The escape - the most variable in appearance of a plant organ. The main type of shoot of a green plant is an aerial (aerial) assimilating shoot bearing normal green leaves on the axis. However, assimilating shoots are not the same. They can be elongated and shortened (rosette), orthotropic and plagiotropic, annual and perennial (skeletal). Often, along with the main function of photosynthesis, these shoots have others: the deposition of reserves and the supporting function, vegetative reproduction, the formation of flowers and inflorescences. A change in the growth forms of the same shoot is very common, associated with a change in functions, for example, a rosette vegetative shoot is replaced by an elongated flowering section of the shoot (radish, cumin) or a plagiotropic creeping shoot bends up and gives an orthotropic rosette part (creeping tenacious).
Along with internal factors regulating the change of different shoot forms in one plant, external factors play a huge role in the selection of specialized types of shoots in different plants, adapting to different habitat conditions. Sometimes the shoot or part of it specializes so deeply that they speak of its metamorphosis; this is most often associated with a complete or almost complete loss of photosynthetic function and the acquisition or enhancement of other functions. This is especially true of escapes living underground, common for perennial plants... Photosynthesis is impossible underground, since there is no access to light, and underground shoots act as organs of survival of an unfavorable period, organs of storage and renewal. Moreover, in the course of adaptive evolution, leaves and stems, and sometimes buds, are usually simultaneously metamorphosed.
Trunk and branches of trees ... In deciduous trees, each annual shoot loses its assimilation function after the first growing season, in evergreens - after a few years. Some part of the shoots in the system dies off completely after the loss of leaves, but most of them remain as the main skeletal axes, performing supporting, conducting and storing functions for tens of years. Remain and change, significantly thickening due to the activity of the cambium, stem parts of shoots and a number of buds, which turn into dormant.
Caudex ... In perennial grasses and semi-shrubs with a well-developed taproot that persists throughout life, a kind of perennial shoot organ called caudex is formed. 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. Caudex is usually underground, rarely aboveground and is formed from the lower parts of shortened aboveground shoots sinking into the soil. The border between stem and root in adult plants is usually unclear, so caudex, together with the root, is sometimes referred to as stem root. There are many caudex plants among legumes (alfalfa, lupins), umbellates (thighs, ferula), and Asteraceae (dandelion, wormwood).
Rhizome. It is customary to call a rhizome, or rhizome, a more or less durable underground shoot, horizontal, oblique or vertical in the direction of growth, performing the functions of depositing stocks, and sometimes vegetative propagation in perennial plants, as a rule, do not have a main root in the adult state. Reserve substances, mainly starch, are deposited in the axial (stem) part of the rhizome, which is thickened and rich in parenchymal tissues. The rhizome usually does not bear green leaves, but it has, at least in the young part, a well-defined metameric structure. The nodes are distinguished either by leaf scars and remnants of dry leaves, or by living scaly leaves, as well as by the location of axillary buds. On these grounds, the rhizome can be easily distinguished from the root. As a rule, adventitious roots are formed on the rhizome, located in nodes or in internodes, singly or in groups (lobes). From the buds of the rhizome, its lateral branches and aerial shoots grow.
Growing up in the apical part, the rhizome can gradually die off and collapse in the older part. The young part of the rhizome usually "moves" forward, transferring the buds of renewal to new points, at a certain distance from the previous aerial shoots. Depending on the predominance of short or long internodes or on the intensity of the growth of rhizomes, respectively, short and long rhizomes, short-rhizome and long-rhizome plants are distinguished.
In general, the rhizome can be monopodium (raven eye) or sympodium (kupena). Rhizomes are formed either initially underground (lily of the valley, kupena, blueberries), or at first they grow as aboveground assimilating shoots, which then submerge into the soil and turn into rhizomes (lungwort, hoof, strawberry).
When the rhizomes branch, forming several daughter rhizomes, a clump of aerial shoots is formed, which actually belong to one individual, while they are connected by underground "communications" - sections of rhizome systems. If the connecting parts are destroyed, then individual parts of the rhizome systems are isolated and vegetative propagation occurs. A collection of new individuals formed from one vegetatively is called a clone. Rhizomes are typical mainly for herbaceous perennials, but there are also shrubs (euonymus) and shrubs (lingonberry, blueberry). The life span of rhizomes ranges from two to three to several decades.
Underground stolons and tubers. Short-lived thin underground shoots are called underground stolons. Stolons have no storage function. Stolons, most often growing horizontally, serve mainly for vegetative propagation of plants. The apical buds of stolons often grow, thicken and turn into tubers (potatoes). Tubers differ from rhizomes in shape (spherical, oval), more powerful thickening of the axis and stronger reduction of leaves. Tubers do not always develop on stolons. In some perennial plants, the hypocotyl and the base of the main shoot (cyclamen) grow tuberous and thicken. In all cases, the tuber is a storage organ.
Aboveground stolons and whiskers. Aboveground stolons are short-lived creeping shoots that serve to capture territory and vegetative propagation. If such an shoot bears green leaves and participates in photosynthesis, it is called a whip (creeping tenacious, bone). Near the forest and garden strawberry aerial stolons are more highly specialized for the function of vegetative propagation. They lack developed green leaves, their stems are thin, fragile, with very long internodes. Such overground stolons are commonly referred to as whiskers.
Bulb - it is an underground, rarely aboveground shoot with a very short flattened axis - the bottom - and scaly, fleshy, succulent leaves that store water and soluble nutrients, mainly sugar. Aerial shoots grow from the apical and axillary buds of the bulbs, and adventitious roots form at the bottom. Thus, the bulb is a typical organ of vegetative renewal and reproduction. Bulbs are most typical for plants from the lily family (lilies, tulips, onions) and related amaryllis plants (amaryllis, daffodils, hyacinths) (Fig. 74).
As an organ of renewal and storage, the bulb is adapted mainly to climates of the Mediterranean type - with mild and warm humid autumns, rather mild winters and very hot dry summers. It serves not so much for a safe wintering as for experiencing a severe summer drought. The storage of water in the parenchymal tissues of the bulbous scales is provided due to the production of special mucous substances by the cells of these tissues, which swell and firmly hold water. In most cases, bulbous plants behave like ephemeroids, i.e. their above-ground flowering shoots live very shortly, appearing in early spring, and by the beginning of summer, after fruiting, they completely die off, "fleeing" from drought. Only the underground bulb remains as a perennial organ for summer and winter. In our country, bulbous plants are most abundant in the steppes, semi-deserts and some deserts, as well as in the highlands and deciduous forests. Many bulbous plants, mainly from South Africa, are bred in rooms (krinums, amaryllis, etc.).
Corms. Outwardly, these organs resemble bulbs, but their scaly leaves are not storing, they are dry, filmy. The actual storage organ is the stem part of the corm, it is thickened and parenchymalized. The corm is more of a leafy tuber than a bulb. Corms are typical for plants such as gladiolus, saffron.
Succulent shoots ... Juicy, fleshy, adapted for the accumulation of water can be not only underground shoots - bulbs, but also aerial shoots, usually in plants living in conditions of prolonged lack of moisture. Such plants are called succulents (Latin Succus - juice; succulents - succulent plants). In this case, the actual water-storage organs can be either leaves or stems, sometimes even buds.
Leafy succulents are very characteristic of the jumbo family, for which it got its name (stonecrop, rhodiola, or golden root; rejuvenated, etc.). In addition, the families of liliaceae and amaryllis and those close to them (for example, agave) (aloe, agave, etc.) are rich in leaf succulents, as well as bulbous plants. These are plants of the deserts of South Africa, Central and South America. Their shoots retain their main function - they participate in photosynthesis. But the leaves, in addition to the green mesophyll, have many layers of water-storing mucous membrane of the parenchyma.
One of the few examples of the metamorphosis of a kidney into a succulent organ is the head of cabbage, which is formed in common cultivated cabbage. Numerous heads of cabbage are almost colorless, contain few chloroplasts, fleshy and accumulate a lot of water and soluble storage substances, mainly sugars. The emergence of this specialization is easily explained by the Mediterranean origin of cabbage. Here, after a warm, humid spring, a hot, dry summer begins, which such a water-storing bud survives (it is natural that in wild ancestral forms it was not as hypertrophied as in cultivated varieties).
Stem succulents are most vividly represented and varied in the purely American cactus family, and are also characteristic of many African euphorbia, some of the gorse and haze. Usually, loss or metamorphosis of leaves is associated with the formation of a succulent stem; the succulent stem performs both functions - both assimilation and water storage. Most cacti have columnar or spherical stems, leaves on them are not formed at all or are represented by rapidly falling scales; in the nodes are metamorphosed shortened lateral shoots with bunches of spines or hairs instead of leaves, the so-called "areoles". There is an amazing convergent similarity between succulent shoots of some African euphorbia and American cacti, which can only be distinguished during the flowering period. On the example of cacti and other stem succulents, it is clearly seen that metamorphosis affects not just the stem or leaves, but the entire shoot as a whole.
Thorns. Cactus spines are of leaf origin. They express the plant's reaction to a lack of moisture and a tendency towards a decrease in the evaporating surface of the plant. The secondary biological role of these thorns may be to protect plants from being eaten by animals, which certainly contributes to the survival of the thorny forms in the process of natural selection. Leafy thorns are also found in other non-succulent plants (barberry).
In many plants, the thorns are not of a leaf, but of a stem origin. In a wild apple tree, a wild pear, a laxative buckthorn, shortened shoots with limited growth and ending in a sharp metamorphosis into thorns. They acquire the appearance of a hard lignified thorn after the leaves have fallen off. In the hawthorn, the thorns that form in the axils of the leaves and correspond to the lateral shoots are completely leafless from the very beginning. In Gleditsia, powerful branched spines form on the trunks from dormant buds.
The formation of thorns of any origin is usually the result of a lack of moisture, permanent or temporary. When thorny plants are grown in an artificial humid atmosphere, they lose thorns: instead of stem thorns, normal leafy shoots grow (for example, in English gorse).
Phylloclades and cladodia. Adaptation to a lack of moisture is very often expressed in early loss, metamorphosis, reduction of leaves that lose the main function of photosynthesis. This is compensated by the fact that the role of the assimilating organ is assumed by the stem. Sometimes such an assimilating stem of a leafless shoot remains outwardly unchanged, but it can metamorphose into phylloclades or cladodia. These are flattened leaf-like stems or whole shoots. The most common example is butcher (Ruscus). On the shoots of butcher's broom, in the axils of scale-like leaves, flat leafy phylloclades develop, topographically corresponding to the whole axillary shoot and having limited growth (like a leaf). On phylloclades, in turn, scaly leaves and inflorescences are formed, which never happens on normal leaves. The same phenomenon is characteristic of species of the large tropical genus Phyllanthus from the Euphorbia family. The genus of asparagus (Asparagus), which is closely related to butterflies, is characterized by small, sometimes needle-like phylloclades sitting in the axils of scale-like leaves of the main skeletal shoot.
The flattened green stems with a rather rigid consistency functionally replace the leaves, but in general they help to reduce the evaporating surface. At the same time, as in other cases, it is not the leaves or stems that are metamorphosed separately, but the entire shoot, more often their system.
Cladodia, in contrast to phyllocladia, are called flattened stems that retain the ability to grow for a long time. They are found, for example, in the Australian Muhlenbeckia (Muhlenbeckia platyclada) and in the Mexican shrub Colletia.
Antennae. Many climbing plants are characterized by the modification of leaves or parts of them, and sometimes whole shoots into tendrils, which have the ability to twist around a support (other plants, hedges, stones and other solid objects). Their stem is usually thin and weak, unable to maintain an upright position on its own.
In many legumes with pinnate leaves, the upper part of the leaf turns into antennae (the central vein and several leaves, for example, in peas, peas). In some species of the rank (Lathyrus), for example, in L. aphaca, the entire leaf blade is transformed into a branched antennae, and large green stipules take over the photosynthetic function. In other cases, stipules turn into antennae while maintaining a normal leaf blade (sarsaparilla - Srnilax excelsa). Antennae of shoot origin can be observed in different types grapes, passionflower and a number of other plants.
Metamorphoses - modification of organs with a change in form and function.
Thorns Plants of hot dry habitats can be of both stem and leaf origin. They serve two purposes: they reduce the evaporating surface and protect against damage by animals. Spines of stem origin develop at the top of the stem, in the axils of the leaves, or are located on the stem node opposite to the leaf (hawthorn, pear, blackthorn). If parts of the leaf are involved in the formation of a thorn, then prickly teeth (thistles) are formed. Often the stipules (white acacia) or the entire leaf (cactus, barberry) are modified into a thorn.
Phyloclades- Greek. phillon- sheet; clados- a branch is a modified lateral shoots that take the form of a leaf blade and perform the function of photosynthesis (butcher), in general, they contribute to a decrease in the transpiring surface. Leaf-like phylloclades, topographically corresponding to the whole axillary shoot and having limited growth, also develop on the shoots of the butcher, in the axils of the scaly leaves. Leafy phylloclades are also characteristic of species of the tropical genus Phyllanthus. Asparagus is characterized by small, sometimes needle-like phylloclades, sitting in the axils of scale-like leaves of the main skeletal shoot.
Tubers- These are strongly thickened fleshy underground or aboveground shoots. In underground tubers, the leaves are reduced to small, early falling scales, in the axils of which there are buds, called eyes (potato tubers). Shoots develop from the buds. Aerial tubers are formed by strong growth of the stem and bear normal leaves (kohlrabi cabbage).
Bulbs - modified shortened underground (less often aboveground) shoots. Underground bulbs - in onions, garlic, wild onions. The lower part of the bulb, its dense base, is a shortened modified stem, which is called the bottom. The bottom has a flat or conical shape. In its lower part, a large amount of adventitious roots, and modified leaves (fleshy scales) are sent upward from it, storing water and nutrients. Outer dry or membranous scales - modified leaves that play a protective role, protect the fleshy leaves from drying out.
Rhizome- an underground modified shoot, which serves for vegetative propagation and for storing food. The rhizome ends with a bud, not a root cap. On the rhizomes, nodes are often clearly visible, on which scales are formed - reduced leaves. In the axils of the scales, there are buds that give rise to aboveground and underground shoots, and adventitious roots are formed from the nodes.
Corms - These are modified, shortened, tuber-like thickened stems that look like a bulb (gladiolus, crocus). Unlike the bulb, the corm lacks juicy scales, so nutrients are concentrated in the stem part. The roots develop on the lower thickened part - the bottom, and in the upper part there is a central bud, from which a peduncle with leaves is formed. Outside, the corm is covered with dry films - leaves, in the axils of which there are buds.
Mustache - creeping stems with long internodes (strawberries, drupes). Many climbing plants are characterized by the modification of leaves or parts, and sometimes whole shoots into tendrils, which have the ability to twist around a support during a long apical growth. Their stem is usually thin and weak, unable to maintain an upright position on its own. In many legumes with pinnate leaves, the upper part of the leaf (rachis and several leaves) is modified into antennae. Very characteristic tendrils of leaf origin are formed in pumpkin . Antennae of shoot origin can be observed in different types of grapes (wild and cultivated, in passionflower and a number of other plants).
Life forms of plants
Life form, or biomorph - in the external appearance of plants, which arises in ontogenesis as a result of growth in certain ecological conditions and is of an adaptive nature.
Trees have a well-defined lignified main trunk, which grows vertically more intensively than other shoots and persists throughout the life of the plant from several tens to several hundred and even thousands of years.
Shrubs- the main trunk is absent or weakly expressed, branching begins almost at the very ground, therefore, several more or less thin trunks are formed. As the main stem and the closest daughter ones appear in the center of the bush, new ones appear on the periphery as they die off. The life span of a shrub reaches several hundred years, but each stem lives for 10-40 years (yellow acacia, lilacs - up to 60 years). The height of the shrubs does not exceed 4-6 m (barberry, cotoneaster, irga, rose hips, currants).
Shrubs are characterized by the same branching method as shrubs, but they are shorter and have a shorter lifespan of skeletal axes - 5-10 years. Blueberries, lingonberries, blueberries, cranberries, heather, crowberry.
Dwarf shrubs and dwarf shrubs have shoots that remain perennial in the lower part and become corky, and in the upper part they are annual and die off or dry out in winter. The lifespan of their skeletal axes is 5 to 8 years. They are typical for desert and semi-desert areas (wormwood, saltwort).
Herbaceous plants characterized by the fact that their stems do not lignify and the aboveground parts, as a rule, die off by the end of the growing season. Herbs are annual, biennial and perennial.
Plants-pillows- squat forms in the form of dense pillows. Leaves-bearing shoots, perennial; shoots bearing flowers die off by winter. Pillow plants are characterized by inhibition of growth of all shoots. They are confined to the most unfavorable habitats with low temperatures air and soil, with cold winds (tundra, highlands, deserts, rocks, talus), where free access of light suppresses the growth of shoots.
Succulents- forms with succulent leaves and stems that contain a lot of water (sedum, rejuvenated).
Vines- forms with a long stem (woody or herbaceous), which needs support to keep it upright (hops, bindweed, lemongrass, grapes).
Types of tillering of cereals
Depending on the length of the underground part of the shoots and the direction of their growth, rhizomatous, densely bushy and loose shrubs are distinguished.
1. Have rhizome of cereals, extravaginal shoots form long branching rhizomes underground, from which leafy aerial shoots extend, as a rule, remote from each other (creeping wheatgrass ). Long - rhizome, or scion grasses have long rhizomes. This feature of long-rhizome grasses is used when fixing sands (spikelet species). Short rhizome cereals, or bush with short, hardly distinguishable rhizomes (meadow fescue, sweet spikelet, hedgehog, meadow timothy, etc.). The buds of the renewal of rhizome plants are laid from the previous autumn and, as a rule, overwinter in the soil at different depths, and in early spring aerial shoots appear in these plants.
2. Have friable In cereals, the underground part of the extravaginal shoots is short, from 2 to 10 cm, the ends of the shoots, bending towards the soil surface, turn into aerial shoots, forming a loose turf. Loose turf is a mother plant with lateral barren shoots extending from it at some distance (meadow timothy ).
3. Have tightly bushy cereals, intravaginal renewal, therefore a dense turf is formed, lateral shoots grow vertically and tightly pressed to the stem of the mother plant (turf pike) .
Sheet
Sheet- lateral organ of a plant of limited growth, growing at its base. Leaf functions:
1. photosynthesis and transpiration;
2. gas exchange;
3. storage;
The main parts of the sheet:
L earnest record - the main part of the leaf is the main organ of photosynthesis.
Petiole serves to attach the leaf to the stem and for a better arrangement of the leaves in relation to the light, helps to weaken the blows on the leaf blade of drops of rain, hail, wind. Participates in the movement of leaves.
Vagina - the expanded lower part of the leaf, which more or less covers the stem, protects the axillary buds and increases the strength of the stem when bent (in cereals, some umbellates).
Stipules- paired lateral outgrowths at the base of the leaf of various shapes . They protect the young leaf in the bud.
Petiolate leaves with a petiole.
Sessile leaves- in the absence of a petiole.
Simple leaves have one leaf blade, whole or sometimes strongly dissected.
Compound leaves consist of several leaf blades (leaflets), which are attached to the rachis (common axis of a complex leaf) using their own petioles.
A- a simple apple tree leaf: 1 - leaf blade; 2 - petiole; 3 - stipules; B- complex rowan leaf
Flower
Flower - shortened and limited growth shoot; generative organ of sexual reproduction.
Flower structure:
A, B- flower structure diagrams: 1 - receptacle; 2- sepals;
3 - petals; 4 - stamens; 5 - pistil
Bracts - covering leaves, in the axils of which there is a flower.
Pedicel - part of the stem under the flower.
Peduncle - part of the stem bearing the inflorescence.
Sedentary the flower has no pedicels (flowers are in the heads of some clovers, in aster baskets).
Receptacle- the upper expanded part of the pedicel, serves to attach all the other parts of the flower.
Cup consists of green loose or accrete sepals.
Corolla composed of free or accrete dyed in different colors petals. The cup and corolla make up perianth, or integument, flower. The perianth protects the flower itself (stamens and pistils) from external adverse influences and attracts pollinating insects.
Simple perianth formed only by a calyx (turtle, nettle, sorrel, male oak flowers, elm) or only by a corolla (tulip, lily, lily of the valley, scrub).
Double perianth consists of a cup and a corolla (apple tree, gravilat, chubushnik, lilac).
Bareless flowers(willow, ash, poplar) do not have a perianth.
Stamen consists of a filament and an anther, sessile anthers without a filament (magnolia) are rarely formed or anthers are underdeveloped. In the anthers, pollen is formed, which serves for pollination.
Pestle formed as a result of accretion of one or more carpels. Each pistil contains an ovary, a column and a stigma.
Ovary- this is the lower expanded part of the pistil. Stigma pistil adapted to capture and retain pollen. Inside the ovary is formed ovules(ovules).
Nectars - special glands that secrete a sugary liquid - nectar.
Bloom- opening of anthers and functioning of stigmas of pistils.
Pollination - transfer of pollen from the anthers of the stamens to the stigmas of the pistils.
At self-pollination pollen is transferred to the stigma of the pistil within a given flower or a given individual. Self-pollination is considered as a phenomenon caused by unfavorable environmental conditions, i.e. unfavorable for cross-pollination; it performs an insuring role. Self-pollination is more common in annuals with a short life cycle growing in unfavorable ecological conditions on dry and poor soils (shepherd's purse, rough clover, crowded clover). This type of pollination allows them to quickly restore the population of the species.
Cross pollination- the main type of pollination of flowering plants. It is biologically more perfect.
Biotic pollination:
Entomophily - pollination with insects. Insects visit flowers to collect pollen, nectar, and sometimes in search of shelter, laying eggs, looking for a partner. Flowers attract insects with their scent. Scent essential oil not always pleasant. The smell of rotting meat is emitted by the flowers of rafflesia, staples, and some kirkazones. This scent attracts flies as a place to lay eggs.
Ornithophilia- bird pollination is a tropical phenomenon. Birds (hummingbirds, sunbirds, flower girls) pollinate eucalyptus, cannes, aloe, acacias, some cacti, fuchsias. The flowers of these plants are odorless, but have a bright color, emitting a lot of watery nectar.
Chiropterophilia- pollination bats, distributed in the tropics of Asia and America. Plants such as banana, agave, baobab are pollinated by them. The flowers are greenish-yellow, brown or purple in color, which is better perceived by bats at night. In addition, these flowers have strong "landing sites" - thick pedicels, strong leafless areas of branches, a musty smell that imitates the smell of bats themselves.
Abiotic pollination:
Anemophilia- wind pollination. Wind-pollinated plants bloom before leafing (hazel, birch), their flowers are without perianth, odorless and colorless petals (nondescript), but with large feathery stigmas. Flowers are collected in inflorescences (earring, brush, ear). Stamens hanging freely.
Hydrophilia - transport of pollen by water or along the water surface. This pollination is typical for a few aquatic plants(vallisneria, elodea, etc.). In Vallisneria, pollination occurs on the surface of the water. The pollinated female flower then goes under water again.
Fertilization - it is the fusion of two sex cells - gametes (male and female), as a result of which a new cell is formed - a zygote, from which the embryo of a new organism develops.
Seed. Fetus
Fetus Is an organ that develops from the ovary after fertilization. Protects seeds and promotes seed propagation.
After the fertilization process, the ovule (ovule) turns into a seed.
Bean seed:
a -general form; b-the embryo; 1 - root; 2 -semy entrance; 3 -shub; 4 - seed suture; 5 - kidney; 6 - stalk; 7 - cotyledon
Seed- the reproductive organ of all seed plants.
Peel the seed is a modified integument of the ovule. It protects seeds from drying out, premature germination, and possible mechanical damage.
Embryo semen usually develops from a fertilized egg . The embryo consists of a root, always facing the vas deferens, a rudimentary stalk (hypocotyl knee, or hypocotyl), cotyledons - the first leaves of the embryo and a bud. The bud consists of a growth cone and leaf buds.
Endosperm - tissue that stores nutrients necessary for the development of the embryo.
Techniques for accelerating seed germination
1. Soaking the seeds in water at a temperature of 25 ... 30 0 С for 24 ... 48 hours, depending on the density of the seed shells. Germinate in bowls on gauze, cotton wool, napkin, adding water just above the seed level. Containers with seeds are covered with foil or glass. Swollen seeds are slightly dried and sown immediately.
2. Stratification- exposure of seeds for some time at a low temperature (0 ... 5 0 С) in a moist substrate (sand, peat, moss). In autumn, seeds are mixed with sand 1: 3, the mixture is poured into boxes. Store at a temperature of +5 0 C. In the spring, before sowing, the seeds are separated from the sand through a sieve.
3. Scarification- mechanical damage to thick and hard seed shells.
4. Seed treatment hot water 80 ... 85 0 С for 24 hours.
5. Soaking seeds in solutions chemical substances... It is carried out to soften the hard seed covers or stimulate growth.
Plant growth and development
Height- This is a process of neoplasm of elements of the body's structure, which is accompanied by an increase in mass and size.
Development - these are qualitative changes in the structure and functional activity of a plant and its parts during development.
Growth phases:
1. Embryonic phase - growth is carried out due to the division of meristematic cells. High cost nutrients and energy.
2. Stretching phase - cells increase in size, vacuoles appear in them, which later merge into one large one.
3. Differentiation phase- the final formation of the cell takes place, its transformation into a specialized cell (conductive, mechanical, etc.) with the dominance of the corresponding structures or organelles.
4. Stationary phase- the number of cells and their biomass changes little.
5. Degradation phase- cell death.
Ontogenesis – individual development organism from the moment of formation of the zygote until death.
Stages of plant development
1. The embryonic period in seed plants lasts from the moment the embryo (seed) is formed to the beginning of seed germination. In vegetatively propagating plants - from the moment of bud formation in the organs of vegetative propagation until the beginning of their germination. Growth processes are in a latent phase.
2. Juvenile period of inception of growth and development of vegetative organs from germination of a seed or vegetative bud to the appearance of the ability to form reproductive organs. Plants increase in size, growth processes prevail.
3. Maturity - the period from the appearance of the first rudiments of the reproductive organs to the formation of buds, onionization. The growth processes are combined with the formation of flowers, the vegetative organs of plants continue to grow.
4. Reproduction - fruiting, development of the fruit, seeds, tubers. The processes of formation of flowers, seeds, tubers, and bulbs predominate.
5. Old age - from the complete cessation of fruiting to natural withering away. Growth is rare (stump growth, fattening shoots).
Metamorphoses are hereditarily fixed modifications of organs associated with a change in their main functions. Metamorphoses of vegetative organs of plants are unusually diverse.
Root metamorphosis
One of the most interesting phenomena in root biology is its mutually beneficial cohabitation with fungi. Does this phenomenon have a special name? mycorrhiza (which literally means fungus root) and an extensive literature is devoted to it. Mycorrhiza is characteristic of the vast majority of flowering plants (probably no less than 90%). Due to such a wide distribution, mycorrhiza is more the rule than the exception, but following the established tradition, we still consider it as a modification of the root.
On the other hand, many plants, such as orchids, especially those leading a saprophytic lifestyle, are so closely related to fungi that they cannot even develop without being "infected" with a specific mycorrhizal fungus.
Mycorrhiza is of two different types.
The first type is ectomycorrhiza(external mycorrhiza). In this case, the fungal hyphae entwine the plant roots with a thick cover (hyphae mantle) and also penetrate into the intercellular spaces (but not the cells of the cortex). Under the influence of hormones secreted by the fungus, young roots branch abundantly and their ends thicken. Ectomycorrhiza is characteristic of many trees of the temperate zone, including species of oak, birch, willows, maples, conifers, poplar and others. Ectomycorrhiza is formed almost exclusively by basidiomycetes, less often ascomycetes.
A wider, almost universal distribution is endomycorrhiza(internal mycorrhiza). It can be observed, for example, in apple, pear, strawberry, tomato, cereal, orchid and many other species. It is typical for most flowering plants. With endomycorrhiza, the fungal cover does not form around the root, the root hairs do not die off, but the hyphae penetrate much deeper into the root tissue and are embedded in the cells of the parenchyma of the cortex. There are several different types endomycorrhiza, and some of them are very different from each other.
The most specialized type of endomycorrhiza can be seen in orchids. Orchids do not have a hyphae mantle around the roots and the mycelium is almost entirely inside the root. The hyphae of the fungus in the cells of the cortex form peculiar tangles. These tangles are subsequently digested by the host plant. The fungi that form orchid mycorrhiza are capable of decomposing complex organic substances and supplying the roots with their decomposition products. And this is of particular importance for the saprophytic way of nutrition. The fungal component of this type of endomycorrhiza is almost always represented by oomycetes.
Mycorrhiza is of great importance in tropical rain forests. Due to the strong leaching regime (daily precipitation), these forests are practically devoid of soil (all nutrients are washed out of the soil). Plants face the acute problem of nutrition. At the same time, there is a lot of fresh organic matter: fallen branches, leaves, fruits, seeds. But this organic matter is inaccessible to higher plants, and they come into close contact with saprotrophic fungi. Thus, the main source of minerals under these conditions is not soil, but soil fungi. Minerals enter the root directly from the hyphae mycorrhizal fungi, which is why rainforest plants are characterized by a shallow root system. How effectively mycorrhiza works can be judged at least by the fact that tropical rain forests are the most productive communities on Earth, the maximum possible biomass develops here.
Cohabitation of plant roots with nitrogen-fixing bacteria is much less common. True, the biological significance of this phenomenon is extremely high. In addition to the well-known legumes, root nodules are also noted in representatives of other families, for example, in some conifers, in alder, in a number of casuarines, buckthorns, and lochs. Dwell on this in detail known phenomenon we will not.
Usually, a certain amount of reserve nutrients, mainly carbohydrates, is deposited in the roots of any plants: especially starch and sugar; in other species? inulin. But in some cases, the storage function is hypertrophied and comes to the fore. In this case, the roots thicken, become fleshy. Most often, there is a structure called a root crop. It is especially typical for biennial plants: beets, radishes, rutabagas, turnips, carrots, celery and many others. Exotics include ginseng, chicory. Root crops have a complex morphological nature, since both the root and the stem (more precisely, the hypocotyl) take part in the formation of the root crop. But in order to establish: which part of the root crop is represented by the root and which by the stem? special anatomical studies are required.
Root cones are also found in plants with a fibrous root system, such as the dahlia.
In many cases, the roots are adapted for vegetative propagation. In a number of perennial plants, aerial shoots develop from root adventitious buds. These shoots are called root suckers. Root-sprouting plants include: aspen, plum, cherry, lilac, loach, badan, sow-thistle. The latter are vicious and difficult to eradicate weeds. Small pieces of horses cut during soil cultivation easily take root and give rise to new plants.
In many climbing plants, for example, in ivy, special adventitious roots-attachments are formed on the stem, which penetrate into cracks and irregularities in a tree, rocks, or walls and firmly hold the plants.
There are even hook roots, like those of a ficus strangler.
The so-called contractile (shortening) or retracting roots have a completely different function. They are characteristic of many rhizome, bulbous and corms. Crocus is a classic example of a plant with contractile roots. In addition to the usual roots, crocus develops longer contractile roots, which, when contracted, pull the corms into the ground. In this case, the contractile roots seem to fall off, become transversely wrinkled, and by this feature they easily differ from ordinary roots.
In special cases, the roots can serve as reservoirs for storing water. In many tropical epiphytic orchids (and epiphytes are plants that are used as a substrate for the growth of other plants) outer part The bark, called velamen, is made up of large, empty cells that can absorb water like a sponge. During rainstorms, these cells are filled with water, which is stored in them and used by the plant as needed. By origin, velamen is a multi-layered rhizoderm.
Do many tropical woody plants, mainly mangroves (eg, Avicenia), growing in freshwater tropical swamps, as well as in shallow waters of ocean coasts, develop special ventilation or respiratory roots? pneumatophores. They appear on underground lateral roots and grow vertically above water or soil. It is noteworthy that negative geotropism is characteristic of such roots.
The same mangrove plants form a different type of roots called stilted roots. These are adventitious roots - props. They appear on trunks and branches and grow downward, penetrate into the substrate and firmly hold the plant, for example, in soft silt. Such roots have a widespread plant of mangroves - rhizophora. But the most spectacular are the stilted roots of the ficus-banyan tree ( Ficus benghalensis). The numerous adventitious roots of the banyan tree grow downward, take root and develop their own root system... Thanks to this, one banyan tree grows into a whole grove. These groves can cover impressive areas.
No less interesting are the supporting plank-like roots characteristic of large trees in the tropical rainforest. For known reasons, rainforest trees have a shallow root system, while the trunks of the first tier trees reach enormous sizes. The roots of the usual structure cannot anchor the plant in the soil (which, moreover, does not exist), keeping these giants during frequent storms and downpours. Therefore, the roots of such trees spreading over the soil surface develop special vertical outgrowths, like boards adjacent to the tree trunk.
At first, the planky roots are rounded in cross section, but then there is a strong one-sided secondary growth. In a tropical rainforest, the height of the board-like roots often exceeds human growth.
The adventitious roots of our ordinary marsh plants are no less peculiar - they have a "storey" structure. True, these roots do not have a special name.
Escape metamorphoses
The shoot is the most variable organ of the plant. It is characterized by such properties as:
- multifunctionality;
- lability of behavior;
- plastic.
Already in the first approximation, shoots are divided into two types: 1) vegetative and 2) generative.
There is a distinct change in the growth forms and functions of the shoot in the process of its biological development. For example:
- capture of a new area (whip or rhizome);
- enhanced nutrition (outlet stage);
- the formation of flowers and fruits (generative stage).
Let's consider the main types of specialized and metamorphosed organs of shoot origin.
Caudex
It develops in perennial grasses and shrubs with a well-developed taproot. Is it a kind of perennial shoot organ? usually lignified lower sections of the shoots, turning into a ligneous taproot.
Caudex carries numerous renewal buds. In addition, caudex usually serves as a storage site for reserve nutrients.
As a rule, caudex is underground and rarely enough? aboveground.
The shoot origin of caudex can be established by leaf scars and the regular arrangement of the buds. Caudex differs from rhizomes in the way of withering away. Gradual dying off proceeds from the center to the periphery, while the organ is divided (cracked) longitudinally into separate areas - particulars. Accordingly, the process of division is called particularization. As a result, a structure is formed, which is often called: multi-headed rhizome, gnarled rhizome, multi-headed stem stem, stem root. These names quite accurately reflect the appearance of the caudex, create its image.
It should be noted that particulation is characteristic of old (bluish) plants.
Caudex is especially pronounced in semi-desert, desert and alpine plants. In some species, caudexes reach enormous size and weight, for example, in representatives of the Pangos genus, up to 15 kg.
In a systematic respect, there are many caudex plants among legumes (alfalfa), umbelliferous (thigh), Compositae (dandelion, wormwood).
Rhizome
Rhizome or rhizome (root-like)? it is a long-lasting underground shoot that performs the functions of vegetative renewal, reproduction, and often the deposition of stocks. The rhizome usually does not bear green leaves, but it has a clear metameric structure and this differs significantly from the root. Nodules are distinguished along sheet scales, scars, or axillary buds.
As a rule, abundant adventitious roots are formed on the rhizome, located at the nodes in lobes or singly.
Growing up with the tip - the distal part, the rhizome gradually dies off in the old one? the proximal part.
Depending on the degree of development of internodes of rhizomes, plants are divided into:
- long-rhizome;
- short rhizome;
- dense sod.
When the rhizome branches, a curtain of aerial shoots is formed, which actually belong to one individual. Such clumps are called clones.
So many plants are characterized by a clonal growth. There are two ways to form rhizomes.
In some plants, the entire shoot is initially aerial. It bears both scale-like and green rosette leaves. In the future, the leaves die off, and the stem part is drawn into the soil, thickens there due to the deposition of reserve substances and turns into a rhizome.
Thus, two phases can be distinguished in the structure of the shoot: aboveground and underground. In the course of ontogeny, the shoot undergoes a real transformation, literal metamorphosis. Such rhizomes are called submerging or epigeogenic - overground-born. Such a picture is observed during the formation of rhizomes: cuffs, gravilata, strawberries, lungwort and others.
In other plants, the rhizome begins its growth phase from a bud located underground. Such rhizomes of originally underground origin are called hypogeogenic. They are observed in many perennial grasses and shrubs: wheatgrass, raven eye, kupena, Veronica long-leaved and others.
In this case, the rhizomes are thin and serve more for vegetative propagation.
Underground stolons and tubers
Tubers of thickening of the underground shoot like potatoes, Jerusalem artichoke. Do tuberous nodules begin to develop at the ends of underground stems? stolons. Stolons are short-lived and are usually destroyed during the growing season, this is how they differ from rhizomes.
In tubers, mainly parenchymal cells of the core grow. Conductive tissues are very poorly developed and are noticeable at the border of the core and cortex. Outside, the tuber is covered with periderm with a thick layer of cork, which helps to endure long winter dormancy.
The leaves on the tuber fall off very early, but leave scars in the form of the so-called tuber eyes. Each eye contains 2-3 axillary buds, of which only one germinates. Kidneys at favorable conditions They germinate easily, feeding on the reserve substances of the tuber and grow into an independent plant.
So the third leading function of underground shoots? vegetative renewal and reproduction.
Some plant species form very peculiar leaf tubers (for example, a thin-leaved core). These are modified leaf blades sitting on the petioles of rhizomes. These leaf tubers have lobes, feathery venation, and even mesophilic tissue, but they are chlorophyll-free and are adapted for storing spare starch.
Corms and bulbs
The gladiolus corm is similar in outward appearance on the onion. However, on a longitudinal section, it can be seen that its stem part is highly developed and turned into a tuber containing reserve substances. From the bottom of the corm, numerous adventitious roots appear, forming a fibrous system. Among them there are also contractile (retractable) roots.
The bulb is another type of highly shortened underground shoot. In contrast to the tuber, does it have a relatively small stem part? the bottom. Numerous succulent leaves are attached to the bottom, overlapping each other and called bulbous scales.
In garden onions, for example, the fleshy scales on the outside are covered with protective membranous dry scales, therefore, the entire onion of this type is called filmy tunicate or concentric. In lilies, fleshy scales overlap each other tiled, respectively, and the bulb is called tiled.
The succulent scales of the bulb are only the bottom feeding leaves of the shoot. The upper green leaves are located in the apical bud of the bottom.
All bulbs are grouped into two categories: with rhizomes and without rhizomes. Bulbs with rhizomes have the ability to reproduce by shedding: rhizomes grow from the bottom of the bulb, which lengthen horizontally in the soil and, at some distance from the mother bulb, form a new bulb - recumbent. The bulb takes root and can bloom in a few years. Some tulips and wild onions fall into this category.
Bulbs without rhizomes are familiar to everyone, because they serve as usual planting material in vegetable growing and floriculture.
In the axils of succulent leaves, daughter bulbs (babies or teeth) are laid, which develop before flowering. Many bulbs develop, for example, in garlic.
The storage of water in the parenchymal cells of the juicy scales is provided due to the production of special mucous substances by these cells, which swell strongly in water and retain water.
In most cases, bulbs behave like ephemeroids. Their aerial shoots exist for a very short time: they appear in early spring and die off already at the beginning of summer. Plants seem to "run away from drought."
Succulents
Succulents are plants that have succulent, fleshy leaves or stems, which serve as a kind of reservoirs for storing moisture. Succulents use this moisture very carefully and economically during the dry period.
Succulents are divided into two large groups:
Stem succulents
Stem succulents - have fleshy stems, the leaves tend to turn into thorns (to reduce transpiration). As examples of stem succulents, we can name the well-known American cacti and African milkweed very similar to them.
Leafy succulents
Leafy succulents - have thick, fleshy leaves. These include Crassulaceae: stonecrop, golden root; liliaceae, amaryllis, agave, aloe, gasteria, havortia.
Other shoot metamorphoses
A special interesting case of metamorphosis of the bud into a succulent organ - the head of cabbage - is observed in common cultivated cabbage. As you know, cabbage is a biennial plant. In the first year, rosette, slightly succulent leaves appear, then the bud sharply increases in size and turns into a head of cabbage. In the second year after overwintering, cabbage, as a typical biennial, gives an elongated flowering shoot.
Plants have a wide variety of thorns and thorns, which, moreover, have different origins. For example, in cacti and barberries thorns are modified leaves... Usually, such spines are designed primarily to reduce transpiration, while the protective function in most cases is secondary.
Other plants (hawthorn, wild apple) have shoot spines Are modified shortened shoots. Often they begin to develop as normal leafy shoots, and then lignify and lose their leaves.
A further step in the underdevelopment of leaves and the transfer of their functions to green stems leads to the formation of such metamorphosed organs as phylloclades and cladodes.
Phyloclades
Phylloclades (Greek phillon - leaf, clados - branch) are flat leaf-like stems and even whole shoots. The most famous example of plants with metamorphoses of this kind is butcher's broom (Ruscus). These plants grow in the Crimea and the Caucasus; they often get divorced and in indoor conditions... Interestingly, scaly leaves and inflorescences develop on the leaf-like shoots of butcher's broomstick, which never happens on normal leaves. In addition, phylloclades, like leaves, have limited growth.
Cladodia
Cladodia are also called flattened stems, which, unlike phyllocladia, retained the ability to grow for a long time. These are quite rare modifications and are found, for example, in the Australian Mühlenbecky.
Many climbing plants(peas, ranks, pumpkins, etc.), the leaves change into tendrils, which have the ability to twist around the support. The stem of such plants is usually thin and weak, unable to maintain an upright position.
Creeping plants(strawberries, drupes, etc.) form a special type of shoots that serve for vegetative propagation, such as whips and stolons. They are classified as aerial creepers.
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Rhizomes have sympodial or monopodial branching, like aerial shoots. When branching rhizomes, daughter rhizomes are formed, which leads to the formation of clumps of aerial shoots. If individual parts of the rhizome are destroyed, the clumps are isolated, which is observed during vegetative propagation. A collection of new individuals formed from one vegetatively is called a clone. The formation of rhizomes is characteristic of perennial herbaceous plants (many representatives of the families of cereals and sedges), but sometimes it occurs in shrubs (euonymus) and some shrubs (lingonberries, blueberries).
Aerial shoot metamorphoses include aerial stolons ╫ whips and whiskers. In some plants, young shoots begin to grow horizontally along the soil surface, like lashes. After a while, the apical bud of such a shoot bends upwards and gives rise to a rosette, which then takes root. In this case, the lashes are destroyed, and the daughter individuals begin to exist on their own. The function of the lashes is to capture the area and settle new individuals, i.e. they perform the function of vegetative reproduction. Scourges are aerial stolons that have green leaves and are involved in the process of photosynthesis. They are found in many plants (bone, zelenchuk, tenacious, etc.). In some plants (strawberries, partly drupes), aerial stolons do not have green leaves, their stems are thin with long internodes. They are called mustaches. The apical whisker buds take root, after which the whiskers usually collapse.
Other metamorphoses of aerial shoots include thorns of leaf (cactus, barberry) and stem (wild apple, wild pear, hawthorn, etc.) origin. The formation of thorns is associated with the adaptation of plants to a lack of moisture. In addition, in some plants of arid habitats, shoots flatten, forming the so-called phylloclades (for example, in the butcher's) and cladodes (for example, in the collection). On the shoots of butcher, in the axils of scale-like leaves, flat leaf-like phylloclades are formed, corresponding to the whole axillary shoot and having limited growth. Claudia, unlike phyllocladia, are flattened stems that have the ability to grow for a long time. Shoots, and sometimes leaves, can turn into antennae, which, in the process of prolonged apical growth, are able to twist around the support.
SHEET
The leaf is a lateral organ of the shoot, usually flat in shape, with limited growth and performing the functions of photosynthesis, respiration (gas exchange) and water evaporation (transpiration). Sometimes water accumulates in the leaf and reserve nutrients are deposited. It can play supporting and protective functions, be an organ of vegetative reproduction, act as traps for animals in carnivorous plants, etc.
Leaves in flowering plants are formed from the meristem of the shoot growth cone. The buds of leaves appear at some distance from the top of the shoot, forming protrusions on the surface in the form of tubercles and ridges. As they grow, they acquire a flat shape and dorsiventral (i.e., with pronounced dorsal and ventral sides) structure, in contrast to the more or less cylindrical and radially symmetric axial organs ╫ of the stem and root.
The upper and lower sides of the leaf differ sharply in the conditions in which they are found (especially in relation to the light regime), and as a result, in the anatomical structure, the structure of the conducting bundles, pubescence and other signs associated with functional differences of the sides. The upper side of the leaf is called the inner (or ventral), the lower ╫ outer (or dorsal).
Leaves have limited growth, since the cells of the intercalary meristem, due to which the leaf grows, quickly lose their ability to divide. Having reached a certain size, the leaf remains unchanged until the end of its life.
The leaves are arranged on the stem in a specific order, reflecting the symmetry in the structure of the shoot. There are three types of leaf placement: alternate (spiral), opposite and whorled. With the next leaf arrangement, the leaves are placed on the stem in a spiral, while one leaf departs from each node of the stem. The arrangement of leaves at each node in pairs, one against the other, is called opposite, three or more leaves ╫ whorled. Typically, the leaves are placed on the plant so as to provide the least mutual shading. This phenomenon is called sheet mosaic.
Leaf morphology. A typical leaf consists of a leaf blade, petiole, base and stipules. If the base of the leaf expands to cover the stem, a sheath is formed, in the formation of which the petiole can also take part. The leaf connected to the stem by the base of the petiole is called petiolate, and the leaf connected to it by the base of the leaf blade is sessile. In vaginal leaves, the base covers the internode located above, in whole or in part, over a greater or lesser extent. In some plant species (representatives of the families of legumes, rosaceae, etc.), paired lateral outgrowths appear at the base of the leaf ╫ stipules, which protect it at early stages of development. The sizes and shapes of stipules are different. deploying the leaf on the shoot.
The forms of the leaf blade are varied. They are determined by the ratio of its length and width and the position of the widest part. The plates are round, oval, oblong, ovate, obovate, broadly ovate, obovate, broadly ovate, linear. According to the outline, shape, consistency, the leaves are scaly, acicular, bristly, xiphoid, braid, thyroid, etc. In the morphological description of the leaves, the peculiarities of the base, apex and edge of the plate are taken into account. The base of the leaf can be wedge-shaped, rounded, heart-shaped, unequal, cut, narrowed, sagittal and spear-shaped. The apex of the leaf is dull, sharp, pointed, pointed, notched. The edge of the sheet has cutouts of different depths. If they do not go deeper than 1/4 of the width of the half-plate, the sheet is called solid, and its edge is ╫ cut. The edge can be wavy, notched, crenate, dentate, fingerlike, double-serrate, etc. Leaves, in which the notches of the edge are deeper than 1/4 of the half-plate, are called dissected. The dissection can be trifoliate, fingerlike, and pinnate. If the notches are not deeper than 1/2 the width of the half-plate, the leaves are considered lobed, if they are deeper than 1/2 the width of the half-plate, but do not reach the midrib, ╫ separate; if they reach the midvein or base of the lamina ╫ dissected.
The protruding parts of lobed leaves are called lobes, in separate ╫ lobes, in dissected ╫ segments. Pinnately dissected leaves with narrow parallel segments are called comb-shaped; leaves are pinnate or pinnately dissected, with triangular lobes or segments with an expanded base, ╫ ply-shaped, pinnately divided, with a large terminal lobe and smaller lateral lobes ╫ lyre-shaped.
Leaves are simple and complex. A simple leaf has a petiole and one blade and falls off entirely. If a leaf consists of several leaf blades, each of which has a small petiole (called a petiole), it is considered complex. In a complex leaf, leaf blades usually fall off independently of one another. Leaves can be ternate, palmate, and pinnate. If the common petiole is branched, multi-syllable leaves are formed: double-pinnate, triple-pinnate, etc.
The leaf blade has a highly branched system of conductive bundles called veins; their totality determines the venation of the leaf. The venation is open and closed. With open venation, the veins end near the edges of the leaf blade, without connecting to each other. By the nature of the branching of the veins, such venation is called dichotomous or fan-shaped. With closed venation, the veins are repeatedly interconnected and form a network ╫ reticular venation. Reticulated venation is called pinnate, when lateral, thinner, multi-branching veins extend to the sides from the midvein. With finger venation at the base of the leaf blade, more or less identical veins diverge radially. Dicotyledonous plants are characterized by reticular venation, monocotyledonous plants have parallel and arcuate venation, when veins of approximately equal thickness, emerging from the base of the plate, merge together at its apex.
Depending on the specifics of the growing conditions of plants, their leaves can change, acquiring adaptive, adaptive features of the external and internal structure ╫ metamorphosis. The most common leaf modifications are spines, tendrils and phyllodia, and these can be metamorphoses of a whole leaf or its parts. Phillodia, for example, is a metamorphosis of a leaf in which leaf blades do not develop, and the function of photosynthesis is performed by an expanding flattened petiole. Phyllodia is an adaptation to a lack of moisture in hot conditions and is found, for example, in many Australian acacias. Thorns of leaf origin (for example, in cacti) are also adaptations to a lack of moisture. Antennae (for example, in legumes) help climbing plants to cling to various supports. Many interesting biological adaptations develop in the leaves of carnivorous or carnivorous plants.
Leaf anatomy. In connection with the main functions (photosynthesis ╫ see the section "Photosynthesis" on p. 482, gas exchange, transpiration), two types of tissues are well developed in the leaf: assimilation, in which the processes of photosynthesis take place, and integumentary, which regulate water evaporation and gas exchange. There are also tissues in the sheet that perform other functions: conductive tissues (functions of supplying water with mineral nutrients dissolved in it and outflow of assimilation products) and mechanical tissues that give strength to the sheet.
The arrangement of tissues in a leaf, the degree of their development, and the characteristics of cells vary greatly depending on the habitat of plants.
Usually the leaf is covered with a single layer of epidermis (epidermis) on the upper and lower sides. Under the upper epidermis is a columnar (palisade) mesophyll (parenchyma), consisting of one or more layers of cells. These elongated cells lie very densely, they contain many chloroplasts. Photosynthesis mainly occurs in the columnar mesophyll. Under it is the spongy mesophyll (spongy parenchyma), formed by cells of irregular shape, between which there is a system of large intercellular spaces filled with air. The intercellular spaces play an important role in gas exchange and transpiration. The cells of the spongy parenchyma contain significantly fewer chloroplasts than the columnar ones. Some cells of the spongy mesophyll contain calcium oxalate drusen and large mechanical supporting cells ╫ sclereids. The spongy mesophyll is underlain by the lower stomata (Figure 1.3). Gas exchange depends on how wide the stomata are open: the exchange of oxygen, CO2 and other gases, as well as water vapor (transpiration) between the inside of the leaf and the air surrounding the leaf.
Figure 1.3. The stomata and adjacent cells in the leaf of common thyme (Thymus serpyllum). A ╫ plan view, B ╫ sectional view: 1 ╫ front yard; 2 ╫ central slit of the stomata; 3 ╫ back yard; 4 ╫ respiratory cavity; 5 ╫ cuticle allowance for students universities Russian State University of Oil ... scientists biologists, physicians ... Raynaud's syndrome / N. Guseva, d.m.s., professor, head of ... metals, incoming in ... 144 p. 2. Kamenskaya E.N. Psychology...
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Stem succulents are also distributed in the families of Euphorbiaceae, Grimaceae, and Haze. Here we observe the convergent properties of evolution - under the same ecological conditions. different plants are similar in structure.
Metamorphosis of the kidney into a succulent organ occurs during the formation of a roach (for example, in cabbage). First, a rosette of slightly succulent leaves is formed, the bud begins to grow vigorously. There are few chloroplasts in the leaves (they are greenish). After overwintering, the apical bud gives a flowering shoot. The emergence of succulence is due to its Mediterranean origin.
Various modifications of leaf and stem
Thorns- the leaves, its parts, the entire shoot as a whole can change. The thorns are of leaf origin in cacti, barberry; from stipules - in white acacia; from the petiole - from the astrogal; from the edge of the leaf blade - at sow thistle, thistle, thistle, from the stem - wild apple, pear, buckthorn, lemon. In camel thorn, the leaves are of shoot origin - this proves that leaves and flowers can form on them. The thorns can branch (gladichia), can be curved.
Thorns- are smaller. Than pegs and a flat triangular shape. The formation of thorns and thorns is the result of a permanent or temporary lack of moisture.
Often the stem flattens and turns into leaf-like organs - phyllocladia, cladodia, phyllodia.
Phyllocladiodia- leafy organs or whole shoots. Flowers can develop along the edges of the phylacladodia (in butchery, epiphyllium, asparagus). It is difficult to distinguish between the leaf and stem parts in them.
Cladodia- flattened stems, growing in length for a long time. In the Balfour cocculus, they are xiphoid or sickle-shaped. Flowers and fruits appear on them.
Phillodies- flattened leaf petioles in the form of a leaf blade. They have a xeromorphic structure, oriented edge to the sun (Australian acacia, Brazilian oxalis). In ontogeny, the leaf blades are reduced, and the petioles turn into phyllodia, which photosynthesize.
Antennae- keep apical growth for a long time. The upper part of the pinnate leaves (peas) can turn into antennae. In the rank, the entire leaf blade turns into a tendril, and the stipules perform the function of assimilation. Antennae of leaf origin are characteristic of pumpkin. In some plants, only stipules are modified into antennae. Antennae of shoot origin are characteristic of grapes and posiflora. Antennae can be cold (in cucumber), complex branched (two-part - in a watermelon, multi-part - in a pumpkin).
Fishing apparatus
Characteristic carnivorous plants... There are 4 genera and more than 100 species in the sundew family. There are 4 species in the European region.
Round-leaved sundew- a small plant of peat bogs. Rounded leaves are collected in a basal rosette. Top part and leaf margins are seated with tentacle hairs with a reddish glandular head. They are short in the center of the leaf, longer at the edges. The head of the hair is surrounded by thick, sticky droplets. Gooey mucus. Insects, attracted by the glitter of the droplets, fall on the leaf and stick. The hairs of the leaf bend and envelop the victim with mucus, which contains digestive enzymes (digest for several days).
Aldrovanda bladder- lives in lakes and oxbows of our republic. Trapping leaves consist of two semicircular, spoon-shaped halves, covered with bristles and hairs that perceive irritation. When touched by small aquatic animals, the leaf halves quickly fold along the midrib. The leaves are digested once and then die off and are replaced with new ones.
Venus flytrap- endemic to coastal North Carolina. The leaves are raised above the ground, collected in a rosette around the peduncle. The petiole is flat and wide, the leaf blade is two rounded valves, lying at an angle to each other, equipped with long, strong teeth at the edges. The upper half of the valves contains three sensitive hairs. The inner surface is dotted with reddish glands containing digestive enzymes and formic acid.