live?
For a long time, it was believed that the oldest living trees in the world are sequoias, which grow in the central Pacific coast of the United States of America. Some of these trees are almost 4,000 years old. However, a few decades ago, a coniferous tree was discovered that lives even longer: it is a bristlecone pine that grows in the United States of America in the states of Nevada, Arizona and southern California. The oldest of these living trees is 4,600 years old.

Why do some trees drop leaves in autumn?
The loss of leaves prepares such trees for a lack of water in winter: there is little moisture in the cold, dry air, and the snow can only give water after it has melted. In addition, since the soil freezes in winter, it is difficult for the tree to get water from its roots. In spring and summer, gases and moisture escape from the tree through thousands of microscopic stomata in the leaves. Without leaves, a tree can retain maximum water. Also, if the trees did not drop their leaves, then the mass of snow on the leaves of the tree branches most likely would not stand and break.

What are vegetables?
Vegetables are the parts of plants that we eat: roots, stems, leaves. Carrots and potatoes are essentially roots. Asparagus are the stems of plants. Cabbage, spinach, salads are the leaves. In everyday life, we also call many fruits vegetables - zucchini, tomatoes, cucumbers, and so on.

The root in plants has various mechanical and physiological functions. The most important of them are: absorption of water, organic and mineral substances from the soil and their transfer to roots and leaves. In addition, the roots help the plant to gain a foothold in the soil, it is less sensitive to the effects of atmospheric phenomena (strong wind, rain, etc.). They practically grow together with, therefore, quite often, when the plant is pulled out from the tiny hairs, soil particles remain.

With the help of the roots, the plant is connected with the organisms that inhabit the layer (mycorrhiza). This indispensable part of the plant organism helps in the synthesis and accumulates substances useful for plant growth. In addition, the root is responsible for vegetative reproduction - the formation of a new plant, which appears by the decay of tubers or rhizomes in the mother.

But not all plants have the same roots. A fairly common structure is the taproot. Such an underground structure of a plant organism has one large rod, from which a large number of small hairs extend. There is a tuft, in which there are several large rod hairs (for example, many types of herbs). Such plants are extremely useful for the soil, since their dense structure is from erosion.

Everyone knows plants that, as they grow, accumulate many useful substances in the roots. Sweet potatoes are a prime example. In addition, there are plants that do not need soil. So, some types of orchids are on trees, and they receive all the necessary substances and moisture from the air, and, for example, poison ivy is attached to trees with the help of aerial roots.

Core root system

The tap root system is characterized by a developed main root. It has the shape of a rod, and it is because of this similarity that this type got its name. The lateral roots of such plants are extremely weak. The root has the ability to grow indefinitely, and the main root in taproot plants reaches impressive sizes. This is necessary to optimize the extraction of water and nutrients from soils, where groundwater occurs at significant depths. Many species have a core root system - trees, shrubs, as well as herbaceous plants: birch, oak, dandelion, sunflower,.

Fibrous root system

In plants with a fibrous root system, the main root is practically undeveloped. Instead, they are characterized by numerous branching adventitious or lateral roots of approximately the same length. Often, in plants, the main root first grows, from which the lateral roots begin to depart, but in the process of further development of the plant, it dies off. A fibrous root system is characteristic of plants that reproduce vegetatively. It is usually found in - coconut palm, orchids, paparotnikovid, cereals.

Mixed root system

A mixed or combined root system is also often distinguished. Plants belonging to this type have a well-differentiated main root and multiple lateral and adventitious roots. This structure of the root system can be observed, for example, in strawberries and strawberries.

Root modifications

The roots of some plants are so modified that it is difficult at first glance to attribute them to any type. These modifications include root crops - thickening of the main root and lower part of the stem, which can be seen in turnips and carrots, as well as root tubers - thickening of lateral and adventitious roots, which can be observed in sweet potatoes. Also, some roots may not serve for the absorption of water with salts dissolved in it, but for breathing (respiratory roots) or additional support (stilted roots).

The roots fix the plant in the soil, provide soil water and mineral nutrition, sometimes serve as a place for the deposition of reserve nutrients. In the process of adapting to environmental conditions, the roots of some plants acquire additional functions and are modified.

What are the types of roots

In plants, there are main, adventitious and lateral roots. When a seed germinates, an embryonic root first develops from it, which later becomes the main root. Adventitious roots grow on the stems and leaves of some plants. Side roots can also extend from the main and adventitious roots.

Root systems

All the roots of the plant fold into the root system, which is tap and fibrous. In the core system, the main root is more developed than the others and resembles a core, and in the fibrous system it is insufficiently developed or dies off early. The first is most typical for, the second - for monocots. However, the main root is usually well expressed only in young dicotyledonous plants, and in old ones it gradually dies off, giving way to adventitious roots growing from the stem.

How deep are the roots

The depth of the roots in the soil depends on the growing conditions of the plant. Wheat roots, for example, grow on dry fields by 2.5 m, and on irrigated fields - no more than half a meter. However, in the latter case, the root system is more dense.

Tundra plants themselves are undersized, and their roots are concentrated near the surface due to permafrost. In dwarf birch, for example, they are at a maximum depth of about 20 cm. The roots of desert plants, on the contrary, are very long - this is necessary to reach the groundwater. For example, a leafless barnyard is rooted in the soil by 15 m.

Root modifications

To adapt to environmental conditions, the roots of some plants have been modified and acquired additional functions. Thus, the roots of radishes, beets, turnips, turnips and turnips, formed by the main root and the lower parts of the stem, store nutrients. The thickening of the lateral and adventitious roots of the cleaver and dahlias became root tubers. Ivy attachment roots help the plant to attach to a support (wall, tree) and bring the leaves to the light.