Ryabova M.S., Shirokova N.P. Branching of shoots and the structure of the stem of some types of woody plants
Table: Escape (leaf, stem, bud)
THE ESCAPE
The escape is the aerial part of the plant. A vegetative shoot is laid in the process of development of the embryo, in which it is represented by a kidney. kidney- this is a stalk and leaf primordia, can be considered the first bud of a plant. The apical meristem of the kidney during the development of the embryo forms new leaves, and the stem elongates and differentiates into nodes and internodes.
The escape- a complex organ consisting of a stem, leaves, buds. The stem has nodes and internodes. Knot- the part of the stem that contains the leaf and bud. The section of the stem between the nodes internode. The angle formed by a leaf and stem above a node is called leaf sinus. The kidneys, which occupy a lateral position on the node, are called lateral (or axillary). At the top of the stem is the apical bud.
Escape modifications can perform various functions: storage and the function of vegetative reproduction (tubers, rhizomes, bulbs), protective (thorns), serve as an attachment organ (antennae), etc.
- tubers- shortened and thickened underground shoots with buds (potatoes).
- Rhizome- an underground shoot resembling a root, bears scaly leaves and buds, 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).
- tendrils- a means of attachment (grapes).
SHEET
Sheet- a flat lateral organ of the shoot.
External leaf structure. In dicotyledonous plants, the leaf consists of a flat expanded plate and a stem-like petiole with stipules. The leaves of monocotyledonous plants are characterized by the absence of petioles, the base of the leaf, they are expanded, into the vagina, covering the stem. In cereals, the entire internode is covered with a vagina: The leaves of dicotyledonous plants are simple and complex. Simple leaves have one leaf blade, sometimes strongly dissected 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 extending like a fan from the top of the main petiole.
The internal structure of the leaf. Outside the leaf is a peel of colorless cells, covered with a waxy substance - the cuticle. Under the skin are located cells columnar parenchyma containing chlorophyll. Deeper are the cells of the spongy parenchyma with intercellular spaces filled with air. The vessels of the conducting bundle are located in the parenchyma. 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 provides a constant flow of water from the roots to the leaves. The rate of transpiration depends on the 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 enhancing the evaporation of water and gas exchange. In the process of gas exchange, oxygen enters the cells for respiration or is excreted into the atmosphere during photosynthesis.
Cellular structure of the leaf.
Leaf modifications: antennae - serve to fix the stem in a vertical position; needles (in cactus) play a protective role; scales - small leaves that have lost their photosynthetic function; hunting apparatus - the leaves are equipped with columnar glands that secrete mucus, which is used to capture small insects that have fallen 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 stem functions include; transport - carrying water with substances dissolved in it from the root to the ground organs; photosynthetic; storage - deposition in its tissues of proteins, fats, carbohydrates.
Stem fabrics:
- Conductive: the inner part of the cortex is represented by sieve tubes and satellite cells of the bast (phloem), wood cells (xylem) are located closer to the center, along which transport of substances.
- Cover- skin in young and cork in old lignified stems.
- Reserve- specialized cells of bast and wood.
- Educational(cambium) - constantly dividing cells that attack all tissues of the stem. Due to the activity of the cambium stem grows in thickness, and annual rings are formed.
Stem modifications: tuber - storage underground shoot; the entire mass of the tuber consists of a storage parenchyma together with a 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 strongly shortened stem with thick, overlapping leaves.
Cellular structure of the stem:
BUD
Bud- a rudimentary short shoot from which new shoots (vegetative buds) or flowers (generative buds) can develop. New shoots grow from the bud in spring. There are apical, axillary, (located in the leaf axils) and accessory buds. Adnexal 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 - kidney scales. There are apical and lateral (axillary) vegetative buds. The apical bud is located at the top of the stem and consists of growth cone cells 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, which are formed in the apical bud, the growth and development of lateral (sleeping) buds is inhibited, which begin to grow only when the apical bud is damaged or dies.
Generative kidneys larger than vegetative; they bear fewer rudimentary leaves, and at the top of the rudimentary stem are the rudiments of a flower or inflorescence. A generative bud containing one flower is called a bud. On the internodes of the stem, roots and leaves, adnexal buds can form, providing vegetative reproduction.
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§ 22. Escape and kidneys
1. What is the structure of the seed embryo? 2. What fabric is called educational?
The escape. A stem with leaves and buds on it is called escape. The stem is the axial part of the shoot, the leaves are lateral. The parts of the stem where leaves develop are called knots, and the sections of the stem between the two nearest nodes of one shoot - internodes.
Many plants have two types of shoots, one with long and one 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 in a spiral on the stem. Such an arrangement of leaves have, for example, birch, willow. If the leaves grow two at a node - one leaf against another, for example, in a maple, lilac, then this arrangement is called opposite. In plants with whorled by the arrangement of leaves, they develop three or more in nodes, as, for example, in elodea, oleander.
When the seed germinates, the shoot is formed from the bud of the seed germ. In perennial plants, shoots develop from a bud.
73. Leaf arrangement
74. Apple shoots
Kidneys. At the top of the shoot there is usually apical kidney, and in the axils of the leaves - axillary kidneys. Buds that do not develop in the leaf axil (on internodes, leaves, roots) are called adnexal.
The arrangement of axillary buds repeats the arrangement of leaves on the stem. Poplar, cherry, birch, bird cherry, hazel have another arrangement of buds.
The buds are located oppositely on the shoots of lilac, elderberry, jasmine, honeysuckle and indoor plants of fuchsia, pilea, coleus, which are characterized by the same leaf arrangement.
After the leaves fall on the shoots remain leaf scars, above which are the axillary buds.
Each type of plant is characterized by a certain location of the buds on the shoots, their shape, size, color, pubescence. By these and some other features, you can determine the name of a tree or shrub even in winter.
The structure of the kidneys . Outside, the kidneys are covered with dense leathery kidney scales that protect them from exposure to adverse environmental conditions.
In a magnifying glass on a longitudinal section of the kidney is clearly visible germinal stem, at the top of which is cone growth, consisting of cells of the educational tissue.
On the stem are very small embryonic leaves. In the axils of these leaves are rudimentary kidneys; they are so small that they can only be seen with a magnifying glass. Thus, the kidney is rudimentary escape.
75. Structure of chestnut buds
Inside some buds on the rudimentary stem, only rudimentary leaves are located. Such kidneys are called vegetative, or sheet. 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. The location of the buds on the stem
1. Consider the shoots of different plants. Determine how the buds are located on the stem, sketch.
2. Separate the kidneys from the shoot, consider their external structure. What adaptations help the kidneys to endure adverse conditions?
3. Cut the vegetative bud along, examine it under a magnifying glass. Using the drawing, find the scales, rudimentary stem, rudimentary leaves and growth cone. Sketch a vegetative bud in section and label the names of its parts.
4. Examine the generative kidney. What do vegetative and flower buds have in common and how do they differ? Use the picture for comparison in the textbook.
5. Compare the structure of the kidney and shoot. Make a conclusion.
Growth and development of the shoot. You have established that the kidney is a rudimentary, not yet developed shoot. Shoot development begins with bud break . When the kidney scales fall off, intensive growth of the shoot begins. The shoot is lengthened due to cell division 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 apex 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 the location.
76. Development of shoot from the kidney
The growth and development of shoots can be controlled. If you remove the apical bud, then the shoot stops growing in length, but it has lateral shoots. If you cut off the top of the side shoot, then it will also stop growing in length and begin to branch.
By pruning shoots, skilled gardeners often give bizarre, beautiful shapes to trees and shrubs. It has been established that the longevity and productivity of fruit trees, as well as the quality of fruits, depend on the shape of the crown.
THE ESCAPE. BUD. APICAL, AXIS, ADDITIONAL KIDNEYS. VEGETATIVE, GENERATIVE KIDNEYS. CONE OF GROWTH. NODE. INTERNODE. SINS OF THE LEAF. ORDINARY, OPPOSITE, WHORLED LEAF ARRIVAL
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 the 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?
Put 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 put into the water, when its buds swell, the scales open, a shoot appears and leaves blossom.
In addition to apical growth, in most plants, shoot internodes are elongated due to intercalary growth. For example, in wheat, bamboo, and other cereals, interstitial growth occurs as a result of the division and growth of cells located at the bases of all internodes. Due to this, the young stems of some plants grow very quickly. For example, bamboo stalks 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. Watch what happens to the plants in one to two weeks.
2. Cut off the top of a ficus or other houseplant. Watch the shoots grow.
Try to identify the names of trees and shrubs growing near your home and school by the characteristics of their buds.
By the location of the buds, their shape, size, color, pubescence, and some other features, you can even determine in winter which tree or shrub is in front of us.
The buds are usually located directly on the stem. The exception is alder: her kidneys sit on special legs. By this sign, as well as by catkins and small cones, alder is easy to distinguish from other trees before the leaves bloom.
Poplar is recognized by its sticky, resinous, pointed buds, which have a peculiar pleasant smell.
The willow bud is covered with only one scale, resembling a cap.
The buckthorn has no kidney scales at all.
77. Buds on the shoots of various trees and shrubs
The oblong large rowan buds are pubescent and therefore well distinguishable from the buds of other trees. .
Bird cherry and blackcurrant buds have a pleasant smell. Oppositely located elderberry buds, on the contrary, have an unpleasant smell. Smelling them, you will immediately distinguish the elderberry from other shrubs.
§ 23. External structure of the sheet
1. What vegetative organs are distinguished in a flowering plant? 2. On which organ of a flowering plant are leaves located? 3. Are the sizes and shapes of leaves the same for different plants?
The leaf is part of the shoot. It performs three main functions - photosynthesis(formation of organic substances), gas exchange and water evaporation.
Leaf shape. Although the leaves of different plants differ 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. Petiolate leaves are apple, cherry, maple, birch. 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.
Outgrowths sometimes develop at the base of the petiole - stipules.
78. Attaching leaves to the stem
In shape, the leaves are round, oval, heart-shaped, needle-shaped, etc. The leaves are also diverse in shape of the edge of the plate. For example, an apple leaf has a jagged edge, an aspen leaf has a serrated edge, 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. Such leaves in ash, mountain ash and many others .
79. Different shapes of the edge of the leaves
80. Simple leaves
81. Compound leaves
82. Leaf venation
Venation . Leaf blades are pierced in different directions conductive bundles, who are called veins.
The veins not only conduct nutrient solutions, but also give the sheet strength.
If the veins are parallel to one another, as in many monocotyledonous plants (wheat, rye, barley, onion and some others), such venation is called parallel.
Wider leaves of lily of the valley and houseplant aspidistra have arc venation, which is also characteristic of monocotyledonous plants.
Reticulate venation typical of the leaves of dicotyledonous plants, the veins in them, as a rule, branch many times and form a continuous network. But there are exceptions: for example, in a dicotyledonous plantain, the venation is arcuated, and the leaves of the monocotyledonous plant, the crow's eye, have mesh venation.
Leaves simple and compound, their venation and leaf arrangement
1. Examine the leaves of houseplants 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 is the venation of the leaves you selected?
3. What leaf arrangement do the plants you have viewed have?
4. Fill in the table.
LEAF PLATE, PETLE. LEAVES PETILE AND SESSIONABLE. LEAVES SIMPLE AND COMPLEX. VENATION NETWORK, 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 venation.
An inhabitant of the tropics, Amazonian Victoria, related to our water lilies, has a leaf so large that a three-year-old child can sit on it, like on a raft, and the leaf keeps it on the water.
The woodlice weed 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 corner.
§ 24. Cellular structure of the leaf
1. What is the function of the integumentary tissue? 2. What are the structural features of the cells of the integumentary tissue? 3. What is the function and where are the cells of the main tissue located? 4. What are intercellular spaces?
Familiarity with the internal structure of the leaf blade will help to better understand the significance of green leaves in plant life.
The structure of the skin. Above and below the leaf is covered with a thin transparent skin, its cells protect the leaf from damage and drying out. Peel - one of the types of integumentary tissue of a plant.
Among the colorless and transparent cells of the skin, there are arranged in pairs closing cells with green plastids in their cytoplasm chloroplasts. There is a gap between them. These cells and the gap between them are called stoma. Air enters the leaf through the stomatal opening and water evaporates.
In most plants, the 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, there are more than a million of them on a linden leaf, and several million stomata on a cabbage leaf.
83. Stomata with surrounding skin cells
The structure of the skin of the leaf
1. Take a piece of a clivia leaf (amaryllis, pelargonium, tradescantia), break it and carefully remove a small area 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 preparations of the skin of the leaf.)
2. Look for colorless skin cells. Consider their shape and structure. What cells do you already know they look like?
3. Find stomatal cells? How are stomatal cells different from other onion skin cells?
4. Sketch the skin of the onion under the microscope Draw the stomata separately. Write captions for pictures.
5. Draw a conclusion about the meaning of the skin of the leaf.
The structure of the leaf pulp. Under the skin is the pulp of the leaf, consisting of the 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. In the cytoplasm of these cells, there are especially many chloroplasts.
Beneath the columnar tissue lie more rounded or irregularly shaped cells. They are not close 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 sponge fabric.
84. Internal structure of the leaf
The structure of leaf veins. If we look at a cross section of a leaf blade under a microscope, we can see in it conductive bundles leaf - veins, consisting of vessels, sieve tubes and fibers. Strongly elongated cells with thick walls - fibers - give the sheet strength. Vessels move water and minerals dissolved in it. Sieve tubes, unlike vessels, are formed by living long cells. The transverse partitions between them are pierced with narrow channels and look like sieves. Solutions of organic substances move through the sieve tubes from the leaves.
Cellular structure of the leaf
1. Examine the prepared micropreparations of the leaf cut Find the cells of the upper and lower skin, stomata.
2. Examine the cells of the pulp of the leaf. What shape do they have? How are they located?
3. Find intercellular spaces. What is their meaning?
4. Locate the conductive leaf bundles. What kind of cells are they made up of? What functions do they perform? Compare the slides with the textbook drawing.
5. Draw a cross section of the sheet and sign all the parts.
PEEL OF THE LEAF. STATE. CHLOROPLAST. COLUMN AND SPONGE FABRICS. LEAF PULP. CONDUCTIVE BEAM. VESSELS. SIEVE TUBES. FIBER
1. What cells form a leaf blade? 2. What is the significance of the skin of the leaf? What tissue cells is it formed by? 3. What are stomata and where are they located? 4. What is the structure of leaf pulp cells? What type of tissue are they? 5. Which leaf cells have the most chloroplasts? 6. What is the function of the conductive leaf bundles? What tissue cells are they formed from?
Place two bulbs in jars of water so that the water touches their base. Put one jar in a dark place, and the other in a lighted place. Watch the leaves grow. How do they differ? Why?
The number and arrangement of stomata on the upper and lower surfaces of the leaves is related to the conditions in which the plants grow.
The number of stomata in different plants per 1 mm 2 leaf surface
The more polluted the air, the lower the number of stomata: leaves collected from trees growing in the suburbs, where the air is relatively clean, have 10 times more stomata per unit 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 moisture factor. The leaves of plants in wet places are usually large with a large number of stomata. A lot of moisture evaporates from the surface of these leaves. These plants include monstera, ficus, and begonia, often grown in rooms.
The leaves of dryland plants are small and have adaptations to reduce evaporation. This is a dense pubescence, wax coating, a relatively small number of stomata, etc. Some plants, such as aloe, agave, have soft and juicy leaves. They store water.
Leaves and lighting conditions. The leaves of shade-tolerant plants have only two or three layers of rounded, loosely adjacent cells. Large chloroplasts are located in them so that they do not obscure each other. Shade leaves tend to be thinner and darker green in color as they contain more chlorophyll.
In plants of open places, the pulp of the leaf has several layers of columnar cells tightly adjacent to each other. They contain less chlorophyll, so the light leaves are lighter in color. Those and other leaves can sometimes be found in the crown of the same tree. .
85. Light and shadow lilac leaves
86. Leaf modifications
Leaf modifications. In the process of adaptation to environmental conditions, the leaves of some plants have changed because they began to play a role not characteristic of typical leaves. For example, in barberry, part of the leaves has changed into thorns. 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 antennae. They serve to keep the stem of the plant upright.
Of interest are the leaves of insectivorous plants that live on soils poor in nitrogenous substances. A small sundew plant grows on peat bogs . Its leaf blades are covered with hairs that secrete a sticky liquid. Brilliant as dew, sticky droplets attract insects. Insects that have settled on a leaf get bogged down in a sticky liquid. First, the hairs, and then the leaf blade, are bent and cover the victim. When the plate and leaf hairs unfold again, only its integuments remain from the insect. All living tissues of the insect will be "digested" by the leaf of the plant and sucked in.
87. Sundew round-leaved
LIGHT LEAVES. SHADOW LEAVES. SHEET MODIFICATIONS
1. Is it possible to distinguish between plants of wet places and dry areas by appearance? 2. Prove that the structure of the leaf is related to the living conditions of plants. 3. Why do floating leaves of aquatic plants have stomata only on the upper side of the leaf, while submerged leaves 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 places, and the shady ones 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. On what basis did you draw your conclusion?
Prepare and examine preparations of leaves of aloe, tradescantia, uzambara violet and other plants under a microscope.
Among cacti, only Peyrescia (often grown indoors) has true leaves that fall off during a drought.
In such typical steppe and semi-desert plants as feather grass, the stomata are located on the upper side of the leaf, and the leaf, under conditions of lack of moisture, is able to curl up into a tube. The stomata then find themselves inside the tube and are isolated from the surrounding dry air. In the cavity of the tube, the concentration of water vapor increases, which leads to a decrease in evaporation. .
88. Feather leaf
§ 26. The structure of the stem
1. What is called an escape? 2. What functions do mechanical, conductive, integumentary tissues perform? 3. What stems do the plants you know have? 4. What is the difference between the stems of trees, shrubs, herbs?
stem - the axial part of the shoot of the plant, it conducts nutrients and brings the leaves to the light. Reserve nutrients can be deposited in the stem. It develops leaves, flowers, fruits with seeds.
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 shell of their cells - lignin. Lignification occurs at the stems of trees and shrubs starting from the second half of the 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 hot tropics and in permafrost regions.
In the direction of growth, the stems are divided into erect, curly, climbing, creeping. .
Most plants have stems erect, they grow vertically upwards. The erect stems have a well-developed mechanical tissue, they can be lignified (birch, apple) or herbaceous (sunflower, corn).
90. Layers on the trunk of a sawn tree
curly the stems, rising up, wrap around the support (field bindweed, beans, hops).
climbers the stems rise up, clinging to the support with tendrils (grapes, peas) or adventitious roots growing from the stem (ivy).
Creeping stems creep along the ground and can take root at the nodes (strawberries, cinquefoil).
Internal structure of the stem. On a cross section of a branch or saw cut of a tree, it is easy to distinguish the following areas: bark, cambium, wood and core .
Young (annual) stems are covered on the outside skin, which is then replaced by a cork consisting of dead cells filled with air. Peel and cork are integumentary tissues. They protect the stem cells located deeper from excessive evaporation, various damages, 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. In a traffic jam develop lentils - small tubercles with holes, clearly visible from the outside, especially in elderberry, oak and bird cherry. The lenticels are formed by large cells of the underlying tissue with large intercellular spaces. They carry out gas exchange. .
91. Cross section of a branch under a microscope
Some trees form thick layers traffic jams. A particularly powerful cork develops on the trunk of a cork oak. It is used for various household needs.
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, in which the transverse walls 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 tissue of the bast, along 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, the bast fibers are especially well developed and very strong. Linen is made from bast fibers of flax, 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, lying deeper, is wood - the main part of the stem. It is formed by cells of various shapes and sizes: vessels of the conductive tissue, wood fibers of the mechanical tissue, and cells of the underlying tissue.
All layers of wood cells formed in spring, summer and autumn make up the annual growth ring.
Small autumn cells are different from the large spring wood cells of the next year, located next to them. Therefore, the boundary between adjacent growth rings on the cross section of wood in many trees is clearly visible. By counting the number of growth rings with a magnifying glass, you can determine the age of a cut tree or a cut branch.
By the thickness of the growth rings, you can find out in what conditions the tree grew in different years of life. Narrow growth rings indicate a lack of moisture, the 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 you can feel it by tearing off part of the bark from the surface of the wood and running your fingers over the exposed area. At the same time, the cambium cells are torn, 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 towards the wood. The stem grows in thickness. When dividing the cambium, wood cells form much more than bast. In autumn, cell division slows down, and in winter it stops completely.
In the center of the stem is a looser layer - core, in which nutrient reserves are deposited, clearly visible, for example, in aspen, elderberry and some other plants. In birch and oak, it is very dense, and it is difficult to see the border with wood. The core consists of large cells of the main tissue with thin membranes. Some plants have large intercellular spaces between cells. Such a core is very loose.
From the core in the radial direction through the wood and the bast pass core rays. They consist of cells of the main tissue and perform storage and conduction functions.
The internal structure of a tree branch
1. Examine the branch, find the lenticels (tubercles with holes). What role do they play in the life of the tree?
2. Prepare transverse and longitudinal sections of the branch. Using a magnifying glass, examine the layers of the stem in sections. Using the tutorial, determine the name of each layer.
3. Separate the bark with a needle, try to bend it, break it, stretch it. Read in the textbook what the outer layer of the cortex is called. What is a bast, where is it located, what is its significance for a plant?
4. On a longitudinal section, consider the bark, wood, core. Test each layer for durability.
5. Separate the bark from the wood, run your finger over the wood. What do you feel? Read the textbook about this layer and its meaning.
6. Sketch the cross and longitudinal sections of the branch and sign the names of each part of the stem.
7. Find wood on the saw cut of a woody stem, count the number of growth rings with a magnifying glass and determine the age of the tree.
8. Consider growth rings. Are they the same thickness? Explain how wood formed in spring differs from wood formed later in the year.
9. Determine which layers of wood are older in age - 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, the cells do not become lignified, and the mechanical tissues are poorly developed. The cells of the main tissue are well developed in the stems of grasses.
The stems of dicotyledonous plants have an educational tissue cambium, and the stems of monocotyledonous plants do not have a cambium, so they almost do not grow in thickness.
HERBAL STEM. WOODEN STEM. upright, climbing, climbing, creeping stems. Lentils. CORK. BARK. LUB. SIEVE TUBES. BAST FIBERS. CAMBIUM. WOOD. CORE. CORE RAYS
1. What is the internal structure of the stem of a tree or shrub? 2. What is the importance of peel and cork? 3. Where is the bast located and what cells does it consist of? 4. What is a cambium? Where it is located? 5. What layers are visible on the cross section of the stem when viewed with the naked eye and with a microscope? 6. What are growth rings? What can be determined from annual rings? Why do many tropical plants have no growth rings?
1. Consider lentils on the branches of elderberry, bird cherry, oak and other trees and shrubs.
2. Determine the age of any cut tree from the growth rings. Draw a saw cut. Indicate in the picture the side that the tree was facing north.
3. Take branches of an apple tree, wild rosemary (Siberian rhododendron), cherry and put them in a vessel with water in a warm, bright room. Pour fresh water into the vessel. After 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 fissured bark. It consists of alternating layers of cork and other dead bark tissue.
In fruit trees, the bark usually forms on the 6th–8th, in linden - on the 10th–12th, in oak - on the 25th–30th year of life. In some trees (sycamore, eucalyptus), the crust does not form 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 - over 1 m.
According to annual rings, it was possible to establish that the baobab and dracaena can be considered the most durable trees; specimens were found in Africa that are about 6 thousand years old.
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.
In plants? This is an organ that is located on the stem in the axil of the leaf or at its top. In our article, we will consider the structural features of this part of plants, the types and the role that it plays in their life.
Plant bud: definition
This plant organ is a special type of shoot. A flower or leaves develop from it. Therefore, it would be correct to say that a bud is a rudimentary shoot of a plant.
How is it formed? One of the parts of the seed germ is the kidney. It contains all parts of a leafy plant, but they are greatly shortened. The kidney consists of a stem, on which there are closely spaced rudimentary leaves.
The cells of the meristem, or educational tissue, form a growth cone. Due to the division of its cells, the stem grows in thickness, new leaves and outer buds appear.
Types of plant buds
Plant shoots are distinguished by their diversity. Since the kidney is a rudimentary version of this organ, there are several types of this part of the plant.
What features underlie this classification? These are the features of the internal structure, the location on the stem and the physiological state. Let's consider each of these types in more detail.
location on the plant
On this basis, apical and lateral buds are distinguished. How to distinguish them? The apical kidney of the shoot is one. On the branch, it is the highest, so it will not be difficult to find it. Such a kidney is the beginning of a young shoot and is a continuation of the main axis. Developing, it will give rise to new branches, ensure the growth of the shoot in length. Initially, it is formed from the bud of the seed germ. If the shoot begins to branch, then it dies off.
All other buds located on the stem are lateral. They are of two types: adnexal and axillary. The first develop at the internodes. This is the distance between the places of attachment of leaves to the stem of the shoot.
Sometimes adventitious buds form on leaves or roots. In this case, adnexal buds provide vegetative propagation of the plant. For example, in Kalanchoe, such structures are located along the entire edge of the leaf blade. From them, small plants are immediately formed, consisting of green shoots with adventitious roots. They fall away from the mother's body and move on to an independent existence.
And what is a kidney in a plant called cabbage? This is her head of cabbage, or forks. It is an overgrown apical bud, which consists of a shortened stem and wide leaves.
The axillary buds are located where the leaf is attached to the stem. They constantly form as the plant grows. Their formation occurs in the axils of young leaves. They are also kept in winter. During this period, the type of leaf arrangement can be determined by the nature of their attachment.
Brood buds are a special type of axillary buds. Modified shoots are formed from them - nodules or bulbs.
Features of the internal structure
What is a kidney in plants can also be considered using the example of their anatomical features. On this basis, three types of rudimentary shoots are distinguished: vegetative, generative and mixed.
In the first case, a shoot develops from the kidney. Therefore, the parts of such a structure are the rudimentary stem, leaves, scales and growth cone. Each of them performs its own functions. The stem and leaves give rise to new organs. The cone of growth is the point of growth or the tip of the stem. It consists of young and constantly dividing cells of the educational tissue.
Kidney scales are modifications of the outer leaves. They perform a protective function, protecting internal structures from negative manifestations of the environment. This is mainly hypothermia, exposure to direct sunlight and excessive loss of moisture. The scales do not contain chloroplasts, therefore they do not carry out photosynthesis. They are formed by dead cork tissue cells. Falling off, they leave scars on the stem. By counting their number, you can determine how many years I will run.
Generative buds give rise to flowers. Their structure is different from the vegetative ones. In addition to a shortened stem and scales, they also contain the beginnings of flowers. Some plants develop mixed buds. They have the beginnings of both future leaves and flowers. Generative and mixed kidneys are easy to distinguish. They have a rounded shape and are much larger than vegetative ones.
The kidneys may differ in a number of other ways. For example, in spruce and pine, the scales stick together with the help of resin, and in poplar - with a special adhesive substance. They can be with additional pubescence or naked. And in viburnum, kidney scales do not develop at all.
Physiological state
What are buds in plants whose organs do not die off in frosty winters or dry summers? And do they persist at all in such unfavorable periods? Undoubtedly. Such buds are called dormant. Such structures provide many years of periodic plant growth. In winter, they are at rest, with the onset of sunny days they give new shoots. Annual plants do not form such buds.
There is another type of rudimentary shoots. These are dormant buds. They are alive, but may not develop throughout the life of the plant. How do you "force" them to do it? You just need to remove the part of the stem that is above the dormant buds. In this case, they will give rise to young shoots. Thus, the development of dormant buds occurs as needed. It can be inactive for a long time or immediately give rise to new shoots.
Functions of plant buds
Rudimentary shoots contain all the organs of the aerial part of the future plant organism. Therefore, the main function of the kidneys is the implementation of its growth and development. In angiosperms, they also ensure the formation of a flower, and hence sexual reproduction.
Kidneys can also be located on modified organs. Potato tubers are a typical example of this. The buds of this modification of the shoot are called eyes. Their function is vegetative reproduction.
We are sure that now everyone will be able to answer the question of what a kidney is in plants. This is a rudimentary and shortened shoot, from which stems, leaves and flowers develop.
The kidney is the organ of the escape, which ensures its apical growth and branching. The structure of the kidney: kidney scales, rudimentary leaves, primordia of lateral shoots, growth cone.
By external structure exposed - naked(pride) and closed- dressed in kidney scales.
As of- growing (spring), dormant (autumn), dormant (winter).
Rest of the kidney is a seasonal phenomenon. Sleeping buds are able not to bloom for a long time. In oak, they "sleep" up to 100 years, in birch - up to 50, in aspen - 40, in honeysuckle - 35, in hawthorn - 25 years.
According to the location of the kidney, there may be apical and axillary and adnexal
Apical - provide growth in length.
Axillary (lateral) - are found in the axils of the leaves. In the axil of one leaf there may be 1 or more buds.
Adnexal - usually found in internodes (kalanchoe, ferns). Adnexal buds develop on stumps after felling many tree species, forming the so-called stump growth. It occurs in oak, elm, birch, linden, hazel. Sleeping buds also participate in the formation of stump shoots.
By internal structure: vegetative and generative and mixed.
Vegetative kidney- consists of a shortened stem and rudimentary leaves located on it.
Generative (flower) - in addition to the leaves, there are the beginnings of flowers or a single flower. They differ from the vegetative: in size and shape. They are larger. The germ of a single flower bud. The tip of the primordial stem - cone of growth.
In mixed kidneys both vegetative and reproductive parts (lilac) are equally well formed.
Kidney location:
Opposite:single(lilac, maple, chestnut) serial(Tatar honeysuckle) in the leaf axil there are several vertically arranged buds.
Next:single(linden, apple tree) serial(Manchurian walnut)
collateral (turn) in the axil of the leaf several buds located horizontally.
Whorled- three or more leaf sinuses depart from each node,
having one kidney each (oleander, pine).
Define "leaf". Describe the morphological structure of the leaf. Describe the functions of a leaf.
leaf morphology.
The leaf is the vegetative organ of the plant.
Functions:
1. pho t osynthesis;
2. gas exchange;
3. transpiration - evaporation of water;
4. protection of the plant (scales, spines, attachment to the support with antennae);
5. supply of nutrients and water;
6. vegetative reproduction.
The sheet consists of: leaf blade, petiole and base.
The sheet consists of records , petiole and grounds (with it there are stipules).
leaf blade- the most important part of a typical leaf. Its lamellar shape creates the largest surface area per unit volume of tissues, which is the best way to fulfill all the indicated functions of a green leaf.
petiole- narrow stem-like part between lamina and base. Orients the leaf in relation to the light and weakens the impact on the plate of rain, hail, snow. Leaves without petioles - sedentary (cornflower meadow, aloe, cloves).
leaf base- this is the part of it with which the leaf is connected to the stem. Morphologically, the base is not always well expressed.
Stipules- paired lateral outgrowths at the base of the leaf. They usually develop earlier than the lamina and petiole, and protect the leaf blade from damage in the kidney (at birch, linden, bird cherry, apple tree); when the kidney opens, they fall off. In some plant species, stipules grow, turn green and perform the same functions as the leaf blade (in peas, violets, roses, ranks).
Leaves are simple and complex. A simple leaf has one leaf blade, which falls entirely in autumn. complex sheet consists of several leaf blades attached to a common petiole with the help of their own petioles. As a result, woody plants compound leaf in autumn falls off in parts - at first one by one the leaves, then the petiole.
Rachis- main axis (central vein with petiole) of a compound leaf. Depending on the location of the leaves, there are pinnate and palmately complex leaves. At pinnate leaflets are located in two rows on both sides of the rachis, which is an overgrown elongated petiole (raspberries, mountain ash, peas).
Classical palmately complex leaf in species horse chestnut, lupine. In palmately complex and their particular case - ternary there are no rachis leaves and leaflets extend from the top of the petiole. According to the degree of branching of the rachis, they distinguish once, twice and thrice pinnate leaves. If a rachis of any order of a pinnate leaf ends at the apex with an unpaired leaflet, the leaf is unpaired pinnate, in the absence of leaves - paired pinnate. The thrice-paired-pinnate leaf type is known only in one plant - a tropical species. moringa(Moringapterigosperma). Doubly-pinnately compound leaves are very common in representatives of the mimosa subfamily (family legumes). The number of small leaves of such a sheet sometimes reaches 10 thousand.
Answer left Guest
The escape. A stem with leaves and buds on it is called a shoot. The stem is the axial part of the shoot, the leaves are lateral. The sections of the stem on which leaves develop are called nodes, and the sections of the stem between the two nearest nodes of the same shoot are called internodes. Many plants have two types of shoots, one with long and one with short internodes. The angle between the leaf and the internode above is called the leaf axil.Leaf arrangement (Fig. 17). In most plants, there is an alternate, or spiral, leaf arrangement, in which the leaves grow one at a node and are arranged alternately in a spiral on the stem. Such an arrangement of leaves have, for example, birch, willow. If the leaves grow two at a node - one leaf against another, for example, in maple, lilac, then this arrangement is called opposite. In plants with a whorled arrangement of leaves, they develop three or more at the nodes, as, for example, in elodea, oleander.Rice. 17. Leaf arrangement
When the seed germinates, the shoot is formed from the bud of the seed germ. In perennial plants, shoots develop from a bud. Kidneys. There is usually an apical bud at the top of the shoot, and axillary buds in the axils of the leaves (Fig. 18). Kidneys that do not develop in the axil of the leaf (on internodes, leaves, roots) are called adnexal. The arrangement of axillary buds repeats the arrangement of leaves on the stem. Poplar, cherry, birch, bird cherry, hazel have another arrangement of buds. The buds are located oppositely on the shoots of lilac, elderberry, jasmine, honeysuckle and indoor plants of fuchsia, pilea, coleus, which are characterized by the same leaf arrangement.
Rice. 18. Apple shoots
After the leaves fall, leaf scars remain on the shoots, over which the axillary buds are located. Each type of plant is characterized by a certain location of the buds on the shoots, their shape, size, color, pubescence. By these and some other features, you can determine the name of a tree or shrub even in winter. The structure of the kidneys (Fig. 19). Outside, the kidneys are covered with dense leathery kidney scales that protect them from exposure to adverse environmental conditions. In a magnifying glass on a longitudinal section of the kidney, the rudimentary stem is clearly visible, at the top of which there is a growth cone consisting of cells of the educational tissue.
Rice. 19. The structure of chestnut buds
On the stalk of the kidney 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 a rudimentary shoot.Inside some buds on the rudimentary stem, only rudimentary leaves are located. Such buds are called vegetative or leaf buds. Generative, or flower, buds are rudimentary buds or inflorescences, they are larger than vegetative ones and have a more rounded shape.The structure of the kidneys. The location of the buds on the stem1. Consider the shoots of different plants. Determine how the buds are located on the stem, and sketch them.2. Separate the kidneys from the shoot, consider their external structure. What devices help the kidneys to endure adverse conditions?3. Cut the vegetative bud lengthwise, examine it under a magnifying glass. Using Figure 19, locate the scales, primordial stem, primordial leaves, and growth cone. Sketch a vegetative bud in section and label the names of its parts.4. Examine the generative kidney. What do vegetative and flower buds have in common and how do they differ? Use Figure 19.5 for comparison. Compare the structure of a kidney and a shoot. Make a conclusion.Growth and development of the shoot. You have established that the kidney is a rudimentary, not yet developed shoot. Shoot development begins with bud break (Fig. 20). When the kidney scales fall off, intensive growth of the shoot begins. The shoot is lengthened due to cell division 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 apex 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 the location.
Rice. 20. Development of shoot from the kidney
The growth and development of shoots can be controlled. If you remove the apical bud, then the shoot stops growing in length, but it has lateral shoots. If you cut off the top of the side shoot, it will also stop growing in length and begin to branch.
A kidney is a rudimentary shortened shoot that has not yet developed. A head of cabbage is also a very overgrown bud (Fig. 62). The growth of the stem in height in most flowering plants is due to apical kidneys, or growth cone; in some plants (cereals, hops, etc.) - due to the intercalary growth of shoots (Fig. 63). Side, or axillary, the buds give lateral shoots of the following order, they are laid in the axils of the leaves and have the same structure as the apical ones. The growth cone is represented by the primary educational tissue, the cells of which are continuously dividing (see Fig. 19, BUT). The cone is protected by rudimentary leaflets, in the axils of which rudimentary lateral buds are laid.
Many axillary buds are in a dormant state, which is why they are called sleeping or eyes(Fig. 64). Dormant buds constantly grow with their axis inside the trunk by the thickness of the annual annual growth of wood. As a result of various types of pruning, freezing, biting by animals and other damage, as well as weakening crown growth, these dormant buds can sprout, for example tops(see fig. 61), on the trunks of old fruit trees. In the first year or two, the leaves on the tops are larger, and the buds are very small. In fruit growing, tops are also called water shoots and they are usually destroyed, as they take a lot of nutrients and due to them the number of flower buds decreases. In ornamental gardening, when pruning (removing the apical bud), young shoots develop from dormant buds, with the help of which they form the crowns of many ornamental trees and shrubs. In vegetable growing
Rice. 63. Insertion growth of shoots: A - growing young shoots of hops on the rhizome, at the base of last year's dead shoot; B - a diagram of a longitudinal section of such an escape; B - scheme of "telescopic" growth of a cereal shoot; LPL - leaf blades, Vl - leaf sheaths, Pr - stipules; intercalary growth zones are marked in a box
the growth of lateral shoots is also stimulated by pinching the apical shoot (cucumbers, tomatoes, etc.).
In the kidneys, embryonic flowers can also be laid. The buds, in the rudiments of which there is a rudimentary stem and rudimentary leaves and flowers, are called mixed, or vegetative-generative, and the buds, in which only the rudimentary stem with leaves is laid, - vegetative(Fig. 65). The buds from which only flowers develop are called floral.
Kidneys that fall into a dormant state for the winter are called wintering. Outside, the buds of wintering shoots are covered with specialized covering leathery bud scales, which are the outer leaves or parts of these leaves. Covering scales protect the internal parts of the kidney from adverse winter conditions (evaporation, sudden temperature fluctuations, etc.) and such kidneys are called closed(Fig. 66). Often the covering scales are covered with hairs or resinous, sticky secretions, etc., which further enhances their protective functions. Each type of plant has its own color, shape, number of bud scales, hairs (or their absence) and other additional protective devices of the covering scales from the adverse effects of the environment. For example, oak has up to 20 covering scales, male plants of sea buckthorn of Central Asian origin have up to 32, and female plants of sea buckthorn have only 3–4, and willow has 2. Only a few wintering buds of some plants do not have typical protective kidney scales, for example, lilac , barberry, brittle buckthorn, viburnum pride, etc. Such kidneys are called open(Fig. 67, BUT). They are also found in aquatic flowering plants (Fig. 67, B).
Under wintering buds on leafless branches, you can always see a leaf scar - the place of attachment of a fallen leaf, and on it a leaf trace - the ends of dangling vascular bundles, kidney rings (Fig. 68). By the shape, color, pubescence and other signs of buds, one can determine the type of woody plant in a leafless state.
Woody plants of tropical latitudes, where there is a dry season, as well as rhizomes and other modified shoots of perennial grasses, have buds. renewal, from which in the spring of next year the above-ground
shoots. In herbaceous plants, these buds are not brown, but green, and the inner parts of the bud can protect, for example, the bases of petioles of dead leaves, the remaining leaf sheaths, etc.
Kidneys are distinguished by location adnexal. They can be formed in many plants due to the activity of the cambium, pericycle, and other educational tissues in various vegetative organs (root, stem, leaf). These buds appear on the stumps of many trees, forming stump shoots (oak, birch, linden, hazel, etc.), as well as in most perennial herbaceous plants (yarrow, kupyr, sow thistle, etc.). Kidneys that do not have a dormant period are called kidneys. enrichment from which enrichment shoots grow. Enrichment shoots are characteristic of most annuals (beans, wood lice, Ivan da Marya, types of rattles, etc.). A large number of shoots of one plant significantly increases its photosynthetic surface.
Buds on the shoots can be located singly and in groups. With a single location of the kidneys on the shoot, they secrete apical and axillary opposite the location of the kidneys (horse chestnut, maple, lilac, spirea, etc.), apical and axillary
another(willow, elm, poplar, hazel, etc.); with a group arrangement of the kidneys - serial(aristolochia, etc.); collateral(wolf's bark) and whorled(domestic plum, oleander, elodea, common juniper, crow's eye, piperomia clauseolist, etc.) (Fig. 69).