The shoot of a plant is one of the main vegetative organs. It consists of three parts: root, stem and leaf. In all currently existing higher plants, they are homologous to each other and perform different functions.

Shoot phylogeny

In the context of the historical development of organisms, called phylogeny, escape is regarded as an adaptation to a terrestrial lifestyle. It arose as a result of the transformation of rhinophytes of telomes (leafless cylindrical organs) in primitive vascular plants. The emergence of a shoot is the largest aromorphosis in the history of the development of the plant world. This progressive change led to an increase in the photosynthetic surface area associated with this transpiration and, as a result, promoted the development of true roots.

Ontogenesis

With the individual development of the organism (ontogenesis), the shoot of the plant is formed from the buds of the embryo, or adnexal or axillary buds. They are, in fact, the beginnings. When the seed germinates from the germinal bud, the first shoot of the plant develops, also called the main or first order. Lateral branches develop from it.

Types of shoots depending on the function performed

• Vegetative shoots are unmodified. They consist of a stem, buds and leaves. The main function is air supply and ensuring the process of synthesis of inorganic and organic substances.
• Generative shoots are modified. In them, the process of photosynthesis is not carried out, as a rule. However, sporangia are formed on them, the main task of which is to ensure the process of plant reproduction.
• Vegetative-generative, that is, a partially modified shoot. It has leaves, stem, buds and flowers or inflorescences at the same time. Accordingly, it combines the two functions mentioned above at once.

Often the shoot on which the formation of flowers occurs is called the flower-bearing or abbreviated "peduncle".

Escape: building

Without exception, all shoots carry leaves that are not always visible to the eye (for example, scaly on rhizomes). A woody plant is characterized by their absence in perennial plots. Old leaves, after the formation of a special separating tissue, fall off at the end of each season - this is a feature of deciduous species. In the spring, the growth process begins anew.

The place where a leaf is attached to a stem is called a node. In many plants, it is thicker than in other areas. The part of the shoot located between the nodes is the internode. Their alternation expresses the metameric structure of the branches. The repeating structural unit in this case is a node with a leaf and an internode - a phytomer.

Often, the length of the internode can differ significantly on the shoots of the same plant. Quite often one can meet in nature fluctuations in one direction or another. So, strongly shortened internodes lead to the emergence of rosette shoots and bulbs, and excessively elongated, to the development of stolons or peduncles.

Growth Features

Summarizing the above, we can say that the stem with leaves and buds, formed from the meristem, is an unmodified vegetative shoot. In temperate latitudes, their growth and development is periodic. As a rule, in most shrubs, trees and perennial grasses, it occurs once a year (in spring or summer). Such shoots that grow in one year are called annual shoots. In perennial plants, an apical bud is formed at their end; in fact, it is the beginning of a future shoot, which is a continuation of the main axis.

In cases where the growing season consists of several stages of growth, which are separated by a weakly pronounced dormant period, the growing shoots are called elementary. This is especially true for oak. The tree forms shoots in spring and mid-summer. In the tropics there is no clear division into seasons. In this regard, many citrus fruits, a tea bush, etc., can form from 3 to 7 elementary shoots per year.

branching shoots

The process of formation of lateral branches by a shoot, their relative position on a stem, rhizome or perennial branch is called branching. In this way, the plant increases the above-ground mass and surface area, and hence the power of photosynthesis. The order in which the main shoot and buds are located serves as a criterion for classifying branching. It can be dichotomous, monopodial and sympodial. These species are characteristic of higher plants; in lower plants, branching leads to the formation of a thallus (thallus).

The main shoot or axis of the first order develops from the apical bud, its lateral stems are the axes of the second order. They keep branching out. In this case, axes of the third, fourth, etc. order are formed. Let's dwell on each type of branching in more detail.

Dichotomous branching

This type of branching is the most primitive. It is characteristic of algae, such as fucus, club mosses, some gymnosperms, mosses and ferns. With dichotomous branching, the growth cone is divided in two, as a result, two side branches are formed. They, in turn, grow in a similar way further. At the same time, the shoot, the structure of which was discussed above, forms a bizarre "tree" (pictured).

Dichotomous branching can be isotomous, when the newly formed branches are of the same length, or anisotomous, when they are unequal.

Monopodial branching

More progressive in evolutionary terms is monopodial branching. Plants with this type of shoot structure retain the apical bud throughout their lives. The increase in height occurs due to the main axis. Lateral branching shoots can depart from it. However, they are never above the main. Monopodial branching can most often be found in representatives of the group of gymnosperms, some angiosperms (palms, orchids, etc.) plants. A classic example is the pleasing phalaenopsis, common in room culture, which has only one vegetative shoot.

Sympodial branching

Sympodial branching is the most advanced and complex type compared to the previous ones. It is characteristic of angiosperms. The escape structure, which falls under this type, is distinguished by the fact that its bud (apical), ending its development, dies off or stops its growth. New stems begin to develop at its base. Moreover, such side shoots outgrow the main one, take on its direction and appearance. Sympodial branching has, in particular, birch, linden, hazel, and most flowering plants.

The most variable in appearance organ of plants is the shoot. Its structure remains the same, but it can take on a variety of forms. This property is mainly associated with the multifunctionality of all vegetative organs that arose in the course of evolution, and the changes that occur in ontogeny, which are due to the adaptation of the plant to various external conditions.

Shoot metamorphoses have a very wide range: from small deviations from the typical structure to completely changed forms. Both underground and above-ground parts can be modified.

Metamorphoses of above-ground shoots

The modifications that occur with the shoot, listed below, are the consequences of the adaptation of the plant to special conditions of existence or an unusual way of life. These formations can serve not only for reproduction and reproduction, the accumulation of nutrients, but also perform other functions.

• Whiskers and elevated stolons. These modifications of the stem are intended for vegetative reproduction of the plant, i.e., the settlement of its daughter individuals. Such shoots can carry leaves and carry out photosynthesis in parallel. A typical example is the whiskers of wild strawberries, stolons of indoor chlorophytum.
• Antennae.

• As a rule, climbing plants have them. The antennae are a flagellate shoot (branched or solitary), devoid of leaves. They are highly specialized formations that perform a supporting function in species that cannot independently maintain a vertical position. Antennae have, for example, such climbing plants as peas, morning glory, as well as representatives of the Pumpkin family (cucumber, watermelon, pumpkin, melon).
• Thorns are strongly shortened lignified leafless shoots with a sharp top. They are a protective adaptation of plants.
• Rosette escapes. They have very short internodes, as a result of which the leaves are arranged in a rosette. For example, like plantain, dandelion, daisy.
• Phyllocadium is a lateral shoot with limited growth, flattened and performing the function of a leaf. Characteristic for representatives of the genus asparagus, phyllanthus.
• Claudius. In order to understand what it is, just look at parts of the stem of the indoor Decembrist, prickly pear cactus. This is a modified shoot, characterized by long growth. It has flattened stems that act as leaves, while the latter are practically reduced.

Metamorphoses of underground shoots

Shoots located underground are very different from those above ground. They almost completely lost the function of photosynthesis, but acquired others, no less important. For example, the supply of nutrients, reproduction, resumption of vegetative growth. Modifications of the underground shoot are: caudex, rhizome, stolon, bulb and corm.

• Caudex - a modified section of the stem, located between the cotyledon leaves and the tap root. It has the appearance of a thickening, persists throughout the life of the plant and serves as a storage place for reserve nutrients, and also carries numerous renewal buds, including dormant ones. For example, lupins, adenium, alfalfa.
• Rhizome - a modified underground shoot, characteristic of perennial grasses, shrubs and semi-shrubs. Outwardly, it is very similar to the root. The main difference lies in the location and growth in a horizontal plane, the presence of scale-like leaves and the absence of a root cap.
• An underground stolon is an annual thin elongated shoot located underground, at the end of which tubers and bulbs (potatoes, adoxas) can develop.
• The bulb is a specialized, greatly shortened shoot, most often underground. It is a typical organ of vegetative renewal and reproduction.
• The corm is also a shortened modified underground shoot. However, in addition to the function of vegetative reproduction, it stores assimilates in itself. For example, gladioli, dahlias, cyclamen, callas, etc.

Escape: functions, structure and diversity

When one or another plant is callednie, then in our imagination fussKakaet is just an escape, because, in fromdifference from the root, the escape is visible,the aerial part of the plant. Any dea roar rising from the earth isrun. Even the most powerful. In naturethere are also underground shoots.Are there plants without flowers?stems, without a stem, but always with a cor him and run away!

escape functions. Main escape function -air supply plants. This process is called photosynthesis . To absorb carbon dioxide (it is only 0.03% in the air) and to capture the sun's rays, the plant needs a large surface, which is provided by the complex structure of the shoot.

Shoots capable of forming adventitious roots, plants can multiply. Flowers appear on some shoots, fruits and seeds ripen.

Escape structure. A shoot consisting of a stem, leaves and buds is called vegetative . If the shoot also bears flowers, it is calledgenerative .

At the top of the shoot, in the apical bud isshoot growth cone (BUT). The tender cells of its educational tissue are protected by young rudimentary leaves. Due to cell division of the apical educational tissue and their growth, the shoot grows in length. In the internodes isinsert educational fabric (B).

Unlike the apical one, the interstitial educational tissue retains the ability to divide cells only during the growth of the internode. In the adult shoot, these cells turn into cells of permanent tissues, after which the growth of the internode in length stops. In some plants, intercalary growth continues for a long time ( wheat, rye, beans ).

Make captions for the drawing "Escape structure". (Interactive task)

Leaf arrangement. For some shoots, only one leaf can depart from the node (linden, maple, geranium ). This arrangement of leaves is called next . If there are two leaves on a node, then the leaves are located opposite (lilac, elderberry, chickweed ). If a node has three or more leaves, then this whorled leaf arrangement ( raven eye, lily ).

Determine how the leaves are arranged. (Interactive task)

biological game

The arrangement of the leaves on the stem ensures that they receive a stream of sunlight. In conditions of insufficient lighting in indoor plants ( balsam, ivy), on the lower branches of trees ( linden, maple) leaf petioles are bent, leaves are displaced, smaller ones fit between large ones.

Leaf mosaic

As a result, all leaves, regardless of the type of leaf arrangement, turn towards the light. Such a phenomenon is calledsheet mosaic .

Escape in a leafless state. In most woody plants, the leaves fall in autumn, and the shoots become leafless. Traces of fallen leaves are clearly visible under each bud. They are calledleaf scars . In place of last year's apical bud remains renal ring .

In winter, trees and shrubs can be easily recognized not only by the shape of the crown, but also by the shape and size of the buds and leaf scars, the color and shape of the stem.

All plants have special characteristics. For example, at alder kidneys sit on special legs. In addition, she has clearly visible earrings and small bumps - fruits. Bud and you covered with a cap. And at buckthorn the kidneys do not have covering scales at all. kidneys mountain ash pubescent. kidneys poplars sticky and resinous. Many plants can be identified by smell. Pleasant, fresh scent poplars, and here at elderberry there is no such smell. You can’t confuse the smell of twigs with anything black currant .

Escape variety. Shoots with well-defined internodes are calledelongated . The internodes do not always elongate (there is no interstitial growth), as a result of which the shoot will consist only of nodes, leaves and buds. Such escapes are called shortened . They are found in both trees and grasses. The short shoots of grasses are called socket (strawberry, dandelion, plantain ).

The shoot emerging from the seedling grows vertically upwards. He - upright (A) (trees and shrubs, as well as many herbaceous plants -rye, bluebell, aster ). But in the future, shoots are formed from its buds, which can grow in different directions. In accordance with the location in space, there are rising (B) (blackhead, carnation grass ), recumbent (bird buckwheat, wood lice ), creeping (D) (hoof, budra, meadow tea ) shoots; creepers: curly (AT) ( bindweed, lemongrass, beans ), clinging (G) (peas, chin, grapes ), climbing (ivy, blackberry).

One type of plant can have different types of shoots. For example, at woodlice there are both rising and lying shoots.

Tops of elongated shoots during growth make circular motions. In climbing plants, the scope of circular movements is especially large. Having found support, the shoot wraps around it. Interestingly, some types of plants wrap around the support clockwise, while others wrap it counterclockwise. If such an escape does not find support, then its winding stem will fall to the ground. The tendrils of climbing shoots can be formed from a leaf or part of it ( peas, peas), from side shoots ( grape). Blackberry clings to the support with spikes - outgrowths on the stem, and ivy- short adventitious roots. The botanical names of some plant species reflect the structure of their shoots:creeping clover, creeping ranunculus .

Interactive lesson simulator. (Go through all the pages of the lesson and complete all the tasks)

Shoot - a complex organ of a plant, consisting of a stem, buds and leaves. The structure of the shoot ensures the fulfillment of its main function - air supply. Shoots can be not only vegetative, but also generative. The stem part of the shoot consists of nodes and internodes. The nodes contain leaves and buds.

From the germinal bud, the first shoot of the plant is formed - its main shoot, or first order escape.

From the main shoot are formed side shoots, or second order shoots, and when branching is repeated - of the third order, etc.

Adventitious shoots are formed from adnexal buds.

This is how the system of shoots is formed, represented by the main shoot and side shoots of the second and subsequent orders. The shoot system increases the total area of ​​contact of the plant with the air.

Depending on the function performed, shoots are distinguished as vegetative, vegetative-generative and generative. Vegetative (unmodified) shoots, consisting of a stem, leaves and buds, and vegetative-generative (partially modified), additionally consisting of a flower or inflorescence, perform the functions of air nutrition and provide the synthesis of organic and inorganic substances. In generative (completely modified) shoots, photosynthesis most often does not occur, but sporangia are formed there, the task of which is to ensure the reproduction of the plant (a flower also belongs to such shoots).

The shoot that produces flowers is called flowering shoot, or peduncle(sometimes the term "peduncle" is understood in a narrower sense - as a section of the stem, on which the flowers are located).

Main escape organs

A vegetative unmodified shoot is a single plant organ, consisting of a stem, leaves and buds, formed from a common array of meristems (the cone of growth of the shoot) and having a single conducting system. The stems and leaves, which are the main structural elements of the shoot, are often considered as its constituent organs, that is, organs of the second order. In addition, the obligatory affiliation of the escape is the kidneys. The main external feature that distinguishes the shoot from the root is the presence of leaves.

Monopodial branching

Monopodial branching is the next stage in the evolution of shoot branching. In plants with a monopodial type of shoot structure, the apical bud is preserved throughout the life of the shoot. The monopodial type of branching is often found among gymnosperms, it is also found in many angiosperms (for example, in many species of palms, as well as plants from the Orchid family - gastrochilus, phalaenopsis and others). Some of them have a single vegetative shoot (for example, Phalaenopsis is pleasant).

monopodial plants- the term most often used in the description of plants of tropical and subtropical flora, as well as in popular science literature on indoor and greenhouse floriculture.

Monopodial plants can vary significantly in appearance. Among them there are rosette, with an elongated shoot, bushy.

Sympodial branching

In plants with a sympodial type of shoot structure, the apical bud, having completed development, dies off or gives rise to generative run away. After flowering, this shoot no longer grows, and a new one begins to develop at its base. The structure of the shoot in plants with a sympodial type of branching is more complicated than in plants with; sympodial branching is an evolutionarily more advanced type of branching. The word "simpoidal" is derived from the Greek. sym("together" or "many") and pod("leg").

Sympodial branching is characteristic of many angiosperms: for example, lindens, willows, and many orchids.

In orchids, in addition to the apical ones, some sympodial orchids also form lateral inflorescences, developing from buds located at the base of the shoot (Pafinia comb). The part of the shoot pressed against the substrate is called the rhizome. It is located, as a rule, horizontally and does not have true leaves, only scaly. A reduced, almost indistinguishable rhizome occurs in many Masdevallia, Dendrobiums and Oncidiums; well distinguishable and thickened - in cattleyas and lelias, elongated - in bulbophyllums and cologins, reaching 10 or more centimeters. The vertical part of the shoot is often thickened, forming the so-called tuberidium, or pseudobulb. Pseudobulbs can be of various shapes - from almost spherical to cylindrical, cone-shaped, club-shaped and elongated, resembling reed stalks. Pseudobulbs are storage organs.

sympodial plants- the term most often used in the description of plants of tropical and subtropical flora, as well as in popular science literature on indoor and greenhouse floriculture.

Evolution of branch types

Shoot modifications (metamorphosis)

The shoot is the most variable in appearance organ of the plant. This is due not only to the general multifunctionality of vegetative organs that arose in the process of evolution, but also to the changes that occur in the process of plant ontogenesis, due to adaptation to a variety of environmental conditions, and in cultivated plants - under the influence of man.

The main type of shoot of a green plant is an above-ground (aerial) assimilating shoot, bearing green leaves of the middle formation on the axis. However, assimilating shoots are not the same. Often, along with the main function of photosynthesis, these shoots also have others: the deposition of reserves and the supporting function (mostly in perennial stems), vegetative reproduction (creeping shoots, lashes).

Modification of underground shoots

Shoots living underground, under the influence of a complex of conditions that are sharply different from the terrestrial environment, almost completely lost the functions of photosynthesis and acquired other equally important vital functions, such as organs for enduring an unfavorable period, storing nutrients, vegetative renewal and reproduction of plants. Modified underground shoots include: rhizome, caudex, underground stolon and tuber, bulb, corm.

caudex- a perennial organ of shoot origin of perennial grasses and semi-shrubs with a well-developed taproot that persists throughout the life of the plant. Together with the root, it serves as a place of deposition of reserve substances and bears many renewal buds, some of which may be dormant. There are many caudex plants among the umbrella plants (femur, ferula), legumes (alfalfa, lupins), composites (dandelion, wormwood, rough cornflower).

underground stolon- an annual elongated thin underground shoot with underdeveloped scaly leaves. At the thickened ends of the stolons, plants can accumulate reserve substances, forming tubers or bulbs (potatoes, stolons, adoxas).

stem tuber- a modified shoot with a pronounced storage function of the stem, the presence of scaly leaves that quickly peel off, and buds that form in the axils of the leaves and are called eyes (potato, Jerusalem artichoke).

Bulb- underground (rarely above-ground) highly shortened specialized shoot, in which reserve substances are deposited in scales of leafy nature, and the stem is transformed into the bottom. The bulb is a typical organ of vegetative renewal and reproduction. Bulbs are characteristic of monocotyledonous plants from the Lily family (lily, tulip, onion), Amaryllis (amaryllis, narcissus, hyacinth), etc. As an exception, they are also found in dicotyledonous plants - in some species of sour and butterwort.

Corm- a modified underground shortened shoot with a thick stem storing assimilants, adventitious roots growing from the underside of the corm, and preserved dried leaf bases (membraneous scales), which together form a protective cover. Corms have saffron, gladiolus, colchicum.

Modifications of above-ground shoots

An unusual way of life and / or adaptation to the special conditions of the existence of plants lead to various modifications of the shoots. At the same time, shoots can serve not only to store nutrients, reproduce and reproduce plants, but also perform other functions. There are frequent cases when not the entire shoot is modified, but only its leaves, and some of their metamorphoses are outwardly and functionally similar to shoot metamorphoses (thorns, antennae).

thorn- strongly lignified leafless shortened shoot with a sharp tip. Spines of shoot origin perform mainly a protective function. At the wild apple tree, wild pear, laxative buckthorn ( Rhamnus cathartica) shortened shoots turn into spines, having limited growth and ending in a point. In honey locust ( Gleditschia triacanthos) powerful branched spines are formed on the trunks of dormant buds. Many species of hawthorn have spines that form from axillary leaf buds, which topographically corresponds to lateral shoots.

Claudius- a modified lateral shoot with the ability to grow long, with green flat long stems that act as a leaf. As an organ of photosynthesis, the cladodium has a well-developed chlorophyll-bearing tissue located under the epidermis. Plants with cladodias include Mühlenbeckia flatiflora ( Muhlenbekia platyclada), Decembrist cactus ( Zygocactus truncates), southern carmichelia ( Carmichaelia australis), collection ( Colletia cruciata) and prickly pear ( Opuntia).

Phyllocladius- a modified leaf-like flattened lateral shoot with limited growth and performing the functions of a leaf. Phyllocladia develop from lateral buds, so they are always found in the axil of a small membranous or scaly leaf. Performing the function of photosynthesis, the shoots of phylloclades also outwardly acquire a resemblance to a leaf, which manifests itself in limited growth and complete loss of the metameric structure. The phenomenon of phylloclady is characteristic of such plants as the needle, swept away, species of the asparagus genera ( Asparagus), phyllanthus ( Phyllanhtus). Phylloclads are found not only in angiosperms, but also in some gymnosperms, in particular, in a coniferous plant from the Nogocarp family - phyllocladus.

Notes

Literature

• Korovkin O. A. Anatomy and morphology of higher plants: a dictionary of terms. - M: Bustard, 2007. - 272 p. - ISBN 978-5-358-01214-1
• Nukhimovsky E. L. Fundamentals of biomorphology of seed plants: Habitus and forms of growth in the organization of biomorphs. - M: Overlay, 2002. - T. 2. - 859 p. - 750 copies. - ISBN 5-85493-067-6
• Botany with the basics of phytocenology: Anatomy and morphology of plants: Proc. for universities / Serebryakova T. I. and others. - M: ICC "Akademkniga", 2007. - S. 341-365. - 2,000 copies. - ISBN 978-5-94628-237-6

• Timonin A.K. Botany: in 4 volumes - M: Publishing Center "Academy", 2007. - T. 3. - S. 52-69. - 3,000 copies. - ISBN 978-5-7695-3184-2
• Botany. Textbook for universities: in 4 volumes. T. 1. Cell biology. Anatomy. Morphology. Based on the textbook by E. Strasburger / Ed. A. K. Timonina, V. V. Chuba. - M: Publishing Center "Academy", 2007. - T. 1. - S. 261-266. - 3,000 copies. - ISBN 978-5-7695-2744-9
• Lotova L. I. Botany: Morphology and anatomy of higher plants: Textbook. - M: KomKniga, 2007. - S. 312-321. - 1,500 copies. - ISBN 978-5-484-00698-4
• Barabanov E.I., Zaichikova S.G. Botany: textbook. for stud. universities. - M: Publishing Center "Academy", 2006. - S. 82-85. - 3,000 copies. - ISBN 5-7695-2656-4

• Yakovlev G. P., Chelombitko V. A. Botany: textbook. for stud. universities. - St. Petersburg: Spetslit, publishing house SPHFA, 2003. - S. 129-132. - 5,000 copies. - ISBN 5-299-00237-8
• Andreeva I. I., Rodman L. S. Botany. - M: KolosS, 2005. - S. 172-175. - 3,000 copies. - ISBN 5-9532-0114-1
• Tropical and subtropical plants. Collections of the Main Botanical Garden of the USSR Academy of Sciences (Cactaceae-Compositae). Moscow: Nauka, 1976.
• Smirnova E.S. Morphology of orchid shoot systems. - M.: Nauka, 1990

And kidneys. This is the main part of the plant, consisting of nodes and internodes, which grows in length due to the apical and intercalated meristems (educational tissue). The stem performs a variety of functions: conducting aqueous solutions from the root to the leaves and vice versa; increasing the surface of the plant by branching; formation of leaves and flowers; accumulation of nutrients; vegetative; support The place of attachment of leaves and buds to the stem is called a node. The section of the stem located between the nodes is called the internode. The kidney is a rudimentary shoot. It contains a cone of growth of the stem and rudimentary leaves, as well as kidney scales covering the educational tissue.

By location on escape There are apical buds, due to which the stem is lengthened, axillary, adnexal. According to the function of the kidney, there are:

a) vegetative - consist of an adventitious stem, scales, rudimentary leaves and a growth cone
b) generative - consist of a rudimentary stem, scales and the rudiment of a flower or inflorescence.

Any the escape develops from the kidney due to the division of the meristem in the growth cone. Most plants are apical.

Internal: on the cut surface, a bark is distinguished, consisting of cork and bast. Deeper is the wood - the main fabric, in the center - a loose core.

Between the bark and the wood is the cambium, an educational tissue on which the thickening of the stem depends.
Thanks to the division of cambial cells, the stems of trees, shrubs and perennial grasses grow in thickness. All layers of wood cells formed in spring, summer and autumn make up the annual growth ring. By counting the number of annual rings, you can determine the age of a cut tree or a cut branch.

Cork protects the deeper cells of the stem from excessive evaporation, from the penetration of atmospheric dust with microorganisms that cause plant diseases.

In the cork, lenticels develop - small tubercles with holes, through which gas exchange takes place. The composition of the bast includes sieve tubes, through which solutions of organic substances move, and thick-walled bast. Wood makes up the bulk of a tree trunk. It is formed by cells of various shapes and sizes. The shells of many cells are thickened and impregnated with a substance that gives them density. The composition of wood includes long tubular vessels. The cambium plays a large role in the life of the stem. Its cells divide, resulting in new layers on both sides of the cambium. Those cells that are deposited towards the bark become new cells of the bast, and the cells deposited by the cambium towards the wood become new cells of the wood. The core consists of large cells with thin membranes. This is where nutrients are stored.

Water with minerals dissolved in it rises through the vessels of wood; root pressure and evaporation of water by leaves are of great importance for raising water. In the bast there are sieve tubes, through which organic substances move from the leaves to other organs of the plant.

Modified shoots are rhizomes (nettle, couch grass, iris), tubers (potatoes, corydalis, Jerusalem artichoke), bulbs (onion, lily, tulip, narcissus).

Theory for preparation for block No. 4 of the Unified State Examination in biology: with system and diversity of the organic world.

Root

Root- underground vegetative organ of higher plants, which has unlimited growth in length.

Root functions

1. Fixing the plant in the substrate
2. Absorption, conduction of water and minerals
3. Supply of nutrients
4. Interaction with the roots of other plants, fungi, microorganisms living in the soil (mycorrhiza, nodules of legumes)
5. Vegetative reproduction
6. Synthesis of biologically active substances
7. In many plants, the roots perform special functions (aerial roots, sucker roots)
8. Modifications and specialization of roots
9. The roots of some buildings are prone to metamorphosis

The roots are different, namely, they can be modified.

Root modifications

• A root crop is a modified juicy 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 crops consist mainly of storage basic tissue (turnips, carrots, parsley).
• Root tubers - root tubers (root cones) are formed as a result of thickening of the lateral and adventitious roots (tulips, dahlias, potatoes).
• Aerial roots - lateral roots, grow down. They absorb rainwater and oxygen from the air. Formed in many tropical plants in conditions of high humidity.
• Mycorrhiza is the cohabitation of the roots of higher plants with fungal hyphae. With such a mutually beneficial cohabitation, called symbiosis, the plant receives water from the fungus with nutrients dissolved in it, and the fungus receives organic substances. Mycorrhiza is characteristic of the roots of many higher plants, especially woody ones. Fungal hyphae, braiding thick lignified roots of trees and shrubs, act as root hairs.
• Bacterial nodules on the roots of higher plants - the cohabitation of higher plants with nitrogen-fixing bacteria - are modified lateral roots adapted to symbiosis with bacteria. Bacteria penetrate the root hairs into young roots and cause them to form nodules.
• Respiratory roots - in tropical plants - perform the function of additional respiration.

Distinguish:

• main root
• lateral roots
• adventitious roots

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

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

Types of root systems

• Rod
• fibrous
• branched

AT pivotal In the root system, the main root is strongly developed and is clearly visible among other roots (typical for dicots). The tap root system usually penetrates deeper into the soil than the fibrous root system.

AT fibrous root system in the early stages of development, the main root, formed by the germinal root, dies off, and the root system is composed of adventitious roots (typical for monocots). The fibrous root system better braids the adjacent soil particles, especially in its upper fertile layer.

AT branched the root system is dominated by equally developed main and several lateral roots (in tree species, strawberries).

The escape

The escape- This is a stem with leaves and buds located on it.

The components of the shoot are the stem, leaves, buds. When the seed germinates from the germinal bud, the first shoot of the plant is formed - its main shoot, or first-order shoot. Lateral shoots, or shoots of the second order, are formed from the main shoot, and when branching is repeated, the third order, etc. Adventitious shoots are formed from adventitious buds.

This is how the system of shoots is formed, represented by the main shoot and side shoots of the second and subsequent orders. The shoot system increases the total area of ​​contact of the plant with the air.

The shoot on which flowers are formed is called a flowering shoot, or peduncle (sometimes the term "peduncle" is understood in a narrower sense - as the section of the stem on which the flowers are located).

A vegetative unmodified shoot is a single plant organ, consisting of a stem, leaves and buds, formed from a common array of meristems (the cone of growth of the shoot) and having a single conducting system. The stems and leaves, which are the main structural elements of the shoot, are often considered as its constituent organs, that is, organs of the second order. In addition, the obligatory affiliation of the escape is the kidneys. The main external feature that distinguishes the shoot from the root is the presence of leaves.

In the seasonal climate of temperate latitudes, the growth and development of shoots from buds is periodic. In shrubs and trees, as well as in most perennial grasses, this happens once a year - in spring or early summer, after which wintering buds of the next year are formed, and at the end of summer - in autumn, shoot growth ends.

Escape structure

A (with leaves). one - stem; 2 - sheet; 3 - node; four - internode; 5 - leaf axil; 6 - axillary kidney; 7 - apical kidney.

B (after leaf fall). 1 - apical kidney; 2 - renal rings; 3 - leaf scars; 4 - lateral kidneys.

Shoot types

1 - upright; 2 - rising; 3 - creeping; 4 - creeping; 5 - curly; 6 - climbing.

Shoot modifications

• The thorn is a strongly lignified, leafless, shortened shoot with a sharp apex. Spines of shoot origin perform mainly a protective function. In the wild apple, wild pear, laxative buckthorn (Rhamnus cathartica), shortened shoots turn into spines, having limited growth and ending in a point.
• Antennae is a flagellate, branched or unbranched shoot of a metameric structure, typically devoid of leaves. Stem tendrils, as a highly specialized shoot, perform a supporting function.
• Rhizome - an underground shoot with scale-like leaves of the lower formation, buds and adventitious roots. Thick, highly branched creeping rhizomes are characteristic of couch grass, short and rather fleshy - for kupena, iris, very thick - for capsules, water lilies.
• The stem tuber is a modified shoot with a pronounced storage function of the stem, the presence of scale-like leaves that quickly peel off, and buds that form in the axils of the leaves and are called eyes (Jerusalem artichoke).
• Bulb - an underground (rarely above-ground) highly shortened specialized shoot, in which reserve substances are deposited in the scales of a leafy nature, and the stem is transformed into a bottom. The bulb is a typical organ of vegetative renewal and reproduction. Bulbs are characteristic of monocotyledonous plants from the Lily family (lily, tulip, onion), Amaryllis (amaryllis, narcissus, hyacinth), etc. As an exception, they are also found in dicotyledonous plants - in some types of oxalis and butterwort.
• A corm is a modified underground shortened shoot with a thick stem that stores assimilants, adventitious roots growing from the underside of the corm, and preserved dried leaf bases (membrane scales), which together form a protective cover. Corms have colchicum, gladiolus, ixia, saffron.

Stem

Stem- an elongated shoot of higher plants, serving as a mechanical axis, also plays the role of a producing and supporting base for leaves, buds, flowers.

stem classification

According to the location relative to the level of the soil:

elevated

underground

According to the degree of woodiness:

• herbaceous
• woody (for example, the trunk is the main perennial stem of a tree; the stems of shrubs are called trunks)

According to the direction and nature of growth:

• upright (e.g. sunflower)
• recumbent (creeping) - the stems lie on the surface of the soil without rooting (monetary loosestrife)
• ascending (ascending) - the lower part of the stem lies on the surface of the soil, and the upper one rises vertically (cinquefoil)
• creeping - the stems spread along the ground and take root due to the formation of adventitious roots at the nodes (ivy-shaped budra)
• clinging (climbing) - attached to a support with antennae (peas)
• curly - thin stems wrapping around a support (moonseed)

According to the shape of the cross section:

• rounded
• flattened
• three-, four-, polyhedral (faceted)
• ribbed
• grooved (grooved)
• winged - stems in which flat grassy outgrowths stretch along sharp edges (forest rank) or bases of leaves flowing down to the stem (comfrey officinalis)

stem structure

Outside, the stem is protected by integumentary tissues. In young stems in spring, the cells of the integumentary tissue are covered with a thin skin. In perennial plants, by the end of the first year of life, the skin is replaced by a multilayer cork consisting of dead cells filled with air. For breathing in the skin (in young shoots) there are stomata, and later lenticels are formed - large, loosely located cells with large intercellular spaces.

The cortex, formed by different tissues, adjoins the integumentary tissue. The outer part of the cortex is represented by layers of mechanical tissue cells with thickened membranes and thin-walled cells of the underlying tissue. The inner part of the cortex is formed by the cells of the conductive tissue and is called the bast.

The composition of the bast includes sieve tubes, through which there is a downward current: organic substances move from the leaves. Sieve tubes are made up of cells connected at their ends to form a long tube. There are small holes between neighboring cells. Through them, like through a sieve, organic substances formed in the leaves move.

Sieve tubes remain alive for a short time, more often 2-3 years, occasionally - 10-15 years. They are constantly being replaced by new ones. The sieve tubes make up a small part of the bast and are usually collected in bundles. In addition to these bundles in the bast, there are cells of mechanical tissue, mainly in the saw fibers, and cells of the main tissue.

To the center of the bast in the stem is another conductive tissue - wood.

Wood is formed by cells of different shapes and sizes and consists of vessels (tracheas), tracheids and wood fibers. An ascending current flows along them: water with substances dissolved in it moves from the roots to the leaves.

In the center of the stem lies a thick layer of loose cells of the main tissue, in which nutrient reserves are deposited - this is the core.

In some plants (dahlia, tulip, cucumber, bamboo), the core is occupied by an air cavity.

Between wood and bast in dicotyledonous plants there is a thin layer of cells of the educational tissue - the cambium. As a result of cell division of the cambium, the thickness of the stem increases (grows). Cambium cells divide along their axis. One of the daughter cells that appears goes to the wood, and the other to the bast. The increase is especially noticeable in wood. Cambial cell division depends on the seasonal rhythm - in spring and summer it is active (large cells are formed), slows down in autumn (small cells are formed), and stops in winter. As a result, an annual growth of wood is formed, which is clearly visible in many trees, called the annual ring. By the number of growth rings, you can calculate the age of the shoot and the tree as a whole.

The width of annual rings in woody plants depends on environmental conditions. So, in a cold climate, on swampy soils, the size of the growth rings of wood is very small. In favorable climatic conditions, on rich soils, the thickness of annual rings increases. Comparing the alternation of wide and narrow growth rings near the trunk, it is possible to determine the conditions under which the plant lived, as well as to establish fluctuations in weather conditions over many years.

stem functions

• conductive (main function)

The stem serves as a support for the plant, it holds the weight of the leaves, flowers and fruits on it.

• support

Reserve nutrients can be deposited in the stem. This manifests the storage function of the stem. With the help of the stem, the shoot brings its leaves and buds to the light during the growth of the plant. This shows the important axial function of the stem and the growth function.

Sheet

Sheet- one of the most important organs of plants, the main functions of which are photosynthesis, gas exchange and transpiration.

The internal structure of the leaf

The sheet consists of the following fabrics:

• The epidermis is a layer of cells that protect against the harmful effects of the environment and excessive evaporation of water. Often, on top of the epidermis, the leaf is covered with a protective layer of waxy origin (cuticle).
• Parenchyma is an internal chlorophyll-bearing tissue that performs the main function - photosynthesis.
• A network of veins formed by conducting bundles, consisting of vessels and sieve tubes, to move water, dissolved salts, sugars and mechanical elements.
• Stomata are special complexes of cells located mainly on the lower surface of the leaves; Through them, water evaporation and gas exchange occur.

External leaf structure

The sheet externally consists of:

• petiole (leaf stalk)
• leaf blade (blade)
• stipules (paired appendages located on both sides of the petiole base)
• the place where the petiole meets the stem is called the leaf sheath
• the angle formed by the leaf (leaf petiole) and the superior internode of the stem is called the leaf axil
• in the axil of the leaf, a bud (which in this case is called an axillary bud), a flower (called an axillary flower), an inflorescence (called an axillary inflorescence) can form

Not all plants have all parts of the leaves; in some species, paired stipules are not clearly expressed or absent; the petiole may be absent, and the leaf structure may not be lamellar.