Shoot growth occurs exogenously leaf rudiment. It is located below the top of the shoot and looks like an oval tubercle. The cells of the leaf rudiment divide in all directions, thus, the leaflet grows both in thickness and in height. As soon as the growth in thickness stops, the leaf takes on a flat appearance.
There are two parts of the leaf rudiment: apical(upper) and basal(lower). The apical growth of the leaf rudiment is limited and does not last long. When the top of the leaf stops growing, the base continues to grow. In other words, acropetal growth ends and basipetal growth begins. Thus, the apical meristem completes its growth function, and the intercalary meristems begin their development.
The leaf blade and petiole develop directly from the upper part of the leaf rudiment, and the base of the leaf and stipules develop directly from the lower part. Sometimes the laying of parts of the leaf is already formed in the kidney, and when it enters from the kidney, the already laid parts grow and their anatomical structures differentiate. One of the last to grow is the petiole.
Remark 1
It is worth noting that not all leaves have a petiole.
The leaf blade increases in size fairly evenly. The leaf is monosymmetrical in most plants. The leaf has two surfaces - dorsal (dorsal) and ventral (abdominal). The dorsal surface in the kidney is located inside, thus adjacent to the stem, and in the developed leaf - at the top. The abdominal, on the contrary, is located outside in the kidney, and below in the developed leaf.
The leaves are modified depending on the growing conditions of the plant, and in connection with the adaptation of plants to certain functions. Spines, scales, tendrils, phyllodes, the growth of hairs on the leaf are all a modification of the leaves.
Spines in plants perform two functions, less evaporation of water (cactus in the desert) and protection from animals. The spines have a different arrangement on the stem. For example, in barberry, the thorn is located under the leaf; in hawthorn, it is located in the axil of the leaf. In a cactus, the leaf blade has turned into a thorn. In the astragalus, the rachis of a complex leaf has changed into a thorn, in the acacia, the stipules.
The shoots of vines have adapted for support in order to take a certain position in space. A similar function is performed by modified leaves in the tendrils of peas, ranks, they help the plant move due to their tenacity.
Scales in bulbous plants play a special role, they accumulate nutrients. Also, the covering scales of the kidneys, bulbs, rhizomes perform a protective function.
Trapping devices, as a modification of leaves, are characteristic of insectivorous plants. The leaves are modified and resemble water lilies, urns, slamming sticky plates. The sticky hairs of the sundew nourish the plants, the insect gets on the sticky surface, the leaf closes and the decomposition of the animal begins, under the action of enzymes. This modification occurred due to the fact that the plant grew on soil with a deficiency of minerals.
Saccular modifications of leaves are found in an epiphytic plant of a humid tropical forest. Water and humus accumulate in such formations. As a result, adventitious roots are formed in the leaves, supplying the plants with moisture.
Phyllodes cover the shoots of the club moss, i.e. are outgrowths on the stem. They are green, and so on. they can photosynthesize, or they can carry sporangia in the form of sacs in which spores are formed. Acacia also has phyllodes. The petiole of acacia is turned into a flat leaf-like formation.
The hairy coat and waxy coating on the leaves is adapted to retain moisture and delay the evaporation process. The shiny surface of the ficus reflects the rays of light, which contributes to less evaporation of water by the plant.
The teeth along the edges of plants are adapted to express the processes of photosynthesis and transpiration. Thus, condensation occurs, which leads to the formation of dew.
Pheromones, poisons, aromatic oils, crystallization minerals produced by leaves can repel pests. Petals pollinate insects.
Remark 2
Thus, the modification of leaves is able to adapt plants to the environment, and have resistance to adverse conditions.
Leaf arrangement of leaves, or phyllotaxis is the order in which the leaves are placed on the stem, thus reflecting the symmetry in the structure of the shoot. The arrangement of the leaf depends on the order of the laid leaf primordia on the cone of growth. In most plants, the leaves are located directly on the stems and branches, so that a general rule for their arrangement can be established. At first glance, the leaves seem to be arranged randomly. But if you look closely at the leaves, you will see that the leaves sit in pairs, one against the other, such an arrangement is called opposite. On some plants, the leaf pairs alternate so that they overlap each other, this is called criss-crossing. If there are three leaves on one node, which alternate with each other, and maybe even from $4-10$ or more leaves, then the arrangement is called ringed. If on stems with annular leaves, the leaves sit on top of each other, then several verticals and lines parallel to each other are obtained, which are called orthosts. If you draw a line from the very first bottom to the nearest sheet, then from the second to the nearest, etc. to the end, a spiral line is formed, then such a leaf arrangement is called spiral.
In each polynomial leaf arrangement, in addition to the main spiral, secondary steeper spirals are observed. They are called parastihas.
Picture 1.
If three or more leaves depart from the node, the leaf arrangement is called whorled. With a rosette leaf arrangement, the leaves are in a rosette, i.e. a bundle of leaves is arranged in a circle from one common center.
Definition 1
Leaf mosaic- this is a kind of arrangement of the leaves of a plant in the same plane, in such a way as to ensure the least shading of each other's leaves. The leaves are directed perpendicular to the direction of the light rays. All this is the result of uneven growth of petioles and leaf blades that reach for the light and fill every lighted gap. A leaf mosaic is formed in absolutely any leaf arrangement - opposite, whorled, rosette, alternate or opposite opposite.
In its development, the leaf goes through two phases: intrarenal and extrarenal. During the first phase, the leaf primordium increases mainly due to cell division. At the same time, it gradually acquires a shape characteristic of an adult leaf. However, in the bud, the leaf remains miniature, folded or rolled up. During the transition to the second phase, the sheet unfolds. In the second phase, it grows strongly due to cell division and stretching. A leaf primordium that does not have signs of differentiation is called a primordia. At first, it grows evenly due to cell division in all directions. But soon its growth is differentiated, it becomes uneven. Usually, cell divisions of the apex of the leaf germ are stopped first. After that, it can grow only due to the intercalary and marginal meristem. Quite early, the rudimentary leaf differentiates into 2 parts: basal (lower) and apical (upper). The development of these parts goes on unequally. The base of the leaf develops from the basal part (as well as stipules, sheath - if any), from the apical part - the lamina and petiole.
Reaching final size sheet can live for a different time, however, compared with the axial organs, the leaves of perennial plants are short-lived. In most plants, they live for several months, and in evergreens from 1.5 to 20 years. The evergreenness of these plants is explained by the fact that the old leaves are gradually replaced by new ones, that is, they do not have a one-time fall of all the leaves.
Coniferous leaves have the longest lifespan. Yes, at Scotch pine leaf lives 2-4 years, and ate- 5-7 years old, yew- 6-10 years. In the same plant species, when climbing mountains and moving north, the life span of leaves increases. Yes, at Norway spruce in the Khibiny needles live 12-18 years.
LEAF FALL fall of leaves usually in trees and shrubs, less often in herbs (nettle, touchy). Leaves can fall off all at the same time during a certain period of the year (for example, in deciduous trees) or gradually one at a time over a long time (in evergreens). Deciduous trees in humid tropical regions. forests stand without leaves, sometimes just a few. days, in the temperate zone - up to 8-9 months. L. - normal fiziol. leaf aging process. Before L. in leaves there are deep biochemical., fiziol. and structural changes. Chlorophyll is usually destroyed, carotenoids last longer and cause the autumn color of the leaves. Nutrition. substances from the leaves flow into storage organs (tubers, rhizomes, etc.) to growth points, to growing young leaves. The mechanism of L. is associated with the appearance of the base of the leaf (or main petiole) of the separating layer of easily separable parenchymal cells. Conductive bundles that hold the leaf on the stem are torn under the weight of the leaf and gusts of wind. L. - an adaptation developed in the process of evolution to reduce the surface of terrestrial organs under unfavorable conditions, which reduces the loss of moisture and prevents the branches from breaking under the weight of snow.
Leaf metamorphoses - irreversible changes in the shape of leaves developed during evolution as a result of the adaptation of plant organs to environmental conditions (i.e., with the performance of new functions by leaves).
1. spines- one of the most common modifications; they serve as a defense against being eaten by animals. In this case, the leaf either completely turns into a thorn (cacti, euphorbia, barberry, white locust, camel thorn), or part of it turns into a thorn (thistle, thistle, holly).
2. tendrils(in compound leaves of some plant species) cling to a support, carrying the entire shoot to the light. At the same time, either the upper leaves of a complex leaf (pea, vetch), or the entire leaf can turn into a tendril, and the stipules (some types of ranks) perform the function of photosynthesis.
3. The storage function is performed juicy scales bulbs (onion, garlic), aloe leaves, head of cabbage.
4. Covering scales buds protect delicate rudimentary leaves and growth cone from adverse environmental conditions.
5. trapping devices provide the life of insectivorous plants in swamps in conditions of a lack of nitrogen and other elements of mineral nutrition. The leaves of such plants have changed beyond recognition, turning into traps (Venus flytrap), jugs (nepenthes). The leaves of some plants with their shiny, brightly colored droplets on the hairs attract ants, flies, mosquitoes, and other small insects; the juice released at the same time contains digestive enzymes (dew).
Anatomical structure of a typical leaf.
The anatomical structure of the leaf is formed in the cone of growth simultaneously with the formation of the stem. At the beginning of formation, the leaf grows with its upper part, then the apical growth fades, and the growth zone is preserved only at the base of the leaf. In ferns, the leaf grows with the tip throughout its life.
Both sides of the sheet are covered epidermis, which protects the internal tissues of the leaf from the adverse effects of the external environment. Gas exchange and evaporation of water is carried out through stomata. Between the two layers of the epidermis is mesophyll, or chlorenchyma, which makes up the bulk of the sheet (Fig. 37).
Rice. 37. Anatomical structure of the Japanese camellia leaf (Camellia japonica): 1 - upper epidermis; 2 - columnar mesophyll; 3 - spongy mesophyll; 4 - lower epidermis; 5 - supporting cells; 6 - collecting cells, 7 - collecting cells with drusen; 8 - stomata; 9 - xylem; 10 - phloem; 11 - sclerenchyma
Columnar mesophyll
In leaves arranged horizontally, the mesophyll is differentiated into columnar and spongy tissue. The columnar mesophyll adjoins the upper side of the leaf. Its cells are elongated perpendicular to the leaf surface, they contain many chloroplasts, its main function is photosynthesis. This tissue is most well expressed in plants growing under conditions of intense illumination. In shade-loving plants, on the contrary, the columnar mesophyll is less pronounced, the length of its cells slightly exceeds their width.
spongy mesophyll
Adjacent to the lower epidermis is a spongy mesophyll, which consists of rounded, loosely arranged cells. There are large air cavities that communicate with stomata. The main function of this tissue is gas exchange and water evaporation, although photosynthesis also occurs in its cells. In aquatic and marsh plants, large air cavities form in the mesophyll, turning it into aerenchyma.
In leaves arranged vertically, there is no sharp difference between columnar and spongy tissue (in cereals). In arid climates, the columnar mesophyll is also located on the underside of the leaf (in swans).
Conductive bundles
In the mesophyll are conductive bundles that form veins. Most often they collateral, and the xylem in the bundle is turned to the top, and the phloem - to the underside of the leaf. Conductive leaf bundles are usually devoid of cambium, i.e., they are closed. Conductive leaf elements are delimited from intercellular spaces and mesophyll cells by densely closed parietal cells. Large veins contain sclerenchyma, and very thin veins have a simplified structure: xylem may include one or two conductive elements, and phloem - one sieve tube with a companion cell.
The leaf is a very important plant organ. This is the part of the shoot whose main functions are transpiration and photosynthesis. The structural features of the leaf are its high morphological plasticity, great adaptive capabilities and variety of forms. The base can expand in the form of stipules - leaf-shaped oblique formations on each side. In some cases, they are so large that they play a certain role in photosynthesis. Stipules are attached to the petiole or free, they can be shifted to the inside, and then they are called axillary.
Leaf blades vary in size: they can be from a few millimeters to ten to fifteen meters, and for palm trees - even as much as twenty meters. The structure of the leaf determines the life span of the vegetative organ, it is usually short - no more than a few months, although for some it ranges from one and a half to fifteen years. Shape and size are hereditary traits.
The leaf is a lateral vegetative organ that grows from the stem, has a growth zone at the base and bilateral symmetry. It usually consists of a petiole (with the exception of sessile leaves) and a leaf blade. In a number of families, the leaf structure also suggests the presence of stipules. The external organs of plants can be simple - with one plate, and complex - with several plates.
The leaf cushion (base) is the part that connects the leaf to the stem. The educational tissue located here gives rise to the petiole and leaf blade.
The petiole is a narrowed part, connecting the stem and the leaf blade with its base. It orients the leaf relative to the light, acts as a place where the intercalated educational tissue is located, due to which the growth of the vegetative organ occurs. In addition, the petiole weakens the impact on the leaf during rain, wind, hail.
Leaf blade - usually a flat expanded part that performs the functions of gas exchange, photosynthesis, transpiration, and in some species also the function of vegetative reproduction.
Speaking about the anatomical structure of the leaf, it is necessary to say about the stipules. These are leaf-shaped paired formations at the base of the vegetative organ. When the sheet is unfolded, they may fall off or remain. Designed to protect the axillary lateral kidneys and insert educational tissue.
The structure of a leaf is considered simple if it has one leaf blade, and complex if there are several or many plates with joints. Due to the latter, the plates of complex leaves do not fall together, but one at a time. But some plants may fall completely.
Whole leaves in shape can be lobed, separate or dissected. In a bladed leaf, cuts along the edge of the plate are up to 1/4 of its width. A separate organ is characterized by a larger depression, its lobes are called lobes. The dissected leaf has cutouts along the edges of the plate, reaching almost to the midrib.
If the plate is elongated, with triangular segments and lobes, the leaf is called plow-shaped (for example, in a dandelion). If the lateral lobes decrease towards the base, are uneven in size, and the final lobe is round and large, a lyre-shaped external organ of the plant is obtained (for example, in a radish).
The structure of a sheet with several plates is significantly different. Allocate palmate, ternary, pinnate organs. If a complex leaf includes three plates, it is called trifoliate, or trifoliate (for example, maple). A leaf is considered palmately complex when its petioles are attached to the main petiole at one point, and the plates diverge radially (for example, lupine). If the side plates on the main petiole are present on both sides along the length, the leaf is called pinnate.
In different plants, the forms of leaf blades are not the same in terms of the degree of dissection, shape, type of base and top. They can have round, oval, triangular, elliptical and other outlines. The plate is elongated, and its free end can be blunt, pointed, sharp or pointed. The base is attenuated and narrowed towards the stem, it can be heart-shaped or rounded.
Considering the structure of the leaf of a plant, a few words should be said about how it is attached to the shoot. Attachment is carried out using long or short petioles. There are also sessile leaves. In some plants, their bases grow together with the shoot (downward leaf), and it happens that the shoot pierces through the plate (pierced leaf).
The epidermis (upper skin) is an integumentary tissue located on the reverse side of a plant organ, often covered with cuticles, hairs, and wax. The internal structure of the leaf is such that on the outside it has a skin that protects it from drying out, mechanical damage, the penetration of pathogens to internal tissues and other adverse effects.
Skin cells are alive, they are different in shape and size: some are transparent, large, colorless, tightly adjacent to each other; others are smaller, with chloroplasts that give them a green color, such cells can change shape and are arranged in pairs.
Skin cells can move away from each other, in which case a gap appears between them, which is called stomatal. When the cells are saturated with water, the stomata open, and when the fluid drains, it closes.
The anatomical structure of the leaf is such that air enters the inner cells through the stomatal gaps and gaseous substances come out through them. When plants are not sufficiently provided with water (this happens in hot and dry weather), the stomata close. So representatives of the flora protect themselves from drying out, since with closed stomatal crevices, water vapor does not go outside and is stored in the intercellular spaces. Thus, during the dry period, plants retain water.
The internal structure of the leaf cannot do without columnar tissue, the cells of which are located in the upper side facing the light, tightly adjoin each other, and have a cylindrical shape. All cells have a thin shell, nucleus, chloroplasts, cytoplasm, vacuole.
Another main fabric is spongy. Its cells are round in shape, located loosely, between them there are large intercellular spaces filled with air.
What will be the structure of the leaf of the plant, how many layers of spongy and columnar tissues are formed, depends on the lighting. In leaves grown in the light, the columnar tissue is much more developed than in those that grew in dark conditions.
The organism of a flowering plant 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 escape- 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- 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.
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).
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 the organ an increase 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, under certain conditions, of developing 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. Sleeping buds play a special role 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.
| Way | Picture | Description | Example |
Creeping shoots |  | Creeping shoots or tendrils, in the nodes of which small plants with leaves and roots develop | Clover, cranberry, chlorophytum |
rhizome |  | With the help of horizontal rhizomes, plants quickly capture a large area, sometimes several 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 |
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-defined metameric structure, the nodes are distinguished either by leaf scars and dry leaf remains, or by leaf scars and dry leaf remains, or by live scaly leaves and by 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- underground, rarely 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. The popular name for these aboveground stolons is mustache.
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.
Root- underground vegetative organ of higher plants, which has unlimited growth in length.
The roots are different, namely, they can be modified.
Distinguish:
The main root develops from the germinal root. Lateral roots occur on any root as a lateral branch. Adventitious roots are formed by the shoot and its parts.
The set of roots of one plant is called the root system.
AT rod In the root system, the main root is strongly developed and is clearly visible among other roots (typical for dicots). The tap root system usually penetrates deeper into the soil than the fibrous root system.
AT fibrous root system in the early stages of development, the main root, formed by the germinal root, dies off, and the root system is composed of adventitious roots (typical for monocots). The fibrous root system better braids the adjacent soil particles, especially in its upper fertile layer.
AT branchy the root system is dominated by equally developed main and several lateral roots (in tree species, strawberries).
The escape- This is a stem with leaves and buds located on it.
The components of the shoot are the stem, leaves, buds. When the seed germinates from the germinal bud, the first shoot of the plant is formed - its main shoot, or first-order shoot. Lateral shoots, or shoots of the second order, are formed from the main shoot, and when branching is repeated, the third order, etc. Adventitious shoots are formed from adventitious buds.
This is how the system of shoots is formed, represented by the main shoot and side shoots of the second and subsequent orders. The shoot system increases the total area of contact of the plant with the air.
The shoot on which flowers are formed is called a flowering shoot, or peduncle (sometimes the term "peduncle" is understood in a narrower sense - as the section of the stem on which the flowers are located).
A vegetative unmodified shoot is a single plant organ, consisting of a stem, leaves and buds, formed from a common array of meristems (the shoot growth cone) and having a single conducting system. The stems and leaves, which are the main structural elements of the shoot, are often considered as its constituent organs, that is, organs of the second order. In addition, the obligatory affiliation of the escape is the kidneys. The main external feature that distinguishes the shoot from the root is the presence of leaves.
In the seasonal climate of temperate latitudes, the growth and development of shoots from buds is periodic. In shrubs and trees, as well as in most perennial grasses, this happens once a year - in spring or early summer, after which wintering buds of the next year are formed, and at the end of summer - in autumn, shoot growth ends.
A (with leaves). one - stem; 2 - sheet; 3 - node; four - internode; 5 - leaf axil; 6 - axillary kidney; 7 - apical kidney.
B (after leaf fall). 1 - apical kidney; 2 - renal rings; 3 - leaf scars; 4 - lateral kidneys.
1 - upright; 2 - rising; 3 - creeping; 4 - creeping; 5 - curly; 6 - climbing.
Stem- an elongated shoot of higher plants, serving as a mechanical axis, also plays the role of a producing and supporting base for leaves, buds, flowers.
According to the location relative to the level of the soil:
elevated
underground
According to the degree of woodiness:
According to the direction and nature of growth:
According to the shape of the cross section:
Outside, the stem is protected by integumentary tissues. In young stems in spring, the cells of the integumentary tissue are covered with a thin skin. In perennial plants, by the end of the first year of life, the skin is replaced by a multilayer cork consisting of dead cells filled with air. For breathing in the skin (in young shoots) there are stomata, and later lenticels are formed - large, loosely arranged cells with large intercellular spaces.
The cortex, formed by different tissues, adjoins the integumentary tissue. The outer part of the cortex is represented by layers of mechanical tissue cells with thickened membranes and thin-walled cells of the underlying tissue. The inner part of the cortex is formed by the cells of the conductive tissue and is called the bast.
The composition of the bast includes sieve tubes, through which there is a downward current: organic substances move from the leaves. Sieve tubes are made up of cells connected at their ends to form a long tube. There are small holes between adjacent cells. Through them, like through a sieve, organic substances formed in the leaves move.
Sieve tubes remain alive for a short time, more often 2-3 years, occasionally - 10-15 years. They are constantly being replaced by new ones. The sieve tubes make up a small part of the bast and are usually collected in bundles. In addition to these bundles in the bast, there are cells of mechanical tissue, mainly in the saw fibers, and cells of the main tissue.
To the center of the bast in the stem is another conductive tissue - wood.
Wood is formed by cells of different shapes and sizes and consists of vessels (tracheas), tracheids and wood fibers. An ascending current flows along them: water with substances dissolved in it moves from the roots to the leaves.
In the center of the stem lies a thick layer of loose cells of the main tissue, in which nutrient reserves are deposited - this is the core.
In some plants (dahlia, tulip, cucumber, bamboo), the core is occupied by an air cavity.
Between wood and bast in dicotyledonous plants there is a thin layer of cells of the educational tissue - the cambium. As a result of cell division of the cambium, the thickness of the stem increases (grows). Cambium cells divide along their axis. One of the daughter cells that appears goes to the wood, and the other to the bast. The increase is especially noticeable in wood. The division of cambial cells depends on the seasonal rhythm - in spring and summer it is active (large cells are formed), slows down in autumn (small cells are formed), and stops in winter. As a result, an annual growth of wood is formed, which is clearly visible in many trees, called the annual ring. By the number of growth rings, you can calculate the age of the shoot and the tree as a whole.
The width of annual rings in woody plants depends on environmental conditions. So, in a cold climate, on marsh soils, the size of the growth rings of wood is very small. In favorable climatic conditions, on rich soils, the thickness of annual rings increases. Comparing the alternation of wide and narrow growth rings near the trunk, one can determine the conditions under which the plant lived, as well as establish fluctuations in weather conditions over many years.
The stem serves as a support for the plant, it holds the weight of the leaves, flowers and fruits on it.
Reserve nutrients can be deposited in the stem. This manifests the storage function of the stem. With the help of the stem, the shoot brings its leaves and buds to the light during the growth of the plant. This shows the important axial function of the stem and the growth function.
Sheet- one of the most important organs of plants, the main functions of which are photosynthesis, gas exchange and transpiration.
The sheet consists of the following fabrics:
The sheet externally consists of:
Not all plants have all parts of the leaves; in some species, paired stipules are not clearly expressed or absent; the petiole may be absent, and the leaf structure may not be lamellar.
