What is a side run. Escape: structure and types
Or accessory (adventive) kidney. Thus, the kidney is a rudimentary shoot. When the seed germinates 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. Stems and leaves, which are the main building blocks shoot - 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: e.g. for limes, 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.
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Bulbophyllum grandiflorum |
Cirrhopetalum macraei. Curtis "s botanical magazine vol. 127 ser. 3 nr. 57 tab. 7787, 1901 |
Oncidium dasystyle. Curtis "s botanical magazine vol. 127 ser. 3 nr. 57 tab. 7787, 1901 |
Dendrobium senile. Curtis "s botanical magazine vol. 127 ser. 3 nr. 57 tab. 7787, 1901 |
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.
rosette shoots- abnormal shoots that form on pine trees due to damage done to pine trees by some harmful insects, for example, a nun butterfly, etc .; such shoots are extremely short and have tufts of short and wide needles.
Shoot - one of the main organs of higher plants, consisting of a stem, leaves and buds. On the stem of the shoot are nodes and internodes. The node is the place where the leaves and buds are connected to the stem. The angle between the stem and the leaf is called the leaf axil. The kidney that is located there is called axillary. In addition to the axillary buds, there are also apical ones.
The stem is the axial part of the shoot of a plant, has nodes and internodes and is a support for leaves, buds and generative organs. The main function of the stem is leading. The movement of substances occurs along the leading elements: organic (from leaves to all organs) and mineral solutions (from roots to aboveground organs). Spare substances accumulate in the stem; green stems are photosynthetic; through stomata in the skin of the stem and lentils in the cork, the function of gas exchange is carried out. By growth and placement in space, the stems are divided into erect (sunflower), curly (field birch), creeping (white clover), tenacious (grapes). According to the presence of wood, the stems are divided into herbaceous (knotweed, plantain) and woody (birch, oak, currant).
Annual plants live throughout the year or only the favorable season. Biennial plants in the first year of life are exclusively vegetative organs and accumulate nutrients in their underground (carrots, beets, dahlias) or aboveground (cabbage) parts. The next year they form fruits and seeds. Perennial plants live three or more. Among them there are trees, bushes, semi-bushes and herbaceous plants. The stems can have various shapes on a cross section: a circle (linden, poplar), a tetrahedron (sage, mint), a trihedron (sedge), a polyhedron (valerian) or be flattened (opuntia cactus) and others.
Both aboveground and underground shoots can be modified, performing additional functions.
Rhizome - a modified underground shoot that looks like a root; differs from it in the presence of nodes and internodes, axillary buds and the absence of a root cap. The rhizome grows with an apex - the place where the apical bud is located. Every year, new above-ground shoots develop from the buds of the rhizome. The rhizome performs the functions of a reserve, reproduction and distribution of the plant, ensures survival in adverse conditions. external environment(wheatgrass, sow thistle).
The bulb is a very shortened flat shoot-bottom with close succulent leaves. Adventitious roots extend from the bottom. The bulb of tulips, lilies, snowdrops, garlic, onions and other plants. The axillary buds change and turn into daughter bulbs. The bulb performs a reserve function, ensures the reproduction of plants and contributes to survival in an unfavorable period.
Stem tubers - thickening of one or more internodes of the stem. Such thickenings can be both underground (potatoes, Jerusalem artichoke) and aboveground (kohlrabi cabbage). They perform the functions of a supply of nutrients, reproduction, and the transfer of an unfavorable period.
Thorns - a modification of the above-ground shoot (thorn, wild pear, hawthorn). They protect the plant from eating, located in the axils of the leaves.
Stolons are elongated creeping shoots, often with scaly leaves. They live one year and give rise to new individuals (nettle) such shoots in everyday life are called "mustache". Shoots can be modified into tendrils (grapes, pumpkin, melon, cucumber) - curly shoots, wrap around various supports and support the stem in a certain position (support function).
Escape and escape systems
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 with the root, the shoot has a 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.
Main feature, which 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. In seed plants, they are located 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 different plants and does not always have the form of 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 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 last case kidney 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 grasses). 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. In trees and shrubs, as well as in many perennial herbaceous plants, buds unfold into shoots once a year - in spring or early summer, after which new wintering buds are formed 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 kidneys 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 total number formed inflorescences 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 - creeper 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 a special case of 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 ( A- 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, during the development of the shoot from the bud and its further growth, the location of the leaves can be influenced by external factors, mainly lighting 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 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 the trees temperate climate such unbranched forms are almost never 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 the life form branch very strongly Tumbleweed, characteristic for 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. At 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 the majority remain as skeletal axes, performing supporting, conducting, 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 (strawberries, 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 collapse, the tubers overwinter, and the next year they 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 storage, 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 for 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 growing many thorny plants in an artificial humid atmosphere, they lose their spines: normal leaves (camel thorn) or leafy shoots (English gorse) grow instead.
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. Scale-like leaves and inflorescences are formed on phylloclades, which never happens 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 keep vertical 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.
Stem
The stem is the axis of the shoot, consisting of nodes and internodes. The main functions of the stem are supporting (carrier) and conducting. The stem is the link between roots and leaves. Reserve nutrients are usually deposited in perennial stems. Young stems with chlorenchyma under the epidermis are actively involved in photosynthesis.
The stem is usually cylindrical in shape and is characterized by radial symmetry in the arrangement of tissues. However, in cross section, it can be not only rounded, but also angular - three-,four- or multifaceted,ribbed,furrowed, sometimes completely flat, flattened, or bearing protruding flat ribs - winged(rice. 4.27).
Rice. 4.27. Stem types by cross-sectional shape: 1 - rounded; 2 - flattened; 3 - trihedral; 4 - tetrahedral; 5 - multifaceted; 6 - ribbed; 7 - furrowed; 8, 9 - winged.
The stems of woody and herbaceous plants differ dramatically in lifespan. Above-ground shoots of seasonal climate grasses live, as a rule, for one year; the lifespan of the shoots is determined by the lifespan of the stem. In woody plants, the stem exists for many years.
The anatomical structure of the stem corresponds to its main functions. A complex system of conductive tissues is developed in the stem, which links all the organs of the plant into a single whole; the presence of mechanical tissues ensures the performance of the support function. The stem, like the shoot as a whole, is an “open” growth system; it grows for a long time and new organs appear on it.
The tissues of the stem are formed as a result of the activity complex system meristems: apical, lateral and intercalary ( rice. 4.28). The primary structure is formed as a result of the work of primary meristems. Initial cells apical meristems are concentrated in the growth cone of the shoot. Leaf rudiments appear at the shoot apex with the correct frequency, which leads to early isolation of the nodes, and the development of internodes is delayed. Often the growth of internodes and the development of permanent tissues in them continue for a long time due to the work of residual intercalary meristems that are preserved at the bases of young internodes. good example such intercalary (intercalary) growth can be the stem of cereals, in which the apical meristem is spent very early on the formation of an inflorescence, and the rapid elongation of the shoot is due precisely to intercalary growth.
Rice. 4.28. Scheme of distribution of meristems in the stem: 1 - apical meristem; 2 - intercalary meristem; 3 - procambium; 4 - cambium.
The outermost layer of apex cells becomes protoderma from which the epidermis develops - the integumentary tissue of the future leaf and stem. At the level of the first leaf tubercles in the apical meristem, strands of narrower and longer cells are indicated - these are procambium giving rise to primary conductive tissues. The procambium may occur as individual bundles or as a continuous ring. With further growth, the procambium spreads both into the growing leaf primordia and into the stem, forming the basis of the future shoot conducting system that connects the leaves and stems. The rest of the apex is occupied main meristem, from which parenchymal storage and assimilating tissues, as well as primary mechanical tissues, are subsequently formed. The main meristem, located between the protoderm and procambium, turns into the primary bark of the stem, and the core is formed from the main meristem, located in the center.
The primary structure of the stem in spore and monocot plants persists throughout life. In gymnosperms and dicots, inside the procambium occurs cambium, which deposits secondary conductive tissues, resulting in secondary thickening of the stem.
The primary structure of the stem. In the stem, which has a primary structure, as in the root, integumentary tissue,primary cortex And stele(axial, or central cylinder) (rice. 4.29).
Integumentary tissue is epidermis typical structure. Part primary cortex includes the main parenchyma, as well as mechanical, excretory and some other tissues. More common among mechanical tissues collenchyma, it forms either a solid cylinder, or has the form of individual strands, usually located along the protrusions - the edges of the stem ( rice. 4.29). Immediately below the collenchyma or epidermis, if collenchyma is absent, under conditions favorable for photosynthesis, is located chlorenchyma. It can form with collenchyma or sclerenchyma alternating stripes along the stem. The boundary between the crust and the stele is much less pronounced.
organism flowering plant It is a system of roots and shoots. The main function of aboveground shoots is the creation of organic substances from carbon dioxide and water using solar energy. This process is called air nutrition of plants.
The shoot is a complex organ consisting of a stem, leaves, and buds formed during one summer.
main escape- a shoot that develops from the bud of the seed germ.
side escape- an escape that appeared from the lateral axillary bud, due to which the stem branches.
Elongated shoot- escape, with elongated internodes.
Shortened Escape- escape, with shortened internodes.
vegetative shoot- shoot bearing leaves and buds.
generative escape- an escape bearing reproductive organs - flowers, then fruits and seeds.
Branching and tillering shoots
branching- this is the formation of lateral shoots from axillary buds. A highly branched system of shoots is obtained when side shoots grow on one (“mother”) shoot, and on them, the next side ones, and so on. In this way, as much air supply medium as possible is captured. The branched crown of the tree creates a huge leaf surface.
tillering- this is branching, in which large side shoots grow from the lowest buds located near the surface of the earth or even underground. As a result of tillering, a bush is formed. Very dense perennial bushes are called tufts.
Shoot branching types
In the course of evolution, branching appeared in thallus (lower) plants; in these plants, the growth points simply bifurcate. Such a branch is called dichotomous, it is characteristic of pre-shoot forms - algae, lichens, liverworts and anthocerot mosses, as well as outgrowths of horsetails and ferns.
With the appearance of developed shoots and buds, monopodial branching, in which one apical bud retains its dominant position throughout the life of the plant. Such shoots are ordered, and the crowns are slender (cypress, spruce). But if the apical bud is damaged, this type of branching is not restored, and the tree loses its typical appearance (habitus).
The most recent type of branching in time of occurrence - sympodial, in which any nearest bud can develop into an escape and replace the previous one. Trees and shrubs with this type of branching are easy to pruning, crown formation, and in a few years they are overgrown with new shoots without losing their habit (linden, apple, poplar).
A kind of sympodial branching false dichotomous, which is characteristic of shoots with an opposite arrangement of leaves and buds, therefore, instead of the previous shoot, two grow at once (lilac, maple, mock orange).
The structure of the kidneys
Bud- a rudimentary, not yet unfolded shoot, at the top of which there is a growth cone.
Vegetative (leaf bud)- a bud consisting of a shortened stem with rudimentary leaves and a growth cone.
Generative (flower) bud- a bud, represented by a shortened stem with the rudiments of a flower or inflorescence. A flower bud containing 1 flower is called a bud.
apical bud- a bud located at the top of the stem, covered with young leaf buds overlapping each other. Due to the apical bud, the shoot grows in length. It has an inhibitory effect on the axillary kidneys; removing it leads to the activity of dormant kidneys. Inhibitory reactions are disturbed, and the kidneys open.
At the top of the embryonic stem is the growth part of the shoot - growth cone. This is the apical part of the stem or root, consisting of educational tissue, the cells of which are constantly dividing by mitosis and give an increase to the organ in length. At the top of the stem, the growth cone is protected by bud scaly leaves; all elements of the shoot are laid in it - the stem, leaves, buds, inflorescences, flowers. The root growth cone is protected by a root cap.
Lateral axillary kidney- a bud that occurs in the axil of the leaf, from which a lateral branching shoot is formed. The axillary buds have the same structure as the apical bud. Lateral branches, therefore, also grow with their tips, and on each side branch the terminal bud is also apical.
At the top of the shoot, there is usually an apical bud, and axillary buds in the axils of the leaves.
In addition to apical and axillary buds, plants often form so-called adnexal buds. These kidneys do not have a certain regularity in location and arise from internal tissues. The source of their formation can be the pericycle, cambium, parenchyma of the medullary rays. Adnexal buds can form on stems, leaves, and even roots. However, in structure, these kidneys are no different from ordinary apical and axillary ones. They provide intensive vegetative renewal and reproduction and are of great biological importance. In particular, with the help of adventitious buds, root shoot plants reproduce.
dormant buds. Not all buds realize their ability to grow into a long or short annual shoot. Some buds do not expand into shoots for many years. At the same time, they remain alive, capable of certain conditions develop into a leafy or flower-bearing shoot.
They seem to be sleeping, which is why they are called sleeping buds. When the main trunk slows down its growth or is cut down, dormant buds begin to grow, and leafy shoots grow from them. Thus, dormant buds are a very important reserve for the growth of shoots. And even without external damage, old trees can “rejuvenate” due to them.
Dormant buds, very characteristic of deciduous trees, shrubs and a number of perennial herbs. These buds do not develop into normal shoots for many years, often dormant throughout the life of the plant. Usually dormant buds grow annually, exactly as much as the stem thickens, which is why they are not buried by growing tissues. The stimulus for awakening dormant buds is usually the death of the trunk. When birch is felled, for example, stump shoots are formed from such dormant buds. special role dormant buds play in the life of shrubs. A shrub differs from a tree in its versatility. Usually, in shrubs, the main maternal stem does not function for long for several years. When the growth of the main stem is attenuated, dormant buds awaken and daughter stems are formed from them, which overtake the parent in growth. Thus, the shrub form itself arises as a result of the activity of dormant buds.
mixed kidney- a bud consisting of a shortened stem, rudimentary leaves and flowers.
kidney renewal- wintering bud of a perennial plant, from which an escape develops.
Vegetative propagation of plants
| Way | Drawing | Description | Example |
Creeping shoots |  | Creeping shoots or tendrils, in the nodes of which small plants with leaves and roots develop | Clover, cranberry, chlorophytum |
rhizome |  | With the help of horizontal rhizomes, plants quickly capture a large area, sometimes several times. square meters. At the rhizomes, older parts gradually die off and collapse, and individual branches are separated and become independent. | Lingonberry, blueberry, wheatgrass, lily of the valley |
tubers |  | When there are not enough tubers, it is possible to propagate by parts of the tuber, eye-buds, sprouts and tops of the tubers. | Jerusalem artichoke, potatoes |
bulbs |  | From the lateral buds on the mother bulb, daughter ones are formed - babies that are easily separated. Each daughter bulb can give rise to a new plant. | onion, tulip |
leaf cuttings |  | The leaves are planted in wet sand, and adventitious buds and adventitious roots develop on them. | Violet, sansevier |
layering |  | In the spring, bend the young shoot so that its middle part touches the ground, and the top is directed upwards. On the lower part of the shoot under the kidney, it is necessary to cut the bark, pin the shoot to the soil at the place of the cut and spud it with moist earth. By autumn adventitious roots are formed. | Currant, gooseberry, viburnum, apple tree |
shoot cuttings | A cut branch with 3-4 leaves is placed in water, or planted in wet sand and covered to create favorable conditions. Adventitious roots form on the lower part of the cutting. | Tradescantia, willow, poplar, currant |
|
Root cuttings |  | The root cutting is a segment of the root 15-20 cm long. If you cut off a piece of dandelion root with a shovel, adventitious buds form on it in the summer, from which new plants | Raspberry, rosehip, dandelion |
Root offspring |  | Some plants are able to form buds on their roots. | |
Grafting with a cutting |  | First, annual seedlings are grown from seeds - wildlings. They serve as a base. WITH cultivated plant cuttings are cut - this is a scion. Then the stem parts of the scion and rootstock are connected, trying to connect their cambium. This makes the tissue grow more easily. | Fruit trees and shrubs |
Kidney vaccination |  | A one-year-old shoot is cut from a fruit tree. Leaves are removed, leaving the petiole. An incision is made with a knife in the bark in the form of the letter T. A developed bud is inserted from a cultivated plant 2-3 cm long. The grafting site is tightly tied. | Fruit trees and shrubs |
tissue culture |  | Growing a plant from cells of educational tissue placed in a special nutrient medium. | Orchid, Carnation, Gerbera, Ginseng, Potato |
Modifications of underground shoots
Rhizome- an underground shoot that performs the functions of deposition of reserve substances, renewal, and sometimes vegetative reproduction. The rhizome has no leaves, but has a well-pronounced metameric structure, the nodes are distinguished either by leaf scars and the remains of dry leaves, or by leaf scars and the remains of dry leaves, or by living scaly leaves and the location of axillary buds. Adventitious roots may form on the rhizome. From the buds of the rhizome, its lateral branches and above-ground shoots grow.
Rhizomes are characteristic mainly of herbaceous perennials - hoof, violet, lily of the valley, couch grass, strawberry, etc., but are found in shrubs and shrubs. The life span of rhizomes varies from two to three to several decades.
tubers- thickened fleshy parts of the stem, consisting of one or more internodes. There are aboveground and underground.
Elevated- thickening of the main stem, side shoots. They often have leaves. Above-ground tubers are a reservoir of reserve nutrients and serve for vegetative propagation; they may contain metamorphosed axillary buds with leaf primordia, which fall off and also serve for vegetative propagation.
Underground tubers - thickening of the hypocotyl knee or underground shoots. On underground tubers, the leaves are reduced to scales that fall off. In the axils of the leaves are buds - eyes. Underground tubers usually develop on stolons - daughter shoots - from buds located at the base of the main shoot, look like very thin white stalks, bearing small colorless scale-like leaves, grow horizontally. Tubers develop from the apical buds of stolons.
Bulb- an underground, less often above-ground shoot with a very short thickened stem (bottom) and scaly, fleshy, succulent leaves that store water and nutrients, mainly sugar. Aerial shoots grow from the apical and axillary buds of the bulbs, and adventitious roots form on the bottom. Depending on the placement of the leaves, bulbs are scaly (onion), tiled (lily) and prefabricated or complex (garlic). In the sinus of some scales of the bulb there are buds from which the daughter bulbs develop - babies. Bulbs help the plant survive in adverse conditions and are the organ of vegetative reproduction.
Corms- outwardly similar to bulbs, but their leaves do not serve as storage organs, they are dry, membranous, often these are the remains of the sheaths of dead green leaves. The storage organ is the stem part of the corm, it is thickened.
Aboveground stolons (lashes)- short-lived creeping shoots that serve for vegetative propagation. They are found in many plants (drupe, bent grass, strawberry). Usually they lack developed green leaves, their stems are thin, fragile, with very long internodes. The apical bud of the stolon, bending upward, gives a rosette of leaves, which takes root easily. After the new plant takes root, the stolons are destroyed. vernacular name these aboveground stolons are whiskers.
spines- shortened shoots with limited growth. In some plants, they form in the axils of the leaves and correspond to lateral shoots (hawthorn) or form on trunks from dormant buds (gleditsia). Characteristic for plants of hot and dry places of growth. They perform a protective function.
succulent shoots- above-ground shoots adapted for the accumulation of water. Usually, the loss or metamorphosis (turning into spines) of leaves is associated with the formation of a succulent shoot. The succulent stem performs two functions - assimilation and water storage. Typical for plants living in conditions of prolonged lack of moisture. Stem succulents are most represented in the cactus family, Euphorbiaceae.
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 with the root, the shoot has a 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. In seed plants, they are located 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 grasses). 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. In trees and shrubs, as well as in many perennial herbaceous plants, buds unfold into shoots once a year - in spring or early summer, after which new wintering buds are formed 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 - creeper 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 a special case of 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 ( A- 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, during the development of the shoot from the bud and its further growth, the location of the leaves can be influenced by external factors, mainly lighting 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; smaller leaves fill the gaps between the larger 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 the 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 evergreen trees - after a few years. Some of the shoots die off completely after the loss of leaves, but the majority remain as skeletal axes, performing supporting, conducting, 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 (strawberries, 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 collapse, the tubers overwinter, and the next year they 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 storage, 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 for 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 thorns: instead, normal leaves (camel thorn) or leafy shoots (English gorse) grow.
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. Scale-like leaves and inflorescences are formed on phylloclades, which never happens 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.
