Escape- a vegetative organ that, due to branching, forms an above-ground system and ensures the life of the plant in the air. Unlike the root, the shoot has stem, buds, leaves. Stem is the axis of the shoot and it carries out the movement of substances along the stem and communication between parts of the plant. The stem contains leaves, the main functions of which are photosynthesis, transpiration and gas exchange. Thanks to kidneys the shoot branches and forms a shoot system, increasing the plant feeding area. Most plants have clearly visible nodes and internodes on the stem. Knot called the area of the stem where the leaf or leaves are attached. IN flower plants In addition to leaves, the nodes may bear axillary buds, which are formed in the leaf axils. Puff sinus called the angle between the leaf and the stem. Internodes - this is the area between two neighboring nodes. Of course, the shoot has several nodes and internodes. Such repetition of shoot segments having organs of the same name is called metamerism.
So, the structure of the shoot is adapted to carry out such basic functions as:
photosynthetic(perform leaves and green stems)
gas exchange and transpiration(through leaf stomata)
transport(movement of organic and inorganic substances along the stem and leaves)
formation of generative organs(cones form on the shoots in conifers, flowers in angiosperms).
variety of shoots
Plant shoots differ in many ways. Based on their origin, the main and side shoots are distinguished. Main called the first shoot of a plant that develops from the embryonic shoot of a seed. Shoots formed on the main one are called lateral. Depending on their functions, shoots are divided into vegetative and reproductive. Vegetative shoots perform the basic vital functions of the plant (respiration, nutrition, excretion, etc.), and reproductive - carry out reproduction. According to the length of internodes, shoots can be elongated (for example, fruit shoots of an apple tree) and shortened (for example, barren shoots of an apple tree). In some plants, the internodes are so short that the leaves form a basal rosette (for example, dandelion, plantain). Such shortened shoots are called rosette. Shortened shoots of fruit trees (apple trees, pears), on which flowers and fruits form, are called fruitcakes and carefully stored on trees. And the elongated shoots on these trees, which are called tops, are infertile and attempts are made to remove them immediately. Based on the direction of growth, vertical and horizontal shoots are distinguished. Vertical (or erect) shoots are shoots that grow upward (such as the main shoots of trees). And creeping shoots of strawberries, lying shoots of melon, watermelon, and lateral branches of trees are examples of horizontally growing shoots. There are also shoots in plants that first grow horizontally and then vertically (for example, in wheatgrass, motherwort).
So, scientists associate the diversity of shoots with their origin, functions, length of internodes, direction of growth, and the like.
Development and growth of shoot
Development- qualitative changes occurring in organs and throughout the body. Each shoot develops from a bud. IN annual species all buds develop during the warm season, and in perennial plants shoot growth stops in winter, and the buds overwinter. With the coming favorable conditions the cells of the apical forming tissue of the bud growth cone rapidly divide, the internodes and leaves lengthen, the integumentary scales move apart and a young stem with green leaves appears. Shoot development usually occurs from the apical bud. However, often the tip of the shoot ceases to exist (if damaged or with a certain type of branching), and then the development of this shoot in length stops and is no longer restored, although the growth of the branch can continue in the same direction due to the nearest lateral buds. The apical bud is not restored even when it is reproductive. After the flower or inflorescence blooms, this flowering shoot can no longer grow at the top.
Height- this is a quantitative increase in the size, volume and mass of both the whole organism and its individual parts. Plant shoots can grow very quickly. For example, bamboo shoots can grow up to 1 m in a day. Willow shoots grow quite quickly, growing up to 1 m in one growing season. Scientists have noticed that plant growth occurs mainly at night, and during the day it is inhibited. Growth is caused by the division and enlargement of cells of the forming tissue. The shoot is characterized by upright and insertive types of growth, which determine its extension. Apical (apical) height is carried out due to the apical forming tissue of the cone of growth of the apical buds, and plug-in (intercalary) height - due to the inserted forming tissue of the areas at the base of the internodes (in cereals). Thus, shoot development occurs mainly from the apical bud. Growth in most shoots is superior for some plants (monocots) Inserted is typical.
Branching of the shoot and its types
Branching- this is the formation of shoots from axillary buds, which are located on the main stem. Thanks to branching, the stem increases its photosynthetic surface. Branching especially increases when the apical bud of this stem is damaged or removed. Each side branch, like the main stem, has apical and lateral buds. The apical bud provides elongation of the branches, and new lateral shoots grow from the axillary buds, which also branch. Branching in trees, bushes, and grasses can be carried out in various ways. In trees, branching of the trunk is observed, as a result of which a crown is formed. Crown- the totality of all above-ground shoots located above the beginning of the branching of the trunk. In a branched plant, the main stem is called the axis of the first order, the lateral stems developed from its axillary buds are called the axes of the second order, on which axes of the third order are formed, etc. Trees can have up to 10 such axes. The formation of the crown depends not only on the method of branching, but also on the influence of external factors. Knowing the patterns of branching, a person artificially forms the crowns of fruit and ornamental woody plants to meet his needs.
In bushes, branching begins at the very surface of the soil, resulting in the formation of several lateral shoots, and in grasses, tillering is observed, that is, the formation of lateral shoots from the lowest buds of the stem or even from underground shoots. Plants have several types of branching:
1 ) dichotomous- two branches grow from the apical bud (for example, in mosses, mosses)
2 ) monopodial- the apical bud continues the growth of the main stem throughout life (in pine, spruce)
3 ) sympodial- the apical bud does not develop and shoot growth occurs due to the lateral bud closest to it (for example, in an apple tree, linden tree).
So, thanks to branching, the formation of more leaves is ensured and a significant surface for photosynthesis is created.
shoot modifications
Modifications of shoots can be aboveground or underground. The main above-ground modifications of the shoot are antennae, spines And mustache. Mustache There are elongated thin shoots that attach plants to objects (for example, grapes, cucumbers). Tendrils emerge from the axils of the leaves. spines - These are shortened shoots, the main function of which is to reduce the surface area for water evaporation. They are widespread in dicotyledonous woody plants with high drought resistance (lemon, hawthorn, honey locust, wild species of apple trees, pears, plums and other plants). If these plants are moved under conditions of sufficient moisture, the spines may not develop. Along with this, the spines also perform a protective function: they protect the plant from being eaten. These modifications are also located in the leaf axils or in the node opposite the leaf, which indicates their origin from shoots. Strawberries, stone fruits, and zelenchuk have elongated thin shoots called mustache(ground stolons). They take root in the nodes and from the lateral buds give rise to new plants, thus realizing vegetative propagation.
Underground modifications of shoots - rhizome, tuber and bulb - perform storage functions nutrients and vegetative propagation. Rhizome stems throughout the area(for example, lily of the valley, valerian). The stem of the rhizome can be long (in wheatgrass) and short (in cockerels), on which apical and axillary buds are located. The fact that the rhizome is a modified shoot is evidenced by the following signs: on the rhizome, forum of the root cap and root hairs, there are always rudimentary leaves in the form of small scales, additional roots are formed from the nodes, etc. Every year, young above-ground shoots develop from the buds of the rhizome in the spring. Bulba is an underground modification of the shoot that accumulates nutrients in the area of one or more internodes of the stem. Tubers can be aboveground (for example, in kohlrabi, epiphytic orchids) and underground (in potatoes, Jerusalem artichoke). In potatoes, tubers are the thickened upper parts of underground shoots; their residual leaves are called edges, and the buds are called eyes. Tubers differ from rhizomes in their spherical or oval shape, greater thickness, durability, which is 1-2 years (perennial rhizomes). Bulb - this is an underground modification of the shoot that accumulates nutrients in inner leaves (for example, onions, garlic, tulips, daffodils). In onions, the bulb consists of a shortened stem (bottom), outer dry and inner fleshy leaves and buds. An above-ground shoot is formed from the apical bud at the bottom, and a new bulb is formed from the lateral axillary bud. In garlic, daughter bulbs (“cloves” or “children”) develop from the axillary buds, forming a complex bulb.
So, modifications of shoulder straps differ from each other in the structure and purpose of their components - stems, leaves and buds.
Escape modifications and their functions
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aboveground |
underground |
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Mustache - attachment to objects (grapes, melons, pumpkin, cucumbers). spines - protection from eating (hawthorn, plum, sloe, sea buckthorn, wild pear). Mustache- vegetative propagation (strawberries, stone fruits). Phyllocladia- photosynthesis, flower formation (ruscus, asparagus) |
Rhizome- vegetative propagation and storage of substances (wheatgrass, iris, sedge). stem tubers- vegetative propagation and storage of substances (underground tubers in potatoes, Jerusalem artichoke, aboveground tubers in kohlrabi). Bulb- vegetative propagation and storage of substances (tulip, garlic). Corm - vegetative propagation and storage of substances (mowers, saffron) |
Escape - vegetative organ of a plant, consisting of a stem with leaves and buds located on it. The main function of the shoot is photosynthesis. In addition, the shoot can provide vegetative propagation of plants, be a site for the deposition of reserve nutrients, perform protective functions, and even participate in supplying the plant with nitrogen-containing substances.
Each shoot develops from a bud. The first shoot of a plant developing from the bud of the embryo is called main escape. All other shoots - side shoots. Some of them, formed from buds in the axils of the leaves, are called axillary shoots. The second, formed from adventitious buds that form on any part of the plant except the leaf axil, are called adventitious shoots. A shoot formed during one growing season is called annual escape. If a shoot lives for several years, it is called
Rice. 12.
L- diagram of the structure of a cereal shoot, divided into metameres; B- diagram of the shoot structure; IN- diagram of the structure of the metamer (according to V.G. Khrzhanovsky, 1972, O.A. Korovkin, 2007):
- 1 - stem; 2 - node; 3 - leaf; 4 - internode;
- 5 - leaf axil; 6 - axillary bud; 7 - apical bud for perennials. The growth of annual and perennial shoots is carried out due to the activity of the apical (apical) meristem located in the apical bud of the shoot.
Unlike the root, the shoot is characterized metameric structure - repeatability of its constituent elements along the axis from the base to the top (Fig. 12, A). Metamer, or phytomer, called a structural unit of a shoot, consisting of an internode, a node, a leaf (several leaves) and an axillary bud (several buds) (Fig. 12, B, C).
According to the characteristics of growth and position in space, shoots are divided into erect (flax, sunflower, rye), climbing (bindweed, hops), clinging (peas, grapes, china), creeping (watermelon, cranberries, pumpkin) and creeping (creeping clover, loosestrife coin-shaped). Unlike creeping shoots, creeping shoots are capable of taking root - adventitious roots are formed on their stem (Fig. 13).
Rice. 13.
A- erect; B- rising; IN- curly;
G- clinging; D- creeping; E- creeping
The development of the shoot usually ends with the formation of an apical flower or inflorescence. If a shoot blooms in the first year of life, it is called monocyclic, if it blooms in the second year - di-cyclic, in the third year - tricyclic. Shoots that develop over several years are called polycyclic. A shoot that blooms and bears fruit once in a lifetime is called monocarpic, several times (due to the formation of axillary flowers) - polycarpic.
During his life cycle fruit tree forms various types shoots and
Types of fruit shoots
1. Spear.
2. Fruit bag. 3 Whorl
buds, and it is important to know their role in the development of the tree in order to be able to regulate their growth and influence the interdependent processes associated with their development.
As already mentioned, the basis for the formation of the skeletal structure of the crown is the central conductor, which is a continuation of the trunk, and skeletal branches or twigs. Develop from skeletal branches fouling branches, which are small branches of tree shoots. New overgrowing branches develop every year, and often annual branches, especially long ones, are mistakenly called shoots. It is necessary to separate these two terms: a shoot is considered to be the growth of the current year, which essentially remains a shoot as long as it bears foliage. As soon as in the fall a shoot that has already become quite woody sheds its leaves, it becomes a branch. Overgrowing branches are divided into vegetative, or height, and generative, or fruit.
Vegetative shoots provide an increase in the total mass and dimensions of the tree and differ in origin and functions performed by them in the crown. Grow from the apical buds continuation shoots main or overgrowing branches, they are also called gains, since they annually increase their length and thereby replenish the volume of the tree crown.
If the terminal bud blooms in the year of its formation, a young shoot grows from it, called summer growth. This growth is very tender, susceptible to frost and therefore undesirable. One or two buds located below the apical one,
give competing branches. They received their name because, in terms of growth strength and placement, they compete for a leading position with legitimate continuation branches. Below are the lateral branches, which grow respectively from the lateral buds. If the lateral branches are directed inside the crown, it means that they developed from internal buds and, therefore, are internal. From the outer buds branches develop that are directed outward and are called accordingly outdoor branches. It is important to distinguish between them to determine the location and orientation of the branch near which the cut will be made when forming the crown or pruning.
Vegetative shoots
Vegetative shoots are shoots without generative organs, consisting of an axis, leaves and buds. They can be apical and lateral, shortened and elongated. Elongated vegetative shoots are often called growth shoots. In fruit growing, vegetative shoots include continuation shoots, competing shoots, regenerative shoots, top shoots and root shoots.
Vegetative shoots differ from generative shoots in terms of growth duration and length. In some fruit crops, such as apple, pear, plum, etc., these differences are clearly expressed, in others they are less noticeable. After the leaves fall, the vegetative shoots, depending on the type of buds they bear, turn into various vegetative and generative branches.
A special position among vegetative branches is occupied by tops, or water shoots, which are also often called fatty shoots.
Thin, strong, vertically growing young shoots with large internodes are formed V dense tree crown, lacking light. As a rule, they appear on perennial parts of large branches from a dormant bud that has not been touched for years to grow. Factors that stimulate the formation of tops can be aging of the tree, freezing or damage to the upper part of the branch. Due to poor lighting, the tops become useless and can only lay a flower bud if the conditions for their development inside the crown improve, so it is recommended to remove these branches.
Top shoots
Top shoots (tops, fat or water shoots) develop from a dormant bud. They usually form on old parts of perennial branches or on the trunk of a tree during its natural aging. The process of formation of spiny shoots can be caused by freezing of the tree, its mechanical damage as a result of improper pruning, hail, wind, etc. Top shoots are characterized by intense, protracted, clearly defined vertical growth, elongated internodes, shadow-type leaves located inside the crown, as well as increased water content and loose tissue.
Often, at the trunk of a tree, branches appear from the ground, growing from the roots. This is the so-called root shoots, extremely undesirable for a tree, since it is forced to spend additional strength, moisture, and nutrients on its completely unproductive parts. Root growth should be destroyed without waiting for it to grow.
Generative shoots are constituent elements of the tree crown on which the flower bud is formed, and are directly involved in the formation of the crop. These branches got their name due to the fact that only on them can generative buds be placed (even if they do not develop in any year), which determine the propensity of the generative branches to bear fruit and their purpose for ensuring the harvest.
Generative shoots include:
fruit twig - a thin, often downward-curved annual branch more than 15 cm long with a flower bud at the apex;
spear - a straight, shortened lateral branch 5-15 cm long, noticeably tapering towards the apex, with a flower bud;
kolchatka - the shortest annual branch, up to 2-3 cm long, very fragile with one well-formed leaf or flower bud;
fruits - shoots 2-3 years old, once bearing fruit;
spurs- short fruit formations from 0.5 to 10 cm long;
whorls - short fruiting structures up to only 3 cm long with a group of buds at the top.
Generative shoots
A generative, or flowering, shoot is a shoot that bears individual flowers or inflorescences, and subsequently fruits. A generative shoot develops from a generative bud that has the rudiments of a flower or inflorescence. Generative shoots can differ greatly from vegetative shoots, as, for example, in pome and stone fruit species, or differ little, as, for example, in sea buckthorn, honeysuckle and actinidia. Based on the relationship between the vegetative and flowering zones, the following are distinguished:
unspecialized generative shoots, which are characterized by a strong predominance of the vegetative zone and late flowering in the leafy state. This type of generative shoots is characteristic of actinidia, lemongrass, and honeysuckle;
semi-specialized generative shoots, characterized by a clearly defined vegetative zone, apical arrangement of flowers or inflorescences, flowering in a leafy state, which occurs simultaneously with the appearance of leaves or immediately before it. This type of generative shoots is typical for quince, viburnum, apple, pear, rowan, and chokeberry;
specialized generative shoots, characterized by a highly reduced vegetative zone. Externally, they appear as a single shoot or inflorescence; they bloom in a leafless state and very early, which often causes damage to the flowers by late spring night frosts.
This type of generative shoots is typical for cherry plums, plums, cherries, cherries, peaches, apricots, and hazelnuts.
Fruit bags They are thickened formations on the fruit twig, spear or ringlet, which serve to form fruits. When a flower bud awakens, a swelling appears on the generative branch, resembling a bag in shape, which explains its name. Additional generative shoots in the form of ringlets, spears, and fruit twigs can develop from the fruit bag. Annually growing in length, the generative branches turn into fruits and fruits,
A stem is a vegetative organ of a plant that has negative geotropism (it grows in the opposite direction of gravity), representing the shoot axis, bearing leaves, buds, and reproductive organs. Its main functions:
- Supporting - due to mechanical tissues (wood fibers in the xylem) it brings the leaves to the light
- Conductive - thanks to conductive tissues - xylem (ascending current) and phloem (descending current) - transports substances between the root and leaves
- Storage - in the center of the stem there is a core where the reserve plant nutrient - starch - is stored
- Vegetative propagation - possible here different options and methods, for example: cuttings, layering
- Photosynthesis - in some cases the stems themselves photosynthesize (aloe, horsetail)
Escape
Remember the "formula"! Shoot = stem + leaves + buds. As can be seen from the formula, a shoot consists of a stem and leaves and buds located on it; the shoot itself develops from a bud or seed. Only adventitious roots can emerge from the shoot. It grows upward due to the constant division by mitosis of the cells of the growth cone, located at the top of the stem and protected by bud scale-like leaves. All elements of the shoot are laid in the growth cone - stem, leaves, inflorescences, buds, flowers. Lateral buds provide shoot branching. The stem grows in thickness due to phellogen and cambium.
The section of the stem on which a leaf or leaves is located is called a node. The distance between two adjacent nodes is the internode. Leaf axil is the area between the base of the leaf and the stem; in the leaf axil there is an axillary bud. In general, the shoot has a segmented (metameric) structure, a metamer is each repeating node. Shoots in which internodes are well defined and neighboring leaves are distant from each other are called elongated. If there are almost no internodes on the shoot, and the nodes are very close together, such shoots are called shortened.
The following stem structures are distinguished: primary and secondary.
- Primary - formed as a result of the activity of the apical (apical) meristem
- Secondary - formed due to the activity of the cambium
In monocotyledonous plants, at the initial stages of shoot development, the primary structure of the stem is formed, which persists throughout life. In perennial dicotyledonous plants and gymnosperms, this structure undergoes a number of changes, so that gradually a secondary structure is formed from the primary structure of the stem.
Stem cut
The stems of different plants have different anatomical organizations, but the structure of the stem of seed plants must be remembered. It is given below.
A clear understanding of the location of tissues in the stem, as well as their function, should be developed. The most superficially located integumentary tissues protect the plant from adverse factors. external environment: epidermis, cork, crust. Deeper lies the bast (phloem) - a conductive tissue through which a downward flow of organic substances occurs. Next comes the cambium layer, educational fabric, due to which the stem grows in thickness. Wood (xylem) lies even deeper - a conductive tissue that provides an upward current of water and mineral salts to the leaves.
In the spaces between the conducting tissues there is parenchymal tissue - medullary rays. In the thickness of the conductive tissues there are mechanical tissues that provide support to the plant. Mechanical tissues are represented in the xylem by wood fibers, and in the phloem by sclerenchyma elements. At the center of the stem lies the pith, which belongs to the group of main plant tissues. The core is a storage tissue; starch, a reserve plant nutrient, is stored here.
As a result of the activity of cambium cells, secondary xylem and phloem are formed, and the stem gradually thickens. There is always more secondary xylem than secondary phloem. Subsequently, the primary cover (epidermis) is replaced by a cork formed by phellogen (cork cambium), which deposits the phellem (or cork) outward, and the phelloderm (cork skin) inward. Let me remind you that the periderm is a collection of tissues: cork skin, cork and cork cambium.
Branching pattern of the shoot
Occurs as the shoot grows. Branching of the shoot is necessary to increase the area of contact with the habitat. There are 4 types of branching:
- Dichotomous (forked) - two identical branches develop from the growth cone of the apical bud, that is, the growth cone is divided in two (in mosses, multicellular algae, mosses).
- Monopodial - the shoot grows for a long time due to the apical bud. Characteristic of gymnosperms - pine, spruce.
- Sympodial - the apical meristem (bud) functions for a certain period of time (season), after which it dies, and its function is taken over by the lateral bud, growth continues. Present in bird cherry.
- False dichotomous - the apical bud dies, and two oppositely located lateral buds form two apical shoots. In lilacs, horse chestnuts.
Method of locating the escape in space
According to its location in space, the escape can be:
- Erect - constantly growing upward
- Elevating - some part of the stem develops on the surface of the substrate, then grows upward as an erect stem
- Creeping - grows horizontally, takes root at nodes
- Creeping - grows horizontally, without rooting nodes
- Twisting around a support - due to poor development of mechanical tissues, the stem is forced to create additional support for itself
- Clinging to a support - the same situation as that of a twining stem, but clinging to the support with the help of tendrils
As they say, it is better to see once than to hear a hundred times.
Modifications of shoots
Long-term evolution has led to the emergence of unique mechanisms of plant adaptation to environmental conditions, in particular to the development of modified shoots. The modified shoot is necessary for the plant to perform important functions, such as: vegetative propagation, accumulation of nutrients, protection, attachment to the substrate.
Modified shoots are of two types: aboveground and underground. It is important to understand that no matter where the shoot is located, it will satisfy the formula given above: shoot = stem + leaves + buds. Don't forget it, it will be extremely useful to you!
Let's move on to the classification of shoot modifications.
© Bellevich Yuri Sergeevich 2018-2020
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The first shoot of the plant is formed from the embryonic bud - its main escape, or first order escape.
From the main shoot they form side shoots, or second order shoots, and when repeating branching - third order, etc.
Adventitious shoots are formed from accessory buds.
This is how a system of shoots is formed, represented by the main shoot and lateral 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 divided into 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 the reproduction of the plant (the flower is one of these shoots).
The shoot on which flowers are formed is called flowering shoot, or peduncle(sometimes the term “peduncle” is understood in a narrower sense - as the section of the stem on which the flowers are located).
Main organs of the shoot
A vegetative unmodified shoot is a single plant organ, consisting of a stem, leaves and buds, formed from a common array of meristem (shoot growth cone) and possessing a single conducting system. Stems and leaves, which are the main structural elements of the shoot, are often considered as its constituent organs, that is, second-order organs. In addition, a mandatory accessory to the shoot is the buds. The main external feature that distinguishes a shoot from a 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 retained throughout the life of the shoot. The monopodial type of branching is often found among gymnosperms, and is also found in many angiosperms (for example, in many types 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 pleasant).
Monopodial plants- a term most often used in describing plants of tropical and subtropical flora, as well as in popular scientific literature on indoor and greenhouse floriculture.
Monopodial plants can vary significantly in appearance. Among them there are rosettes, with elongated shoots, and bush-like ones.
Sympodial branching
In plants with a sympodial type of shoot structure, the apical bud, having completed development, dies or gives rise to generative I'll run. After flowering, this shoot no longer grows, and a new one begins to develop at its base. The shoot structure of plants with a sympodial type of branching is more complex than that of plants with; sympodial branching is an evolutionarily more advanced type of branching. The word “sympoidal” 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 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 to the substrate is called the rhizome. It is usually located horizontally and does not have true leaves, only scale-like ones. A reduced, almost indistinguishable rhizome occurs in many masdevallias, dendrobiums and oncidiums; clearly distinguishable and thickened - in cattleyas and laelias, elongated - in bulbophyllums and coelogines, 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 stems. Pseudobulbs are storage organs.
Sympodial plants- a term most often used in describing plants of tropical and subtropical flora, as well as in popular scientific literature on indoor and greenhouse floriculture.
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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 branching types
Modifications of shoots (metamorphoses)
The shoot is the most variable plant organ in appearance. This is due not only to the general multifunctionality of vegetative organs that arose in the process of evolution, but also to changes occurring during plant ontogenesis, due to adaptation to a variety of conditions environment, and in cultivated plants - under human influence.
Basic type of escape green plant- aboveground (aerial) assimilating shoot, bearing green leaves of the middle formation on its axis. However, assimilating shoots are not the same. Often, along with the main function of photosynthesis, these shoots also have others: deposition of reserves and support function (mostly in perennial stems), vegetative propagation (creeping shoots, lashes).
Modification of underground shoots
Shoots living underground, under the influence of a set 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 surviving unfavorable periods, storing nutrients, vegetative regeneration and plant reproduction. Underground modified shoots include: rhizome, caudex, underground stolon and tuber, bulb, corm.
Caudex- a perennial organ of shoot origin of perennial grasses and subshrubs with a well-developed taproot that persists throughout the life of the plant. Together with the root, it serves as a place for the deposition of reserve substances and bears many renewal buds, some of which may be dormant. There are many caudex plants among the umbelliferous plants (female, ferula), legumes (alfalfa, lupins), and Asteraceae (dandelion, wormwood, rough cornflower).
underground stolon- an annual elongated thin underground shoot with underdeveloped scale-like leaves. At the thickened ends of stolons, plants can accumulate reserve substances, forming tubers or bulbs (potatoes, rosemary, adoxa).
Stem tuber- a modified shoot with a pronounced storage function of the stem, the presence of scale-like leaves that quickly peel off, and buds that form in the axils of the leaves and are called eyes (potatoes, Jerusalem artichokes).
Bulb- an underground (less often above-ground) highly shortened specialized shoot, in which reserve substances are deposited in leaf scales, and the stem is transformed into a bottom. The bulb is a typical organ of vegetative renewal and reproduction. Bulbs are characteristic of monocotyledonous plants from the family Liliaceae (lily, tulip, onion), Amaryllidaceae (amaryllis, narcissus, hyacinth), etc. As an exception, they are also found in dicotyledons - in some species of oxalis and butterwort.
Corm- a modified underground shortened shoot with a thick stem storing assimilates, adventitious roots growing from the underside of the corm, and preserved dried leaf bases (membranous scales), which together constitute a protective cover. Corms include saffron, gladiolus, and colchicum.
Modifications of aboveground shoots
Unusual lifestyle and/or adaptations special conditions the existence of plants lead to various modifications of shoots. In this case, shoots can serve not only for storing nutrients, reproduction and propagation of 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 externally and functionally similar to the metamorphoses of the shoot (spines, tendrils).
Thorn- a highly lignified, leafless, shortened shoot with a sharp tip. The spines of shoot origin perform mainly a protective function. The wild apple, wild pear, laxative buckthorn ( Rhamnus cathartica) shortened shoots that have limited growth and end with a point turn into spines. In honey locust ( Gleditschia triacanthos) powerful branched spines are formed on the trunks from dormant buds. Many hawthorn species have spines that form from the axillary buds of the leaves, which topographically correspond to the lateral shoots.
Cladodius- a modified lateral shoot with the ability for long-term growth, with green, flat, long stems that perform the functions of a leaf. As an organ of photosynthesis, the cladodium has well-developed chlorophyll-bearing tissue located under the epidermis. Plants with cladodes include Mühlenbeckia planiflora ( Muhlenbekia platyclada), Decembrist cactus ( Zygocactus truncates), carmichelia southern ( Carmichaelia australis), collection ( Colletia cruciata) and prickly pear ( Opuntia).
Phyllocladium- a modified leaf-shaped flattened lateral shoot that has limited growth and performs the functions of a leaf. Phyllocladia develop from lateral buds, so they are always found in the axil of a small filmy or scale-like leaf. Performing the function of photosynthesis, phyllocladian shoots also externally acquire a resemblance to a leaf, which is manifested in limited growth and complete loss of metameric structure. The phenomenon of phylloclady is characteristic of plants such as butcher's broom, moss, and species of the genera asparagus ( Asparagus), phyllanthus ( Phyllanthus). Phyllocladies are found not only in angiosperms, but also in some gymnosperms, in particular in coniferous plant from the family Legocladaceae - phyllocladus.
Notes
Literature
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