The shoot is one of the main vegetative organs of higher plants. It consists of a stem on which buds and leaves are placed. The shoot is the most variable in appearance structural element of the plant.

The aerial part of the plant is a shoot or shoot system.

The shoot consists of a stem (axis) and leaves and buds located on it. The place where the leaf is attached to the stem is called a node, and the area between two adjacent nodes is called an internode. The angle between the stem and the leaf is called the leaf axil. The shoot develops from the kidney.

A bud is a rudimentary shoot with very short internodes. The central part in the kidney is occupied by the embryonic stem, at the top of which there is a growth cone, which is an educational tissue. On the stem are rudimentary leaves. Outside, the kidney is covered with bud scales that can protect the embryonic leaves and the growth cone from adverse environmental conditions. To perform a protective function, thick pubescence is formed in the kidney scales, resinous substances are released, etc. A modified shoot is a plant organ in which the shape and function of the stem, buds and leaves are irreversibly changed in the process of evolutionary adaptations to certain conditions of the organism's existence. In cultivated plants, the modification of the shoot is due to human intervention.

Shoot metamorphoses can be both insignificant and significant - up to highly modified plant forms. Both the main and side shoots, as well as buds and leaves, undergo metamorphoses.

The main types of shoots of green plants are aboveground and underground. Above-ground (air) shoots are assimilating, along the axis of which the leaves are located. Assimilation shoots are very diverse in appearance. In many cases, in addition to the main function of photosynthesis, such shoots play the role of a storage and supporting plant organ, as well as the function of vegetative reproduction.

Shoot modifications
Name	Functions	Plant
Rhizome (formed underground or when the shoot is pulled into the soil)	Stock of substances, reproduction, resettlement	Sow thistle, anemone, backache, marigold,
Caudex (a thickened main shoot that turns into a taproot. When the plant ages, it dies off, starting from the center.)	Stock of substances	Bathing suit, asparagus, lungwort, raven's eye, minnik, wheatgrass, hoof, amazing violet, strawberry, cuff, iris, lingonberry, gravel, batun onion, blueberry, lily of the valley
Whiskers (thin shoots with scaly leaves and rosettes in internodes)
Tuber (formed at the ends of underground stolon shoots)	Reproduction and resettlement	Strawberries, cinquefoil, goose, sedumnik, stone fruit
Corm	Stock of substances and reproduction	Gladiolus, corydalis
Bulb	Stock of substances and reproduction	Onion, lily-saranka, tulip, narcissus, hazel grouse
succulent shoots	Water supply	cacti, spurge
Spines (located in the axils of the leaves, and when they fall over the leaf scar)		Hawthorn, apple tree
Phyllocladia (leaf-like shoots)	Photosynthesis	Asparagus, needle
Cladodia (flat photosynthetic shoots)	Photosynthesis	Phyllocactus, horsetails, zygocactus, horsetails
	Support attachment	Pumpkin, cucumber, hops

Modifications of above-ground shoots

Modified shoots are those that perform some additional functions: protection, climbing, storage of nutrients, etc. Modified shoots include thorns, tendrils, tubers, succulent shoots, stolons, shoots of insectivorous plants. Spines are needle-like structures that protect the plant from being eaten by animals. Spines can be formed from a leaf (barberry), stipules (yellow acacia), shoots (sea buckthorn, hawthorn). Antennae - filiform axillary shoots (grapes, cucumber), which perform a supporting function. In peas, part of the leaf turns into antennae. A tuber is a thickened shoot that performs the function of a supply of nutrients (kohlrabi cabbage - approx. biofile.ru). Stolons (common name - "whiskers") - horizontal creeping shoots that contribute to the reproduction of the plant. Rosettes with adventitious roots are located on each stolon. After the rooting of the outlet, the horizontal shoot dies off (strawberries, creeping tenacity).

Succulent shoots - the adaptation of plants to a hot and dry climate. Their function is to store moisture. Water can accumulate in the leaves (stonecrop, young, aloe) or in the stem (euphorbia, cactus). Mexican cacti have fleshy stems of a wide variety of shapes: ribbed balls, columns, cylinders, even candelabra and tortillas. Cacti do not have green leaves: they have turned into bunches of thorns. The function of photosynthesis is performed by the stems.

Underground modified shoots.

Stolons and tubers can be both aboveground and underground. In addition to them, underground shoots include rhizome and bulb. The underground stolons perform the same functions as the aboveground stolons - the resettlement and reproduction of the plant. This explains the similarity in their structure. Tuber. This shoot has a short and thick stem. Leaves-scales quickly die off and scars remain in their place (in potatoes, they are popularly called “eyebrows”). In their sinuses are the kidneys "eyes". The tuber performs the function of a supply of nutrients (for example, starch), experiencing an unfavorable season and reproduction. Not only potatoes have tubers, but also Jerusalem artichoke, Corydalis. They appear on underground stolons. The rhizome outwardly often looks like a root, but the rhizome also has scaly leaves, and in their axils there are lateral buds, at the top there are apical buds. Adventitious roots form on the rhizome. Unlike the stolon, the rhizome is a perennial shoot that allows the plant to survive adverse conditions. This underground shoot is characteristic of many plants and can perform a variety of functions. In thick short rhizomes of iris, nutrients are stored. In creeping couch grass, mouse pea, lily of the valley May rhizomes are long and thin. They are able not only to store nutrients, but also to capture new territories. The rhizome not only grows rapidly in length (for a butterbur, it is 1.5 meters per year, for a coltsfoot - per meter - approx. biofile.ru), but also branches. As a result, the mother plant may break up into several daughter plants. Rural residents know how difficult it is to deal with long-rhizome weeds: wheatgrass, goutweed, coltsfoot. Sea buckthorn, wild rose, raspberries grow rapidly. Bulb - a strongly shortened modified shoot with a flat stem - "bottom", with leaves in the form of scales. The scales can be juicy (reserve) or dry coverts), can be narrow and only slightly cover each other (lily) or wrap around each other almost completely (hyacinth, tulip, onion). The bulb allows the plant to survive the unfavorable period of the year. Axillary buds can turn into bulbs - babies. Therefore, the bulb is also a breeding shoot. In colchicum, gladiolus, the underground shoot is called a corm. Outwardly, the corm resembles an onion, but differs from it in a strongly overgrown bottom, to which scaly small leaves are attached, and serves as an organ for the accumulation of reserve nutrients. In the corm, the apical and axillary buds are well developed, giving rise to a flowering shoot and child corms.

VEGETATIVE REPRODUCTION, the formation of a new organism from a part of the mother; one of the ways of asexual reproduction of multicellular organisms. In lower plants (for example, algae) it is more often carried out by division, in fungi - by budding (for example, in yeasts, some basidiomycetes) or parts of the mycelium (for example, in cap mushrooms), in higher plants - by parts of vegetative organs ( root, stem, leaf), but more often their altered forms - rhizomes (couch grass, pigweed, etc.), tubers (potatoes, dahlias, etc.), bulbs (onions, tulips, etc.), root suckers (raspberries, cherries, plums, etc.), mustaches (strawberries, wild strawberries), etc. It is characteristic of almost all perennial plants (based on their ability to regenerate). The vegetative offspring of one individual is called a clone. Artificial methods of vegetative propagation include all natural ones, as well as reproduction cuttings(currant, sea buckthorn, grapes, aloe, begonias, etc.), vaccination cuttings and bud (pear, apple, rose, lilac, etc.), layering(currant, hazelnut, etc.). Vegetative propagation of cultivated plants has been used for many centuries. In modern practice, effective methods of tissue culture (micropropagation) are used. Clonal micropropagation is based on obtaining planting material from cells of the apical meristem (shoot tips). This method makes it possible to obtain several thousand plants from one plant during the year, which have the characteristics of the mother and are free from viral and other infections. Thus, planting material of vegetable, fruit and ornamental plants is obtained. In animals, vegetative reproduction is carried out either by fragmentation - separation of body parts from the mother's body, which then complete building themselves up to the whole organism, or by budding. When budding, an outgrowth (bud) is formed on the mother's organism, from which a new individual develops. Vegetative reproduction is characteristic of some worms, sponges, coelenterates, and tunicates.

Rhizome - underground shoot of perennial grasses, shrubs and shrubs. Outwardly, the rhizome is similar to the root, but differs from it in its horizontal location in the soil, the presence of scaly leaves, scars from fallen buds and adventitious roots. An apical bud develops at the top of the rhizome, and axillary buds develop in the axils of the scales. From the buds of the rhizome, above-ground shoots develop annually, dying off in the fall. The internal structure of the rhizome is typically stem. Most often, the rhizome is an organ of vegetative reproduction, and in a number of plants (water lily, lily of the valley) it serves as a storage place for nutrients.

Tuber a modified shoot with a strongly thickened stem in which nutrients are stored. They appear as thickenings on a thin underground shoot - a stolon. The place of attachment of the tuber to the stolon is called its base. The tuber has apical and lateral buds - eyes. Tubers are formed in plants such as potatoes, Jerusalem artichoke. They perform a storage function and are organs of vegetative reproduction.

Bulb- a shortened underground shoot with succulent leaves attached to a short stem - bottom. At the top of the bottom there is an apical bud, in the axils of juicy scales - lateral buds, giving rise to young baby bulbs. Juicy scales store reserve nutrients. Outside, the bulb is often covered with dry scales that play a protective role. Bulbs are formed in onions, lilies, garlic, tulips.

Corm outwardly similar to an onion, but differs from it in a strongly overgrown bottom, where nutrients are stored. From above it is covered with dry membranous leaves. In the corm, apical and axillary buds are well developed, giving rise to a flowering shoot and baby corms. Corms are formed in colchicum, gladiolus, saffron.

Fig.27. A-rhizome: 1-lily of the valley, 2-couch grass; B-potato tubers, B-bulbs: 1-onion, 2-lily-saranka, 3-tulip; G-crocus corm.

Sheet

A leaf is a lateral vegetative organ growing from a stem, having bilateral symmetry and a growth zone at the base. The main functions of the sheet:

Photosynthesis;

Gas exchange;

transpiration;

Depot of reserve nutrients;

Organ of vegetative reproduction.

The leaves of most plants have a petiole and a leaf blade. Leaves that do not have a petiole are called sessile.

Leaves are simple and complex. Simple leaves have one leaf plate. A compound leaf consists of several leaf blades attached to a common petiole with the help of their own petioles.

Fig.28. The leaves are simple and compound: 1-lilac, 2-apple, 3-maple, 4-clover, 5-dandelion, 6-wild rose, 7-raspberry, 8-strawberry, 9-lupine.

The leaves are arranged on the stem in a certain order. leaf arrangement there are three types: another - in the stem node there are one leaf each (birch, poplar); opposite - two sheets depart from the node, located opposite each other (maple, lilac); whorled - at least three leaves depart from the node (bamboo).

Fig.29. Leaf arrangement: 1- next; 2-opposite; 3- whorled

In addition, the leaves differ in type venation. Veins - these are vascular fibrous bundles, clearly visible on the leaf blade. They perform mechanical and conductive functions. There are three main types of venation: reticulate, parallel and arcuate. Reticulate venation subdivided into pinnate: smaller ones (oak, aspen) depart from the main vein; and palmate: the main veins depart from the base of the leaf blade (maple). Such venation is more common in dicotyledonous plants. For monocotyledonous plants, it is more characteristic parallel venation: veins are parallel to each other (wheat, corn); and arc - the veins are arranged in the form of arcs (lily of the valley).

The internal structure of the leaf corresponds to the performance of their main functions. Both sides of the sheet are covered skinned (epidermis), the cells of which are colorless and transparent, which contributes to the transmission of light to the main tissues of the leaf. The outer skin cells, especially on the upper side of the leaf, are thickened and covered with a layer of wax or a waxy substance, which protects the leaf from overheating and excessive evaporation of water. This is facilitated by the immersion of the stomata deep into the leaf, various types of pubescence. Among the colorless

Fig.30. The inner skin cells contain paired bean-shaped cells,

leaf structure containing chloroplasts, between which there is a gap. This

stomata , and the gap between them is called stomatal gap . There are 40-300 stomata per 1 sq. mm of a leaf, and sometimes more. Through stomata, gas exchange is carried out during photosynthesis and respiration, and stomata also regulate the process of evaporation of water by leaves. (transpiration). Under the skin is leaf pulp (mesophyll). She is educated basic a tissue that is photosynthetic and is represented by two types of cells. Under the upper epidermis is one or two layers columnar or palisade parenchyma. Its cells are filled with chloroplasts, tightly adjacent to each other. The main function is photosynthesis. Below is a loose (spongy) parenchyma. Its cells are arranged randomly, they have fewer chloroplasts, many large intercellular spaces. Spongy parenchyma, in addition to photosynthesis, is involved in gas exchange and transpiration.

Conductive fabric sheet is presented veins or vascular fibrous bundles. Their vessels conduct water and mineral salts, and sieve tubes conduct organic substances. The mechanical fibers of the veins give the leaves strength.

When the leaves perform additional functions and under the influence of environmental conditions, leaf modifications. It can be:

- leaf spines (cactus, barberry) - perform a protective function;

- antennae (legumes) - perform a mechanical function, supporting the stem;

- fleshy leaves (aloe) - accumulate and retain moisture;

- hunting leaves (dew, flycatcher) - capture insects and digest them.

With the onset of autumn, the processes of photosynthesis and evaporation slow down in the leaves. The leaves "age" and become ballast for the plant. Aging is associated with the accumulation in their cells of a large amount of minerals and metabolic products. Therefore, dropping leaves has a healing value for plants. In autumn, the leaves change color, which is associated with the destruction of chlorophyll. The necrosis of the leaves leads to the formation of a separating layer at the base of the petiole and their fall. Leaf fall is a natural physiological phenomenon in plants, which reduces the evaporation of moisture in autumn and winter, when the roots absorb water worse. Fallen leaves are a good organic fertilizer, in addition, they protect the roots from freezing. Plants that shed their leaves for the winter are called deciduous.

The escape is one of the main vegetative organs of higher plants. It consists of a stem on which buds and leaves are placed. The shoot is the most variable in appearance structural element of the plant. Modified Escape is a plant organ in which the shape and function of the stem, buds and leaves are irreversibly changed in the process of evolutionary adaptations to certain conditions of the organism's existence. In cultivated plants, the modification of the shoot is due to human intervention.

Shoot metamorphoses can be both insignificant and significant - up to highly modified plant forms. Both the main and side shoots, as well as buds and leaves, undergo metamorphoses.

The main types of shoots of green plants - aboveground and underground. Above-ground (air) shoots are assimilating, along the axis of which the leaves are located. Assimilation shoots are very diverse in appearance. In many cases, in addition to the main function of photosynthesis, such shoots play the role of a storage and supporting plant organ, as well as the function of vegetative propagation.

To modifications of above-ground shoots include spines, antennae, cladodes, phylloclades. In some cases, the plant does not modify the entire shoot, but only its leaves, and the metamorphoses are outwardly similar to those of the shoot as a whole (antennae, spines).

The thorn is a lignified shortened shoot without leaves with a sharp top. The role of spines originating from shoots is mainly protective. Such thorns are in the wild apple tree, laxative buckthorn, wild pear. In honey locust, thick, branched spines appear on trunks from dormant buds. The spines of the hawthorn also form from the axillary buds of the leaves and are found where other plants have lateral shoots.

A tendril is a shoot of a metameric structure without leaves, having a flagellate shape with or without branches. Due to the presence of stem tendrils, the plant receives additional support. The straightened section of the antennae without branching is the first internode of the axillary shoot, and the twisted, thinner section is a modified leaf. Antennae develop in plants that are unable to stand upright on their own. The blue passion flower, grapes, many members of the Pumpkin family (pumpkin, watermelon, melon, cucumber) have antennae.

Cladodium is a modified lateral shoot that is capable of continuous growth and has green flattened long stems that take on the functions of leaves. Cladodium performs the function of photosynthesis, since well-developed chlorophyll-bearing cells are located under the epidermis. The group of plants with cladodia includes the Decembrist cactus, prickly pear, Mühlenbeckia flat-flowered, southern carmichelia.

Phyllocladium is a modified flat, leaf-like lateral shoot that has limited growth and acts as a leaf in the life of the plant. The lateral buds of the shoot give rise to phylloclades, and therefore, phylloclades are always located in the axils of small scaly or membranous leaves. Such modified shoots perform the function of photosynthesis, so they look like leaves. Their growth is limited, and there is no metameric structure of the structure. Phyllocladia are inherent in such plants as phyllanthus, swept away, butcher's needle, some representatives of the Asparagus genus.

Modified underground shoots- these are rhizome, caudex, bulb, corm, underground tuber and stolon. The conditions for the existence of shoots located underground are very different from the terrestrial environment. Therefore, they have other important functions, such as the ability to endure an unfavorable period of life, the deposition of nutrients in the reserve, the possibility of vegetative propagation.

Rhizome (rhizome) is an underground shoot with scaly leaves, adventitious roots and buds. The rhizomes of wheatgrass are thick and branched. Kupena and iris have short and fleshy rhizomes, while water lilies and pods have the thickest of all plants.

caudex is a perennial structure originating from the shoot, characteristic of perennial grasses and subshrubs with a tap root system. Caudex, along with the root, is a place of accumulation of reserve nutrients and has many buds on it. Plants that have caudex are lupins and alfalfa from Legumes, femur and ferula from Umbelliferae, dandelion, wormwood from Compositae.

Bulb- This is a specialized underground shortened shoot. In it, organic substances are stored in scales of leaf origin, the stem in the bulb is transformed into the bottom. Bulbs are used for vegetative propagation. Bulbs are formed in monocotyledons of the Amaryllis family (hyacinth, narcissus), the Lily family (onion, tulip, lily), less often in dicotyledonous plants.

Corm- also a modified underground shoot that has a thickened stem where nutrients are stored, adventitious roots growing on the lower surface of the corm, and a protective cover of dried leaf bases. Corms are typical for saffron, gladiolus, ixia, colchicum.

underground stolon is a one-year long underground shoot. This thin shoot with underdeveloped scaly leaves has a tuber or bulb at the thickened end with a supply of organic matter. Underground stolons are formed in potatoes, adoxas, and septenaries.

underground tuber- a modified underground shoot, in which the storage function comes to the fore. This shoot has scale-like leaves that fall off quickly and buds located in the axils of the leaves.

Modified shoots, in comparison with traditional above-ground organs of plants, are able to perform additional functions. What structural features make this possible?

Features of the structure of the shoot

The shoot is the above ground part of the plant. Its base is the stem. This is the axial part of the shoot, on which the leaves and buds are located. Depending on the location in space, erect, creeping, curly, creeping, clinging shoots are distinguished.

The places where the leaves attach to the stem are called nodes, and the distance between them is called an internode. On the shoot are also rudimentary organs called kidneys. If leaves develop from them, they are vegetative, and if flowers are generative.

Escape functions

The aboveground organ of plants performs the function of vegetative propagation. During this process, a multicellular part is split off from the whole organism, due to which its integrity is restored.

The shoot plays an important role in the implementation of growth and regeneration. Due to the presence of chloroplasts in the cells of green plastids, the leaf provides the plant with organic substances that are synthesized during photosynthesis. The resulting carbohydrates are used to carry out various life processes.

Modified underground shoots

But to perform additional functions, typical structural features are not enough. Therefore, modified shoots are often found in nature. Due to the formation of various thickenings and changes in shape, they can store water and nutrients, ensure the viability of plants in an unfavorable period, and occupy an advantageous position in space.

Modifications or metamorphoses of the shoot can develop in the soil or be above ground. The first group includes tubers, bulbs and rhizomes. Above-ground modifications of the shoot are mustaches, antennae, spines. Let's consider their structure in more detail.

Bulb

Well-known onions and garlic are also an underground modification of the shoot. At its base is a flat stem, which is called the bottom. Vegetative buds develop on it, from which leaves are formed. They are of three types:

• membranous;
• juicy;
• young.

Leaves of the first type will perform the main function of the bulb. They store water with mineral solutions. Dry membranous leaves are a protection against mechanical damage and adverse conditions. Young leaves grow from the vegetative buds of the donets, which are often called green onions.

Bulbous plants underground tolerate drought and frost. So, for example, tulips, crocuses, lilies grow and fade during the wet and warm season, after which young bulbs form underground. They are usually dug up after flowering, stored in a cool place, and seated at the end of summer.

Why is a tuber a modified shoot?

Many modified shoots grow underground. For example, potato or Jerusalem artichoke tubers. Therefore, they are often confused with another vegetative organ of plants - the root. It is very easy to prove that a tuber is a modified shoot. Its thickened part is the stem. It accumulates the reserve carbohydrate of plants starch. The covering tissue of this shoot is the bark. We cut it when we "peel potatoes". Another proof is the presence of kidneys. They are called eyes. In the spring, young shoots develop from them.

Rhizome

The rhizome is a modified shoot, which is also located underground. Despite the name, it has nothing to do with the underground plant organ. The rhizome consists of elongated internodes, on which vegetative buds develop. Leaves develop from them in spring. Soil nutrition is carried out by a fibrous root system, which grows in bunches.

If you've ever tried to get rid of the nasty wheatgrass weed, you know that it can be quite difficult to do so. Often, tearing leaves out of the soil, we leave the shoot itself with viable vegetative buds, so after a certain time they appear again. The presence of a rhizome is typical for lily of the valley, kupena, mint, irises, asparagus.

Mustache and moustache

And these above-ground modified shoots are often confused with each other because of similar names. In fact, they have different origins, and therefore functions. Mustaches, or stolons, are found in strawberries, strawberries, chlorophytum, saxifrage. Most often, these are creeping shoots with elongated internodes and a system of adventitious roots. They develop simple leaves. These structures are able to take root and give rise to a new organism. This is how they reproduce sexually.

Antennae are formed in grapes, ranks, peas, beans. They can develop from a stem or leaves. They help climbing plants hold onto a support. As it grows, the antennae, like a spiral, twist around various objects. As a rule, if such structures do not come into contact with the support, they dry out and die.

Claudius

Almost every lover of indoor flowers has a zygocactus ("Decembrist") growing in their house. His escape is called the cladode. This modification is a flattened stem that acts as a leaf. This is manifested in the fact that the cladodium carries out photosynthesis. Stem origin proves the formation of flowers on it, which never form on leaves. The same modified shoots are found in prickly pear, asparagus, and smilax.

The meaning of escape modifications

Metamorphoses of vegetative organs significantly increase the adaptive capacity of plants. Modified shoots perform additional functions in the plant body in the form of maintaining a reserve of substances and providing an additional method of vegetative propagation.

Thanks to them, a person receives a large amount of planting material. We eat potato tubers, leeks and garlic, which are rich in carbohydrates, biologically active substances and vitamins. Medicinal infusions are prepared from the rhizomes of valerian and lily of the valley.

The most common modified shoots in nature are bulbs, tubers, mustaches, tendrils and rhizomes.

They amaze with their diversity and originality. But environmental conditions often require new adaptations from representatives of this kingdom. Modified shoots are able to perform additional functions. Thus, they provide a higher viability of organisms.

Modifications of underground shoots

These metamorphoses may be above ground or underground. Modified underground shoots are the most common and widely represented in nature.

One of them is the rhizome. Both in name and in appearance, it resembles a root. But, unlike the underground organ, it consists of elongated internodes and nodes. Adnexal buds are located on the stem of the rhizome, from which, with the onset of favorable conditions, leaves grow. The nodes are also located. The elongated horizontal stem is located underground, where temperature changes and drought have less effect on the vital activity of the plant. And the supply of water and nutrients greatly increases the chances of the plant organism to survive.

Many are faced with a situation where you need to get rid of the annoying couch grass, overgrown lilies of the valley or other plants with rhizomes. It is not so easy to do this. Modified shoots grow strongly, their parts often remain in the ground, forming new shoots. But, on the other hand, this ability is often used for vegetative propagation of plants.

Tuber

A tuber is a modified shoot, which is also underground and stores. Everyone knows that they are of great economic importance. They accumulate large amounts of starch.

Some mistakenly consider this modified shoot to be a fruit. In fact, potato fruits are formed on above-ground shoots after flowering. The tuber is a thickened stem with apical and lateral buds - eyes. Growing, the eyes form young shoots.

Elongated oblong and short-lived shoots are also called stolons.

Plants such as saffron and gladiolus have a corm - a thickened stem with adventitious roots. The layer of dead leaves protects the inner contents of the corm.

Bulb

Onion, garlic, tulip and lily have another modification - the bulb. On a flat stem, which is called the bottom, are the kidneys. Several types of scaly leaves develop from them. Some of them are thick and fleshy. They store water with nutrients, providing life to the plant. From above they are protected by dry membranous leaves. From the bottom grow young onion leaves, the so-called green onions. Bulbs are also typical for plants of the steppe natural zone. In conditions of cold winters with little snow and hot dry summers, this modification makes it possible for the plant underground to survive an unfavorable period in this form.

Above-ground modifications of shoots

Modified shoots of plants can also be above the ground. So, on the branches of hawthorn and blackthorn there are thorns - shortened and lignified modified shoots. They are the result of branching and sharpening of the stem, reliably protecting their owners from being eaten by animals. Plants with thorns have tasty, juicy fruits with bright colors, so they just need additional protection.

Strawberries and wild strawberries have an additional device for vegetative propagation - elongated mustache shoots. They are fixed in the soil, forming a new plant.

Mustaches should not be confused with tendrils of grapes. They have a completely different functionality. With the help of tendrils, the plant is attached to the support, occupying the most advantageous position in relation to the sun. Such a device is also characteristic of pumpkin, cucumber, watermelon.

Modifications of shoots in the direction of growth

Depending on the growing conditions, the shoots can also be modified. In woody and herbaceous plants, erect stems are most often found, directed towards the sun. Creeping and creeping stems grow very quickly, cover the surface of the soil with shoots with leaves. This provides them with a prosperous existence. Plants with climbing stems are called vines. They are typical for tropical and humid equatorial forests, although they are often found in the temperate zone. For fastening to a support, creepers use special devices: hooks, trailers, bristles.

Internal structure of shoot modifications

Despite external differences, various modifications retain all the features of the internal structure. For example, a potato tuber, being a thickened stem, is covered with bark on top. This is what we peel off when we peel potatoes. On the longitudinal section of the tuber, a dark strip is clearly visible - wood. And in the core, loose basic tissue, reserve nutrients are actively deposited.

If potato tubers are left in the light for a long time, they will begin to turn green. This indicates that the colorless plastids leukoplasts, in which starch accumulates, turn into green plastids chloroplasts in the light. Such a product should not be eaten, since it contains the alkaloid solanine, poisonous to the body, which causes poisoning.

Functions of modified shoots

It is the modified shoots that determine the survival of plants in adverse conditions. By storing valuable nutrients, they allow plants to survive during periods of drought. Biennial and perennial plants survive only thanks to the presence of bulbs and rhizomes. Their leaves, which appear on the surface in spring and develop all summer, die off with the onset of cold autumn. And the underground part lives, feeding on stocks of thickened stems. With the onset of heat, the plant resumes growth again.

Many modifications of the shoot serve for vegetative reproduction, quickly increasing the number of valuable plants. This property is actively used by man in agriculture.

Flower origin

A flower is a modified shoot. It is very easy to prove this fact. It develops from a specialized generative kidney. This part of the shoot acquires characteristic features to perform the most important additional function - the sexual reproduction of plants. That's what a flower is for. The modified shoot is significantly shortened compared to ordinary stems. Its main parts are in which the sex cells are located - sperm and egg, respectively. The bright color of the flower petals is needed to attract pollinating insects. Small flowers are collected in groups - inflorescences. So they are much more noticeable, and their aroma spreads more strongly.

After pollination and fertilization, a fruit is formed in place of the flower. It consists of seeds and pericarp. Seeds give rise to a new plant, and the pericarp nourishes and warms them.

In addition, a flower is a modified shoot that has been giving people aesthetic pleasure for many centuries, inspiring poets and musicians.

Modified shoots are one of the main adaptations of higher plants to environmental conditions. In the process of evolution, they appeared to increase the viability of plant organisms due to the need for the emergence of new functions in constantly changing living conditions.