On growing shoots of plants can develop. Escape, its structure. Stem - shoot axis
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 neighboring nodes. Between the stem and the leaf there is an upper corner 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 short shoots herbaceous plants(dandelion, carrot, beet, etc.) leaves are located close to each other and form a 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, in the second - they bloom, give fruits and seeds. perennial plants live three or 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 propagation.
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 various 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 mineral substances. 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 the branches of the last order. Crowns have different shape: pyramidal (poplar), rounded (spherical) (sharp maple), columnar (cypress), flat (some pines), etc. A person forms the crown of 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 stem buds - 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 creeper . 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, lip flowers), 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 the external environment occurs through 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 central location in the stem. 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. The 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.
Behind growing season plants, one annual ring is formed. Light rings are rings of wood with large thin-walled cells, vessels (tracheids) of 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 the climatic conditions in a given 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.
Embryo either from an axillary or adnexal (adventitious) 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), consisting additionally 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 the section of the stem on which the flowers are located).
Main escape organs
A vegetative unmodified shoot is a single plant organ, consisting of a stem, leaves and buds, formed from a common array of meristems (the cone of growth of the shoot) and having a single conducting system. The stems and leaves, which are the main structural elements of the shoot, are often considered as its constituent organs, that is, organs of the second order. In addition, the obligatory affiliation of the escape is the kidneys. The main external feature that distinguishes the shoot from the root is the presence of leaves.
Monopodial branching
Monopodial branching is the next stage in the evolution of shoot branching. In plants with a monopodial type of shoot structure, the apical bud is preserved throughout the life of the shoot. The monopodial type of branching is often found among gymnosperms, it is also found in many angiosperms (for example, in many species of palms, as well as plants from the Orchid family - gastrohilus, phalaenopsis and others). Some of them have a single vegetative shoot (for example, Phalaenopsis is pleasant).
monopodial plants- the term most often used in the description of plants of tropical and subtropical flora, as well as in popular science literature on indoor and greenhouse floriculture.
Monopodial plants can vary significantly in appearance. Among them there are rosette, with an elongated shoot, bushy.
Sympodial branching
In plants with a sympodial type of shoot structure, the apical bud, having completed development, dies off or gives rise to generative run away. After flowering, this shoot no longer grows, and a new one begins to develop at its base. The structure of the shoot in plants with a sympodial type of branching is more complicated than in plants with; sympodial branching is an evolutionarily more advanced type of branching. The word "simpoidal" is derived from the Greek. sym ("together" or "many") and pod ("leg").
Sympodial branching is characteristic of many angiosperms: for example, for lindens, willows and many orchids.
In orchids, in addition to the apical ones, some sympodial orchids also form lateral inflorescences, developing from buds located at the base of the shoot (Pafinia comb). The part of the shoot pressed against the substrate is called the rhizome. It is located, as a rule, horizontally and does not have true leaves, only scaly. A reduced, almost indistinguishable rhizome occurs in many Masdevallia, Dendrobiums and Oncidiums; well distinguishable and thickened - in cattleyas and lelias, elongated - in bulbophyllums and cologins, reaching 10 or more centimeters. The vertical part of the shoot is often thickened, forming the so-called tuberidium, or pseudobulb. Pseudobulbs can be of various shapes - from almost spherical to cylindrical, cone-shaped, club-shaped and elongated, resembling reed stalks. Pseudobulbs are storage organs.
sympodial plants- the term most often used in the description of plants of tropical and subtropical flora, as well as in popular science literature on indoor and greenhouse floriculture.
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Bulbophyllum grandiflorum |
Cirrhopetalum macraei |
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 conditions. environment, and in cultivated plants - under the influence of man.
A rhizome is formed or initially as an underground organ (kupena, raven eye, lily of the valley, blueberries), 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 to vegetative propagation, settling and capturing territory. 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 form on phylloclades, which never happens on normal leaves, which means that the phyllocladium corresponds to the whole axillary escape. 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.
The aerial part of plants is called the term "escape". Its structure is determined by the functions it performs. Of course, each organ is irreplaceable and determines the possibility of existence species. Nutritional functions, growth processes, the ability to adapt - these are just some of the most important functions of the visible part of plant organisms.
Biology: the structure of the shoot
In morphology, the axial and lateral parts of this organ are distinguished: the stem and the leaf. The structure is striking in its diversity: from microscopic water duckweed to giant forest sequoia. It is due to the different structure constituent parts aerial parts associated with the characteristics of the habitat and climatic conditions. There are also shortened rudimentary shoots - buds.
The place where the leaf is attached to the axial part is called the node, and the angle that forms between them is called the sinus. Here are specialized buds that form leaves or flowers. The distance between two leaf attachment points is called an internode.
Stem
The structure of the shoot initially depends on the direction of growth and location in space of the stem. Depending on these features, erect, creeping, creeping, curly and clinging species are distinguished. The stems and the nature of the surface are varied. It can be naked or with outgrowths, smooth or rough. If you cut the stem across, you can determine the shape: rounded, ribbed, with a certain number of faces or flattened.
Strawberry mustache is also its shoot, which has shortened internodes.
Depending on the life form, grassy and woody stems are distinguished. The first do not have a cambium - lateral In the first years of life, outwardly, new shoots of trees and shrubs look like them. They are green in color and capable of photosynthesis. Over time, they become woody, becoming more durable. They are able to hold large fruits and withstand strong gusts of wind.
stem types
Depending on the characteristics of the development cycle, plants can be one-, two-, and perennial. For example, asters bloom in autumn, after which they completely die off. Carrots and beets develop differently. In the first year of life, they form roots, which are organs that store nutrients. In autumn, their stem dies. But the plant exists in the form of a modified stem. With the onset of favorable conditions, the shoot grows again. At the same time, in the second year of life, as a result of flowering, seeds are formed on it, with the help of which the plant reproduces.
We will consider the life cycle of perennial plants by studying the structural features of the shoots of coniferous plants. These are shrubs or trees that have a single powerful stem - the trunk. Its development begins with the germination of the seed. As a result of its growth, a seedling is formed, and then an adult plant. The life cycle of perennial plants ends with death. Conifers are rightfully considered real centenarians. So, pine lives for about 400 years, spruce - up to 500, and juniper - as many as 1000!
Sheet
The lateral part of the shoot is no less functional and diverse. It provides air nutrition, transpiration - evaporation of water from the surface, vegetative propagation. The shoot, the structure of which is determined by the functions performed, is characterized by a variety of leaves.
Cactus needles are needed to reduce the amount of evaporated moisture. And the wide palmate ones of the horse chestnut, on the contrary, increase its quantity.
Leaves with one blade are called simple, and with several, located on the same petiole, they are called complex. Looking at them, you can see a certain pattern. It is created by veins. These are vascular-fibrous bundles. By the nature of venation, leaves are distinguished with mesh (maple, apple), parallel (corn, rye) and arc (plantain, lily of the valley) venation.
leaf arrangement
The shoot, the structure of which also depends on the amount of solar energy received, is characterized by a different arrangement of leaves on the stem. In the case of their arrangement in a spiral, another is formed, and if in a circle - opposite, or whorled.
In nature, there are no plants that do not renew foliage. It is shed by both pine and spruce. Since not all leaves fall at once, no one notices this.
Escape modifications
If it becomes necessary to perform additional functions, the shoots and their components are modified. The leaves may turn into spines or scales. In plant predators, they are able to capture and digest small insects.
The tubers of the Jerusalem artichoke, which is also called the earthen pear, also form a modification of the shoot - a tuber. On a thickened fleshy stem there are scar-like buds from which young shoots grow.
Underground stems with elongated internodes are rhizomes. They look like whips, have well-developed mechanical and conductive tissues. From the buds located on the rhizome, leaves are formed. Those who are new to the structure of rhizomes believe that if you get rid of the leaves, the whole plant will die. But this opinion is erroneous, because the main part of the plant is reliably protected and is underground.
The relationship of structure and functions
The structure of the escape depends on the functions performed. This can be proved by considering the structural elements of its parts. The leaf is covered on the outside with a living tissue skin, in which there are holes - stomata. They are essential for protection and gas exchange. The internal content of the leaf is represented by the main storage and chlorophyll-bearing tissue, which is responsible for the autotrophic nutrition of the entire plant. Conductive and vein-forming elements are the basis for transporting the entire range of essential nutrients.
They are the root (its underground part) and the shoot. The structure of the generative parts does not allow them to perform such functions. They carry out the process of sexual reproduction and distribution of plants. But the flower develops precisely on the stem, and its development requires organic substances formed in the leaves.
It can be concluded that the plant is a single organism, the functioning of the parts of which are interconnected.
Deployment of the shoot from the kidney and its development. There are 2 stages in the life of an escape. The period of formation of the shoot as a rudimentary formation is called intrarenal or embryonic. When the kidney is deployed, the embryonic period in the life of the shoot is replaced by extrarenal or postembryonic period. With the onset of spring, the buds begin to grow and new shoots grow (stems with leaves and buds). You can observe the process of the shoot unfolding even before the onset of spring by placing branches of trees or shrubs in the water (especially in the second half of winter). The deployment of the shoot begins with swelling of the kidney, the kidney scales move apart, the rudiments of green leaves increase in size. Shortly after bud germination, the bud scales fall off, and the remaining scars from fallen scales form a bud ring on the shoot. By long-lasting kidney scars, you can determine the age of a branch of a tree or shrub. At the same time, an elongation of internodes is observed due to actively dividing cells of the interstitial meristem. During this period, intensive growth of leaf blades from the morphologically upper side occurs, and the leaf is folded away from the stem. Due to the intercalated growth, a petiole is formed between the base of the leaf and the blade. The laying of lateral shoots occurs both inside the maternal bud and during the period of extra-bud growth of the shoot.
The concept of annual and elementary shoots.annual shoot - shoot, the growth and formation of which in the extrarenal period of life ends within one year. In a seasonal climate, this occurs in one growing season. The intensity of growth and development of individual metameres is different. Often, at the base of the shoot, the internodes are short and the nodes are close together; higher along the shoot, they become longer, and at the apex, a decrease in the length of the internodes is again observed (the maximum sizes of the internodes, leaves, and buds correspond to the median metameres). Development elementary shoot occurs along a unimodal curve in one growth spurt, or one period of visible growth. Often in an oak, when studying a one-year shoot, it can be noted that it was formed as a result of two periods of growth. Thus, it should be said that the annual shoot consists of two elementary shoots. There are no scaly leaves between two elementary shoots, that is, a bud ring is not formed. In plants of a seasonless climate, annual shoots usually consist of several elementary shoots.
Morphological types of shoots. Escapes vary:
1. Along the length of the internodes.elongated- an escape in which internodes are clearly expressed and the nodes are far from each other. shortened- shoots in which the nodes are close together, and the internodes are practically not expressed or absent (plantain). In the same plant, along with elongated shoots, short ones (apple, birch, hairy sedge) can also develop. Usually shortened shoots are characterized by a small annual increase.
In some plants (pine, club moss), annual shoots are usually more than 10 cm long, but have close internodes. Such escapes are better called long(Fig. 6). The shortened shoots of herbaceous plants are called socket(primrose, dandelion, plantain). Half socket shoots (creeping tenacious, cornflower, meadow cornflower, peach-leaved bellflower) are characterized by contiguous nodes in the basal part of the shoot and elongated ones in its middle part. In the region of the inflorescence, the nodes can be either elongated (spreading bell) or contiguous (crowded bell). In shepherd's purse, wild radish and others, as the flowers open, the nodes in the inflorescence lengthen.
2. By functions. In many plants, specialization of shoots is observed. In woody plants, elongated shoots often vegetative(perform growth and trophic function), and shortened - generative. In elm, bean, wolf's bast, green leaves on generative shoots are completely absent. In herbaceous plants, an inverse correlation is often observed. Shortened shoots are vegetative, and elongated shoots are generative (lily of the valley, plantain).
3. Position of shoots in space. Shoots can be upright (or orthotropic), horizontal (or plagiotropic), ascending (or anisotropic), inclined, twisting around a support, clinging to a support (Fig. 4). The diversity of the position of the shoots of different plants in space allows a greater number of species to grow in a given territory.
4. By the time of formation of shoots from the kidneys. We have already considered (see Variety of buds) the peculiarities of the formation of enrichment shoots (sylleptic), renewal shoots and water shoots.
Escape system formation. The formation of the shoot system occurs due to their branching and growth. Branching of a shoot is a process leading to the formation of a shoot on a mother shoot, that is, shoots of the next order are formed on a shoot of one order.
There are two types of shoot branching: 1) apical, 2) lateral. In the process of historical development of plants, the nature of branching changed. Apical, or dichotomous branching is characteristic of club mosses, some ferns, and individual seed plants (some palms). Equally dichotomous (equally forked) branching is distinguished - the emerging shoots are the same and unequally dichotomous (unequally forked) - one shoot turns out to be more powerful and is, as it were, a continuation of the maternal shoot.
Rice. 4. Types of shoots by location in space: 1) - orthotropic (Fischer's carnation); 2) - plagiotropic (monetary loosestrife); 3) - anisotropic (moss); 4) - curly (field bindweed); 5) - clinging (mouse peas); 6) - inclined (drooping birch)
The vast majority of seed plants are characterized by lateral branching. Lateral buds give rise to a new shoot. The formation of side shoots increases their total number. The total surface of the air nutrition organs increases, which is extremely important for plants leading an “attached” lifestyle.
Due to the apical bud, the shoot grows in length. Over a number of years, as a result of the activity of one meristem, perennial axes of the same order are formed. This type of growth is called monopodial(Fig. 5). This is how maple, spruce and others grow. However, in a number of plants, the apical meristem forms an inflorescence at a certain stage, and further monopodial growth becomes impossible.
In some species (birch, willow, linden), the apical bud or even part of the shoot dies off. The growth of such plants comes from lateral buds. In autumn, after the death of the apical bud and part of the shoot, one of the lateral buds becomes apical in position, but the presence of a scar from the dead apex of the shoot (branch scar) indicates that this bud is lateral. This type of growth is called sympodial.
Thus, two ways of forming perennial axes are typical for seed plants: 1) monopodial growth and lateral branching (maple, oak, ash), 2) sympodial growth and lateral branching (birch, willow, linden).
Rice. 5. Monopodial growth of perennial axes with lateral branching. American maple branch (2 years): a - apical kidney; b - axillary kidney; c - leaf scar; d - renal ring
Main and side shoots. The main shoot is formed during the germination of seeds from the embryonic bud. From it in the same year (or in subsequent years) a system of shoots begins to form. From the apical bud there is an increase in the main shoot, the shoot of the first order. From the lateral buds, as a result of lateral branching, lateral shoots are formed, shoots of the second order. Lateral shoots of the second also grow and branch, forming shoots of the third order, and so on.
Acrotonia, mesotonia, basitonia. These three variants of shoot branching are distinguished depending on the location of the most strongly developed side shoots on the mother. At acroton(Greek acros - top, tonos - strength, power) branching, the most powerful side shoots are formed at the top of the mother shoot, with mesoton(Greek mezos - middle) - in the middle, and when basitonic(Greek basis - base) - at its base. A special case of lateral branching is the tillering of the shoot. In this case, side shoots are formed from buds located on a shortened part at the base of the shoot.
Formation of the trunk and crown of trees. Trees are characterized by the formation of a single trunk, usually in its upper part there is intensive branching (acrotonic), which leads to the formation of a crown. Stem growth can be either monopodial or sympodial. In the latter case, the trunk is formed as a result of the activity of the lateral buds by origin. The apical buds, and more often the small upper part of the shoot, are poorly developed and quickly die off. Crown formation occurs due to axillary buds and is associated with different branching intensity. The angle of inclination of the lateral branches relative to the trunk also significantly affects the originality of the crown shape. Usually the first lateral branches are weaker and die off quickly. So in spruce, the formation of full-fledged branches of the crown begins only from 6–8 years, and sometimes even later. Often the shape of the crown directly depends on the growing conditions of the plant. Trees standing alone have a much less developed trunk and a more powerful crown. In a dense forest, trees form a tall trunk and a small crown at the very top.
Shrub formation. Shrubs form several stems that replace each other as they age. The formation of new stems occurs due to dormant buds located at the base of the maternal stem. They can be located both surface and underground. The growth of the trunk occurs over several years. Branching occurs due to axillary buds. The degree of branching is different in different species and often depends on the phytocenosis. If the total life span of a shrub can reach several hundred years, then the stems live for about 20–40 years. However, this value varies widely: from 2 for raspberries to 60 for caragana.
Formation of the shoot system in herbs. Herbaceous plants are characterized by a wide variety of shoot systems, which are formed as a result of lateral branching and monopodial or sympodial growth. Usually, most of the annual growth of grasses dies off in the year of formation. Perennial shoot systems are usually located in the soil or tightly pressed against it. Highest value when characterizing the shoot systems of herbaceous plants, it has the type of growth and the length of the annual growth. Based on these features, shoot formation models perennial herbs (long-shoot sympodial - long-leaved veronica, kupena officinalis; semi-rosette sympodial - spiky veronica, peach-leaved bell; rosette monopodial - large plantain, medicinal dandelion; long-shoot monopodial - monetized loosestrife, medicinal veronica).
The concept of monocarpic escape. Monocarpic (mono - one, karpos - fruit) shoot blooms and bears fruit once. The concept of a monocarpic shoot is usually used to characterize herbaceous plants. The fate of a monocarpic shoot in different plants can develop in different ways:
1. The shoot transitioning to flowering in the first year of its development is monocyclic (many-flowered kupena, European hoof).
2. A shoot that starts flowering only in the second year of life is a dicyclic shoot (obscure lungwort, wild strawberry, Kashubian buttercup).
3. If the shoot starts flowering only in the third or subsequent years - a polycyclic shoot (round-leaved wintergreen, sheep fescue).
In addition to the above, there are shoots that never go to flowering. They are called shoots with an incomplete development cycle. The reasons for this may be different: 1) unfavorable conditions; 2) age condition; 3) specialization of shoots in one plant. The last group of plants includes monopodially growing shoots of the large plantain, dandelion officinalis.
leaf arrangement- this is the order of the leaves on the stem (Fig. 6). In some plants, only one leaf departs from the node, as, for example, in birch, oak, linden, buttercup. Such a leaf arrangement is called alternate. If there is more than one leaf on a node, it is whorled, its special case is opposite, in which within the node there are two leaves, usually located opposite each other (opposite), like in maple, elderberry, viburnum, veronica. In a number of species (crow's eye, anemone, elodea, juniper), three or more leaves. In all cases, leaves extending from two neighboring nodes are never located one above the other, but only at an angle to each other. With this leaf arrangement, minimal shading of one leaf by another is achieved. Often, plants have uneven growth of petioles and blades and the placement of leaves in the same plane, while forming a kind of continuous green screen that receives the incident rays of the sun. This arrangement of leaves in relation to the light source (often in shading conditions) is called leaf mosaic.
Rice. 6. Types of leaf arrangement: A - next (linden); B - opposite (monetary loosestrife); B - whorled (common loosestrife)
Stem. The central, axial part of the shoot is the stem. The stem performs supporting, transport and storage functions. Green stems are also involved in the air nutrition of plants. The stem is a support for leaves, flowers, fruits, buds and side shoots developing from them. Through the conductive tissues of the stem, from bottom to top and from top to bottom, water and nutrients dissolved in it are transferred. Spare substances are deposited in the tissues of the stem. Young green stems, along with leaves, are involved in the synthesis of organic substances from inorganic ones. Some plants lack green leaves (saxaul, cactus, asparagus, butcher's needle, and others), and the stem is the main organ of air nutrition.
The stem has nodes and internodes. The shape of the stem is usually determined by its cross section, made at the level of the internode. In different plants, it is not the same, but is constant for a species or even a genus, family. This often has taxonomic significance. More often the stem is rounded with a smooth or ribbed edge. It can be tetrahedral (nettle, sage), trihedral (sedge), winged (forest rank), etc. The stem is smooth or pubescent, which is determined by the presence of various hairs on the epidermis.
Sheet is a lateral organ of the shoot, located on the stem. Leaf functions: 1) photosynthesis, 2) transpiration, 3) gas exchange. You will learn more about these concepts in the course of plant physiology.
The main parts of the sheet are plate, petiole, stipules And base(Fig. 7). Their structure corresponds to the functions that the leaf performs, however, in different plants they are not the same in shape and size (Fig. 8). A lamina is an expanded, lamellar part of a leaf. It is this part of the sheet that performs the functions listed above. With a lamellar form of the organ, its maximum surface is achieved, and as a result, high photosynthetic activity. At the base, the plate passes into a stem-like petiole. Its main function is to place the leaf blade in the most favorable position for the plant in space, as well as to ensure the springiness of the leaf, that is, to prevent damage to the leaf during various impacts. It, in turn, in the lower part passes into the base of the leaf, which is directly connected with the stem. The base is an obligatory part of the sheet. In some plants (carrots, wheat), it grows and covers the stem above the node. This basis is called vagina.
Rice. 7. Simple Leaves: 1 - leaf blade; 2 - petiole; 3 - base; 4 - stipules; a - vagina; b - tongue; c - bell
Stipules are outgrowths at the base of the leaf. Their function is mainly associated with the protection of the leaf blade during the period of intrarenal development. However, in some plants, stipules are able to perform independent functions even in adulthood. They can grow significantly like a pea and resemble a plate, while performing a photosynthetic function. In yellow acacia, gooseberry, stipules turn into spines and serve as protective formations. A leaf is called complete if it has a blade, petiole, base, stipules. A full sheet of mountain ash, rose, oak, bird cherry. In the first two of these plants, all parts of the leaf are preserved throughout life. In oak, adult leaves do not have stipules, as they die early, having performed the functions of protecting the plate of the rudimentary leaf of the kidney. When deploying a kidney and forming a shoot, the stipules of oak, birch, linden and a number of other plants fall off.
Rice. 8. Features of leaf morphology: 1 - parts of the sheet: a - complete sheet; b - compound leaf with stipules; c - stipules fused with petiole; g - bell; d - false leaf arrangement (for example, in bedstraws), f - swollen sheath, g - tubular sheath (for example, in cereals); 2 - position of the leaf on the stem: a - long-leaf, b - short-leaf, c - sessile, d - decurrent, e - stalk-bearing, f - pierced, g - fused leaves; 3 - the shape of the base of the leaf blade: a - wedge-shaped, b - rounded, c - heart-shaped, d - cut, e - swept, f - spear-shaped, g - unequal, h - narrowed; 4 - shape of the leaf apex: a - obtuse, b - truncated, c - sharp, d - pointed, e - pointed, f - notched; 5 - the shape of the edge of the sheet: a - entire, b - serrated, c - double-toothed, d - palmate, e - double-serrate, e - unequally serrate, g - crenate, h - notched, i - wavy, j - ciliated
A leaf is called incomplete if it lacks at least one of its parts: petiole (sessile leaf), stipules or lamina. Sessile leaf of aloe, peach-leaved bell, Fisher's carnation. These plants also lack stipules. The latter are not present in lilac, cabbage, potatoes. Rarely, the plate may be missing. Then its functions are performed by other parts: stipules (leafless rank), flattened petiole (in some acacias).
Rice. 9. Compound Leaves: 1 - single leaf (lemon); 2 - ternary (species name); 3 - fingered (horse chestnut); 4 - paired (meadow rank); 5 - unpaired (forest raspberry); a - base; b - stipules; c - rachis; d - leaflet; d - petiole; e - stipules
Simple and compound leaves. A leaf with one blade that does not have an articulation with a petiole or base is called simple. Leaf called difficult(Fig. 9), if it has one or more plates, each of them has its own articulation with a common petiole - the rachis. Each leaf blade of a complex leaf is called a leaflet, or platelet.
Rice. 10. Types of sheet division
A single-leaf compound leaf - in lemon, tangerine, a three-leaf compound leaf - in strawberries, clover, a palmate leaf - in lupine, horse chestnut, an odd-pinnate leaf - in mountain ash, ash (the upper leaflet is one, and only the lateral leaves are arranged in pairs on a common petiole) and paripinnate - in the nomadic, pea (all leaves occupy a lateral position on a common petiole and are arranged in pairs).
Compound leaves are often confused with simple ones (Fig. 10, 11), which have a deeply dissected plate: triple-dissected - in anemone, palmately dissected - in erect cinquefoil, unpaired pinnate - in goose cinquefoil, lyre-shaped leaf - in potatoes (leaf unpaired pinnately dissected with the largest upper segment) . Each individual part of the plate is called a segment. The segment has no articulation with the petiole. The shape and size of leaves is an important taxonomic feature.
Variety of leaf blades. The blades of simple leaves and leaflets of compound leaves are very diverse in general outline (round, oval, ovate, linear, and others), in the shape of the edge of the plate (the edge can be solid, serrate, serrate, wavy), and in the nature of venation (Fig. 11).
Rice. 11. Blade shapes
Numerous veins cross the plate in different directions. The plate may have one powerful vein running along its middle. This midrib. Thinner lateral branches extend from it to the sides, which in turn branch repeatedly (birch, oak). Such venation of the plate is called pinnate (or pinnate-reticulate). In the presence of several large, more or less identical veins, brought together at the base of the plate and diverging like a fan (geranium, buttercup), the venation is called palmate (or palmate-reticulate). If large veins run parallel to each other along the plate, then the venation is called parallel (wheat, fescue). Arcuate venation is observed in leaves (lily of the valley, plantain), large veins, in addition to the central one, are curved like an arc (Fig. 12).
Rice. 12. Forms of leaf venation: a - dichotomous; b - palmate; c - pinnate; d - parallel; d - arc
Three leaf formations. At the base of the annual shoot there are leaves of the lower formation (bud scales, bulb scales), which perform a protective function. Usually they are scaly or membranous, brown, pale green. Ordinary green leaves form a median formation. The leaves of the top formation are located in the region of the inflorescence, are the covering leaves of flowers and perform a protective function (for buds). In some plants (oak maryannik) they are brightly colored and serve to attract insects.
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; as long as it persists, this escape is capable of further growth in length to form new metamers. 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 kidneys are an obligatory sign of any perennial plant, arboreal or herbaceous, it is they who ensure the longevity of the 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 herbs. 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 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 ( 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, 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 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 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 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.
It is an axis (stem) with leaves and buds located on it - the rudiments of new shoots that arise in certain order on the axle. These rudiments of new shoots ensure the growth of the shoot and its branching, i.e., the formation of a shoot system.
Unlike the root, the shoot is dissected into internodes and nodes, with one or more leaves attached to each node. Internodes can be long, and then the shoots are called elongated; if the internodes are short, the shoots are called shortened. The angle between the stem and the leaf at the point of origin is called the leaf axil. The variety of shoot morphology is also determined by the location of the leaves, the way they are attached, the nature of branching, the type of growth and the biological characteristics of the shoot (its development in the air, underground, in).
In modern plant morphology, the shoot as a whole, as a derivative of a single part of the apical meristem, is taken as a single organ of the same rank as the root. The shoot as a single organ has metamerism, i.e., metameres are well expressed in it, repeating along its longitudinal axis. Each metamere consists of a node with a leaf or leaves extending from it, an axillary bud, and an underlying internode.
The first shoot develops from an embryonic shoot represented by a hypocotyl, cotyledons extending from the cotyledon node, and a bud (apical bud), from which all subsequent metameres of the first, or main, stem are formed.
As long as the apical bud is preserved, the shoot is capable of further growth in length with the formation of new metameres. From the buds located in the axils of the leaves, side shoots develop, each of which has an apical and axillary buds. .
The kidney is covered on the outside with dense leathery scales, under which in the center of the kidney there is a rudimentary stem and small rudimentary leaves. In the axils of these leaves are rudimentary buds, each of which is a shoot. Inside the kidney is the growth center, which ensures the formation of all organs and primary tissues of the shoot.
Buds can be vegetative and generative (floral). A stem with leaves and buds grows from a vegetative bud, an inflorescence or a single flower develops from a generative bud.
branching shoot
The side branches are built and grow in the same way as the main stem. Accordingly, the main stem is called the axis of the first order, the branches developing from its axillary buds are called the axis of the second order, etc.
The degree of branching, the direction of growth of branches and their size determine the appearance of plants, their habit. There are two types of branching: apical and lateral. Apical branching is characterized by the division of the growth cone into two parts, each of which gives rise to an escape. Such branching is called forked, or dichotomous. Dichotomous branching occurs in some bryophytes and lycopods.
Lateral branching develops from axillary buds and may be monopodial or sympodial.
Monopodial branching is characterized by the fact that the growth cone of the main shoot has been functioning for many years, building up the stem and increasing the length of the first-order axis. From the axillary buds, axes of the second order are formed. Monopodial branching is characteristic of gymnosperms (spruce, pine, larch), many woody angiosperms (oak, beech, maple, bird cherry) and many herbaceous rosette plants (plantain, dandelion, clover).
Sympodial branching is due to the death of the upper part of the shoot and the development of a vegetative shoot from the upper axillary bud, which usually continues the main axis (poplar, birch, willow, wild rosemary, lingonberry, cereals, sedges, etc.). Such shoots are called replacement shoots.
False forked branching resembles dichotomous, but is sympodial with opposite leaf arrangement (lilac, dogwood, horse chestnut, etc.).
In the direction of growth, shoots are erect, inclined, drooping, hanging, ascending, recumbent, or creeping, creeping, curly, climbing.
According to the structure and life span of shoots, plants are divided into herbaceous and woody.
According to life expectancy, herbaceous plants can be annuals, biennials and perennials. Annual plants live less than a year. Biennial plants in the first year of life form vegetative organs and accumulate reserve nutrients in the roots; in the second year they bloom and die off after fruiting (carrots, radishes, beets, etc.). Perennial herbaceous plants live for more than two years, they annually develop above-ground shoots from buds. These buds, called renewal buds, are in most cases underground on modified shoots - rhizomes, tubers, bulbs.
Woody plants are characterized by the presence of perennial above-ground, strongly lignified shoots that do not die off for the winter. They are represented by trees and shrubs. The trees have a well-developed main stem - a trunk that usually reaches a great height - and a crown, usually consisting of numerous smaller side branches. In shrubs, the main trunk is short-lived or poorly developed. From the axillary and adnexal buds located at its base, shoots develop that reach significant development (buckthorn, hazel, honeysuckle, etc.).
Shrubs have perennial stems, but their secondary thickening and growth in height are weakly expressed (lingonberries, blueberries, wild rosemary, cranberries, etc.).
In semi-shrubs, the bases of the shoots become woody and persist for several years. The upper parts of the shoots die off by winter. From the axillary buds located on the wintering areas of the shoots, new shoots grow in the spring of next year (some types of wormwood, cinquefoil).
Escape metamorphoses
Plant shoot metamorphoses include various forms modifications of underground and aboveground shoots.
Underground shoots are formed in the soil, and the nature of their modifications is associated with the accumulation of reserve nutrients in order to survive unfavorable seasons for vegetation - winter, drought, etc. Reserve substances can be deposited in such underground shoots as tubers, bulbs, rhizomes.
Tubers are thickenings of an underground shoot. They usually form in the axils of developing underground colorless scaly leaves called stolons (like potatoes). The apical buds of the stolons thicken, while their axis grows and turns into a tuber, and only the edges remain from the scaly leaves. In the bosom of each eyebrow sit groups of kidneys - eyes. Stolons are easily destroyed, and tubers serve as organs of vegetative reproduction.
The bulb is an underground, strongly shortened shoot. The stem in the bulb occupies a small part and is called the bottom. Grassroots succulent leaves, called scales, are attached to the bottom. The outer scales of the bulb are often dry, leathery, and have a protective function. The upper leaves are in the apical bud of the bottom, which develops into aerial green leaves and into a flower-bearing arrow. Adventitious roots develop from the bottom of the bulb. Bulbs are typical for plants from the Liliaceae family (lilies, tulips, onions, etc.), amaryllis (amaryllis, daffodils, etc.). Majority bulbous plants belong to the ephemeroids, which have a very short growing season and live mainly in arid climates.
Rhizome - an underground shoot of a plant that looks like a root or parts of the root system. In the direction of growth, it can be horizontal, oblique or vertical. The rhizome performs the functions of deposition of reserve substances, renewal, sometimes vegetative reproduction in perennial plants that do not have a main root in the adult state. The rhizome does not have green leaves, but at least in the young part it has a well-defined metameric structure. The nodes are distinguished by leaf scars, the remains of dry leaves or living scaly leaves and by the location of the axillary buds. According to these features, it differs from the root. Adventitious roots form on the rhizome, lateral branches and above-ground shoots grow from the buds.
The apical part of the rhizome, constantly growing, moves forward and transfers the renewal buds to new points, while the rhizome in the old part gradually dies off. Depending on the intensity of the growth of rhizomes and the predominance of short and long internodes, long-rhizome and short-rhizome plants are distinguished.
Rhizomes, like aboveground shoots, have sympodial or monopodial branching.
When branching the rhizome, daughter rhizomes are formed, which leads to the formation of above-ground shoots. If destruction occurs in separate parts rhizomes, they separate and vegetative reproduction occurs. A set of new individuals formed from one vegetatively is called a clone.
Rhizome formation is characteristic of perennial herbaceous plants, but sometimes it occurs in shrubs (euonymus) and some shrubs (lingonberries, blueberries).
The metamorphoses of plant shoots also include above-ground modifications - these are above-ground stolons and mustaches. In some plants, young shoots begin to grow horizontally on the surface of the soil, like lashes. After some time, the apical bud of such a shoot bends up and gives a rosette. In this case, the whips are destroyed, and the daughter individuals exist independently, the function of these whips is to capture the area and resettle new individuals, that is, they perform the function of vegetative reproduction. Scourges are aboveground stolons that have green leaves and are involved in the process of photosynthesis. They are found in many plants (bone, Zelenchuk, tenacity, etc.). In some plants (strawberry, partly stone fruit), above-ground stolons do not have green leaves, their stems are thin with long internodes. They got the name mustache. Usually, after rooting of their apical bud, they are destroyed.
Other metamorphoses of aboveground shoots of plants include spines of leaf (cactus, barberry) and stem (wild apple, wild pear, barberry, etc.) origin. The formation of spines is associated with the adaptation of plants to a lack of moisture. In addition, in some plants of arid habitats, a flattening of the stem or shoot occurs, the so-called phyllocladia and cladodia (for example, needle needle) are formed. On the shoots of the needle, in the axils of scaly leaves, flat leaf-shaped phylloclades are formed, corresponding to the whole axillary shoot and having limited growth. Cladodia, unlike phyllocladia, are flattened stems that have the ability to grow for a long time. Shoots of plants, and sometimes leaves, can turn into tendrils, which, in the process of long apical growth, are able to twist around a support.
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 large area, sometimes several 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. Cuttings are cut from a cultivated plant - 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.
Escape structure.
As you already know, a shoot is a vegetative organ of a plant, consisting of a stem with leaves and buds located on it. The axial part of the shoot is the stem. At its top is the apical kidney. The lateral parts of the shoot include leaves and lateral buds, which are located on the stem above the leaf. The angle formed by the leaf and the upstream portion of the stem is called the leaf axil. Thus, the lateral buds located in the leaf axil are axillary buds.
The part of the stem that contains the leaf and the axillary bud is called the node. It is usually somewhat thicker than the internode - the section of the stem between two nodes. The shoot consists of repeating sections: internodes and nodes with leaves and buds.
Rice. 39. Structure of a vegetative shoot Vegetative and generative shoots. The shoots considered earlier, containing the stem, leaves and buds, are called vegetative (Fig. 39). Simultaneously with them, the plant usually has shoots bearing flowers or fruits. Such shoots are called flower-bearing, or generative (Fig. 40). 
Rice. 40. Variety of shoots Long and short shoots. In many plants, the shoots differ markedly in the length of the internodes. On the branches of an apple tree, for example, there are shoots with long and very short internodes (Fig. 40). Shoots with clearly visible internodes are called elongated. If the internodes are very short, such shoots are called shortened.
In some herbaceous plants, such as plantain and dandelion, the shoots have a short stem and the leaves extending from it are arranged in a rosette. Such shortened shoots of herbaceous plants are called rosette shoots (Fig. 40).
Variety of shoots by position in space. Shoots of plants can be located in different ways relative to the soil and adjacent plants. I single out erect, creeping, rising, clinging and curly shoots (Fig. 41). Upright shoots, such as those of sunflowers, bluebells, nettles, hedgehogs, grow vertically upwards and do not need any support. Creeping shoots spread along the ground and take root in the soil with the help of adventitious roots. Such shoots develop in meadow tea, goose cinquefoil. In some plants (carnations, asterisks), the bases of the shoots occupy horizontal position and the top is vertical. They seem to rise above the ground, so they are called risers. Clinging shoots rise up, attaching to the support with antennae (peas, mouse peas, ranks, grapes), or roots with hooks (ivy). Curly shoots (bindweed, hops) carry leaves to the light, twisting around erect stems or artificial supports. Plants with clinging and climbing shoots are called vines.
Rice. 41. Types of shoots by position in space Leaf location. The leaves on the shoot are arranged in a certain order (Fig. 42). One leaf can depart from each node (birch, linden, geranium); two leaves (lilac, maple, nettle), three leaves (elodea) and more leaves (crow's eye) can leave. For each plant, this number is usually constant. 
Rice. 42. Leaf arrangement
If the nodes have leaves one at a time, as if in turn, such a leaf arrangement is called alternate. With opposite leaf arrangement, two leaves on the same node are opposite each other (opposite). In some plants, the leaves form the so-called whorls, located 3 or more on one node. Such a leaf arrangement is called whorled.
