Lateral shoots in annual plants. The escape
Either from the axillary or adnexal (adventitious) kidney. Thus, the kidney is a rudimentary shoot. When the seed germinates from the germinal bud, the first shoot of the plant is formed - its main shoot, or first order escape.
From the main shoot are formed side shoots, or second order shoots, and when branching is repeated - of the third order, etc.
Adventitious shoots are formed from adnexal buds.
This is how the system of shoots is formed, represented by the main shoot and side shoots of the second and subsequent orders. Escape system increases total area contact of the plant with the air.
Depending on the function performed, shoots are distinguished as vegetative, vegetative-generative and generative. Vegetative (unmodified) shoots, consisting of a stem, leaves and buds, and vegetative-generative (partially modified), additionally consisting of a flower or inflorescence, perform the functions of air nutrition and provide the synthesis of organic and inorganic substances. In generative (completely modified) shoots, photosynthesis most often does not occur, but sporangia are formed there, the task of which is to ensure plant reproduction (a flower also belongs to such shoots).
The shoot that produces flowers is called flowering shoot, or peduncle(sometimes the term "peduncle" is understood in a narrower sense - as a section of the stem, on which the flowers are located).
Main escape organs
A vegetative unmodified shoot is a single plant organ, consisting of a stem, leaves and buds, formed from a common array of meristems (the cone of growth of the shoot) and having a single conducting system. The stems and leaves, which are the main structural elements of the shoot, are often considered as its constituent organs, that is, organs of the second order. In addition, the obligatory affiliation of the escape is the kidneys. home external feature that distinguishes the shoot from the root is the presence of leaves.
Monopodial branching
Monopodial branching is the next stage in the evolution of shoot branching. In plants with a monopodial type of shoot structure, the apical bud is preserved throughout the life of the shoot. The monopodial type of branching is often found among gymnosperms, it is also found in many angiosperms (for example, in many species of palms, as well as plants from the Orchid family - gastrochilus, phalaenopsis and others). Some of them have a single vegetative shoot (for example, Phalaenopsis is pleasant).
monopodial plants- the term most often used in the description of plants of tropical and subtropical flora, as well as in popular science literature on indoor and greenhouse floriculture.
Monopodial plants can vary significantly in appearance. Among them there are rosette, with an elongated shoot, bushy.
Sympodial branching
In plants with a sympodial type of shoot structure, the apical bud, having completed development, dies off or gives rise to generative run away. After flowering, this shoot no longer grows, and a new one begins to develop at its base. The structure of the shoot in plants with a sympodial type of branching is more complicated than in plants with; sympodial branching is an evolutionarily more advanced type of branching. The word "simpoidal" is derived from the Greek. sym("together" or "many") and pod("leg").
Sympodial branching is characteristic of many covered seed plants: e.g. for limes, willows and many orchids.
In orchids, in addition to the apical ones, some sympodial orchids also form lateral inflorescences, developing from buds located at the base of the shoot (Pafinia comb). The part of the shoot pressed against the substrate is called the rhizome. It is located, as a rule, horizontally and does not have true leaves, only scaly. A reduced, almost indistinguishable rhizome occurs in many Masdevallia, Dendrobiums and Oncidiums; well distinguishable and thickened - in cattleyas and lelias, elongated - in bulbophyllums and cologins, reaching 10 or more centimeters. The vertical part of the shoot is often thickened, forming the so-called tuberidium, or pseudobulb. Pseudobulbs may be various shapes- from almost spherical to cylindrical, cone-shaped, club-shaped and elongated, resembling reed stalks. Pseudobulbs are storage organs.
sympodial plants- the term most often used in the description of plants of tropical and subtropical flora, as well as in popular science literature on indoor and greenhouse floriculture.
|
Bulbophyllum grandiflorum |
Cirrhopetalum macraei. Curtis "s botanical magazine vol. 127 ser. 3 nr. 57 tab. 7787, 1901 |
Oncidium dasystyle. Curtis "s botanical magazine vol. 127 ser. 3 nr. 57 tab. 7787, 1901 |
Dendrobium senile. Curtis "s botanical magazine vol. 127 ser. 3 nr. 57 tab. 7787, 1901 |
Evolution of branch types
Shoot modifications (metamorphosis)
The shoot is the most variable in appearance organ of the plant. This is due not only to the overall multifunctionality vegetative organs, which arose in the process of evolution, but also with changes occurring in the process of plant ontogenesis, due to adaptation to a variety of conditions environment, and in cultivated plants - under the influence of man.
The main type of shoot of a green plant is an aerial (aerial) assimilating shoot, bearing on the axis green leaves middle formation. However, assimilating shoots are not the same. Often, along with the main function of photosynthesis, these shoots also have others: the deposition of reserves and the support function ( for the most part in perennial stems), vegetative reproduction (creeping shoots, lashes).
Modification of underground shoots
Shoots living underground, under the influence of a complex of conditions that are sharply different from ground environment, almost completely lost the functions of photosynthesis and acquired other equally important vital functions, such as organs for transferring an unfavorable period, storing nutrients, vegetative renewal and plant reproduction. Modified underground shoots include: rhizome, caudex, underground stolon and tuber, bulb, corm.
caudex- a perennial organ of shoot origin of perennial grasses and semi-shrubs with a well-developed taproot that persists throughout the life of the plant. Together with the root, it serves as a place of deposition of reserve substances and bears many renewal buds, some of which may be dormant. There are many caudex plants among the umbrella plants (femur, ferula), legumes (alfalfa, lupins), composites (dandelion, wormwood, rough cornflower).
underground stolon- an annual elongated thin underground shoot with underdeveloped scaly leaves. At the thickened ends of the stolons, plants can accumulate reserve substances, forming tubers or bulbs (potatoes, stolons, adoxas).
stem tuber- a modified shoot with a pronounced storage function of the stem, the presence of scaly leaves that quickly peel off, and buds that form in the axils of the leaves and are called eyes (potato, Jerusalem artichoke).
Bulb- underground (rarely above-ground) highly shortened specialized shoot, in which reserve substances are deposited in scales of leafy nature, and the stem is transformed into the bottom. The bulb is a typical organ of vegetative renewal and reproduction. Bulbs are characteristic of monocotyledonous plants from the Lily family (lily, tulip, onion), Amaryllis (amaryllis, daffodil, hyacinth), etc. As an exception, they are also found in dicotyledonous plants - in some species of sorrel and butterwort.
Corm- a modified underground shortened shoot with a thick stem storing assimilants, adventitious roots growing from the underside of the corm, and preserved dried leaf bases (membraneous scales), which together form a protective cover. Corms have saffron, gladiolus, colchicum.
Modifications of above-ground shoots
An unusual way of life and / or adaptation to the special conditions of the existence of plants lead to various modifications of the shoots. At the same time, shoots can serve not only to store nutrients, reproduce and reproduce plants, but also perform other functions. There are frequent cases when not the entire shoot is modified, but only its leaves, and some of their metamorphoses are outwardly and functionally similar to shoot metamorphoses (thorns, antennae).
thorn- strongly lignified leafless shortened shoot with a sharp tip. Spines of shoot origin perform mainly a protective function. At the wild apple tree, wild pear, laxative buckthorn ( Rhamnus cathartica) shortened shoots turn into spines, having limited growth and ending in a point. In honey locust ( Gleditschia triacanthos) powerful branched spines are formed on the trunks of dormant buds. Many species of hawthorn have spines that form from axillary leaf buds, which topographically corresponds to lateral shoots.
Claudius- a modified lateral shoot with the ability to grow long, with green flat long stems that act as a leaf. As an organ of photosynthesis, the cladodium has a well-developed chlorophyll-bearing tissue located under the epidermis. Plants with cladodias include Mühlenbeckia flatiflora ( Muhlenbekia platyclada), Decembrist cactus ( Zygocactus truncates), southern carmichelia ( Carmichaelia australis), collection ( Colletia cruciata) and prickly pear ( Opuntia).
Phyllocladius- a modified leaf-like flattened lateral shoot with limited growth and performing the functions of a leaf. Phyllocladia develop from lateral buds, so they are always found in the axil of a small membranous or scaly leaf. Performing the function of photosynthesis, the shoots of phylloclades also outwardly acquire a resemblance to a leaf, which manifests itself in limited growth and complete loss of the metameric structure. The phenomenon of phylloclady is characteristic of such plants as the needle,
Task 10. "Escape structure"
Write captions for the drawing.
What is a stem?
What branch of the escape is called a node? Internode?
What is a leaf axil?
Task 11. "Leaf arrangement"
Look at the picture and answer the questions:
What number denotes a plant with opposite leaf arrangement? What leaf arrangement is called opposite?
What number denotes a plant with an alternate leaf arrangement? What leaf arrangement is called alternate?
What number denotes a plant with a whorled leaf arrangement? Which leaf arrangement is whorled?
Task 12. "Branching shoots"
Look at the picture and answer the questions:
What is the name of the branching of the shoots shown in the figure?
What is the difference between the branching of the shoots of plants 1 and 2?
What is the difference between the branching of the shoots of plants 3 and 4?
Task 13. "Tillering"
Look at the picture and answer the questions:
Write captions for the drawing.
What kind of branching is called tillering?
What plants are characterized by tillering?
Task 14. "The structure of the kidneys"
Look at the picture and answer the questions:
Which kidneys are shown in the figure with the letters A and B? Explain the answer.
What is indicated in the figure by the numbers 1 - 5?
What kidneys are called vegetative?
What kidneys are called generative?
Task 15. "The structure of the growth cone"
Look at the picture and answer the questions:
Write captions for the drawing.
What happens to the shoot if you pinch its top?
What is stepchildren?
Why are pinching tomatoes and grapes?
Task 16. "Kidney rings and annual increments"
Look at the picture and answer the questions:
Write captions for the drawing.
What is a kidney ring?
What is the annual shoot growth?
What is a leaf scar?
Task 17. "Underground modifications of shoots"
Look at the picture and answer the questions:
What underground modifications of shoots are indicated in the figure by the letters A - G?
Write captions for the drawing.
Task 18. "Aboveground modifications of shoots"
Look at the picture and answer the questions:
What are the above-ground modifications of the shoots of these plants called?
What functions do these shoots perform?
Task 19. "The most important terms and concepts of the topic"
1. Escape. 2. Knot. 3. Leaf axil. 4. Leaf scar. 5. Kidney ring. 6. Buds are vegetative. 7. Kidneys are generative. 8. Apical buds. 9. Kidneys axillary. 10. Sleeping kidneys. 11. 11. Tillering. 12. Pasynkovanie. 13. Stem succulent.
Task 20. "The location of the shoots in space"
Look at the picture and answer the questions:
Task 21
wood stem"
Look at the picture and answer the questions:
What is indicated in the figure by the numbers 1 - 15?
How old is this plant?
Which ring of wood is the oldest?
Task 22. "Internal structure of a woody stem"
Give your answer in one sentence:
Task 23
Look at the picture and answer the questions:
How old is this tree? How did you determine the age of the tree?
Why is the thickness of different growth rings not the same?
Why does one annual ring have an unequal thickness?
Task 24. "The structure of the stem of herbaceous plants"
Look at the picture and answer the questions:
The stems of what herbaceous plants are depicted in the figures under the letters A and B?
How does the arrangement of vascular bundles in the stem of a herbaceous dicot plant differ from their arrangement in the stem of a monocot plant?
What is indicated in the figure by the numbers 1 - 4?
Than conductive bundles dicot plants different from the vascular bundles of monocot plants?
Task 25. "The most important terms and concepts of the topic"
Define the terms or expand the concepts (in one sentence, emphasizing the most important features):1. Stem. 2. Lentils. 3. Periderm. 4. Primary bark. 5. Lub. 6. Cambium. 7. Xylem. 8 Annual ring. 9. Core. 10. Core rays.
Olympians!
Task 26, 27. “Scheme of the primary structure of the stem. Linden stalk»
H
Linden stem
that is indicated in the figures:
Task 28, 29
What is shown in the pictures:
stem of an apple tree
Task 30, 31. "The structure of the stem of flax, corn"
What is shown in the pictures:
W
task 32, 33. "Structure of the stalk of buttercup, iris"
What is shown in the pictures: 
Task 34. "Structure of a rye stem"
What is shown in the pictures:
Task 35
What is shown in the pictures:
Task 36
What is shown in the pictures:
Scheme of the evolution of the stele
Answers:
Task 10. 1. 1 - stem; 2 - sheet; 3 - node; 4 - internode; 5 - leaf axil; 6 - axillary kidney; 7 - apical kidney. 2. The axis of the shoot, bearing leaves, buds, flowers and fruits. 3. The place of attachment of the leaf to the stem is a node, the distance between two nodes is an internode. 4. Angle between stem and leaf.
Task 11. 1. Number 2. When two sheets extend from the node, located opposite each other. 2. Number 1. When each node has one leaf, and the bases of the leaves can be connected by a conditional spiral line. 3. Number 3. When three or more leaves leave the node.
Task 12. 1. 1 - monopodial, 2 - sympodial, 3 - dichotomous, 4 - false dichotomous. 2. With monopodial branching, the apical bud does not die, but with sympodial branching, it dies off annually and is replaced by the nearest lateral bud. 3. With dichotomous branching, the growth cone is divided into two parts, and with false dichotomy, the apical bud dies off, and two opposite ones form two apical shoots.
Task 13. 1. 1 - weevil; 2 - adventitious roots; 3 - above-ground shoots. 2. Branching, in which lateral shoots develop from underground or surface buds of the mother plant. 3. For shrubs, shrubs, for cereals.
Task 14. 1. A - a vegetative bud, an escape will develop from it. B - generative bud, contains the rudiment of the inflorescence. 2. 1 - rudimentary stem; 2 - rudimentary kidneys; 3 - rudimentary leaves; 4 kidney scales. 3. Buds from which shoots with leaves will develop. 4. Buds from which flowers or inflorescences will develop.
Task 15. 1. 1 - growth cone; 2 - rudimentary stem; 3 - rudimentary leaves; 4 - rudimentary kidneys. 2. The growth of the stem in length stops, side shoots begin to develop from the axillary buds. 3. Removal of unwanted side shoots ("stepchildren"). 4. In order for the fruits to grow better and ripen faster on the main shoot.
Task 16. 1. 1 - kidney ring formed this year; 2 - renal ring formed last year; 3, 5 - the last annual increase; 4 - annual growth of last year. 2. A trace of fallen kidney scales. 3. Growth of shoot during the year. 4. A trace under the kidney from a fallen leaf.
Task 17. 1. A - tuber; B - rhizome; B - bulb; G - corm. 2. 1 - underground stolon; 2 - tuber; 3 - the base of the tuber; 4 - the top of the tuber; 5 - lateral bud and leaf scar: 6 - bark; 7 - wood; 8 - core; 9 - cambium; 10 - apical bud of the rhizome; 11 - scaly leaves; 12 - adventitious roots; 13 - stem; 14 - kidneys; 15 - dry leaves-scales; 16 - juicy leaves.
Task 18. 1. 1 - stem succulent; 2 - thorn of shoot origin; 3 - phyllocladium; 4 - cladode; 5 - above-ground stolon; 6 - mustache of shoot origin. 2. The cactus has water storage and assimilation functions; hawthorn has a protective function; in needles and gorse - assimilation; at the strawberries vegetative propagation; in grapes - fixing the plant.
Task 19. 1. Stem with leaves and buds located on it. 2. The section of the stem from which the leaf departs. 3. The angle formed between the stem and the leaf. 4. The trace left on the stem after the leaf has fallen off. 5. Traces of kidney scales. 6. Buds from which shoots with leaves develop. 7. Buds from which flowers or inflorescences develop. 8. Buds located on the tops of the shoots. 9. Buds located in the axils of the leaves. 10. Buds that do not shoot for a long time. 11. Branching, in which side shoots develop from underground or surface buds of the mother plant. 12. Removal of unwanted side shoots ("stepchildren"). 13. A modified stem that performs a water storage and assimilation function.
Task 20. 1 - upright (sunflower); 2 - rising (cinquefoil paniculata); 3 - creeping (cranberry); 4 - creeping (creeping tenacious); 5 - curly (field bindweed); 6 - climbing (peas).
Task 21. 1. 1 - epidermis; 2 - bark; 3 - cambium; 4 - wood; 5 - core; 6 - lentil; 7 - cork (fellema); 8 - primary bark; 9 - secondary bark; 10 - sieve tubes; 11 - sieve fields; 12, companion cells; 13 - vessels (trachea); 14 - tracheids; 15 - bast parenchyma. 2. Three years. 3. Located next to the core.
Task 22. 1. All tissues lying outside of the cambium. 2. Epidermis, peridermis, crust. 3. Phellem (cork), phellogen (cork cambium), phelloderma. 4. Conductive, mechanical and basic. 5. Sieve cells and sieve tubes, bast fibers and bast parenchyma. 6. Sieve cells and sieve tubes. 7. Stem growth in thickness. 8. Conductive, mechanical and basic. 9. Vessels (tracheas) and tracheids, wood fibers, wood parenchyma and medullary rays. 10. Tracheas and tracheids. 11. Horizontal transport of substances. 12. Reserve.
Task 23. 1. 13 years old. By the number of growth rings in wood. 2. Miscellaneous conditions life in different years than better conditions, the thicker the ring. 3. Usually the ring is wider on the south side, where the trunk is better heated by the sun.
Task 24. 1. A - the stem of a dicotyledonous plant, B - the stem of a monocotyledonous plant. 2. In dicotyledonous plants, vascular bundles are arranged in a circle, in monocotyledonous plants they are in disorder. 3. 1 - mechanical tissue, sclerenchyma; 2 - sieve tubes; 3 - cambium; 4 - vessels. 4. In dicots - with cambium (open), in monocots - without cambium (closed).
Task 25. 1. The axis of the shoot, bearing leaves, buds, flowers and fruits. 2. Areas of loosely located cells of the cortex, providing gas exchange and evaporation. 3. Secondary integumentary tissue formed as a result of the activity of phellogen. 4. Part of the stem between the epidermis and the central cylinder. The endoderm is not always clearly defined. 5. Secondary phloem woody plants formed as a result of the activity of the cambium. 6. A layer of cells of the secondary educational tissue of gymnosperms and dicotyledonous flowering plants, providing a secondary thickening of stems and roots. 7. Wood. 8. Ring of wood formed during one growing season. 9. Tissue formed by parenchymal cells in the center of the stem. 10. Cells in xylem and phloem, providing horizontal transport of substances.
Task 26. The primary structure of the stem. 1 - epidermis. 2 - primary bark; 2a - collenchyma; 2b - parenchyma; 2c - endoderm; 3 - pericyclic zone; 4 - phloem; 5 - xylem; 6 - core.
Task 27. Linden stem structure. a) a cut at the level of the appearance of the procambium; b) at the level of appearance of the cambium; c) at the level of the formed structure; 1 - procambium; 2 - epidermis; 3 - periderm; 4 - collenchyma; 5 - parenchyma of the cortex; 6 - endoderm; 7 - pericyclic zone; 8 - primary phloem; 9 - hard bast; 10 - secondary phloem (soft bast); 11 - core ray (7-11 secondary cortex); 12 - cambial zone; 13 - autumn wood; 14 - spring wood; 15 - secondary wood;, 16 - primary wood; 17, 18 - core.
Task 28. The structure of the stem of an apple tree. 1 - cork; 2 - collenchyma; 3 - parenchyma of the primary cortex; 4 - endoderm; 5 - pericyclic zone; 6 - phloem; 7 - cambium; 8 - secondary xylem; 9 - primary xylem; 10 - core beam; 11 - core; 12 - perimedullary zone.
Task 29. A stalk of a pickaxon. a) a cut at the level of the appearance of the procambium; b) at the level of appearance of the cambium; c) at the level of the formed structure; 1 - procambium; 2 - epidermis; 3 - collenchyma; 4 - parenchyma of the cortex; 5 - endoderm (3-5 primary cortex); 6 - sclerenchyma of the pericycle; 7 - phloem; 8 - xylem; 9 - beam cambium; 10 - interfascicular cambium; 11 - core beam; 12 - core parenchyma (6-12 - central cylinder).
Task 30. Flax stalk. a) - cross section; b and c - bast fibers; 1 - epidermis; 2 - parenchyma of the primary cortex; 3 - endoderm; 4 - bast fibers; 5 - phloem; 6 - cambium; 7 - secondary xylem; 8 - primary xylem; 9 - core beam; 10 - core parenchyma; 11 - cavity; 12 - cell wall; 13 - cell cavity; 14 - pointed ends of the cell.
Task 31. Corn stalk. a) cross section; b) diagram of the cross section; 1 - epidermis; 2 - mechanical fabric; 3 - closed collateral bundle; 4 - sclerenchyma; 5 - the main parenchyma.
Task 32. Buttercup stem. a) a cut at the level of the appearance of the procambium; b) at the level of appearance of the cambium; c) at the level of the formed structure; 1 - procambium; 2 - epidermis; 3 - parenchyma of the cortex; 4 - sclerenchyma; 5 - phloem; 6 - beam cambium; 7 - xylem; 8 - core parenchyma; 9 - cavity.
Task 33. Iris stem. a) cross section; b) diagram of the cross section; 1 - epidermis; 2 - chlorenchyma; 3 - endoderm (2-3 - primary cortex); 4 - sclerenchyma of the pericycle; 5 - closed collateral bundle; 6 - the main parenchyma (4-6 - the central cylinder).
Task 34. A stalk of rye. a) cross section; b) diagram of the cross section; 1 - epidermis; 2 - mechanical tissue; 3 - chlorenchyma; 4 - closed collateral bundle; 5 - sclerenchyma; 6 - main parenchyma; 7 - cavity.
Task 35. Location of conductive tissues in different types of stelae. a) - protostele; b) - siphonostela; c) - eustela; d) - atactostele.
Task 36. Scheme of the evolution of the stele. 1 - protostele (rhinophytes, some club mosses and ferns); 2 - actinostele (some club mosses and ferns); 3 - plectostele (most club mosses); 4,5 - ectofloic and amphifloic siphonostela (many ferns); 6 - dictyostele (most ferns); 7 - artrostelae (horsetails); 8 - eustela (most seed plants); 9 - ataktostele (characteristic of monocots).
The escape - This is the above-ground vegetative part of the plant. It consists of an axial part - a stem on which leaves and buds are located. On some shoots, generative organs - flowers - can also be placed. It has a more complex structure than the root.
On the stem of the shoot, nodes and internodes can be distinguished. Knot - this is the place of attachment of one or more leaves to the stem. Internodes is the distance between two adjacent nodes. Between the stem and the leaf there is an upper corner called leaf sinus . The buds are located at the top of the shoot and in the leaf axils.
Shoots, depending on the degree of elongation of the internodes, can be shortened or elongated. Shortened shoots actually consist of one node. On shortened shoots of herbaceous plants (dandelion, carrots, beets, etc.), the leaves are located close to each other and form a basal rosette.
Herbaceous plants are divided into annuals, biennials and perennials. Annuals develop and grow over one year (one growing season). In the first year of life, biennial plants (carrots, radishes, beets, etc.) form vegetative organs, accumulate nutrients, and in the second year they bloom, produce fruits and seeds. perennial plants live three or more years. Woody plants are perennials.
kidneys
kidneys - these are embryonic shoots with very short internodes. They arose later than the stem and leaves. Thanks to the kidneys, branching of the shoots occurs.
According to the location of the kidney, there are apical - located at the top of the shoot, and lateral or axillary -located in leaf axils. The apical bud provides the growth of the shoot, lateral shoots are formed from the lateral buds, which provide branching.
Buds are vegetative (leaf), generative (flower) and mixed. From vegetatively th buds develop shoot with leaves. From generative - shoot with a flower or inflorescence. The flower buds are always larger than the leaf buds and have a rounded shape. From mixed buds develop shoots with leaves and flowers or inflorescences. Buds that are laid on any other part of the stem, as well as on roots or leaves, are called adnexal , or adventitious . They develop from internal tissues, provide vegetative restoration and vegetative reproduction.
By the presence of scales, the kidneys are closed (if there are scales) and open (naked if there are no scales). Closed buds are characteristic mainly for plants of the cold and temperate zones. The scales of the kidneys are dense, leathery, may be covered with cuticles or resinous substances.
Most buds develop in plants every year. Buds that may not re-grow shoots for several years (even a lifetime), but remain alive, are called sleeping . Such buds resume the growth of shoots when the apical bud, trunk or branch is damaged. Typical for trees, bushes and a number of perennial herbs. By origin, they can be axillary or adnexal.
The internal structure of the kidney
Outside, the kidney may be covered with brown, gray or brown keratinized scales - modified leaves. The axial part of the vegetative bud is the germinal stem. It has germ leaves and buds. All parts together make germ shoot . The apex of the embryonic shoot is growth cone . The cells of the growth cone divide and ensure the growth of the shoot in length. Due to uneven growth, the outer leaf rudiments are directed upwards and towards the center of the bud, bent over the inner leaf primordia and the growth cone, and cover them.
Inside the flower (generative) buds on the germinal shoot is the germinal flower, or inflorescence.
When a shoot grows from a kidney, its scales fall off, and scars remain in their place. They determine the length of the annual increments of the shoot.
Stem
Stem is the axial vegetative organ of plants. The main functions of the stem: provides the interconnection of plant organs among themselves, transports various substances, forms and bears leaves and flowers. Additional stem features: photosynthesis, accumulation of substances, vegetative reproduction, storage of water. They vary greatly in size (for example, eucalyptus trees up to 140-155 m high).
The flow of substances in the stem occurs in two directions: from the leaves to the root (descending current) - organic substances and from the root to the leaves (ascending current) - water and mainly mineral substances. Nutrients move along the core rays from the core to the cortex in a horizontal direction.
The shoot can branch, that is, form side shoots from vegetative buds on the main stem. The main stem of a branched plant is called the axis first order . The lateral stems that developed from its axillary buds are called axes. second order . Axes form on them. third order etc. Up to 10 such axes can develop on a tree.
When branching, trees form a crown. Crown - this is a collection of all above-ground shoots of trees located above the beginning of the branching of the trunk. The youngest branches in the crown are the branches of the last order. Crowns have different shape: pyramidal (poplar), rounded (spherical) (sharp maple), columnar (cypress), flat (some pines), etc. A person forms the crown of cultivated plants. In nature, the formation of the crown depends on the place where the tree grows.
The branching of the stem of the bushes begins at the very surface of the soil, so many side shoots are formed (rose hips, currants, gooseberries, etc.). In semi-shrubs (wormwood), the stems become stiff only in the lower perennial part, from which annual herbaceous shoots grow every year.
In some herbaceous plants (wheat, barley, etc.), shoots grow from underground shoots or from the lowest stem buds - this branching is called tillering .
The stem that carries a flower or one inflorescence is called an arrow (in primrose, onion).
According to the location of the stem in space, they distinguish: erect (poplar, maple, thistle, etc.), creeping (clover), curly (birch, hops, beans) and clinging (step white). Plants with climbing shoots are combined into a group creeper . Creeping stems with long internodes are called mustache , and with shortened ones - whips . Both mustaches and whips are above ground stolons . A shoot that spreads along the ground but does not take root is called creeping (knotweed).
According to the state of the stem, they distinguish herbaceous stems (thistle, sunflower) and woody (beech, oak, lilac).
According to the shape of the stem on a transverse section, they are distinguished: rounded (birch, poplar, etc.), ribbed (valerian), trihedral (sedge), tetrahedral (mint, labiales), polyhedral (umbrella, most cacti), flattened, or flat ( prickly pear), etc.
By pubescence, they are smooth and pubescent.
The internal structure of the stem
On the example of a woody stem of dicotyledonous plants. There are: periderm, bark, cambium, wood and pith.
The epidermis functions for a short time and exfoliates. It replaces periderm , consisting of cork, cork cambium (phellogen) and phelloderm. Outside, the stem is covered with integumentary tissue - cork which is made up of dead cells. Performs a protective function - protects the plant from damage, from excessive evaporation of water. Cork is formed from a layer of cells - phellogen, which lies under it. Phelloderm is the inner layer. Exchange with external environment occurs through the lenticels. They are formed by large cells of the main tissue with large intercellular spaces.
Bark
Distinguish between primary and secondary. The primary is located under the periderm and consists of the colenchyma (mechanical tissue) and the parenchyma of the primary cortex.
Secondary bark or bast
It is represented by conductive tissue - sieve tubes, mechanical tissue - bast fibers, the main one - bast parenchyma. A layer of bast fibers forms a hard bast, other tissues - soft.
Cambium
Cambium(from lat. cambio- change). Located under the bark. This is an educational tissue that looks like a thin ring in a cross section. Outside, cambial cells form bast cells, inside - wood. Wood cells, as a rule, are formed much more. Thanks to the cambium, the stem grows in thickness.
Wood
It consists of conductive tissue - vessels or tracheids, mechanical - wood fibers, the main - wood parenchyma. The length of the vessels can reach 10 cm (sometimes - several meters).
Core
Occupies a central position in the trunk. It consists of thin-walled cells of the main tissue, large in size. The outer layer is represented by living cells, the central part is predominantly dead. In the central part of the stem, a cavity can be obtained - a hollow. Nutrients are stored in living cells. From the core to the bark through the wood passes a series of core cells called core rays. They provide horizontal movement of various connections. Core cells can be filled with metabolic products, air.
Stem modifications
The stems can perform additional functions associated with their modification. Changes occur in the process of evolution.
tendrils
These are curly, long, thin stems with reduced leaves that wrap around various supports. They support the stem in a certain position. Characteristic for grapes, pumpkins, melons, cucumbers, etc.
spines
These are shortened shoots without leaves. They are located in the axils of the leaves and correspond to the lateral axils or are formed from dormant buds on stolons (gleditsia). They protect the plant from being eaten by animals. Stem spines are characteristic for wild pear, plum, blackthorn, sea buckthorn, etc.
Tree ring formation
In trees that live in climates with seasonal changes, growth rings- on the transverse section, there is an alternation of dark and light concentric rings. From them you can determine the age of the plant.
During the growing season of the plant, one annual ring is formed. Light rings are rings of wood with large thin-walled cells, vessels (tracheids) of large diameter, which are formed in spring and during active cell division of the cambium. In summer, the cells are slightly smaller and have thicker cell walls of the conductive tissue. Dark rings are obtained in autumn. Wood cells are small, thick-walled, have more mechanical tissue. Dark rings function more like a mechanical tissue, light ones - as a conductive one. In winter, cambial cells do not divide. The transition in the rings is gradual - from spring to autumn wood, sharply marked - during the transition from autumn to spring. In spring, the activity of the cambium resumes and a new annual ring is formed.
The thickness of annual rings depends on the climatic conditions in a given season. If the conditions were favorable, the light rings are wide.
Annual rings are invisible in tropical plants, as they grow almost evenly throughout the year.
Escape and escape systems
The escape, like the root, is the main organ of the plant. Vegetative shoots typically perform the function of aerial nutrition, but have a number of other functions and are capable of various metamorphoses. spore-bearing shoots (including the flower) are specialized as organs reproductive providing reproduction.
The shoot is formed by the apical meristem as a whole and, therefore, is a single organ of the same rank as the root. However, compared with the root, the shoot has a more complex structure. The vegetative shoot consists of an axial part - stem, which is cylindrical in shape, and leaves- flat lateral organs sitting on the stem. In addition, an obligatory part of the escape are kidneys– rudiments of new shoots, which ensure the growth of the shoot and its branching, i.e. formation of the escape system. The main function of the shoot - photosynthesis - is carried out by leaves; stems are predominantly load-bearing organs that perform mechanical and conductive functions.
The main feature that distinguishes the shoot from the root is its foliage. The part of the stem from which the leaf (leaves) extends is called node. Stem segments between adjacent nodes internodes. Nodes and internodes are repeated along the axis of the shoot. So the escape has metameric structure, metamer(repeating element) of the shoot are a node with a leaf and an axillary bud and an underlying internode ( rice. 4.16).
Rice. 4.16. Escape structure.
The first shoot of a plant main escape, or escape of the first order. It is formed from an embryonic shoot ending kidney, which forms all subsequent metameres of the main shoot. By position, this kidney is apical; while it persists, this shoot is capable of further growth in length with the formation of new metameres. In addition to the apical, on the shoot are formed lateral kidneys. In seed plants, they are located in the axils of the leaves and are called axillary. From the lateral axillary buds develop lateral shoots, and branching occurs, due to which the total photosynthetic surface of the plant increases. Formed escape system, represented by the main shoot (shoot of the first order) and side shoots (shoots of the second order), and when branching is repeated, by side shoots of the third, fourth and subsequent orders. A shoot of any order has its own apical bud and is capable of growing in length.
Bud- this is a rudimentary, not yet unfolded shoot. Inside the kidney is the meristematic tip of the shoot - its apex(rice. 4.17). The apex is an actively working growth center that ensures the formation of all organs and primary tissues of the shoot. The source of constant self-renewal of the apex is the initial cells of the apical meristem, concentrated at the tip of the apex. The vegetative shoot apex, in contrast to the always smooth root apex, regularly forms protrusions on the surface, which are the beginnings of leaves. Only the very tip of the apex, which is called growth cone escape. Its shape varies greatly in different plants and does not always look like a cone; the apical part of the apex can be low, hemispherical, flat, or even concave.
From vegetative buds develop vegetative shoots consisting of a stem, leaves and buds. Such a kidney consists of a meristematic rudimentary axis ending growth cone, and rudimentary leaves of different ages. Due to uneven growth, the lower leaf primordia are bent inward and cover the upper, younger, leaf primordia and the growth cone. The nodes in the kidney are close together, since the internodes have not yet had time to stretch out. In the axils of the leaf buds in the bud, the primordia of the axillary buds may already be laid. next order (rice. 4.17). AT vegetative-generative a number of vegetative metameres are laid in the buds, and the growth cone is turned into a rudimentary flower or inflorescence. Generative, or floral the buds contain only the rudiment of an inflorescence or a single flower, in the latter case the bud is called bud.
Rice. 4.17. The apical bud of the Elodea shoot: A - longitudinal section; B - growth cone (appearance and longitudinal section); C – cells of the apical meristem; D - parenchymal cell of the formed leaf; 1 - growth cone; 2 - leaf rudiment; 3 - the rudiment of the axillary kidney.
The outer leaves of the bud often change into kidney scales, which perform a protective function and protect the meristematic parts of the kidney from drying out and sudden changes in temperature. Such kidneys are called closed(wintering buds of trees and shrubs and some perennial grasses). open kidneys do not have kidney scales.
In addition to the usual, exogenous in inception, axillary buds, plants often form adnexal, or adventive kidneys. They arise not in the meristematic tip of the shoot, but on the adult, already differentiated part of the organ, endogenously, from internal tissues. Adnexal buds can form on stems (then they are usually located in internodes), leaves and roots. Adnexal buds are of great biological importance: they provide active vegetative renewal and reproduction of those perennial plants that have them. In particular, with the help of adnexal kidneys, they renew and multiply root offspring plants (raspberry, aspen, thistle, dandelion). Root offspring- these are shoots that have developed from adventitious buds on the roots. Adnexal buds on the leaves are formed relatively rarely. If such buds immediately give small shoots with adventitious roots that fall off the mother leaf and grow into new individuals, they are called brood(bryophyllum).
In the seasonal climate of the temperate zone, the deployment of shoots from the buds in most plants is periodic. In trees and shrubs, as well as in many perennial herbaceous plants, buds unfold into shoots once a year - in spring or early summer, after which new wintering buds are formed with the beginnings of next year's shoots. Shoots that grow from buds in one growing season are called annual shoots, or annual increments. In trees, they are well distinguished due to the formation renal rings- scars that remain on the stem after the fall of the kidney scales. In the summer of our deciduous trees, the annual shoots of only the current year are covered with leaves; there are no leaves on the annual shoots of previous years. In evergreen trees, leaves can be preserved on the corresponding annual increments of 3-5 past years. In a seasonally unseasoned climate, several shoots may form in one year, separated by small dormant periods. Such shoots formed in one growth cycle are called elementary shoots.
Buds that fall into a dormant state for a while, and then give new elementary and annual shoots, are called wintering or resting. According to their function, they can be called kidneys regular renewal. Such buds are an obligatory feature of any perennial plant, woody or herbaceous, they ensure the perennial existence of an individual. By origin, renewal kidneys can be both exogenous (apical or axillary) and endogenous (adnexal).
If the lateral buds do not have a dormant period and develop simultaneously with the growth of the maternal shoot, they are called kidney enrichment. Deploying ones enrichment shoots greatly increase (enrich) the total photosynthetic surface of the plant, as well as the total number of inflorescences formed and, consequently, seed productivity. Enrichment shoots are typical for most annual grasses and for a number of perennial herbaceous plants with elongated flowering shoots.
A special category is dormant buds, very characteristic of deciduous trees, shrubs, shrubs and a number of perennial herbs. By origin, they, like the buds of regular renewal, can be axillary and adnexal, but, unlike them, do not turn into shoots for many years. The stimulus for awakening dormant buds is usually either damage to the main trunk or branch (stump growth after cutting down a number of trees), or natural aging the maternal system of shoots associated with the attenuation of the vital activity of normal renewal buds (change of stems in shrubs). In some plants, leafless flowering shoots form from dormant buds on the trunk. This phenomenon is called caulifloria and is characteristic of many rainforest trees, such as the chocolate tree. In honey locust, bunches of large branched spines grow from sleeping buds on the trunk - modified shoots ( rice. 4.18).
Rice. 4.18. Shoots from dormant buds: 1 - caulifloria near the chocolate tree; 2 - spines in honey locust from branched dormant buds.
Direction of shoot growth. Shoots growing vertically, perpendicular to the surface of the earth, are called orthotropic. Horizontally growing shoots are called plagiotropic. The direction of growth may change during shoot development.
Depending on the position in space, morphological types of shoots are distinguished ( rice. 4.19). The main shoot in most cases retains orthotropic growth and remains upright. Lateral shoots can grow in different directions, often forming a different angle with the parent shoot. In the process of growth, the shoot can change direction from plagiotropic to orthotropic, then it is called rising, or ascending. Shoots with plagiotropic growth that persists throughout life are called creeping. If they form adventitious roots at the nodes, they are called creeping.
Orthotropic growth is connected in a certain way with the degree of development of mechanical tissues. In the absence of well-developed mechanical tissues in elongated shoots, orthotropic growth is impossible. But often plants that do not have a sufficiently developed internal skeleton still grow upward. This is achieved in various ways. Weak shoots of such plants - creeper twist around some kind of solid support ( curly escapes), climb with the help various kinds spines, hooks, roots - trailers ( climbing shoots), cling with the help of antennae of various origins ( clinging shoots).
Rice. 4.19. Types of shoots by position in space: A - upright; B - clinging; B - curly; G - creeping; D - creeping.
Leaf arrangement.leaf arrangement, or phyllotaxis- the order of placement of leaves on the axis of the shoot. There are several main types of leaf arrangement ( rice. 4.20).
Spiral, or another leaf arrangement is observed when there is one leaf at each node, and the bases of successive leaves can be connected by a conditional spiral line. double row leaf arrangement can be considered as a special case of spiral. At the same time, at each node there is one sheet, covering the entire or almost the entire circumference of the axis with a wide base. Whorled leaf arrangement occurs when several leaves are laid on one node. Opposite leaf arrangement - a special case of whorled, when two leaves are formed on one node, exactly opposite each other; most often such a leaf arrangement occurs cross opposite, i.e. neighboring pairs of leaves are in mutually perpendicular planes ( rice. 4.20).
Rice. 4.20. Types of leaf arrangement: 1 - spiral in oak; 2 - scheme of spiral leaf arrangement; 3 - two-row in gasteria ( a- side view of the plant b– top view, scheme); 4 - whorled in oleander; 5 - opposite in lilac.
The order of initiation of leaf rudiments on the shoot apex is a hereditary trait of each species, sometimes characteristic of a genus and even an entire family of plants. The leaf arrangement of the adult shoot is determined primarily by genetic factors. However, in the process of deployment of a shoot from a bud and its further growth, the arrangement of leaves can be influenced by external factors mainly lighting conditions and gravity. Therefore, the final picture of the leaf arrangement can differ greatly from the initial one and usually acquires a pronounced adaptive character. The leaves are arranged so that their plates are in the most favorable lighting conditions in each case. This is most pronounced in the form sheet mosaic observed on plagiotropic and rosette shoots of plants. In this case, the plates of all leaves are arranged horizontally, the leaves do not obscure each other, but form a single plane where there are no gaps; smaller leaves fill the gaps between the larger ones.
Shoot branching types. Branching is the formation of a system of axes. It provides an increase in the total area of contact of the plant body with air, water or soil. Branching arose in the process of evolution even before the appearance of organs. In the simplest case, the top of the main axis forks and gives rise to two axes of the next order. This is apical, or dichotomous branching. Many multicellular algae have apical branching, as well as some primitive plants, such as club mosses ( rice. 4.21).
Other groups of plants are characterized by a more specialized side branch type. In this case, the lateral branches are laid below the top of the main axis, without affecting its ability to further increase. With this method, the potential for branching and formation of organ systems is much more extensive and biologically beneficial.
Rice. 4.21. Shoot branching types: A - dichotomous (club moss); B - monopodial (juniper); B - sympodial type of monochasia (bird cherry); D - sympodial according to the type of dichasia (maple).
There are two types of lateral branching: monopodial and sympodial(rice. 4.21). With a monopodial branching system, each axis is a monopodium, i.e. the result of the work of one apical meristem. Monopodial branching is characteristic of most gymnosperms and many herbaceous angiosperms. Most angiosperms, however, branch in a sympodial pattern. With sympodial branching, the apical bud of the shoot dies at a certain stage or stops active growth, but the increased development of one or more lateral buds begins. Shoots are formed from them, replacing the shoot that has stopped growing. The resulting axis is a sympodium - a composite axis consisting of axes of several successive orders. The ability of plants to sympodial branching is of great biological importance. In case of damage to the apical bud, the growth of the axis will continue with lateral shoots.
Depending on the number of replacement axes, sympodial branching is distinguished by type monochasia,dichasia and pleiochasia. Branching according to the type of dichasia, or false dichotomous branching is typical for shoots with opposite leaf arrangement (lilac, viburnum).
In some groups of plants, the growth of the main skeletal axes occurs due to one or a few apical buds, lateral skeletal branches are not formed at all or are formed in a very small number. tree plants of this type are found mainly in tropical areas (palm trees, dracaena, yucca, agave, cycads). The crown of these plants is formed not by branches, but by large leaves brought together in a rosette at the top of the trunk. The ability to rapidly grow and capture space, as well as to recover from damage in such plants is often absent or weakly expressed. Among the trees temperate climate such unbranched forms are almost never found.
The other extreme is plants that branch too profusely. They are represented by the life form cushion plants(rice. 4.22). The growth in the length of the shoots of these plants is extremely limited, but on the other hand, many lateral branches are formed annually, diverging in all directions. The surface of the shoot system of the plant looks as if trimmed; some pillows are so dense that they look like stones.
Rice. 4.22. Plants - pillows: 1, 2 - schemes of the structure of pillow plants; 3 - Azorella from Kerguelen Island.
Representatives of a life form branch very strongly Tumbleweed characteristic of steppe plants. A spherically branched, very loose system of shoots is a huge inflorescence, which, after fruit ripening, breaks off at the base of the stem and rolls over the steppe with the wind, scattering the seeds.
Specialization and metamorphoses of shoots. Many plants within the shoot system have a certain specialization. Orthotropic and plagiotropic, elongated and shortened shoots perform different functions.
elongated called shoots with normally developed internodes. In woody plants, they are called growth and are located along the periphery of the crown, determining its shape. Their main function is to capture space, increase the volume of photosynthetic organs. shortened shoots have close nodes and very short internodes ( rice. 4.23). They form inside the crown and absorb scattered light penetrating there. Often shortened shoots of trees are flowering and perform the function of reproduction.
Rice. 4.23. Shortened (A) and elongated (B) sycamore shoots: 1 - internode; 2 - annual increments.
Herbaceous plants usually have shortened rosette shoots perform the function of perennial skeletal and photosynthetic, and elongated ones are formed in the axils rosette leaves and are flower-bearing (plantain, cuff, violets). If axillary peduncles are leafless, they are called arrows. The fact that flowering shoots are short in woody plants and elongated in herbaceous plants is biologically well explained. For successful pollination, grass inflorescences must be raised above the herbage, and in trees, even shortened shoots in the crown are in favorable conditions for pollination.
An example of the specialization of shoots is the perennial axial organs of woody plants - trunks and branches crowns. In deciduous trees, annual shoots lose their assimilation function after the first growing season, in evergreen trees - after a few years. Some of the shoots die off completely after the loss of leaves, but most remain as skeletal axes, performing support, conduction, and storage functions for decades. The leafless skeletal axes are known as boughs and trunks(by the trees) stems(for shrubs).
In the course of adaptation to specific environmental conditions or in connection with a sharp change in functions, shoots can change (metamorphize). Shoots developing underground are especially often metamorphosed. Such shoots lose the function of photosynthesis; they are common in perennial plants, where they act as organs for experiencing an unfavorable period of the year, stock and renewal.
The most common underground shoot metamorphosis is rhizome(rice. 4.24). It is customary to call a rhizome a long-lived underground shoot that performs the functions of deposition of reserve nutrients, renewal, and sometimes vegetative reproduction. The rhizome is formed in perennial plants, which, as a rule, do not have a main root in the adult state. According to its position in space, it can be horizontal,oblique or vertical. The rhizome usually does not bear green leaves, but, being a shoot, retains a metameric structure. The nodes are distinguished either by leaf scars and the remains of dry leaves, or by living scaly leaves; axillary buds are also located in the nodes. According to these features, the rhizome is easy to distinguish from the root. As a rule, adventitious roots are formed on the rhizome; lateral branches of the rhizome and above-ground shoots grow from the buds.
A rhizome is formed or initially as an underground organ (kupena, raven eye, lily of the valley, blueberries), or first as an above-ground assimilating shoot, which then sinks into the soil with the help of retracting roots (strawberries, lungwort, cuff). Rhizomes can grow and branch monopodially (cuff, crow's eye) or sympodially (kupena, lungwort). Depending on the length of the internodes and the intensity of growth, there are long and short rhizomes and, accordingly, long-rhizome and short-rhizome plants.
When branching rhizomes, it is formed curtain elevated shoots connected by sections of the rhizome system. If the connecting parts are destroyed, the shoots are isolated, and vegetative reproduction occurs. The totality of new individuals formed vegetatively is called clone. Rhizomes are characteristic mainly of herbaceous perennials, but are also found in shrubs (euonymus) and shrubs (lingonberries, blueberries).
close to roots underground stolons- short-lived thin underground shoots bearing underdeveloped scaly leaves. Stolons serve for vegetative reproduction, settlement and territory capture. Spare nutrients are not deposited in them.
In some plants (potato, earth pear), by the end of summer, stolons form from the apical buds of stolons. tubers (Fig. 4.24). The tuber has a spherical or oval shape, the stem is strongly thickened, reserve nutrients are deposited in it, the leaves are reduced, and buds form in their axils. The stolons die off and collapse, the tubers overwinter, and the next year they give rise to new above-ground shoots.
Tubers do not always develop on stolons. In some perennial plants, the base of the main shoot grows tuberous and thickens (cyclamen, kohlrabi cabbage) ( rice. 4.24). The functions of the tuber are a supply of nutrients, experiencing an unfavorable period of the year, vegetative renewal and reproduction.
In perennial grasses and dwarf shrubs with a well-developed tap root that persists throughout life, a kind of organ of shoot origin is formed, called caudex. Together with the root, it serves as a place for the deposition of reserve substances and carries many renewal buds, some of which may be dormant. The caudex is usually subterranean and is formed from short shoot bases that sink into the soil. Caudex differs from short rhizomes in the way it dies off. Rhizomes, growing at the top, gradually die off and collapse at the older end; the main root is not preserved. The caudex grows in width, from the lower end it gradually turns into a long-lived thickening root. The death and destruction of the caudex and the root goes from the center to the periphery. A cavity is formed in the center, and then it can be divided longitudinally into separate sections - particles. The process of dividing an individual of a taproot plant with a caudex into parts is called particulation. There are many caudex plants among legumes (lupins, alfalfa), umbrella plants (femur, ferula), and Compositae (dandelion, wormwood).
Bulb- this is usually an underground shoot with a very short flattened stem - bottom and scaly fleshy succulent leaves that store water and soluble nutrients, mainly sugars. Aerial shoots grow from the apical and axillary buds of the bulbs, adventitious roots form on the bottom ( rice. 4.24). Thus, the bulb is a typical organ of vegetative renewal and reproduction. Bulbs are most characteristic of plants from the families of lilies (lilies, tulips), onions (onions) and amaryllis (daffodils, hyacinths).
The structure of the bulb is very diverse. In some cases, bulbs storing scales are only modified leaves that do not have green plates (lily saranka); in others, these are underground sheaths of green assimilating leaves, which thicken and remain in the bulb after the plates die (onion). Bulb axis growth can be monopodial (snowdrop) or sympodial (hyacinth). The outer scales of the bulb consume the supply of nutrients, dry out and play a protective role. The number of onion scales varies from one (garlic) to several hundred (lilies).
As an organ of renewal and storage, the bulb is adapted mainly to climates of the Mediterranean type - with fairly mild, wet winters and very hot, dry summers. It serves not so much for a safe overwintering, but for experiencing a harsh summer drought. The storage of water in the tissues of onion scales occurs due to the formation of mucus, which can retain a large amount of water.
Corm outwardly resembles an onion, but its scaly leaves are not storage; they are dry and membranous, and reserve substances are deposited in the thickened stem part (saffron, gladiolus).
Rice. 4.24. Underground escape metamorphoses: 1, 2, 3, 4 - sequence of development and structure of the potato tuber; 5 - cyclamen tuber; 6 - kohlrabi tuber; 7 - bulbs of a tiger lily; 8 - onion bulb; 9 - lily bulb; 10 - section of a long rhizome of couch grass.
Not only underground, but also above-ground shoots of plants can be modified ( rice. 4.25). Quite common elevated stolons. These are plagiotropic short-lived shoots, the function of which is vegetative reproduction, resettlement and territory capture. If stolons carry green leaves and participate in the process of photosynthesis, they are called lashes(bone, tenacious creeping). In strawberries, stolons are devoid of developed green leaves, their stems are thin and fragile, with very long internodes. Such more highly specialized stolons for the function of vegetative reproduction are called mustache.
Juicy, fleshy, adapted for the accumulation of water can be not only bulbs, but also above-ground shoots, usually in plants living in conditions of lack of moisture. Water storage organs can be leaves or stems, sometimes even buds. Such succulent plants are called succulents. Leaf succulents store water in leaf tissues (aloe, agave, jughead, rhodiola, or golden root). Stem succulents are characteristic of the American cactus family and African euphorbiaceae. The succulent stem performs a water-reserving and assimilating function; leaves are reduced or turned into spines ( rice. 4.25, 1). In most cacti, the stems are columnar or spherical, leaves are not formed on them at all, but the nodes are clearly visible by the location of the axillary shoots - areola having the appearance of warts or elongated outgrowths with spines or tufts of hairs. The transformation of leaves into spines reduces the evaporative surface of the plant and protects it from being eaten by animals. An example of the metamorphosis of a kidney into a succulent organ is head of cabbage serves as a cultivated cabbage.
Rice. 4.25. Elevated shoot metamorphoses: 1 - stem succulent (cactus); 2 - tendrils of grapes; 3 - leafless photosynthetic shoot of gorse; 4 - phyllocladium of butcher's broom; 5 - thorn of honey locust.
spines cacti are leafy. Leaf spines are often found in non-succulent plants (barberry) ( rice. 4.26, 1). In many plants, spines are not of leaf, but of stem origin. At wild apple tree, wild pear, laxative joster, shortened shoots are metamorphosed into spines, having limited growth and ending in a point. They acquire the appearance of a hard lignified thorn after the leaves fall. At the hawthorn ( rice.4.26, 3) the spines that form in the axils of the leaves are completely leafless from the very beginning. In honey locust ( rice. 4.25.5) powerful branched spines are formed on trunks from dormant buds. The formation of spines of any origin, as a rule, is the result of a lack of moisture. When many thorny plants are grown in an artificial humid atmosphere, they lose their spines and instead grow normal leaves (camel thorn) or leafy shoots (English gorse).
Rice. 4.26. Spines of various origins: 1 - barberry leaf spines; 2 - spines of white acacia, modification of stipules; 3 - spines of hawthorn shoot origin; 4 - thorns - rosehip emergents.
The shoots of a number of plants bear spikes. Thorns differ from spines in smaller sizes, these are outgrowths - emergents - of the integumentary tissue and tissues of the stem bark (rose hips, gooseberries) ( rice. 4.26, 4).
Adaptation to a lack of moisture is very often expressed in the early loss, metamorphosis or reduction of leaves that lose the main function of photosynthesis. This is compensated by the fact that the stem takes on the role of the assimilating organ. Sometimes such an assimilating stem of a leafless shoot remains externally unchanged (Spanish gorse, camel thorn) ( rice. 4.25, 3). The next step in this change of functions is the formation of such organs as phyllocladia and cladodia. These are flattened leaf-like stems or whole shoots. On the shoots of the needle ( rice. 4.25, 4), in the axils of scaly leaves, flat leaf-shaped phylloclades develop, which, like a leaf, have limited growth. Scale-like leaves and inflorescences form on phylloclades, which never happens on normal leaves, which means that the phyllocladium corresponds to the whole axillary escape. Small, needle-like phylloclades are formed in asparagus in the axils of the scaly leaves of the main skeletal shoot. Cladodia are flattened stems that, unlike phyllocladia, retain the ability for long-term growth.
Some plants are characterized by the modification of leaves or their parts, and sometimes entire shoots in antennae, which twist around the support, helping the thin and weak stem to maintain an upright position. Many legumes turn into tendrils top part pinnate leaf (peas, peas, rank). In other cases, stipules (sarsaparilla) turn into antennae. Very characteristic tendrils of leafy origin are formed in gourds, and all the transitions from normal to fully metamorphosed leaves can be seen. Antennae of shoot origin can be observed in grapes ( rice. 4.25, 2), passionflower and a number of other plants.
Stem
The stem is the axis of the shoot, consisting of nodes and internodes. The main functions of the stem are supporting (carrier) and conducting. The stem is the link between roots and leaves. Reserve nutrients are usually deposited in perennial stems. Young stems with chlorenchyma under the epidermis are actively involved in photosynthesis.
The stem is usually cylindrical in shape and is characterized by radial symmetry in the arrangement of tissues. However, in cross section, it can be not only rounded, but also angular - three-,four- or multifaceted,ribbed,furrowed, sometimes completely flat, flattened, or bearing protruding flat ribs - winged(rice. 4.27).
Rice. 4.27. Stem types by cross-sectional shape: 1 - rounded; 2 - flattened; 3 - trihedral; 4 - tetrahedral; 5 - multifaceted; 6 - ribbed; 7 - furrowed; 8, 9 - winged.
The stems of woody and herbaceous plants differ dramatically in lifespan. aboveground shoots herbs of a seasonal climate live, as a rule, one year; the lifespan of the shoots is determined by the lifespan of the stem. In woody plants, the stem exists for many years.
Anatomical structure stem corresponds to its main functions. A complex system of conductive tissues is developed in the stem, which links all the organs of the plant into a single whole; the presence of mechanical tissues ensures the performance of the support function. The stem, like the shoot as a whole, is an “open” growth system; it grows for a long time and new organs appear on it.
The tissues of the stem are formed as a result of the activity complex system meristems: apical, lateral and intercalary ( rice. 4.28). The primary structure is formed as a result of the work of primary meristems. Initial cells apical meristems are concentrated in the growth cone of the shoot. At the shoot apex, leaf primordia appear at regular intervals, which leads to early isolation of nodes, and the development of internodes is delayed. Often the growth of internodes and the development of permanent tissues in them continue for a long time due to the work of residual intercalary meristems that are preserved at the bases of young internodes. good example such intercalary (intercalary) growth can be a stem of cereals, in which the apical meristem is spent very early on the formation of an inflorescence, and the rapid elongation of the shoot is due precisely to intercalary growth.
Rice. 4.28. Scheme of distribution of meristems in the stem: 1 - apical meristem; 2 - intercalary meristem; 3 - procambium; 4 - cambium.
The outermost layer of apex cells becomes protoderma from which the epidermis develops - the integumentary tissue of the future leaf and stem. At the level of the first leaf tubercles in the apical meristem, strands of narrower and longer cells are indicated - these are procambium giving rise to primary conductive tissues. The procambium may occur as individual bundles or as a continuous ring. With further growth, the procambium spreads both into the growing leaf primordia and into the stem, forming the basis of the future shoot conducting system that connects the leaves and stems. The rest of the apex is occupied main meristem, from which parenchymal storage and assimilating tissues, as well as primary mechanical tissues, are subsequently formed. The main meristem, located between the protoderm and procambium, turns into the primary bark of the stem, and the core is formed from the main meristem, located in the center.
The primary structure of the stem in spore and monocot plants persists throughout life. In gymnosperms and dicots, inside the procambium occurs cambium, which deposits secondary conductive tissues, resulting in a secondary thickening of the stem.
The primary structure of the stem. In the stem, which has a primary structure, as in the root, integumentary tissue,primary cortex and stele(axial, or central cylinder) (rice. 4.29).
Integumentary tissue is an epidermis typical structure. Part primary cortex includes the main parenchyma, as well as mechanical, excretory and some other tissues. More common among mechanical tissues collenchyma, it forms either a solid cylinder, or has the form of individual strands, usually located along the protrusions - the edges of the stem ( rice. 4.29). Immediately below the collenchyma or epidermis, if collenchyma is absent, under conditions favorable for photosynthesis, is located chlorenchyma. It can form with collenchyma or sclerenchyma alternating stripes along the stem. The boundary between the crust and the stele is much less pronounced.
Or accessory (adventive) kidney. Thus, the kidney is a rudimentary shoot. When the seed germinates from the germinal bud, the first shoot of the plant is formed - its main shoot, or first order escape.
From the main shoot are formed side shoots, or second order shoots, and when branching is repeated - of the third order, etc.
Adventitious shoots are formed from adnexal buds.
This is how the system of shoots is formed, represented by the main shoot and side shoots of the second and subsequent orders. The shoot system increases the total area of contact of the plant with the air.
Depending on the function performed, shoots are distinguished as vegetative, vegetative-generative and generative. Vegetative (unmodified) shoots, consisting of a stem, leaves and buds, and vegetative-generative (partially modified), additionally consisting of a flower or inflorescence, perform the functions of air nutrition and provide the synthesis of organic and inorganic substances. In generative (completely modified) shoots, photosynthesis most often does not occur, but sporangia are formed there, the task of which is to ensure plant reproduction (a flower also belongs to such shoots).
The shoot that produces flowers is called flowering shoot, or peduncle(sometimes the term "peduncle" is understood in a narrower sense - as a section of the stem, on which the flowers are located).
Main escape organs
A vegetative unmodified shoot is a single plant organ, consisting of a stem, leaves and buds, formed from a common array of meristems (the cone of growth of the shoot) and having a single conducting system. The stems and leaves, which are the main structural elements of the shoot, are often considered as its constituent organs, that is, organs of the second order. In addition, the obligatory affiliation of the escape is the kidneys. The main external feature that distinguishes the shoot from the root is the presence of leaves.
Monopodial branching
Monopodial branching is the next stage in the evolution of shoot branching. In plants with a monopodial type of shoot structure, the apical bud is preserved throughout the life of the shoot. The monopodial type of branching is often found among gymnosperms, it is also found in many angiosperms (for example, in many species of palms, as well as plants from the Orchid family - gastrochilus, phalaenopsis and others). Some of them have a single vegetative shoot (for example, Phalaenopsis is pleasant).
monopodial plants- the term most often used in the description of plants of tropical and subtropical flora, as well as in popular science literature on indoor and greenhouse floriculture.
Monopodial plants can vary significantly in appearance. Among them there are rosette, with an elongated shoot, bushy.
Sympodial branching
In plants with a sympodial type of shoot structure, the apical bud, having completed development, dies off or gives rise to generative run away. After flowering, this shoot no longer grows, and a new one begins to develop at its base. The structure of the shoot in plants with a sympodial type of branching is more complicated than in plants with; sympodial branching is an evolutionarily more advanced type of branching. The word "simpoidal" is derived from the Greek. sym("together" or "many") and pod("leg").
Sympodial branching is characteristic of many angiosperms: for example, lindens, willows, and many orchids.
In orchids, in addition to the apical ones, some sympodial orchids also form lateral inflorescences, developing from buds located at the base of the shoot (Pafinia comb). The part of the shoot pressed against the substrate is called the rhizome. It is located, as a rule, horizontally and does not have true leaves, only scaly. A reduced, almost indistinguishable rhizome occurs in many Masdevallia, Dendrobiums and Oncidiums; well distinguishable and thickened - in cattleyas and lelias, elongated - in bulbophyllums and cologins, reaching 10 or more centimeters. The vertical part of the shoot is often thickened, forming the so-called tuberidium, or pseudobulb. Pseudobulbs can be of various shapes - from almost spherical to cylindrical, cone-shaped, club-shaped and elongated, resembling reed stalks. Pseudobulbs are storage organs.
sympodial plants- the term most often used in the description of plants of tropical and subtropical flora, as well as in popular science literature on indoor and greenhouse floriculture.
|
Bulbophyllum grandiflorum |
Cirrhopetalum macraei. Curtis "s botanical magazine vol. 127 ser. 3 nr. 57 tab. 7787, 1901 |
Oncidium dasystyle. Curtis "s botanical magazine vol. 127 ser. 3 nr. 57 tab. 7787, 1901 |
Dendrobium senile. Curtis "s botanical magazine vol. 127 ser. 3 nr. 57 tab. 7787, 1901 |
Evolution of branch types
Shoot modifications (metamorphosis)
The shoot is the most variable in appearance organ of the plant. This is due not only to the general multifunctionality of vegetative organs that arose in the process of evolution, but also to the changes that occur in the process of plant ontogenesis, due to adaptation to a variety of environmental conditions, and in cultivated plants - under the influence of man.
The main type of shoot of a green plant is an aerial (aerial) assimilating shoot, bearing green leaves of the middle formation on the axis. However, assimilating shoots are not the same. Often, along with the main function of photosynthesis, these shoots also have others: the deposition of reserves and the supporting function (mostly in perennial stems), vegetative propagation (creeping shoots, lashes).
Modification of underground shoots
Shoots living underground, under the influence of a complex of conditions that are sharply different from the terrestrial environment, almost completely lost the functions of photosynthesis and acquired other equally important vital functions, such as organs for enduring an unfavorable period, storing nutrients, vegetative renewal and plant reproduction. Modified underground shoots include: rhizome, caudex, underground stolon and tuber, bulb, corm.
caudex- a perennial organ of shoot origin of perennial grasses and semi-shrubs with a well-developed taproot that persists throughout the life of the plant. Together with the root, it serves as a place of deposition of reserve substances and bears many renewal buds, some of which may be dormant. There are many caudex plants among the umbrella plants (femur, ferula), legumes (alfalfa, lupins), composites (dandelion, wormwood, rough cornflower).
underground stolon- an annual elongated thin underground shoot with underdeveloped scaly leaves. At the thickened ends of the stolons, plants can accumulate reserve substances, forming tubers or bulbs (potatoes, stolons, adoxas).
stem tuber- a modified shoot with a pronounced storage function of the stem, the presence of scaly leaves that quickly peel off, and buds that form in the axils of the leaves and are called eyes (potato, Jerusalem artichoke).
Bulb- underground (rarely above-ground) highly shortened specialized shoot, in which reserve substances are deposited in scales of leafy nature, and the stem is transformed into the bottom. The bulb is a typical organ of vegetative renewal and reproduction. Bulbs are characteristic of monocotyledonous plants from the Lily family (lily, tulip, onion), Amaryllis (amaryllis, daffodil, hyacinth), etc. As an exception, they are also found in dicotyledonous plants - in some species of sorrel and butterwort.
Corm- a modified underground shortened shoot with a thick stem storing assimilants, adventitious roots growing from the underside of the corm, and preserved dried leaf bases (membraneous scales), which together form a protective cover. Corms have saffron, gladiolus, colchicum.
Modifications of above-ground shoots
An unusual way of life and / or adaptation to the special conditions of the existence of plants lead to various modifications of the shoots. At the same time, shoots can serve not only to store nutrients, reproduce and reproduce plants, but also perform other functions. There are frequent cases when not the entire shoot is modified, but only its leaves, and some of their metamorphoses are outwardly and functionally similar to shoot metamorphoses (thorns, antennae).
thorn- strongly lignified leafless shortened shoot with a sharp tip. Spines of shoot origin perform mainly a protective function. At the wild apple tree, wild pear, laxative buckthorn ( Rhamnus cathartica) shortened shoots turn into spines, having limited growth and ending in a point. In honey locust ( Gleditschia triacanthos) powerful branched spines are formed on the trunks of dormant buds. Many species of hawthorn have spines that form from axillary leaf buds, which topographically corresponds to lateral shoots.
Claudius- a modified lateral shoot with the ability to grow long, with green flat long stems that act as a leaf. As an organ of photosynthesis, the cladodium has a well-developed chlorophyll-bearing tissue located under the epidermis. Plants with cladodias include Mühlenbeckia flatiflora ( Muhlenbekia platyclada), Decembrist cactus ( Zygocactus truncates), southern carmichelia ( Carmichaelia australis), collection ( Colletia cruciata) and prickly pear ( Opuntia).
Phyllocladius- a modified leaf-like flattened lateral shoot with limited growth and performing the functions of a leaf. Phyllocladia develop from lateral buds, so they are always found in the axil of a small membranous or scaly leaf. Performing the function of photosynthesis, the shoots of phylloclades also outwardly acquire a resemblance to a leaf, which manifests itself in limited growth and complete loss of the metameric structure. The phenomenon of phylloclady is characteristic of such plants as the needle, swept away, species of the asparagus genera ( Asparagus), phyllanthus ( Phyllanhtus). Phyllocladia are found not only in angiosperms, but also in some gymnosperms, in particular, in coniferous plant from the family Nogoplodnikovye - phyllocladus.
rosette shoots- abnormal shoots that form on pine trees due to damage caused to pine trees by some harmful insects, for example, a nun butterfly, etc .; such shoots are extremely short and have tufts of short and wide needles.