Escape of plants: structure and functions. The structure of a flower plant

The escape, like the root, is the main organ of the plant. Vegetative shoots typically perform the function of aerial nutrition, but have a number of other functions and are capable of various metamorphoses. spore-bearing shoots (including the flower) are specialized as organs reproductive providing reproduction.

The shoot is formed by the apical meristem as a whole and, therefore, is a single organ of the same rank as the root. However, compared to the root, the shoot has more complex structure. The vegetative shoot consists of an axial part - stem, which is cylindrical in shape, and leaves- flat lateral organs sitting on the stem. In addition, an obligatory part of the escape are kidneys– rudiments of new shoots, which ensure the growth of the shoot and its branching, i.e. formation of the escape system. The main function of the shoot - photosynthesis - is carried out by leaves; stems are predominantly load-bearing organs that perform mechanical and conductive functions.

The main feature that distinguishes the shoot from the root is its foliage. The part of the stem from which the leaf (leaves) extends is called knot. Stem segments between adjacent nodes internodes. Nodes and internodes are repeated along the axis of the shoot. So the escape has metameric structure, metamer(repeating element) of the shoot are the node with the leaf and the axillary bud and the underlying internode ( rice. 4.16).

Rice. 4.16. Escape structure.

The first shoot of a plant main escape, or escape of the first order. It is formed from an embryonic shoot ending kidney, which forms all subsequent metameres of the main shoot. By position, this kidney is apical; while it persists, this shoot is capable of further growth in length with the formation of new metameres. In addition to the apical, on the shoot are formed lateral kidneys. At seed plants they are found in the axils of the leaves and are called axillary. From the lateral axillary buds develop lateral shoots, and branching occurs, due to which the total photosynthetic surface of the plant increases. Formed escape system, represented by the main shoot (shoot of the first order) and side shoots (shoots of the second order), and when branching is repeated, by side shoots of the third, fourth and subsequent orders. A shoot of any order has its own apical bud and is capable of growing in length.

Bud- this is a rudimentary, not yet unfolded shoot. Inside the kidney is the meristematic tip of the shoot - its apex(rice. 4.17). The apex is an actively working growth center that ensures the formation of all organs and primary tissues of the shoot. The source of constant self-renewal of the apex is the initial cells of the apical meristem, concentrated at the tip of the apex. The vegetative shoot apex, in contrast to the always smooth root apex, regularly forms protrusions on the surface, which are the beginnings of leaves. Only the very tip of the apex, which is called growth cone escape. Its shape varies greatly in different plants and does not always look like a cone; the apical part of the apex can be low, hemispherical, flat, or even concave.

From vegetative buds develop vegetative shoots consisting of a stem, leaves and buds. Such a kidney consists of a meristematic rudimentary axis ending growth cone, and rudimentary leaves of different ages. Due to uneven growth, the lower leaf primordia are bent inward and cover the upper, younger, leaf primordia and the growth cone. The nodes in the kidney are close together, since the internodes have not yet had time to stretch out. In the axils of leaf rudiments in the kidney, the rudiments of axillary buds of the following order can already be laid ( rice. 4.17). IN vegetative-generative a number of vegetative metameres are laid in the buds, and the growth cone is turned into a rudimentary flower or inflorescence. Generative, or floral the buds contain only the rudiment of an inflorescence or a single flower, in the latter case the bud is called bud.

Rice. 4.17. The apical bud of the Elodea shoot: A - longitudinal section; B - growth cone (appearance and longitudinal section); C – cells of the apical meristem; D - parenchymal cell of the formed leaf; 1 - growth cone; 2 - leaf rudiment; 3 - the rudiment of the axillary kidney.

The outer leaves of the bud often change into kidney scales, which perform a protective function and protect the meristematic parts of the kidney from drying out and sudden changes in temperature. Such kidneys are called closed(wintering buds of trees and shrubs and some perennial herbs). open kidneys do not have kidney scales.

In addition to the usual, exogenous in inception, axillary buds, plants often form adnexal, or adventive kidneys. They arise not in the meristematic tip of the shoot, but on the adult, already differentiated part of the organ, endogenously, from internal tissues. Adnexal buds can form on stems (then they are usually located in internodes), leaves and roots. Adnexal buds are of great biological importance: they provide active vegetative renewal and reproduction of those perennial plants that have them. In particular, with the help of adnexal kidneys, they renew and multiply root offspring plants (raspberry, aspen, thistle, dandelion). Root offspring- these are shoots that have developed from adventitious buds on the roots. Adnexal buds on the leaves are formed relatively rarely. If such buds immediately give small shoots with adventitious roots that fall off the mother leaf and grow into new individuals, they are called brood(bryophyllum).

In the seasonal climate of the temperate zone, the deployment of shoots from the buds in most plants is periodic. Trees and shrubs, as well as many perennials herbaceous plants buds unfold into shoots once a year - in spring or early summer, after which new wintering buds form with the beginnings of next year's shoots. Shoots that grow from buds in one growing season are called annual shoots, or annual increments. In trees, they are well distinguished due to the formation renal rings- scars that remain on the stem after the fall of the kidney scales. In the summer of our deciduous trees, the annual shoots of only the current year are covered with leaves; there are no leaves on the annual shoots of previous years. In evergreen trees, leaves can be preserved on the corresponding annual increments of 3-5 past years. In a seasonally unseasoned climate, several shoots may form in one year, separated by small dormant periods. Such shoots formed in one growth cycle are called elementary shoots.

Buds that fall into a dormant state for a while, and then give new elementary and annual shoots, are called wintering or resting. According to their function, they can be called kidney regular renewal. Such buds are an obligatory feature of any perennial plant, woody or herbaceous, they ensure the perennial existence of an individual. By origin, renewal kidneys can be both exogenous (apical or axillary) and endogenous (adnexal).

If the lateral buds do not have a dormant period and develop simultaneously with the growth of the maternal shoot, they are called kidney enrichment. Deploying ones enrichment shoots greatly increase (enrich) the total photosynthetic surface of the plant, as well as the total number of inflorescences formed and, consequently, seed productivity. Enrichment shoots are typical for most annual grasses and for a number of perennial herbaceous plants with elongated flowering shoots.

A special category is dormant buds, very characteristic of deciduous trees, shrubs, shrubs and a number of perennial grasses. By origin, they, like the buds of regular renewal, can be axillary and adnexal, but, unlike them, do not turn into shoots for many years. The stimulus for the awakening of dormant buds is usually either damage to the main trunk or branch (stump growth after cutting down a number of trees), or natural aging of the maternal shoot system associated with the attenuation of the vital activity of normal renewal buds (change of stems in shrubs). In some plants, leafless flowering shoots form from dormant buds on the trunk. This phenomenon is called caulifloria and is characteristic of many rainforest trees, such as the chocolate tree. In honey locust, bunches of large branched spines grow from sleeping buds on the trunk - modified shoots ( rice. 4.18).

Rice. 4.18. Shoots from dormant buds: 1 - caulifloria near the chocolate tree; 2 - spines in honey locust from branched dormant buds.

Direction of shoot growth. Shoots growing vertically, perpendicular to the surface of the earth, are called orthotropic. Horizontally growing shoots are called plagiotropic. The direction of growth may change during shoot development.

Depending on the position in space, morphological types of shoots are distinguished ( rice. 4.19). The main shoot in most cases retains orthotropic growth and remains upright. Lateral shoots can grow in different directions, often forming a different angle with the parent shoot. In the process of growth, the shoot can change direction from plagiotropic to orthotropic, then it is called rising, or ascending. Shoots with plagiotropic growth that persists throughout life are called creeping. If they form adventitious roots at the nodes, they are called creeping.

Orthotropic growth is connected in a certain way with the degree of development of mechanical tissues. In the absence of well-developed mechanical tissues in elongated shoots, orthotropic growth is impossible. But often plants that do not have a sufficiently developed internal skeleton still grow upward. This is achieved in various ways. Weak shoots of such plants - creepers twist around some kind of solid support ( curly shoots), climb with the help of various kinds of spines, hooks, roots - trailers ( climbing shoots), cling with the help of antennae of various origins ( clinging shoots).

Rice. 4.19. Types of shoots by position in space: A - upright; B - clinging; B - curly; G - creeping; D - creeping.

Leaf arrangement. leaf arrangement, or phyllotaxis- the order of placement of leaves on the axis of the shoot. There are several main types of leaf arrangement ( rice. 4.20).

Spiral, or another leaf arrangement is observed when there is one leaf at each node, and the bases of successive leaves can be connected by a conditional spiral line. double row leaf arrangement can be considered as special case spiral. At the same time, at each node there is one sheet, covering the entire or almost the entire circumference of the axis with a wide base. Whorled leaf arrangement occurs when several leaves are laid on one node. Opposite leaf arrangement - a special case of whorled, when two leaves are formed on one node, exactly opposite each other; most often such a leaf arrangement occurs cross opposite, i.e. neighboring pairs of leaves are in mutually perpendicular planes ( rice. 4.20).

Rice. 4.20. Types of leaf arrangement: 1 - spiral in oak; 2 - scheme of spiral leaf arrangement; 3 - two-row in gasteria ( but- side view of the plant b– top view, scheme); 4 - whorled in oleander; 5 - opposite in lilac.

The order of initiation of leaf rudiments on the shoot apex is a hereditary trait of each species, sometimes characteristic of a genus and even an entire family of plants. The leaf arrangement of the adult shoot is determined primarily by genetic factors. However, in the process of deployment of a shoot from a bud and its further growth, the arrangement of leaves can be influenced by external factors mainly light conditions and gravity. Therefore, the final picture of the leaf arrangement can differ greatly from the initial one and usually acquires a pronounced adaptive character. The leaves are arranged so that their plates are in the most favorable lighting conditions in each case. This is most pronounced in the form sheet mosaic observed on plagiotropic and rosette shoots of plants. In this case, the plates of all leaves are arranged horizontally, the leaves do not obscure each other, but form a single plane where there are no gaps; more small leaves fill in the gaps between the big ones.

Shoot branching types. Branching is the formation of a system of axes. It provides an increase in the total area of ​​​​contact of the plant body with air, water or soil. Branching arose in the process of evolution even before the appearance of organs. In the simplest case, the top of the main axis forks and gives rise to two axes of the next order. This apical, or dichotomous branching. Many multicellular algae have apical branching, as well as some primitive plants, such as club mosses ( rice. 4.21).

Other groups of plants are characterized by a more specialized side branch type. In this case, the lateral branches are laid below the top of the main axis, without affecting its ability to further increase. With this method, the potential for branching and formation of organ systems is much more extensive and biologically beneficial.

Rice. 4.21. Shoot branching types: A - dichotomous (club moss); B - monopodial (juniper); B - sympodial type of monochasia (bird cherry); D - sympodial according to the type of dichasia (maple).

There are two types of lateral branching: monopodial And sympodial(rice. 4.21). With a monopodial branching system, each axis is a monopodium, i.e. the result of the work of one apical meristem. Monopodial branching is characteristic of most gymnosperms and many herbaceous angiosperms. Most angiosperms, however, branch in a sympodial pattern. With sympodial branching, the apical bud of the shoot dies off at a certain stage or stops active growth, but an increased development of one or more lateral buds begins. Shoots are formed from them, replacing the shoot that has stopped growing. The resulting axis is a sympodium - a composite axis consisting of axes of several successive orders. The ability of plants to sympodial branching is of great biological importance. In case of damage to the apical bud, the growth of the axis will continue with lateral shoots.

Depending on the number of replacement axes, sympodial branching is distinguished by type monochasia, dichasia And pleiochasia. Branching according to the type of dichasia, or false dichotomous branching is typical for shoots with opposite leaf arrangement (lilac, viburnum).

In some groups of plants, the growth of the main skeletal axes occurs due to one or a few apical buds; lateral skeletal branches are not formed at all or are formed in a very small number. Tree-like plants of this type are found mainly in tropical areas (palm trees, dracaena, yucca, agave, cycads). The crown of these plants is formed not by branches, but by large leaves brought together in a rosette at the top of the trunk. The ability to rapidly grow and capture space, as well as to recover from damage in such plants is often absent or weakly expressed. Among temperate trees, such non-branching forms are practically not found.

The other extreme is plants that branch too profusely. They are represented by the life form cushion plants (rice. 4.22). The growth in the length of the shoots of these plants is extremely limited, but on the other hand, many lateral branches are formed annually, diverging in all directions. The surface of the shoot system of the plant looks as if trimmed; some pillows are so dense that they look like stones.

Rice. 4.22. Plants - pillows: 1, 2 - schemes of the structure of pillow plants; 3 - Azorella from Kerguelen Island.

Representatives of a life form branch very strongly Tumbleweed characteristic of steppe plants. A spherically branched, very loose system of shoots is a huge inflorescence, which, after fruit ripening, breaks off at the base of the stem and rolls over the steppe with the wind, scattering the seeds.

Specialization and metamorphoses of shoots. Many plants within the shoot system have a certain specialization. Orthotropic and plagiotropic, elongated and shortened shoots perform different functions.

elongated called shoots with normally developed internodes. In woody plants, they are called growth and are located along the periphery of the crown, determining its shape. Their main function is to capture space, increase the volume of photosynthetic organs. shortened shoots have close nodes and very short internodes ( rice. 4.23). They form inside the crown and absorb scattered light penetrating there. Often shortened shoots of trees are flowering and perform the function of reproduction.

Rice. 4.23. Shortened (A) and elongated (B) sycamore shoots: 1 - internode; 2 - annual increments.

Herbaceous plants usually have shortened rosette shoots perform the function of perennial skeletal and photosynthetic, and elongated ones are formed in the axils of rosette leaves and are flower-bearing (plantain, cuff, violets). If axillary peduncles are leafless, they are called arrows. The fact that flowering shoots are short in woody plants and elongated in herbaceous plants is biologically well explained. For successful pollination, grass inflorescences must be raised above the herbage, and in trees, even shortened shoots in the crown are in favorable conditions for pollination.

An example of the specialization of shoots is the perennial axial organs of woody plants - trunks And branches crowns. In deciduous trees, annual shoots lose their assimilation function after the first growing season, in evergreens - in a few years. Some of the shoots die off completely after the loss of leaves, but most remain as skeletal axes, performing support, conduction, and storage functions for decades. The leafless skeletal axes are known as boughs And trunks(by the trees) stems(for shrubs).

In the course of adaptation to specific environmental conditions or in connection with a sharp change in functions, shoots can change (metamorphize). Shoots developing underground are especially often metamorphosed. Such shoots lose the function of photosynthesis; they are common in perennial plants, where they act as organs for experiencing an unfavorable period of the year, stock and renewal.

The most common underground shoot metamorphosis is rhizome (rice. 4.24). It is customary to call a rhizome a long-lived underground shoot that performs the functions of deposition of reserve nutrients, renewal, and sometimes vegetative reproduction. The rhizome is formed in perennial plants, which, as a rule, do not have a main root in the adult state. According to its position in space, it can be horizontal, oblique or vertical. The rhizome usually does not bear green leaves, but, being a shoot, retains a metameric structure. The nodes are distinguished either by leaf scars and the remains of dry leaves, or by living scaly leaves; axillary buds are also located in the nodes. According to these features, the rhizome is easy to distinguish from the root. As a rule, adventitious roots are formed on the rhizome; lateral branches of the rhizome and above-ground shoots grow from the buds.

The rhizome is formed either initially as an underground organ (kupena, raven eye, lily of the valley, blueberry), or first as an above-ground assimilating shoot, which then sinks into the soil with the help of retracting roots (strawberry, lungwort, cuff). Rhizomes can grow and branch monopodially (cuff, crow's eye) or sympodially (kupena, lungwort). Depending on the length of the internodes and the intensity of growth, there are long And short rhizomes and, accordingly, long-rhizome And short-rhizome plants.

When branching rhizomes, it is formed curtain elevated shoots connected by sections of the rhizome system. If the connecting parts are destroyed, the shoots are isolated, and vegetative reproduction occurs. The totality of new individuals formed vegetatively is called clone. Rhizomes are characteristic mainly of herbaceous perennials, but are also found in shrubs (euonymus) and shrubs (lingonberries, blueberries).

close to roots underground stolons- short-lived thin underground shoots bearing underdeveloped scaly leaves. Stolons serve for vegetative reproduction, settlement and territory capture. Spare nutrients are not deposited in them.

In some plants (potato, earth pear), by the end of summer, stolons form from the apical buds of stolons. tubers (Fig. 4.24). The tuber has a spherical or oval shape, the stem is strongly thickened, reserve nutrients are deposited in it, the leaves are reduced, and buds form in their axils. The stolons die off and are destroyed, the tubers overwinter, and on next year give rise to new above-ground shoots.

Tubers do not always develop on stolons. In some perennial plants, the base of the main shoot grows tuberous and thickens (cyclamen, kohlrabi cabbage) ( rice. 4.24). The functions of the tuber are a supply of nutrients, experiencing an unfavorable period of the year, vegetative renewal and reproduction.

In perennial grasses and dwarf shrubs with a well-developed tap root that persists throughout life, a kind of organ of shoot origin is formed, called caudex. Together with the root, it serves as a place for the deposition of reserve substances and carries many renewal buds, some of which may be dormant. The caudex is usually subterranean and is formed from short shoot bases that sink into the soil. Caudex differs from short rhizomes in the way it dies off. Rhizomes, growing at the top, gradually die off and collapse at the older end; the main root is not preserved. The caudex grows in width, from the lower end it gradually turns into a long-lived thickening root. The death and destruction of the caudex and the root goes from the center to the periphery. A cavity is formed in the center, and then it can be divided longitudinally into separate sections - particles. The process of dividing an individual of a taproot plant with a caudex into parts is called particulation. There are many caudex plants among legumes (lupins, alfalfa), umbrella plants (femur, ferula), and Compositae (dandelion, wormwood).

Bulb- this is usually an underground shoot with a very short flattened stem - bottom and scaly fleshy succulent leaves that store water and soluble nutrients, mainly sugars. Aerial shoots grow from the apical and axillary buds of the bulbs, adventitious roots form on the bottom ( rice. 4.24). Thus, the bulb is a typical organ of vegetative renewal and reproduction. Bulbs are most characteristic of plants from the families of lilies (lilies, tulips), onions (onions) and amaryllis (daffodils, hyacinths).

The structure of the bulb is very diverse. In some cases, bulbs storing scales are only modified leaves that do not have green plates (lily saranka); in others, these are underground sheaths of green assimilating leaves, which thicken and remain in the bulb after the plates die (onion). Bulb axis growth can be monopodial (snowdrop) or sympodial (hyacinth). The outer scales of the bulb consume the supply of nutrients, dry out and play a protective role. The number of onion scales varies from one (garlic) to several hundred (lilies).

As an organ of renewal and reserve, the bulb is adapted mainly to climates of the Mediterranean type - with fairly mild, wet winters and very hot, dry summers. It serves not so much for a safe overwintering, but for experiencing a harsh summer drought. The storage of water in the tissues of onion scales occurs due to the formation of mucus, which can retain a large amount of water.

Corm outwardly resembles an onion, but its scaly leaves are not storage; they are dry and membranous, and reserve substances are deposited in the thickened stem part (saffron, gladiolus).

Rice. 4.24. Underground escape metamorphoses: 1, 2, 3, 4 - sequence of development and structure of the potato tuber; 5 - cyclamen tuber; 6 - kohlrabi tuber; 7 - bulbs of a tiger lily; 8 - onion bulb; 9 - lily bulb; 10 - section of a long rhizome of couch grass.

Not only underground, but also above-ground shoots of plants can be modified ( rice. 4.25). Quite common elevated stolons. These are plagiotropic short-lived shoots, the function of which is vegetative reproduction, resettlement and territory capture. If stolons carry green leaves and participate in the process of photosynthesis, they are called lashes(bone, tenacious creeping). In strawberries, stolons are devoid of developed green leaves, their stems are thin and fragile, with very long internodes. Such more highly specialized stolons for the function of vegetative reproduction are called mustache.

Juicy, fleshy, adapted to the accumulation of water can be not only bulbs, but also above-ground shoots, usually in plants living in conditions of lack of moisture. Water storage organs can be leaves or stems, sometimes even buds. Such succulent plants are called succulents. Leaf succulents store water in leaf tissues (aloe, agave, jughead, rhodiola, or golden root). Stem succulents are characteristic of the American cactus family and African euphorbiaceae. The succulent stem performs a water-reserving and assimilating function; leaves are reduced or turned into spines ( rice. 4.25, 1). In most cacti, the stems are columnar or spherical, leaves are not formed on them at all, but the nodes are clearly visible by the location of the axillary shoots - areola having the appearance of warts or elongated outgrowths with spines or tufts of hairs. The transformation of leaves into spines reduces the evaporative surface of the plant and protects it from being eaten by animals. An example of the metamorphosis of a kidney into a succulent organ is head of cabbage serves as a cultivated cabbage.

Rice. 4.25. Elevated shoot metamorphoses: 1 - stem succulent (cactus); 2 - tendrils of grapes; 3 - leafless photosynthetic shoot of gorse; 4 - phyllocladium of butcher's broom; 5 - thorn of honey locust.

spines cacti are leafy. Leaf spines are often found in non-succulent plants (barberry) ( rice. 4.26, 1). In many plants, spines are not of leaf, but of stem origin. In the wild apple tree, wild pear, laxative joster, shortened shoots metamorphosed into spines, having limited growth and ending in a point. They acquire the appearance of a hard lignified thorn after the leaves fall. At the hawthorn ( rice. 4.26, 3) the spines that form in the axils of the leaves are completely leafless from the very beginning. In honey locust ( rice. 4.25.5) powerful branched spines are formed on trunks from dormant buds. The formation of spines of any origin, as a rule, is the result of a lack of moisture. When many thorny plants are grown in an artificial humid atmosphere, they lose their spines and instead grow normal leaves (camel thorn) or leafy shoots (English gorse).

Rice. 4.26. Spines of various origins: 1 - barberry leaf spines; 2 - spines of white acacia, modification of stipules; 3 - spines of hawthorn shoot origin; 4 - thorns - rosehip emergents.

The shoots of a number of plants bear spikes. Thorns differ from spines in smaller sizes, these are outgrowths - emergents - of the integumentary tissue and tissues of the stem bark (rose hips, gooseberries) ( rice. 4.26, 4).

Adaptation to a lack of moisture is very often expressed in the early loss, metamorphosis or reduction of leaves that lose the main function of photosynthesis. This is compensated by the fact that the stem takes on the role of the assimilating organ. Sometimes such an assimilating stem of a leafless shoot remains externally unchanged (Spanish gorse, camel thorn) ( rice. 4.25, 3). The next step in this change of functions is the formation of such organs as phyllocladia And cladodia. These are flattened leaf-like stems or whole shoots. On the shoots of the needle ( rice. 4.25, 4), in the axils of scaly leaves, flat leaf-shaped phylloclades develop, which, like a leaf, have limited growth. Phylloclads form scaly leaves and inflorescences, which never happen on normal leaves, which means that the phyllocladium corresponds to a whole axillary shoot. Small, needle-like phylloclades are formed in asparagus in the axils of the scaly leaves of the main skeletal shoot. Cladodia are flattened stems that, unlike phyllocladia, retain the ability for long-term growth.

Some plants are characterized by the modification of leaves or their parts, and sometimes entire shoots in antennae, which twist around the support, helping the thin and weak stem to maintain an upright position. In many legumes, the upper part of the pinnate leaf (peas, peas, rank) turns into antennae. In other cases, stipules (sarsaparilla) turn into antennae. Very characteristic tendrils of leafy origin are formed in gourds, and all the transitions from normal to fully metamorphosed leaves can be seen. Antennae of shoot origin can be observed in grapes ( rice. 4.25, 2), passionflower and a number of other plants.

Table: Escape (leaf, stem, bud)

THE ESCAPE

The escape is the aerial part of the plant. A vegetative shoot is laid in the process of development of the embryo, in which it is represented by a kidney. kidney- this is a stalk and leaf primordia, can be considered the first bud of a plant. The apical meristem of the kidney during the development of the embryo forms new leaves, and the stem elongates and differentiates into nodes and internodes.

The escape- a complex organ consisting of a stem, leaves, buds. The stem has nodes and internodes. Knot- the part of the stem that contains the leaf and bud. The section of the stem between the nodes internode. The angle formed by a leaf and stem above a node is called leaf sinus. The kidneys, which occupy a lateral position on the node, are called lateral (or axillary). At the top of the stem is the apical bud.

Escape modifications can perform various functions: storage and the function of vegetative reproduction (tubers, rhizomes, bulbs), protective (thorns), serve as an attachment organ (antennae), etc.

• tubers- shortened and thickened underground shoots with buds (potatoes).
• Rhizome- an underground shoot resembling a root, bears scaly leaves and buds, often forms above-ground shoots and adventitious roots (wheatgrass).
• Bulb- a shortened stem (bottom), surrounded by succulent leaves (onion).
• spines- means of protection (wild apple tree).
• tendrils- a means of attachment (grapes).

SHEET

Sheet- a flat lateral organ of the shoot.

External leaf structure. In dicotyledonous plants, the leaf consists of a flat expanded plate and a stem-like petiole with stipules. The leaves of monocotyledonous plants are characterized by the absence of petioles, the base of the leaf, they are expanded, into the vagina, covering the stem. In cereals, the entire internode is covered with a vagina: The leaves of dicotyledonous plants are simple and complex. Simple leaves have one leaf blade, sometimes strongly dissected into lobes. Compound leaves have several leaf blades with pronounced cuttings. Pinnate leaves have an axial petiole, on both sides of which there are leaflets. Palmate leaves have leaflets extending like a fan from the top of the main petiole.

The internal structure of the sheet. Outside the leaf is a peel of colorless cells, covered with a waxy substance - the cuticle. Under the skin are located cells columnar parenchyma containing chlorophyll. Deeper are the cells of the spongy parenchyma with intercellular spaces filled with air. The vessels of the conducting bundle are located in the parenchyma. On the lower surface of the leaves, the skin has stomatal cells involved in the evaporation of water. Evaporation of water occurs to prevent overheating of the leaf through the stomata of the epidermis (skin). This process is called transpiration and provides D.C. water from roots to leaves. The rate of transpiration depends on the humidity air, temperature, light, etc.

Under the influence of these factors, the turgor of the guard cells of the stomata changes, they close or close, delaying or enhancing the evaporation of water and gas exchange. In the process of gas exchange, oxygen enters the cells for respiration or is excreted into the atmosphere during photosynthesis.

Cellular structure of the leaf.

Leaf modifications: antennae - serve to fix the stem in a vertical position; needles (in cactus) play a protective role; scales - small leaves that have lost their photosynthetic function; hunting apparatus - the leaves are equipped with columnar glands that secrete mucus, which is used to capture small insects that have fallen on the leaf.

STEM

The stem is the axial part of the shoot, bearing leaves, flowers, inflorescences and fruits. This is the supporting function of the stem. Other stem functions include; transport - carrying water with substances dissolved in it from the root to the ground organs; photosynthetic; storage - deposition in its tissues of proteins, fats, carbohydrates.

Stem fabrics:

1. Conductive: the inner part of the cortex is represented by sieve tubes and satellite cells of the bast (phloem), wood cells (xylem) are located closer to the center, along which transport of substances.
2. Cover- skin in young and cork in old lignified stems.
3. Reserve- specialized cells of bast and wood.
4. Educational(cambium) - constantly dividing cells that attack all tissues of the stem. Due to the activity of the cambium stem grows in thickness, and annual rings are formed.

Stem modifications: tuber - storage underground shoot; the entire mass of the tuber consists of a storage parenchyma together with a conductive tissue (potato); bulb - a shortened conical stem with numerous modified leaves - scales and a shortened stem - bottom (onion, lily); corms (gladiolus, crocus, etc.); head of cabbage - a strongly shortened stem with thick, overlapping leaves.

Cellular structure of the stem:

BUD

Bud- a rudimentary short shoot from which new shoots (vegetative buds) or flowers (generative buds) can develop. New shoots grow from the bud in spring. There are apical, axillary, (located in the leaf axils) and accessory buds. Adnexal buds are formed due to the activity of the cambium and other educational tissues in different places - on the roots, stems, leaves.

Vegetative bud consists of a shortened stem and rudimentary leaves; sometimes covered with protective modified leaves - kidney scales. There are apical and lateral (axillary) vegetative buds. The apical bud is located at the top of the stem and consists of growth cone cells and ensures the growth of the shoot in length, as well as the formation of leaves and lateral buds. Lateral buds are formed in the axils of the leaves. With the help of phytohormones, which are formed in the apical bud, the growth and development of lateral (sleeping) buds is inhibited, which begin to grow only when the apical bud is damaged or dies.

Generative kidneys larger than vegetative; they bear fewer rudimentary leaves, and at the top of the rudimentary stem are the rudiments of a flower or inflorescence. A generative bud containing one flower is called a bud. On the internodes of the stem, roots and leaves, adnexal buds can form, providing vegetative reproduction.

The escape - This is the above-ground vegetative part of the plant. It consists of an axial part - a stem on which leaves and buds are located. On some shoots, generative organs - flowers - can also be placed. It has a more complex structure than the root.

On the stem of the shoot, nodes and internodes can be distinguished. Knot - this is the place of attachment of one or more leaves to the stem. Internodes is the distance between two adjacent nodes. Between stem and leaf upper corner, which is called leaf sinus . The buds are located at the top of the shoot and in the leaf axils.

Shoots, depending on the degree of elongation of the internodes, can be shortened or elongated. Shortened shoots actually consist of one node. On shortened shoots of herbaceous plants (dandelion, carrots, beets, etc.), the leaves are located close to one another and form a basal rosette.

Herbaceous plants are divided into annuals, biennials and perennials. Annuals develop and grow over one year (one growing season). In the first year of life, biennial plants (carrots, radishes, beets, etc.) form vegetative organs, accumulate nutrients, and in the second year they bloom, produce fruits and seeds. perennial plants live three and more years. Woody plants are perennials.

kidneys

kidneys - these are embryonic shoots with very short internodes. They arose later than the stem and leaves. Thanks to the kidneys, branching of the shoots occurs.

According to the location of the kidney, there are apical - located at the top of the shoot, and lateral or axillary -located in leaf axils. The apical bud provides the growth of the shoot, lateral shoots are formed from the lateral buds, which provide branching.

Buds are vegetative (leaf), generative (flower) and mixed. From vegetatively th buds develop shoot with leaves. From generative - shoot with a flower or inflorescence. The flower buds are always larger than the leaf buds and have a rounded shape. From mixed buds develop shoots with leaves and flowers or inflorescences. Buds that are laid on any other part of the stem, as well as on roots or leaves, are called adnexal , or adventitious . They develop from internal tissues, provide vegetative restoration and vegetative reproduction.

By the presence of scales, the kidneys are closed (if there are scales) and open (naked if there are no scales). Closed buds are characteristic mainly for plants of the cold and temperate zones. The scales of the kidneys are dense, leathery, may be covered with cuticles or resinous substances.

Most buds develop in plants every year. Buds that may not re-grow shoots for several years (even a lifetime), but remain alive, are called sleeping . Such buds resume the growth of shoots when the apical bud, trunk or branch is damaged. Typical for trees, bushes and a number of perennial herbs. By origin, they can be axillary or adnexal.

The internal structure of the kidney

Outside, the kidney may be covered with brown, gray or brown keratinized scales - modified leaves. The axial part of the vegetative bud is the germinal stem. It has germ leaves and buds. All parts together make germ shoot . The apex of the embryonic shoot is growth cone . The cells of the growth cone divide and ensure the growth of the shoot in length. Due to uneven growth, the outer leaf rudiments are directed upwards and towards the center of the bud, bent over the inner leaf primordia and the growth cone, and cover them.

Inside the flower (generative) buds on the germinal shoot is the germinal flower, or inflorescence.

When a shoot grows from a kidney, its scales fall off, and scars remain in their place. They determine the length of the annual increments of the shoot.

Stem

Stem is the axial vegetative organ of plants. The main functions of the stem: provides the interconnection of plant organs among themselves, transports different substances, forms and bears leaves and flowers. Additional stem features: photosynthesis, accumulation of substances, vegetative reproduction, storage of water. They vary greatly in size (for example, eucalyptus trees up to 140-155 m high).

The flow of substances in the stem occurs in two directions: from the leaves to the root (descending current) - organic substances and from the root to the leaves (ascending current) - water and mainly minerals. Nutrients move along the core rays from the core to the cortex in a horizontal direction.

The shoot can branch, that is, form side shoots from vegetative buds on the main stem. The main stem of a branched plant is called the axis first order . The lateral stems that developed from its axillary buds are called axes. second order . Axes form on them. third order etc. Up to 10 such axes can develop on a tree.

When branching, trees form a crown. Crown - this is a collection of all above-ground shoots of trees located above the beginning of the branching of the trunk. The youngest branches in the crown are branches last order. The crowns have different shapes: pyramidal (poplar), rounded (spherical) (sharp maple), columnar (cypress), flat (some pines), etc. A person forms a crown cultivated plants. In nature, the formation of the crown depends on the place where the tree grows.

The branching of the stem of the bushes begins at the very surface of the soil, so many side shoots are formed (rose hips, currants, gooseberries, etc.). In semi-shrubs (wormwood), the stems become stiff only in the lower perennial part, from which annual herbaceous shoots grow every year.

In some herbaceous plants (wheat, barley, etc.), shoots grow from underground shoots or from the lowest buds of the stem - this branching is called tillering .

The stem that carries a flower or one inflorescence is called an arrow (in primrose, onion).

According to the location of the stem in space, they distinguish: erect (poplar, maple, thistle, etc.), creeping (Clover), curly (birch, hops, beans) and clinging (step white). Plants with climbing shoots are combined into a group creepers . Creeping stems with long internodes are called mustache , and with shortened ones - whips . Both mustaches and whips are above ground stolons . A shoot that spreads along the ground but does not take root is called creeping (knotweed).

According to the state of the stem, they distinguish herbaceous stems (thistle, sunflower) and woody (beech, oak, lilac).

According to the shape of the stem on a transverse section, they are distinguished: rounded (birch, poplar, etc.), ribbed (valerian), trihedral (sedge), tetrahedral (mint, labiales), polyhedral (umbrella, most cacti), flattened, or flat ( prickly pear), etc.

By pubescence, they are smooth and pubescent.

The internal structure of the stem

On the example of a woody stem of dicotyledonous plants. There are: periderm, bark, cambium, wood and pith.

The epidermis functions for a short time and exfoliates. It replaces periderm , consisting of cork, cork cambium (phellogen) and phelloderm. Outside, the stem is covered with integumentary tissue - cork which is made up of dead cells. Performs a protective function - protects the plant from damage, from excessive evaporation of water. Cork is formed from a layer of cells - phellogen, which lies under it. Phelloderm is the inner layer. Exchange with external environment occurs through the lenticels. They are formed by large cells of the main tissue with large intercellular spaces.

Bark

Distinguish between primary and secondary. The primary is located under the periderm and consists of the colenchyma (mechanical tissue) and the parenchyma of the primary cortex.

Secondary bark or bast

It is represented by conductive tissue - sieve tubes, mechanical tissue - bast fibers, the main one - bast parenchyma. A layer of bast fibers forms a hard bast, other tissues - soft.

Cambium

Cambium(from lat. cambio- change). Located under the bark. This is an educational tissue that looks like a thin ring in a cross section. Outside, cambial cells form bast cells, inside - wood. Wood cells, as a rule, are formed much more. Thanks to the cambium, the stem grows in thickness.

Wood

It consists of conductive tissue - vessels or tracheids, mechanical - wood fibers, the main - wood parenchyma. The length of the vessels can reach 10 cm (sometimes - several meters).

Core

Occupies a central position in the trunk. It consists of thin-walled cells of the main tissue, large in size. The outer layer is represented by living cells, the central part is predominantly dead. In the central part of the stem, a cavity can be obtained - a hollow. Nutrients are stored in living cells. From the core to the bark through the wood passes a series of core cells called core rays. They provide horizontal movement of various connections. Core cells can be filled with metabolic products, air.

Stem modifications

Stems can perform additional functions associated with their modification. Changes occur in the process of evolution.

tendrils

These are curly, long, thin stems with reduced leaves that wrap around various supports. They support the stem in a certain position. Characteristic for grapes, pumpkins, melons, cucumbers, etc.

spines

These are shortened shoots without leaves. They are located in the axils of the leaves and correspond to the lateral axils or are formed from dormant buds on stolons (gleditsia). They protect the plant from being eaten by animals. Stem spines are characteristic for wild pear, plum, blackthorn, sea buckthorn, etc.

Tree ring formation

In trees that live in climates with seasonal changes, growth rings- on the transverse section, there is an alternation of dark and light concentric rings. From them you can determine the age of the plant.

During the growing season of the plant, one annual ring is formed. Light rings are rings of wood that have large thin-walled cells, vessels (tracheids) large diameter, which are formed in spring and during active cell division of the cambium. In summer, the cells are slightly smaller and have thicker cell walls of the conductive tissue. Dark rings are obtained in autumn. Wood cells are small, thick-walled, have more mechanical tissue. Dark rings function more like a mechanical tissue, light ones - as a conductive one. In winter, cambial cells do not divide. The transition in the rings is gradual - from spring to autumn wood, sharply marked - during the transition from autumn to spring. In spring, the activity of the cambium resumes and a new annual ring is formed.

The thickness of annual rings depends on climatic conditions in this season. If the conditions were favorable, the light rings are wide.

Annual rings are invisible tropical plants, as they grow throughout the year almost evenly.

The escape.

This is an organ that arises from the apical meristem and is divided at an early stage of morphogenesis into specialized parts: stem, leaves, buds.

Its main function is photosynthesis. Parts of the shoot can also serve for vegetative propagation, accumulation of reserve products, water.

macroscopic structure.

Escape Parts. The section of the stem at the level of the leaf origin is called a node, and the section of the stem between two nodes is called an internode. Above the node in the axil of the leaf, an axillary bud is formed. In the case of clearly expressed internodes, the shoot is called elongated. If the nodes are close together and the internodes are almost invisible, then this is a shortened shoot (fruit, rosette).

Metamerism. Usually the shoot has several nodes and internodes. Such a repetition of shoot segments with the same organs is called metamerism. Each metamere of a typical shoot consists of a node with a leaf and an axillary bud and an underlying internode.

Bud. This is a rudimentary escape. It consists of a meristematic axis ending in a cone of growth (rudimentary stem) and leaf primordia (rudimentary leaves), that is, from a series of rudimentary metameres. The differentiated leaves located below cover the cone of growth and primordia. This is how the vegetative bud is arranged. In a vegetative-reproductive bud, the cone of growth is turned into a rudimentary flower or rudimentary inflorescence. Reproductive (flower) buds consist only of a rudimentary flower or inflorescence and do not have rudiments of photosynthetic leaves.

Often the outer leaves are modified into bud scales that protect the bud from drying out. Such kidneys are called protected (closed) in contrast to bare (open) kidneys that do not have kidney scales (viburnum, tenacious, cat's foot). It must be remembered that in bare buds, as in any growing buds, the growth cone and leaf primordia are covered with older photosynthetic leaves.

By location, apical and lateral buds are distinguished. The latter by origin can be axillary and adnexal. Axillary buds are laid on the growth cone exogenously (outwardly) in the axils of leaf primordia. axillary kidneys, long time those who do not sprout are called sleepers. Axillary kidneys are located either one by one (single) or several (group). Adnexal buds can arise in any part of the stem endogenously due to the activity of the meristem. Sometimes adventitious buds form on leaves and immediately give small shoots with adventitious roots (bryophyllum) or bulbs (onions). Such accessory buds are called brood buds.

leaf arrangement. There are three main options for leaf arrangement: spiral (regular) - there is only one leaf on the node, the leaves are arranged in a spiral on the stem; opposite - on the node there are two sheets located opposite each other; whorled - there are three or more leaves on the node.

rise. The shoot grows in length, usually with an apex, due to the activity of the apical meristem located there. In addition, the shoots of many plants are significantly elongated due to the growth of the intercalary meristem. If the shoot grows indefinitely due to the same apical meristem, such an increase is called monopodial. However, in many plants, the apical meristem functions for a limited time, usually during one growing season. Then, in the next season, the growth of the shoot continues due to the nearest lateral night. There is a so-called overturning. Such an increase in the shoot is called sympodial.

The ability to replace dead apical buds with lateral ones (sympodial growth) is of great biological importance. This increases the vitality of the plants. Plants in which lateral buds are underdeveloped and unable to replace dead apical buds die if the tops of the stem are damaged (for example, some palm trees). Therefore, in dry (arid) and cold climates, almost all perennials have sympodial growth. The humid tropics are characterized by plants with monopodial growth.

The possibility of sympodial growth is widely used in practice. This phenomenon is based on methods of pruning fruit and ornamental plants. It underlies the growth of grass when mowing and grazing livestock.

branching. Branching is of two types: apical and lateral. With apical (dichotomous) branching, the growth cone is divided into two or more axes. This kind of branching is lower plants(some algae) and only a few higher (lycopsform, some fern-like). With lateral branching, new axes arise below the apex.

As a result of one or more branches, a system of axes is formed. With lateral branching, the axis system can be either monopodial - with monopodial growth, or sympodial - with sympodial growth.

A special form of branching is tillering, in which the largest lateral branches are formed only at the base of the shoots, usually from surface and underground buds. This area of ​​the shoot is called the tillering zone. Tillering is characteristic of shrubs, perennial, and sometimes annual grasses.

In some plants, the lateral buds on the first-order axis are underdeveloped and do not form lateral branches. Such plants have an unbranched stem (most palms, melon tree, agave).

growth direction. Vertically growing shoots can be erect, clinging, curly. Shoots lying on the ground are called creeping. If the creeping shoot forms adventitious roots, it is called creeping. Shoots can change the direction of growth, then they are called ascending, ascending.

Metamorphosed shoots.

Their occurrence is often associated with the performance of the functions of a receptacle for spare products, the transfer is not favorable conditions year, vegetative propagation.

Rhizome- this is a perennial underground shoot with a horizontal, ascending or vertical direction of growth, which performs the functions of accumulating spare products, renewal, vegetative propagation. The rhizome has reduced leaves in the form of scales, buds, adventitious roots. Spare products accumulate in the stem part. Growth and branching occurs in the same way as in a regular shoot. The rhizome is distinguished from the root by the presence of leaves and the absence of a root cap at the top. The rhizome can be long and thin (wheatgrass) or short and thick. Annually, above-ground annual shoots are formed from the apical and axillary buds. The old parts of the rhizome gradually die off. Plants with horizontal long rhizomes that form many above-ground shoots quickly occupy large area, and if these are weeds (wheatgrass), then the fight against them is rather difficult. Such plants are used to fix the sands (grass, aristida). In grassland, cereals with long horizontal rhizomes are called rhizomatous (bent grass, bluegrass), and with short ones - bushy (timothy grass, belous). Rhizomes are found mainly in perennial herbaceous plants, but sometimes in shrubs (euonymus) and shrubs (lingonberries, blueberries).

Tuber- this is a thickened part of the shoot, a container of spare products. Tubers are above ground and underground.

elevated tuberis a thickening of the main (kohlrabi) or side (tropical orchids) shoot and bears normal leaves.

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

Elevated stolon- this is a short-lived creeping shoot that serves to spread (capture the territory) and vegetative propagation. It has long internodes and green leaves. Adventitious roots are formed on the nodes, and a shortened shoot (rosette) is formed from the apical bud, which, after the death of the stolon, continues to exist independently. The aboveground stolon sympodial grows. Aboveground stolons that have lost the function of photosynthesis and perform mainly the function of vegetative reproduction are sometimes called mustaches (strawberries).

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

Cormit looks like an onion, but all its leaf scales are dry, and spare products are deposited in the stem part (saffron, gladiolus).

spineshave various origins- from the shoot (apple, pear, blackthorn, hawthorn, honey locust, citrus fruits), leaf (barberry) or its parts: rachis (astragalus), stipules (white acacia), portion of the plate (composite). Spines are characteristic of plants in hot, dry habitats.

tendrilsare formed from a shoot (grapes), a leaf or its parts: rachis and several leaves (peas), plates (rank.), Stipules (sarsaparilla). Used to attach to a support.

Phyllocladia- These are flat leaf-shaped shoots located in the axils of reduced leaves. Flowers form on them. They are found in plants of predominantly arid habitats (butcher's needle, phyllanthus).

trapping devices- modified leaves characteristic of insectivorous plants (dew, flycatcher). They have the form of jugs, urns, bubbles, or slamming and wrapping plates. Small insects, getting into them, die, dissolve with the help of enzymes and are consumed by plants as mainly additional source minerals.

Bibliography:

Abstract of lectures of the candidate of biological sciences Viktor Aleksandrovich Surkov.

The organs of flowering plants, the most evolutionarily developed representatives of this kingdom of wildlife, have a fairly diverse structure and functions. The underground part of the plant is called the root, the aboveground part is called the shoot. It is the shoot of plants that performs the most important functions: gas exchange, photosynthesis, transpiration, vegetative reproduction and its optimal location in relation to the sun.

Origin of the escape

In the process of evolution, this organ appears in the first land-dwellers - rhinophytes. Its stems were creeping and forked, because they were still poorly developed. But even with such a primitive structure, the photosynthetic surface increased, which means that the plant organism was better provided with carbohydrates.

in plants

A shoot is the aerial part of a plant, consisting of a stem and leaves. All of these organs are vegetative, providing growth, nutrition, and asexual reproduction.

The shoot of plants also contains rudimentary organs - the kidneys. There are two types of kidneys: vegetative and generative. The first type consists of a rudimentary stem and a leaf, on top of which there is a growing cone. If, in addition to the stem and leaves, the bud contains the beginnings of flowers or inflorescences, it is called generative. In appearance, such kidneys are distinguished by larger sizes and a rounded shape.

The place to which the leaf is attached on the stem is called the node, and the distance between the nodes is called the internode. The angle between the stem and the leaf is called the axil.

In the process of development, organs responsible for generative (sexual) reproduction also appear on the shoot: flower, fruit and seed.

Escape development from the kidney

With the onset of favorable conditions in spring, meristem cells begin to actively divide. Shortened internodes increase in size, resulting in a young shoot of plants. At the very top of the stem are the apical buds. They provide the growth of the plant in length. Axillary and adnexal buds are located in the leaf axil or internode, respectively. Due to them, the stem forms lateral shoots, i.e. branches.

Plant branching methods

Depending on the structure, there are several ways of branching shoots:

1. dichotomous. The most primitive type of branching, in which two grow from one point of growth, two from each of them, etc. This is how some algae and higher spore plants grow: club mosses and ferns.
2. Primopodial. Such branching can be seen both in gymnosperms (pine, spruce) and (oak, maple). For a long time, the plants grew in length, followed by the formation of lateral branching.
3. Sympodial. With this method, apical growth, on the contrary, stops. And the lateral buds are actively growing, forming more and more lateral shoots. Pear, cherry and others flowering plants are a typical example this type of growth.

Shoot modifications

What is an escape in plants and how does it look, of course, everyone knows. But environmental conditions often require the appearance of additional functions. This is easily provided by the organs of flowering plants. The shoot is modified, acquiring new structural features, while it consists of parts of a standard shoot.

The main modifications of the escape include:

• Rhizome - located underground, where it most often grows horizontally. It has elongated internodes and buds, from which leaves appear on the surface of the earth in a favorable period. Therefore, plants with rhizomes (lily of the valley, wheatgrass, valerian) are very difficult to get rid of. After tearing off the leaves, the shoot itself remains in the ground, growing more and more.

• The tuber is a thickened internode with buds - eyes. The most prominent representative of plants that form tubers is potatoes. Since it grows in the ground, it is often confused with a modified root. However, there are also above-ground tubers, for example, kohlrabi.
• Bulb - a modified shoot of plants with well-developed leaves located on a flat stem - the bottom. Typical for garlic, onion, tulip, lily. Nutrients accumulate in the inner succulent leaves, while the outer dry ones protect them from damage.
• Spines are a protective device of pear, sea buckthorn, hawthorn and other plants. Being in the axil of the leaf, they reliably protect the plant from animals that want to feast on them.
• Antennae are modified climbing shoots that fix plants in a certain position. Cucumber, grapes, pumpkin are the most common plants that use this device.

• Mustache - thin shoots with long internodes. Strawberries and wild strawberries reproduce vegetatively with the help of whiskers.

As you can see, the shoot of plants consists of parts that are functionally interconnected, can be modified depending on environmental conditions and give each plant its own unique look.