Escape of a flowering plant diagram. Vegetative organs

The escape- a vegetative organ, which, 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 the connection between the parts of the plant. The stem contains leaves, whose main functions are photosynthesis, transpiration and gas exchange. Thanks to kidneys the shoot branches and forms a system of shoots, increasing the area of ​​plant nutrition. In most plants, nodes and internodes are clearly visible on the stem. knot called the area of ​​the stem where the leaf or leaves are attached. In flowering plants, in addition to leaves, nodes can carry axillary buds, which are formed in leaf axils. Puff sinus called the angle between the leaf and the stem. Internodes - is the area between two adjacent nodes. Of course, the shoot has several nodes and internodes. Such a repetition of shoot segments with the same organs is called metamerism.

So, the structure of the shoot is adapted to the implementation of such basic functions as:

photosynthetic(perform leaves and green stems)

gas exchange and transpiration(via leaf stomata)

transport(movement of organic and inorganic substances along the stem and leaves)

formation of generative organs(cones are formed on the shoots in conifers, flowers in angiosperms).

variety of shoots

Plant shoots differ in many ways. By origin, the main and side shoots are distinguished. chief called the first shoot of a plant that develops from the germinal shoot of a seed. Shoots formed on the main are called side. Depending on the functions, the 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. Along the length of the internodes, the 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 rosette (for example, dandelion, plantain). Such shortened shoots are called socketed. Shortened shoots of fruit trees (apple, pear), on which flowers and fruits are formed, are called fruits and carefully stored on trees. And the elongated shoots on these trees, which are called tops, are infertile and are attempted to be removed immediately. In the direction of growth, vertical and horizontal shoots are distinguished. Upright (or erect) shoots are shoots that grow upwards (such as the main shoots of trees). And creeping shoots of strawberries, lying shoots of melon, watermelon, side branches of trees are an example 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.

Escape development and growth

Development- qualitative changes occurring in the 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, the growth of shoots stops in winter, and the buds hibernate. With the onset of favorable conditions, the cells of the apical forming tissue of the growth cone of the kidney are intensively divided, the internodes and leaves are lengthened, 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 (in case of damage 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 kidney is not restored even when it is reproductive. After the blooming of a flower or inflorescence, this flower-bearing shoot can no longer grow at the top.

Growth- 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 per day. Willow shoots grow quite quickly, which grow 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 due to the division and increase in the cells of the forming tissue. Escape is characterized by riding and plug-in type of growth, which determine its extension. Apical (apical) growth carried out due to the apical forming tissue of the cone of growth of the apical buds, and plug-in (intercalary) growth - due to the plug-in generatrix of the tissue areas at the base of the internodes (in cereals). Thus, the development of the shoot occurs mainly from the apical bud. Growth in most shoots is equine for some plants (monocots) inserted is characteristic.

Branching of the shoot and its types

branching- this is the formation of shoots from axillary buds, which are located on the main stem. Through branching, the stem increases its photosynthetic surface. Branching is especially enhanced when the apical bud of this stem is damaged or removed. Each side branch, like the main stem, has a top and side buds. The apical bud elongates the branches, and new lateral shoots grow from the axillary buds, which also branch. Branching in trees, bushes, grasses can be carried out in various ways. In trees, branching of the trunk is observed, as a result of which the 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 side stems that developed from its axillary buds are called the axes of the second order, on which the 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 their needs.

In bushes, branching begins at the very surface of the soil, resulting in the formation of several side shoots, and in grasses, tillering is observed, that is, the formation of side shoots from the lowest buds of the stem or even from underground shoots. There are several types of branching in plants:

1 ) dichotomous- two branches grow from the apical bud (for example, into club 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 the growth of the shoot occurs due to the lateral bud closest to it (for example, in an apple tree, linden).

So, thanks to branching, the formation of more leaves is ensured and a significant surface of photosynthesis is created.

shoot modifications

Modifications of shoots can be aboveground and underground. The main above-ground modifications of the shoot are antennae, spines and mustache. tendrils there are elongated thin shoots that attach plants to objects (for example, in grapes, cucumbers). Antennae emerge from the axils of the leaves. spines - these are shortened shoots, the main function of which is associated with a decrease in the surface of water evaporation. They are widely used 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 transferred in conditions of sufficient moisture, then 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 axils of the leaves or in the node opposite the leaf, which indicates their origin from the shoots. There are elongated thin shoots in strawberries, stone fruits, zelenchuk, which are called mustache(ground stolons). They take root in the nodes and from the lateral buds give rise to new plants, thus carrying out vegetative propagation.

Underground modifications of shoots - rhizome, tuber and bulb - perform the functions of storing nutrients and vegetative reproduction. Rhizome throughout the stems(for example, lily of the valley, valerian). The stalk of the rhizome can be long (in couch grass) and short (in cockerels), on which the apical and axillary buds are located. The fact that the rhizome is a modified shoot is evidenced by the following signs: on the rhizome of the forum of the root cap and root hairs, rudimentary leaves in the form of small scales are obligatory, additional roots are formed from the nodes, etc. Annually, young above-ground shoots develop from the buds of the rhizome in spring. Bulba - this is an underground modification of the shoot, which accumulates nutrients in the area of ​​\u200b\u200bone or more stem internodes. Tubers can be aboveground (for example, in kohlrabi, epiphytic orchids) and underground (in potatoes, Jerusalem artichoke). In potatoes, tubers are the upper thickened parts of underground shoots, their residual leaves are called eyebrows, and the buds are called eyes. Tubers differ from rhizomes in spherical or oval shape, greater thickness, durability, which is 1-2 years (perennial rhizomes). Bulb - this is an underground modification of the shoot, which accumulates nutrients in inner leaves(for example, onions, garlic, tulips, daffodils). In onion, the bulb consists of a shortened stem (bottom), external dry and internal fleshy leaves and buds. An elevated shoot is formed from the apical bud at the bottom, and a new bulb is formed from the lateral axillary bud. In garlic, axillary buds develop into daughter bulbs ("cloves", or "children"), forming a complex bulb.

So, the modifications of the epaulette differ from each other in the structure and the purpose of their components - stems, leaves and buds.

Escape modifications and their functions

During its life cycle, a fruit tree forms various types of 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. From skeletal branches develop fouling branches, which are small branches of tree shoots. New growing branches develop every year, and it is not uncommon for annual branches, especially long ones, to be erroneously called shoots. It is necessary to separate these two terms: the growth of the current year is considered to be a shoot, which in fact remains a shoot as long as it bears foliage. As soon as in autumn the already quite lignified shoot sheds foliage, it passes into the category of branches. Overgrown branches are divided into vegetative, or growth, 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. From the apical buds grow continuation shoots main or overgrowing branches, they are also called gains, as they annually increase the 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 the summer growth. This growth is very delicate, susceptible to frost and therefore undesirable. One or two kidneys located below the apical,

give competing branches. They got their name because they compete for a leading position with legitimate continuation branches in terms of strength of growth and placement. Below are the lateral branches growing respectively from the lateral buds. If the lateral branches are directed inside the crown, then they have developed from internal buds and, therefore, are internal. Outwardly directed branches develop from the external buds and are named 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, regenerative, top and root shoots.

Vegetative shoots differ from generative shoots in the duration of growth 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, vegetative shoots, depending on the type of buds laid on them, turn into various vegetative and generative branches.

A special position among the 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 in dense crown of a tree that is deficient in light. As a rule, they appear on the perennial parts of large branches from a dormant bud that has not been touched for years. Factors stimulating the formation of tops can be aging of the tree, freezing or damage to the higher part of the branch. Due to poor lighting, tops become useless and can lay a flower bud only when the conditions for their development inside the crown improve, so it is recommended to remove these branches.

top shoots

Top shoots (tops, fatty 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 top shoots can be caused by the freezing of a tree, its mechanical damage as a result of improper pruning, hail, wind, etc. Spinning top shoots are characterized by intense, protracted, clearly defined vertical growth, elongated internodes, shadow type of leaves located inside the crown, as well as increased watering and friability of tissues.

Often, near the stem of a tree, branches appear from the ground that have grown from the roots. This so-called root growth, extremely undesirable for a tree, since it is forced to spend additional forces, moisture, nutrients on its completely unproductive parts. Root growth should be destroyed without waiting for its growth.

generative shoots are the constituent elements of the tree crown, on which the flower buds are laid, and are directly involved in the formation of the crop. These branches got their name due to the fact that only generative buds can be placed on them (even if they do not develop in any year), which determine the propensity of generative branches to bear fruit and their purpose for ensuring the harvest.

Generative shoots include:

fruit stick - thin, often downwardly curved annual branch more than 15 cm long with a flower bud at the top;

spear - straight, noticeably tapering towards the apex, a shortened lateral branch 5-15 cm long 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 fruit formations only up to 3 cm long with a group of buds at the top.

generative shoots

A generative, or flower-bearing, shoot is a shoot that bears individual flowers or inflorescences, and subsequently fruits. A generative shoot develops from a generative bud that has the beginnings of a flower or inflorescence. Generative shoots can differ greatly from vegetative ones, as, for example, in pome and stone fruits, or differ little, as, for example, in sea buckthorn, honeysuckle and actinidia. According to the ratio of the vegetative and flowering zones, they distinguish:

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 typical for actinidia, lemongrass, 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, mountain ash, chokeberry;

specialized generative shoots, characterized by a strongly reduced vegetative zone. Outwardly, they are a single shoot or inflorescence, bloom in a leafless state and very early, which often causes damage to flowers by late spring night frosts.

This type of generative shoots is typical for cherry plums, plums, cherries, sweet cherries, peaches, apricots, and hazelnuts.

fruit bags are thickened formations on a 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. From the fruit bag, additional generative shoots can develop in the form of annelids, spears, fruit twigs. Annually growing in length, the generative branches turn into fruits and fruits,

Shoot - one of the main organs of higher plants, consisting of a stem, leaves and buds. On the stem of the shoot are nodes and internodes. The node is the place where the leaves and buds are connected to the stem. The angle between the stem and the leaf is called the leaf axil. The kidney that is located there is called axillary. In addition to the axillary buds, there are also apical ones.

The stem is the axial part of the shoot of a plant, has nodes and internodes and is a support for leaves, buds and generative organs. The main function of the stem is leading. The movement of substances occurs along the leading elements: organic (from leaves to all organs) and mineral solutions (from roots to aboveground organs). Spare substances accumulate in the stem; green stems are photosynthetic; through stomata in the skin of the stem and lentils in the cork, the function of gas exchange is carried out. By growth and placement in space, the stems are divided into erect (sunflower), curly (field birch), creeping (white clover), tenacious (grapes). According to the presence of wood, the stems are divided into herbaceous (knotweed, plantain) and woody (birch, oak, currant).

Annual plants live throughout the year or only the favorable season. Biennial plants in the first year of life are exclusively vegetative organs and accumulate nutrients in their underground (carrots, beets, dahlias) or aboveground (cabbage) parts. The next year they form fruits and seeds. Perennial plants live three or more. Among them there are trees, bushes, semi-bushes and herbaceous plants. The stems can have various shapes on a cross section: a circle (linden, poplar), a tetrahedron (sage, mint), a trihedron (sedge), a polyhedron (valerian) or be flattened (opuntia cactus) and others.

Both aboveground and underground shoots can be modified, performing additional functions.

Rhizome - a modified underground shoot that looks like a root; differs from it in the presence of nodes and internodes, axillary buds and the absence of a root cap. The rhizome grows with an apex - the place where the apical bud is located. Every year, new above-ground shoots develop from the buds of the rhizome. The rhizome performs the functions of a reserve, reproduction and distribution of the plant, ensures survival in adverse environmental conditions (wheatgrass, thistle).

The bulb is a very shortened flat shoot-bottom with close succulent leaves. Adventitious roots extend from the bottom. The bulb of tulips, lilies, snowdrops, garlic, onions and other plants. The axillary buds change and turn into daughter bulbs. The bulb performs a reserve function, ensures the reproduction of plants and contributes to survival in an unfavorable period.

Stem tubers - thickening of one or more internodes of the stem. Such thickenings can be both underground (potatoes, Jerusalem artichoke) and aboveground (kohlrabi cabbage). They perform the functions of a supply of nutrients, reproduction, and the transfer of an unfavorable period.

Thorns - a modification of the above-ground shoot (thorn, wild pear, hawthorn). They protect the plant from eating, located in the axils of the leaves.

Stolons are elongated creeping shoots, often with scaly leaves. They live for one year and give rise to new individuals (nettle) such shoots in everyday life are called "mustache". Shoots can be modified into tendrils (grapes, pumpkin, melon, cucumber) - curly shoots, wrap around various supports and support the stem in a certain position (support function).

The most interesting science of botany tells about what surrounds us - trees, plants and flowers, about how these representatives of the plant world grow and develop.

Today we will consider the external structure of the shoot of a plant, find out what they are, what they consist of, what function they perform, and much more.

What is a plant shoot

The shoot is a stem with buds and leaves that has developed over the summer. It can perform many functions, the main of which is to provide air nutrition (in biology, the process of producing carbohydrates through photosynthesis).

The shoot has the greatest variability among all other elements of the plant.

Escape structure

Captions to the figure reveal the main elements of the structure of the shoot, adopted in botany.

• Stem serves as a support for the leaves, brings water to them from the roots. The stem also stores nutrient reserves;
• Bud. A complex organ, the germ of future leaves and inflorescences;
• Sinus. The angle formed by a stem and a leaf attached to it;
• Axillary kidney. It is located in the axil at the base of the leaf. Potentially may develop into an escape;
• Node. The area on a stem where a leaf grows from. In this place, a growth usually forms. The placement of the nodes is directly related to the location of the leaves on the stem. Distinguish opposite, whorled (annular) and regular leaf arrangement;
• Internode. Stem zone from one node to another.

Branching and tillering shoots

Branching - growth occurs from axillary buds. Repeating on each shoot, allows you to cover a large space for the development of foliage.

Tillering - new shoots grow only from the lower buds located at ground level. Thus, a bush is a set of shoots growing from a single root. Perennial bushes with a large number of densely spaced shoots are called turfs.

Shoot branching types

Different types of branching can be found in different groups of plants. All their diversity comes down to several main types: dichotomous, monopodial and sympodial:

• Dichotomous. The apical bud is divided in two, forming 2 new shoots. Common in ancient, primitive forms - algae, mosses and ferns;
• Monopodial. The apical bud serves exclusively for the growth of the shoot. Branching occurs as a result of the development of lateral axillary buds. Examples of monopoidal branching are widely represented in conifers;
• Sympodial. Similar to monopodial. One of the upper axillary buds sprouts, which deflects the main stem to the side. The cycle repeats, forming a wide branched crown. Modern higher plants, for the most part, belong to the sympodial type.

The structure of the kidneys

The bud is a dormant shoot germ, the internodes of which are greatly reduced.

Morphological differences in the kidneys are very significant:

1. Vegetative. The rudimentary stem, leaves and growth cone are covered with scales.
2. Generative. Future inflorescences dormant. They also have an embryonic shoot.
3. Mixed. Combines properties of vegetative and generative buds. It is typical for fruit trees - apple trees, plums, cherries.
4. Apical. Here there is an active division of cells, the growth of the shoot. Does not form leaves and inflorescences.
5. Axillary. Appears in nodes at the base of the leaf and potentially becomes a shoot.
6. Adnexal. It has a function similar to the axillary, but is laid in the internodes or the root system. For example, in home begonias, such buds form along the edges of the leaf.
7. Sleeping. Serves as a kind of reserve. Such buds are inactive for many years and bloom only if the apical bud is damaged. Common in temperate trees adapted to seasonal climate changes.
8. Renewal kidney. They appear at the end of the growing season, in autumn. They overwinter in a dormant state, in the spring they give new shoots.

Shoot modification

It emerged as a form of adaptation to the environment. There are several main types of modifications.

Modification of underground shoots

They are very similar to roots, but have specific features - nodes, modified colorless leaves and buds.

Modification of above-ground shoots

Thorns and mustaches are distinguished into a special form of shoots. They do not have defining features such as buds, but are always located in nodes and axils, which is typical for shoots.

Vegetative propagation of plants

With vegetative propagation, the daughter plant is formed from part of the old one. In biology, this kind of reproduction is called asexual. In artificial form, it is widely used by gardeners.

The table below schematically presents the main types of vegetative propagation.

Reproduction method	Picture	Description	Examples
natural
rhizomes		The old layer dies, the stem with adventitious roots becomes a daughter plant.	Wheat grass, lily of the valley, iris
bulbs		At the bottom, small onions are born, ready to become independent plants.	Narcissus, tulip, lily
mustache		A special shoot at the top of the tendril takes root and begins to develop.	Strawberry, ranunculus creeping
cuttings		In nature, a broken branch can take root.	willow, poplar
Root offspring		Special buds develop on the roots, from which a new plant begins.	Aspen, lilac, thistle
tubers		At the tuber, part of the kidneys turns into root-like stolons, where new tubers arise.	Potato
Leaves		At a broken leaf, under favorable conditions, an adnexal bud appears, giving life to the plant.	Violet
artificial
division		The bush or turf is divided, the divided parts develop into full-fledged bushes.	Iris, lilac, raspberry
layering		The branches bend down, sprinkle with earth. When the cutting takes root, it is separated and transplanted.	gooseberry, currant
Graft		The addition of a part of one plant to another.	Fruit bushes and trees

Conclusion

Nature is full of mysteries, and the unusual is nearby. Even children already know how potatoes reproduce, and experienced gardeners put their knowledge of shoot structure and plant reproduction into practice with might and main, growing currant bushes and getting a good harvest every year.

; 5 - leaf axil; 6 - axillary kidney; 7 - apical kidney.
B. 1 - apical kidney; 2 - renal rings; 3 - leaf scars; 4 - lateral kidneys.

The place of attachment of the base of the leaf to the stem is called the node, the angle between the petiole of the leaf and the stem is called the leaf axil, the bud located in the axil is called the axillary bud. The distance between two nodes is called an internode. Depending on the degree of development of internodes, there are short shoots - shoots with poorly developed short internodes, in which the nodes are very close together - for example, the fruits of an apple tree. Shortened shoots also include shoots bearing closely spaced leaves, called socket (at the dandelion).

Elongated shoots - shoots with long internodes. Elongated shoots may consist of one internode strongly elongated in length, ending in a flower or inflorescence. Such an escape is called a flower arrow (for onions, tulips).

On the run you can find kidney rings - traces of kidney scales and leaf scars - traces left on the stem after the leaves fall.

According to the nature of the location in space(Fig.) shoots are: erect, with a stem growing vertically upwards, rising - shoots, first growing in a horizontal and then vertical direction, creeping - growing more or less horizontally. Creeping shoots are similar to creeping ones, but unlike them, they take root with the help of adventitious roots formed at the nodes (strawberries). curly shoots are able to wrap around other plants or any supports (field bindweed, hops), climbing shoots have devices (antennae, suckers, hooks, etc.) for holding on supports or on other plants (peas, grapes, ivy).

Kidneys. In addition to leaves, buds are located on the stems. The kidney is a shortened rudimentary shoot. The kidneys may be (Fig. 18) vegetative , shoots with leaves develop from them, generative , from which flowers or inflorescences develop and vegetative-generative (mixed) from which leafy shoots with flowers develop.

Outside, the kidney is protected by kidney scales, which are modified leaves.

Inside the kidney is a rudimentary stem, ending with a growth cone and rudimentary leaves. In the axils of rudimentary leaves, the rudiments of axillary buds are laid.

Due apical buds located at the ends of the main and side shoots, the shoots are elongated. The apical bud, with the help of a special phytohormone (plant hormone), inhibits the development of lateral buds. From side, or axillary kidneys side shoots develop.

If a bud is formed on the adult parts of the stem, root and leaf, then such a bud is called adnexal .

Some kidneys remain unopened for many years. They are called sleeping kidneys . In case of damage to the plant, the buds "wake up", giving rise to new shoots. Shoots from dormant buds can be seen on the stump of a sawn tree or on the trunks of old trees.

Adventitious buds similar to small plants form on the leaves of some plants, they fall to the ground and develop into an adult plant (kalanchoe or bryophyllum). Such kidneys are called brood .

Development of an escape from the kidney. Branching. The development of a shoot from a bud begins with cell division of the growth cone, growth of leaf primordia, and growth of internodes. Kidney scales quickly dry out and fall off when the kidney expands. From the bases of the scales on the shoots, scars remain, the so-called kidney rings . They are located on the border of annual growth.

The growth of the shoot from the kidney is carried out due to the apical meristem - the cone of growth and due to the growth of the internodes of the kidney, intercalated meristems located in the nodes of the shoot. Shoots that grow from buds in one growing season are called annual shoots or annual increments .

Branching - the formation of a system of branched shoots. Due to branching, an increase in the surface of the plant occurs. branching shoot can be of two types (Fig. 19): apical - branching, in which the growth cone is divided into two - dichotomous (many multicellular algae, mosses, club mosses). Most plants are more common lateral branching type , at which lateral axes are formed on the main axis. The shoot system arises due to their development from lateral buds.

There are several types of lateral branching: monopodial - if the shoot grows indefinitely due to the same apical meristem, lateral shoots of the second order depart from the main stem, on which shoots of the third and higher orders are formed. Spruce and pine are typical for gymnosperms. But with the death of the apical bud, upward growth in such plants practically stops.

Fig.. Wheat tillering: 1 - grain; 2 - adventitious roots; 3 - side shoots.

If the apical meristem functions for a limited time (usually during one growing season) and for the next season the shoot is elongated due to the meristem of the nearest lateral bud, such lateral branching is called sympodial (birch, poplar). The ability for sympodial growth gives an advantage; if the apical bud is damaged, the lateral shoot takes over its function, and upward growth continues. A variant of sympodial branching is false dichotomous : the apical bud dies, and two oppositely located lateral buds form two apical shoots (horse chestnut, lilac).

A special type of branching - tillering . In this case, only at the base of the stem (in the tillering zone) lateral shoots are formed, branching occurs either underground or in the surface area (many cereals, shrubs).

The main and side shoots are built and grow in the same way. The main stem is called the axis of the first order, and the shoots developing from the axillary buds are called the axes of the second, third, etc. order.

Escapes can be non-branching if the lateral buds are underdeveloped and the growth is due to one or more apical buds (dracaena, yucca, aloe, palm trees).

Escape modifications. Escape modifications arise in connection with the acquisition of special, additional functions. There are many modifications, they are mainly adaptive in nature, associated with the accumulation of a supply of nutrients, vegetative propagation, protection from being eaten by animals, etc. There are above-ground and underground modifications of shoots (Fig. 20).

Aboveground modified shoots include stolons - shoots with long thin internodes and scaly, colorless, less often green leaves (creeping ranunculus). Short-lived, serve for vegetative reproduction and resettlement. Strawberry stolons are called mustaches.

spines shoot origin come out of the axils of the leaves and perform mainly a protective function. They can be simple, unbranched, like a hawthorn, and complex, branching, like a honey locust.

Mustache are also formed from a bud and develop in plants with a thin and weak stem that is not able to independently maintain a vertical position (watermelon, grapes).

Cladodia - lateral shoots with green flat long stems capable of unlimited growth and photosynthesis (asparagus), leaves are reduced to scales.

Phyllocladia - side shoots with green flat short stems (similar to leaves) with limited growth (needlebill). They form scaly leaves and inflorescences.

stem succulents - fleshy shoots of cacti, milkweeds. They perform water storage and assimilation functions. The stems are columnar, spherical or flat (they look like cakes). Arise in connection with the reduction or metamorphosis of the leaves.

Many plants develop short shoots , their internodes are very close together, flowers and fruits are formed on them - the fruits of an apple tree.

In a dandelion, the leaves of a shortened shoot form a basal rosette, the inflorescence is carried up flower arrow .

A modified escape is head of cabbage - a giant modified bud, develops in the first year, accumulates nutrients in the leaves. Blossoms, forms fruits and seeds the next year, dies off in autumn (cabbage is a biennial plant).

Flowers angiosperms and strobili gymnosperms - also modified shoots that perform the function of sexual reproduction.

Underground modified shoots. Rhizome - perennial underground shoot (lily of the valley, couch grass), performs the functions of renewal, vegetative reproduction and accumulation of nutrients. Outwardly, it resembles a root, but has apical and axillary buds, reduced leaves in the form of colorless scales. Nodes are detected by leaf scars and remnants of dry leaves, or by live scaly leaves. Adventitious roots develop from stem nodes. Spare nutrients are deposited in the stem part of the shoot.

Tuber - a modified shoot, performs a storage function, often serves for vegetative propagation. The tuber is a thickening of the underground shoot (potato). Tuber formation occurs at the top of the underground stolon, the apical bud of the stolon thickens, its axis grows. Small membranous scaly leaves quickly die off and fall off, and in their place leaf scars form - eyebrows. In the axil of each leaf, groups of three to five buds - eyes - appear in the recesses. The apical and lateral buds are arranged spirally on the tuber. On a cross section of a potato tuber, 4 layers can be found: bark, cambium, wood and core.

Bulb . It is a shortened, mainly underground shoot (onions, garlic, lilies). The stem part of the bulb (bottom) with strongly shortened internodes bears numerous succulent modified leaves - scales. The outer scales are quickly depleted, dry out and perform a protective function. Spare nutrients are deposited in juicy scales. In the axils of the bulbous scales there are buds from which above-ground shoots or new bulbs are formed. Adventitious roots form on the bottom.

Corm . It is a shortened shoot, outwardly similar to an onion (gladiolus). It is an intermediate form between a tuber and a bulb. The bulk of the corm is a thickened stem part, covered with scaly dry leaves. A corm is formed by the growth and thickening of one or more internodes. In fact, a corm is a leafy tuber. Nodes, internodes and axillary buds are clearly visible on the axis of the corm.

Key terms and concepts

1. Escape. 2. Kidney ring. 3. Leaf scars. 4. Annual growth. 5. Vegetative, generative, mixed, adnexal, brood, dormant buds. 6. Shoots: rising, creeping, creeping, climbing. 7. tillering. 8. Cladodia. 9. Phyllocladia. 10. Flower arrow.

Essential Review Questions

1. Escape structure.
2. The structure of the kidneys.
3. Apical branching of the shoot.
4. Types of lateral branches - monopodial, sympodial, false dichotomous.
5. Characteristics of above-ground modifications of shoots.
6. What is the difference between the mustache of peas and grapes?
7. What is the difference between the spines of a cactus, blackthorn, wild rose?
8. Characteristics of underground modifications of shoots.