The apical bud develops. Define the term "kidney"

The stem is the part of the plant that connects the main nutritional organs - the root and leaves.

A stem with leaves or buds located on it is called escape. Each shoot develops from a bud. Remember: leaves can be arranged alternately, oppositely and whorled. The places where the leaves are located are called nodes, and the areas between the two closest nodes are called internodes.

There are elongated shoots with long internodes and shortened shoots with short internodes and close nodes.

The angle between the leaf and the internode lying above it is called leaf axils.

At the top of the shoot there is usuallyapical bud,and in the axils of the leaves - axillary, or lateral, buds.

While studying seed germination, you observed the development of a shoot from the embryonic bud of the seed

beans. How does a shoot develop from a bud located on the stem? Consider a shoot of a poplar or apple tree. At the top of these shoots there is one apical bud. On the sides of each branch, in the places where the leaves were, there are lateral buds.

The lateral buds are located on the stem in the same way as the leaves. On the branches of poplar and apple trees, the buds are located singly, one after the other. This arrangement is called the next one. Many trees and shrubs have a regular arrangement of buds: cherry, birch, bird cherry, hazel and others.

If we look at the shoots of lilac, elderberry, jasmine, honeysuckle or indoor fuchsia plant, we will see a completely different arrangement of buds. They are located in twos, one opposite the other - opposite. Let's see what structure the kidneys have.

The outside of the bud is covered with dense leathery scales, protecting it from rain, wind and other adverse conditions.

Let's cut off one of the buds from the shoot and examine it with a magnifying glass. Clearly visible under the scalesrudimentary stem, located in the very center of the kidney, and small, wrinkledrudimentary leaves.In the axils of these leaves arerudimentary buds,similar to grains, barely noticeable even with a magnifying glass. Thus, the kidney isrudimentary shoot.

If you cut several buds, you can see that inside some of them there are only rudimentary leaves around the embryonic shoot. Such kidneys are called vegetative or leafy. Rudimentary buds are visible inside other buds. This flower buds.

Flower buds can be distinguished from vegetative ones by their appearance. They are larger than vegetative ones and have a rounded shape.

According to the location of the buds on the shoots, their shape, size, color, pubescence and some other characteristics characteristic of eachplant species, you can determine the name of a tree or shrub even in winter.

When identifying trees and shrubs in winter, pay attention to the following signs characteristic of buds.

The buds are usually located directly on the stem. The exception is alder. In alder they sit on special legs, and by this feature, as well as by earrings and small cones, alder can be easily distinguished from other trees. Poplar is recognized by its sticky, resinous, pointed buds, which have a peculiar, pleasant odor. The willow bud is covered with only one cap-like scale. Buckthorn has no kidney scales at all. The oblong large buds of rowan are pubescent and therefore clearly distinguishable from the buds of other trees.

A bud is a greatly shortened shoot with rudimentary leaves or reproductive organs. The buds can be vegetative, having shoot and leaf buds; generative, bearing the primordia of a flower or inflorescence, mixed. Based on their location, there are apical buds (at the end of the shoot) and axillary buds (at the nodes between the leaf petiole and the stem).

According to their functional significance, dormant buds are distinguished, which do not bloom annually and remain alive for many years. And they wake up when the upper part of the stem is removed. From them shoots are formed. Adventitious buds are formed inside stems, leaves, and roots from cells of various tissues and provide vegetative propagation. Dormant buds are formed on those organs that do not die off during the winter or during periods of drought. They require a period of rest, then they ensure the perennial existence of woody or herbaceous plants.

When a seed germinates, a shoot develops from the bud of the seed embryo. In perennial plants, a shoot starts from a bud. A bud is an embryonic shoot. It consists of a shortened stem with closely spaced rudimentary leaves. At the top of the stem there is a growth cone consisting of educational tissue. Due to the division of cells of the growth cone, the stem grows in length, the formation of leaves and outer buds. Outside, the bud is protected by bud scales, which are modified lower leaves of the shoot. According to their location on the shoot, the buds are apical and lateral.

Apical bud

This is the bud located at the top of the shoot, the rest of the buds are lateral. They are divided into axillary and accessory.

Axillary buds

They regularly appear in the axils of young leaf primordia near the top of the mother shoot. Their arrangement exactly corresponds to the leaf arrangement. Therefore, in winter, the location of the leaves can be determined by the buds.

Lateral buds

They develop outside the axil on internodes, roots and leaves and are called adventitious. They often provide vegetative propagation of plants. Adventitious buds on the leaves immediately develop into small plants with adventitious roots, which fall off the leaf of the mother plant and grow into new individuals. These buds are called brood buds (bryophyllium, sundews). They can appear in the leaf axil and change into bulbs (tiger lily) and nodules (viviparous knotweed).

The kidneys are not the same in structure. In most plants they are closed (protected), because on the outside they have bud scales, glued with resin (in conifers), other adhesive substances (poplar), some are often omitted. There are plants with open (unprotected, bare) buds. They lack bud scales (viburnum, buckthorn).

Based on their internal structure, the following types of kidneys are distinguished:

1) vegetative - consist of a rudimentary stem, scales, rudimentary leaves and a growth cone;
2) generative - floral, consisting of a rudimentary stem, scales and primordia of a flower or inflorescence (red elderberry);
3) mixed - consist of a rudimentary stem, scales, rudimentary leaves and rudiments of a flower or inflorescence (apple tree, spirea).

Generative and mixed the buds are larger and more rounded than the vegetative ones.

Buds that remain dormant (autumn - winter) and then unfold and produce new shoots are called overwintering or renewal buds. Due to them, shoots grow.

Dormant buds

They remain dormant for a number of years. The stimulus for their awakening is damage to the trunk.



Table: Shoot (leaf, stem, bud)

THE ESCAPE

The escape- This is the above-ground part of the plant. A vegetative shoot is formed during the development of the embryo, in which it is represented by a bud. Kidney- these are the stem and leaf buds, can be considered the first bud of the plant. During the development of the embryo, the apical meristem of the bud forms new leaves, and the stem lengthens and differentiates into nodes and internodes.

The escape- a complex organ consisting of a stem, leaves, and buds. The stem has nodes and internodes. Knot- the section of the stem on which the leaf and bud are located. The area of ​​the stem between the nodes is internode. The angle formed by the leaf and the stem above the node is called leaf sinus. Buds occupying a lateral position on a node are called lateral (or axillary). At the top of the stem there is an apical bud.

Escape modifications can perform various functions: storage and vegetative propagation (tubers, rhizomes, bulbs), protective (spines), serve as an attachment organ (antennae), etc.

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

SHEET

Sheet- flat lateral organ of the shoot.

External leaf structure. In dicotyledonous plants, the leaf consists of a flat, expanded blade and a stem-like petiole with stipules. The leaves of monocotyledonous plants are characterized by the absence of petioles; the base of the leaf is expanded into a sheath that encloses the stem. In cereals, the vagina covers all internodes: The leaves of dicotyledonous plants are simple and complex. Simple leaves have one leaf blade, sometimes strongly divided into lobes. Compound leaves have several leaf blades with pronounced cuttings. Pinnate leaves have an axial petiole, on both sides of which there are leaflets. Palmate leaves have leaflets fanning out from the top of the main petiole.

Internal structure of the leaf. On the outside of the leaf there is a skin of colorless cells, covered with a wax-like substance - cuticle. Located under the skin cells columnar parenchyma containing chlorophyll. Deeper are the cells of spongy parenchyma with intercellular spaces filled with air. The parenchyma contains the vessels of the vascular bundle. On the lower surface of the leaves, the skin has stomatal cells involved in the evaporation of water. Evaporation of water occurs to prevent overheating of the leaf through the stomata of the epidermis (skin). This process is called transpiration and ensures a constant flow of water from the roots to the leaves. Transpiration rate depends on humidity air, temperature, light, etc.

Under the influence of these factors, the turgor of the guard cells of the stomata changes, they close or close, delaying or increasing the evaporation of water and gas exchange. During the process of gas exchange, oxygen is supplied to cells for respiration or released into the atmosphere during photosynthesis.

Cellular structure of the leaf.

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

STEM

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

Stem tissues:

1. Conductive: the inner part of the bark consists of sieve tubes and companion cells of the phloem; wood cells (xylem) are located closer to the center, through which the transport of substances.
2. Pokrovnaya- skin on young stems and cork on old woody stems.
3. Storage- specialized cells of bast and wood.
4. Educational(cambium) - constantly dividing cells that supply attack to all tissues of the stem. Due to the activity of cambium the stem grows in thickness, and tree rings are formed.

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

Cellular structure of the stem:

BUD

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

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

Generative buds larger than vegetative ones; they bear fewer rudimentary leaves, and at the top of the rudimentary stem are the rudiments of a flower or inflorescence. The generative bud containing one flower is called a bud. Adventitious buds can form on the internodes of the stem, roots and leaves, allowing for vegetative propagation.

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§ 22. Escape and buds

1. What structure does the seed embryo have? 2. What kind of fabric is called educational?

The escape. A stem with leaves and buds located on it is called escape. The stem is the axial part of the shoot, the leaves are the lateral parts. The areas of the stem where leaves develop are called nodes, and the sections of the stem between the two nearest nodes of one shoot - internodes.

Many plants have two types of shoots: some with long and others with short internodes.

The angle between the leaf and the internode above is called leaf axils.

Leaf arrangement . Most plants have next, or spiral, leaf arrangement, in which the leaves grow one at a node and are arranged alternately on the stem in a spiral. For example, birch and willow have this arrangement of leaves. If the leaves grow two at a node - one leaf against the other, for example, in maple, lilac, then this arrangement is called opposite. In plants with whorled Due to the arrangement of the leaves, they develop in threes or more at the nodes, as, for example, in elodea and oleander.

When a seed germinates, a shoot is formed from the bud of the seed embryo. In perennial plants, shoots develop from a bud.

73. Leaf arrangement

74. Apple tree shoots

Kidneys. At the top of the shoot there is usually apical bud, and in the axils of the leaves - axillary buds. Buds that do not develop in the leaf axil (on internodes, leaves, roots) are called subordinate clauses.

The arrangement of axillary buds repeats the arrangement of leaves on the stem. Poplar, cherry, birch, bird cherry, hazel have an alternate arrangement of buds.

The buds are located opposite on the shoots of lilac, elderberry, jasmine, honeysuckle and indoor plants fuchsia, pilea, coleus, which are characterized by the same leaf arrangement.

After the leaves fall, they remain on the shoots leaf scars, above which the axillary buds are located.

Each type of plant is characterized by a certain location of buds on the shoots, their shape, size, color, and pubescence. Based on these and some other signs, you can determine the name of a tree or shrub even in winter.

Kidney structure . On the outside, the buds are covered with dense, leathery bud scales that protect them from exposure to adverse environmental conditions.

Through a magnifying glass, a longitudinal section of the kidney is clearly visible rudimentary stem, at the top of which is cone growth, consisting of cells of educational tissue.

There are very small rudimentary leaves. In the axils of these leaves are rudimentary buds; they are so small that they can only be seen with a magnifying glass. Thus, the kidney is rudimentary shoot.

75. Structure of chestnut buds

Inside some buds on the rudimentary stem there are only rudimentary leaves. Such kidneys are called vegetative, or leafy. Generative, or floral, buds are rudimentary buds or inflorescences; they are larger than vegetative ones and have a more rounded shape.

The structure of the kidneys. Location of buds on the stem

1. Consider the shoots of different plants. Determine how the buds are located on the stem and sketch them.

2. Separate the buds from the shoot and examine their external structure. What adaptations help the kidneys withstand adverse conditions?

3. Cut the vegetative bud lengthwise and examine it under a magnifying glass. Using the drawing, find the scales, rudimentary stem, rudimentary leaves and growth cone. Draw a cross-section of a vegetative bud and label the names of its parts.

4. Study the generative bud. What do vegetative and floral buds have in common and how do they differ? Use the picture for comparison in the textbook.

5. Compare the structure of the bud and shoot. Draw a conclusion.

Growth and development of the shoot. You have established that a bud is a rudimentary shoot that has not yet developed. The development of the shoot begins with the opening of the buds . When the bud scales fall off, intensive shoot growth begins. The shoot lengthens due to the division of cells of the growth cone (educational tissue). Young cells grow, forming new sections of the stem with leaves and buds. As you move away from the apical point of growth, the ability of cells to divide weakens and is soon completely lost. New cells turn into cells of the integumentary, main, mechanical or conductive tissue of the shoot, depending on their location.

76. Development of shoot from the bud

The growth and development of shoots can be controlled. If you remove the apical bud, the shoot stops growing in length, but it begins to develop side shoots. If you cut off the top of a side shoot, it will also stop growing in length and begin to branch.

By pruning shoots, skillful gardeners often give trees and shrubs bizarre, beautiful shapes. It has been established that the longevity and productivity of fruit trees, as well as the quality of the fruit, depend on the shape of the crown.

THE ESCAPE. BUD. Apical, axillary, accessory buds. VEGETATIVE, GENERATIVE KIDNEYS. GROWTH CONE. KNOT. INTERNODE. LEAF AXIS. REGULAR, OPPOSITE, whorled leaf arrangement

1. What is an escape? What parts does it consist of? 2. What types of leaf arrangement do you know? 3. What is a kidney? 4. How are kidneys distinguished? 5. How are the buds located on the shoots? 6. What is the structure of a vegetative bud? 7. How do generative buds differ from vegetative ones? 8. How does the shoot grow in length?

Place a branch of a tree or shrub in the water and watch the development of shoots from the buds. Write down when the branch is placed in the water, when its buds swell, its scales open, a shoot appears and leaves bloom.

In addition to apical growth, most plants experience elongation of shoot internodes due to intercalary growth. For example, in wheat, bamboo and other cereals, intercalary growth occurs as a result of the division and growth of cells located at the bases of all internodes. Thanks to this, the young stems of some plants grow very quickly. For example, bamboo stems can grow more than a meter in a day.

1. Sprout two bean or pea seeds in a pot of soil. When the stems of the plants reach 7-10 cm in height, cut off the top of one of them. Observe what happens to the plants after one to two weeks.

2. Trim the top of your ficus or other indoor plant. Watch the shoots grow.

Try to determine the names of trees and shrubs growing near your home and school by the characteristic features of their buds.

By the location of the buds, their shape, size, color, pubescence and some other characteristics, even in winter we can determine which tree or shrub is in front of us.

The buds are usually located directly on the stem. The exception is alder: its buds sit on special legs. By this characteristic, as well as by the earrings and small cones, alder can be easily distinguished from other trees before the leaves bloom.

Poplar is recognized by its sticky, resinous, pointed buds, which have a peculiar, pleasant odor.

The willow bud is covered with only one cap-like scale.

Buckthorn has no kidney scales at all.

77. Buds on the shoots of various trees and shrubs

The oblong large buds of rowan are pubescent and therefore clearly distinguishable from the buds of other trees .

Bird cherry and black currant buds have a pleasant smell. The oppositely located elderberry buds, on the contrary, have an unpleasant odor. By smelling them, you will immediately distinguish elderberry from other shrubs.

§ 23. External structure of the leaf

1. What vegetative organs are distinguished in a flowering plant? 2. On which organ of a flowering plant are the leaves located? 3. Are the sizes and shapes of leaves the same in different plants?

The leaf is part of the shoot. It performs three main functions - photosynthesis(formation of organic substances), gas exchange and evaporation of water.

Leaf shape. Although the leaves of different plants vary greatly in appearance, there are many similarities between them. Most of the leaves are green in color and consist of two parts: leaf blade And petiole. The petiole connects the leaf blade to the stem. Such leaves are called petiolate. Apple, cherry, maple, and birch have petiolate leaves. The leaves of plants such as aloe, wheat, chicory, flax do not have petioles; they are attached to the stem at the base of the leaf blade. They are called sedentary.

At the base of the petiole, outgrowths sometimes develop - stipules

78. Attaching leaves to stem

The shape of the leaves is round, oval, heart-shaped, needle-shaped, etc. The shape of the edge of the leaf blade is also varied. For example, a leaf of an apple tree has a serrated edge, an aspen leaf has a serrated edge, and a lilac leaf has a whole edge. .

The leaves are simple and compound. Simple leaves consisting of one leaf blade, characteristic of birch, maple, oak, bird cherry and other plants .

Compound Leaves consist of several leaf blades connected to a common petiole by small petioles. These are the leaves of ash, rowan and many others. .

79. Different shapes of leaf edges

80. Simple leaves

81. Leaves are compound

82. Leaf venation

Venation . Leaf blades are pierced in different directions conductive bundles, which are called veins.

The veins not only conduct nutrient solutions, but also give the leaf strength.

If the veins are located parallel to one another, as in many monocotyledonous plants (wheat, rye, barley, onions and some others), such venation is called parallel.

The wider leaves of the lily of the valley and the houseplant aspidistra have arc venation, which is also typical for monocots.

Reticulate venation typical of the leaves of dicotyledonous plants, the veins in them, as a rule, branch repeatedly and form a continuous network. But there are exceptions: for example, the dicot plantain has arcuate venation, and the leaves of the monocot raven's eye plant have reticulate venation.

Leaves are simple and compound, their veining and leaf arrangement

1. Examine the leaves of indoor plants and herbarium specimens. Select simple leaves. On what basis do you select them?

2. Select compound leaves. On what basis are you doing this? What kind of veining does the leaves you selected have?

3. What leaf arrangement do the plants you looked at have?

4. Fill out the table.

LEAF PLATE, PETILE. LEAVES PETOILE AND SESSIONAL. LEAVES SIMPLE AND COMPLEX. VENATION RETICULAR, PARALLEL, ARC

1. What is the external structure of the leaf? 2. Which leaves are called complex and which are simple? 3. How do monocots differ from dicots in leaf venation? 4. What is the function of leaf veins?

Make a herbarium of leaves with different shapes of leaf blades and different veins.

The tropical resident Victoria Amazonica, related to our water lilies, has a leaf so large that a three-year-old child can sit on it, like a raft, and the leaf holds him on the water.

The weed plant chickweed has leaves smaller than a fingernail, but they contain a large amount of vitamins. Therefore, they are useful to give to parrots and other birds in your living area.

§ 24. Cellular structure of the leaf

1. What is the function of the integumentary tissue? 2. What structural features do the cells of the integumentary tissue have? 3. What function do the cells of the main tissue perform and where are they located? 4. What are intercellular spaces?

Familiarity with the internal structure of the leaf blade will help you better understand the importance of green leaves in plant life.

Skin structure. The top and bottom of the leaf are covered with a thin transparent skin; its cells protect the leaf from damage and drying out. Peel - one of the types of plant integumentary tissue.

Among the colorless and transparent skin cells there are located in pairs closing cells whose cytoplasm contains green plastids - chloroplasts. There is a gap between them. These cells and the gap between them are called stomata Air enters the leaf through the stomatal fissure and water evaporates.

In most plants, stomata are located mainly on the skin of the underside of the leaf blade. On the leaves of aquatic plants floating on the surface of the water, stomata are found only on the upper side of the leaf, and on underwater leaves there are no stomata at all. The number of stomata is enormous. So, on a linden leaf there are more than a million of them, and on a cabbage leaf there are several million stomata.

83. Stomata with surrounding skin cells

Leaf skin structure

1. Take a piece of clivia leaf (amaryllis, pelargonium, tradescantia), break it and carefully remove a small section of thin transparent skin from the underside. Prepare the preparation in the same way as the onion skin preparation. Examine under a microscope. (You can use ready-made leaf peel preparations.)

2. Look for discolored skin cells. Consider their shape and structure. What cells are they similar to that you already know?

3. Find stomatal cells? How are stomatal cells different from other onion skin cells?

4. Sketch the onion skin under a microscope. Separately sketch the stomata. Write captions for the drawings.

5. Draw a conclusion about the meaning of the leaf skin.

The structure of the leaf pulp. Under the skin is the pulp of the leaf, consisting of cells of the main tissue . Two or three layers directly adjacent to the upper skin are formed by elongated cells tightly adjacent to each other. They resemble columns of almost the same size, so the upper part of the main leaf tissue is called columnar. There are especially many chloroplasts in the cytoplasm of these cells.

Beneath the columnar tissue lie more rounded or irregularly shaped cells. They do not fit tightly to each other. The intercellular spaces are filled with air. There are fewer chloroplasts in these cells than in the cells of columnar tissue. These cells form spongy tissue.

84. Internal structure of a leaf

The structure of leaf veins. If you examine a cross section of a leaf blade under a microscope, you can see conductive bundles leaf - veins consisting of vessels, sieve tubes And fibers Strongly elongated cells with thick walls - fibers - give the sheet strength. Water and minerals dissolved in it move through the vessels. Sieve tubes, unlike vessels, are formed by living long cells. The transverse partitions between them are pierced by narrow channels and look like sieves. Solutions of organic substances move through sieve tubes from the leaves.

Cellular structure of the leaf

1. Study the finished micropreparations of a leaf cut. Find the cells of the upper and lower skin, stomata.

2. Examine the leaf pulp cells. What shape do they have? How are they located?

3. Find intercellular spaces. What is their significance?

4. Find the conductive bundles of the sheet. What cells are they formed by? What functions do they perform? Compare the microscopic slides with the textbook picture.

5. Draw a cross section of the sheet and label all parts.

LEAF SKIN. STOMA. CHLOROPLAST. Columnar and spongy tissues. LEAF PULP. CONDUCTING BAND. VESSELS. SIEVE TUBES. FIBERS

1. What cells form the leaf blade? 2. What is the significance of the leaf skin? What tissue cells is it formed from? 3. What are stomata and where are they located? 4. What structure do the leaf pulp cells have? What type of fabric are they? 5. Which leaf cells contain the most chloroplasts? 6. What function do the conducting bundles of the leaf perform? What tissue cells are they formed by?

Place two onions in jars of water so that the water touches the base. Place one jar in a dark place and the other in a lighted one. Watch the leaves grow. How are they different? Why?

The number and location of stomata on the upper and lower surfaces of leaves is associated with the conditions in which the plants grow.

The number of stomata in different plants per 1 mm2 of leaf surface

The more polluted the air, the lower the number of stomata: leaves collected from trees growing in suburbs, where the air is relatively clean, have 10 times more stomata per unit of leaf surface than leaves from trees in heavily polluted industrial areas.

§ 25. The influence of environmental factors on the structure of the leaf. Leaf modifications

1. What does ecology study? 2. What environmental factors can affect the plant? 3. Remember the differences between dandelions growing in the open with a lack of moisture and in the shade on well-moistened soil.

The shape, size and structure of the leaves largely depend on the living conditions of the plants.

Leaves and humidity factor. The leaves of plants in humid areas are usually large with a large number of stomata. A lot of moisture evaporates from the surface of these leaves. Such plants include monstera, ficus, and begonia, which are often grown in rooms.

The leaves of plants in arid places are small in size and have adaptations that reduce evaporation. This is dense pubescence, a waxy coating, a relatively small number of stomata, etc. Some plants, for example aloe, agave, have soft and succulent leaves. They store water.

Leaves and lighting conditions. The leaves of shade-tolerant plants have only two or three layers of rounded cells, loosely adjacent to each other. Large chloroplasts are located in them so that they do not shade each other. Shade leaves tend to be thinner and darker green in color because they contain more chlorophyll.

In plants in open areas, the leaf pulp contains several layers of columnar cells tightly adjacent to each other. They contain less chlorophyll, so light leaves are lighter in color. Both leaves can sometimes be found in the crown of the same tree. .

85. Light and shadow lilac leaves

86. Modifications of leaves

Leaf modifications. In the process of adapting to environmental conditions, the leaves of some plants have changed because they began to play a role that is not characteristic of typical leaves. For example, some of the leaves of barberry have changed into spines. Turned into thorns and leaves of cacti. They evaporate less moisture and protect plants from being eaten by herbivores .

In peas, the upper parts of the leaves are turned into tendrils. They serve to maintain the plant stem in an upright position.

The leaves of insectivorous plants that live on soils poor in nitrogenous substances are interesting. A small sundew plant grows on peat bogs . Its leaf blades are covered with hairs that secrete a sticky liquid. The sticky droplets, shiny like dew, attract insects. Insects that land on the leaf become stuck in the sticky liquid. First, the hairs, and then the leaf blade, bend and envelop the victim. When the leaf blade and hairs unfold again, only its integument will remain of the insect. The plant leaf will “digest” and absorb all the living tissues of the insect.

87. Round-leaved sundew

LIGHT LEAVES. SHADOW LEAVES. SHEET CHANGES

1. Is it possible to distinguish between plants in humid places and dry areas by appearance? 2. Prove that the structure of the leaf is related to the living conditions of the plants. 3. Why do floating leaves of aquatic plants have stomata only on the upper side of the leaf, while leaves submerged in water have no stomata at all? 4. What is the significance of modified leaves in plant life? Give examples of such leaves. 5. Explain why in the crown of one tree the light leaves are similar in structure to the leaves of plants in open areas, and the shadow leaves are similar to the leaves of shade-tolerant plants.

Consider a few indoor plants. Try to determine the conditions under which they grew in their homeland. Based on what signs did you draw your conclusion?

Prepare and examine under a microscope preparations of leaves of aloe, tradescantia, uzambar violet and other plants.

Among cacti, only Peirescia (often grown indoors) has true leaves that fall off during drought.

In such typical steppe and semi-desert plants as feather grass, stomata are located on the upper side of the leaf, and the leaf, under conditions of lack of moisture, is capable of curling into a tube. The stomata are then inside the tube and isolated from the surrounding dry air. In the cavity of the tube, the concentration of water vapor increases, which leads to a weakening of evaporation .

88. Feather grass leaf

§ 26. Structure of the stem

1. What is called an escape? 2. What functions do mechanical, conductive, and integumentary tissue perform? 3. What stems do plants you know have? 4. How are the stems of trees, shrubs, and grasses different?

Stem - the axial part of the plant shoot, it conducts nutrients and carries leaves to the light. Spare nutrients may be deposited in the stem. Leaves, flowers, fruits with seeds develop on it.

89. Variety of stems

Variety of stems. There are two main types of stems: herbaceous and woody.

herbaceous stems usually exist for one season. These are tender flexible stems of grasses and young shoots of tree species. Woody stems acquire hardness due to the deposition of a special substance in the membrane of their cells - lignin. Lignification occurs in the stems of trees and shrubs starting in the second half of summer of the first year of their life.

Herbaceous plants are better adapted to changing environmental conditions; their forms are very diverse. They grow in water and in very dry places, in the hot tropics and in permafrost areas.

According to the direction of growth, stems are divided into erect, climbing, climbing, and creeping. .

Most plants have stems erect, they grow vertically upward. Erect stems have well-developed mechanical tissue; they can be woody (birch, apple tree) or herbaceous (sunflower, corn).

90. Layers on a cut tree trunk

Curly the stems, rising upward, wrap around the support (field bindweed, beans, hops).

climbing the stems rise upward, clinging to the support with tendrils (grapes, peas) or adventitious roots growing from the stem (ivy).

Creeping stems spread along the ground and can take root at nodes (strawberry, cinquefoil).

Internal structure of the stem. On a cross section of a branch or cut of a tree, the following areas can be easily distinguished: bark, cambium, wood and pith .

Young (annual) stems are covered on the outside peel, which is then replaced by a plug consisting of dead cells filled with air. The skin and cork are integumentary tissues. They protect the deeper cells of the stem from excessive evaporation, various damage, and from the penetration of atmospheric dust with microorganisms that cause plant diseases.

In the skin of the stem, as in the skin of the leaf, there are stomata through which gas exchange occurs. Developing in a traffic jam lentils - small tubercles with holes, clearly visible from the outside, especially in elderberry, oak and bird cherry. Lentils are formed by large cells of the main tissue with large intercellular spaces. Gas exchange occurs through them .

91. Cross section of a branch under a microscope

Some trees develop thick layers traffic jams. A particularly powerful cork develops on the trunk of the cork oak tree. It is used for various household needs.

There are cells under the skin and cork bark, which may contain chlorophyll is the main tissue. The inner layer of the cortex is called bast

It consists of sieve tubes, thick-walled bast fibers and groups of cells of the main tissue.

Sieve tubes - this is a vertical row of elongated living cells, the transverse walls of which are pierced with holes (like a sieve), the nuclei in these cells have collapsed, and the cytoplasm is adjacent to the membrane. This is a conductive bast tissue through which solutions of organic substances move.

bast fibers, elongated cells with destroyed contents and lignified walls represent the mechanical tissue of the stem. In the stems of flax, linden and some other plants, bast fibers are especially well developed and very strong. Linen cloth is made from flax bast fibers, and bast and matting are made from linden bast fibers.

92. The influence of living conditions on the growth of a tree in thickness

The dense, widest layer that lies deeper is wood - main part of the stem. It is formed by cells of different shapes and sizes: vessels of conductive tissue, wood fibers of mechanical tissue and cells of the main tissue.

All layers of wood cells formed in spring, summer and autumn make up the annual growth ring.

The small autumn cells are different from the large spring wood cells of the following year that are next to them. Therefore, the boundary between adjacent annual rings on a cross section of wood in many trees is clearly visible. By counting the number of growth rings using a magnifying glass, you can determine the age of a felled tree or cut branch.

By the thickness of the growth rings you can find out in what conditions the tree grew in different years of its life. Narrow growth rings indicate a lack of moisture, shading of the tree and its poor nutrition .

Lies between bark and wood cambium. It consists of narrow long cells of educational tissue with thin membranes. It cannot be detected with the naked eye, but can be felt by tearing off part of the bark from the surface of the wood and running your fingers over the exposed area. The cambium cells rupture and their contents flow out, moistening the wood.

In spring and summer, the cambium divides vigorously, and as a result, new bast cells are deposited towards the bark, and new wood cells are deposited towards the wood. The stem grows in thickness. When the cambium divides, much more wood cells are formed than bast. In autumn, cell division slows down, and in winter it stops completely.

In the center of the stem there is a looser layer - core, in which reserves of nutrients are deposited, clearly visible, for example, in aspen, elderberry and some other plants. In birch and oak it is very dense, and the border with the wood is difficult to see. The core consists of large cells of the main tissue with thin membranes. Some plants have large intercellular spaces between cells. This core is very loose.

From the core in the radial direction through the wood and bast pass medullary rays. They consist of cells of the main tissue and perform storage and conducting functions.

Internal structure of a tree branch

1. Examine the branch, find lentils (tubercles with holes). What role do they play in the life of a tree?

2. Prepare transverse and longitudinal sections of the branch. Use a magnifying glass to examine the layers of the stem in the sections. Using the tutorial, determine the name of each layer.

3. Use a needle to separate the bark, try to bend it, break it, stretch it. Read in your textbook what the outer layer of the bark is called. What is bast, where is it located, what is its significance for the plant?

4. In a longitudinal section, examine the bark, wood, and pith. Test each layer for strength.

5. Separate the bark from the wood, run your finger along the wood. How do you feel? Read the tutorial about this layer and its meaning.

6. Draw transverse and longitudinal sections of the branch and label the names of each part of the stem.

7. Find wood on a cut tree stem, use a magnifying glass to count the number of growth rings and determine the age of the tree.

8. Consider the growth rings. Are they the same thickness? Explain how wood formed in the spring differs from wood formed later in the year.

9. Determine which layers of wood are older - those lying closer to the middle or to the bark. Explain why you think so.

The structure of the stem of herbaceous plants differs from the structure of the stem of tree species. In herbaceous plants, cells do not become lignified, and mechanical tissues are poorly developed. In the stems of grasses, the cells of the main tissue are well developed.

The stems of dicotyledons have cambium tissue, but the stems of monocots do not have cambium, so they hardly grow in thickness.

GRASS STEM. WOODY STEM. UPREAM, CLIMBING, CLIMBING, CREEPING STEMES. LENTILS. CORK. BARK. LUB. SIEVE TUBES. BAT FIBERS. CAMBIUM. WOOD. CORE. MEDIUM RAYS

1. What is the internal structure of the stem of a tree or shrub? 2. What is the significance of the skin and the cork? 3. Where is the phloem located and what cells does it consist of? 4. What is cambium? Where it is located? 5. What layers are visible on a cross section of a stem when viewed with the naked eye and with a microscope? 6. What are tree rings? What can you tell from the growth rings? Why are the growth rings of many tropical plants not visible?

1. Look at the lentils on the branches of elderberry, bird cherry, oak and other trees and shrubs.

2. Determine the age of any cut tree by its growth rings. Make a drawing of the saw cut. Indicate in the picture the side that the tree faced north.

3. Take branches of apple tree, wild rosemary (Siberian rhododendron), cherry and place them in a vessel with water in a warm, bright room. Add fresh water to the container. In one and a half to two weeks, flowers will bloom on the branches. Use them when studying the structure of a flower.

In most trees, the smooth cork is replaced by a cracked bark. It consists of alternating layers of cork and other dead bark tissues.

In fruit trees, the crust usually forms on the 6th–8th year, in linden – on the 10th–12th year, in oak – on the 25th–30th year of life. Some trees (sycamore, eucalyptus) do not form a crust at all.

Dwarf juniper trees in the tundra have a trunk only 8 cm thick, American sequoias reach 10 m in diameter at the base of the trunk, and our oaks are over 1 m.

Based on the growth rings, it was possible to establish that the most durable trees can be considered baobab and dracaena; specimens were found in Africa whose age is about 6 thousand years.

In our country, cypress trees are the most durable - 3 thousand years; oaks, chestnuts, cedars – 2 thousand years; spruce – 1.6 thousand years; linden – 1 thousand years.

1. What is a kidney? Describe the types of kidneys.

A bud is an embryonic shoot. The top of the bud is covered with bud scales - dense, often pubescent and modified leaves impregnated with resinous substances. The scales protect the kidney from drying out, freezing, and from penetration of bacteria, fungi and other pathogens. Scaly leaves extend from the bud stem, which is called rudimentary. Behind them are the rudiments of green leaves. On the rudimentary stem, in the axil of the scaly and rudimentary leaves, the rudiments of daughter buds are laid. The bud stem ends at the apex with a growth cone. Thus, the bud has everything that is characteristic of an adult shoot: stem, leaves, buds, i.e. a bud is a rudimentary shoot.

Based on their structure, buds are divided into vegetative and generative. Buds that have all the parts of an adult vegetative shoot in their embryonic state are called vegetative. Buds that have on the rudimentary stem, in addition to leaves and daughter buds, the rudiments of a flower or inflorescence, are called generative. For example, in lilac, elderberry, horse chestnut and many other plants, both vegetative and generative buds overwinter. In spring, a vegetative shoot grows from a vegetative bud, and a generative shoot grows from a generative bud.

According to the structure of the buds, there are open (without bud scales) and closed (with bud scales).

Based on their location on the shoot, the buds are divided into apical and lateral (axillary). Sometimes on the shoot, buds develop on leaves and internodes. Such buds are called accessory buds.

Dormant buds. In spring, not all overwintered buds give rise to new shoots. Some of them remain unopened and are called dormant. They remain alive for many years. Their outer leaves peel off, and new leaves are formed at the base of the growth cone. The buds grow slowly at the top, remaining on the surface of the stem - trunk or branch. In case of damage to the plant (cutting, pruning, freezing of young shoots, etc.), the buds begin to grow and give rise to new shoots. Shoots from dormant buds can be seen on the trunks of old trees.

2. How does the escape from the bud unfold?Material from the site

With the onset of spring, the buds begin to grow. They swell, the scales on the surface of the bud disperse, and a new green shoot begins to grow.

The bud scales fall off as the bud expands and the shoot grows. Scars from scales on the stem are brought together and together form a bud ring. It looks like a “float” at the base of a new shoot that grows in the next year. By the bud rings, which are located on the border of annual growth, the age of the branch can be determined.