Modified plant organs. Modifications of shoots Which organ is modified in onions

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 reproduction. 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.

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 reproduction.

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 function 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 with 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.

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.

In our article, we will get acquainted with such a modification of the root as the growth of the rhizome. This is an underground shoot that can easily be confused with a root. Let's look at the structural features and differences between these systems.

Escape modifications

The shoot is called the ground part of the plant, which consists of the axial part - the stem, and the lateral part - the leaves. It also contains rudimentary organs called kidneys. The shoot plays an important role in the life of the plant: it provides growth, vegetative reproduction and photosynthesis.

But for the implementation of additional functions, various organs are modified. The growth of the rhizome is one of the proofs of such metamorphoses. Escape modifications include kohlrabi stem tubers, leek, lily and tulip bulbs, thorn and wild pear thorns, melon and grape tendrils, strawberry and strawberry mustaches.

plant rhizome

The rhizome is a thickening of the shoot, located underground. Such a transformation is typical for couch grass, lily of the valley, crow's eye, gravel, hellebore, valerian, iris.

How to prove that the rhizome is really a shoot? Very simple. Rhizomes are structures that consist of a thickened stem. They can distinguish elongated internodes with axillary and apical buds. Leaves are absent, they are replaced by scales. Mineral nutrition, water supply and fixation in the soil are provided by bundles of adventitious roots.

Since the shoot develops underground, its color is not green, although its cells contain the green pigment chlorophyll. Its growth is due to the apical buds. Of these, ground shoots appear on the surface in spring. Remember what a lily of the valley looks like: the shoot is located underground, and on the surface we see only leaves and fragrant inflorescences.

How to distinguish a rhizome from a root

The root also develops underground, but has a number of distinctive features. Firstly, it provides the plant with minerals by absorbing their aqueous solution from the soil. Rhizomes are shoots, so they cannot perform this function. They only accumulate nutrients, ensuring the viability and development of plants in unfavorable periods.

Another difference is the absence of chloroplasts in root cells. Therefore, it is not capable of photosynthesis. In addition, buds and leaves do not develop on the root.

Rhizome Functions

Elongated and thickened internodes serve to adapt plants to drought and cold conditions. Most often they develop in perennial species. During the period of intensive growth and development, they accumulate a significant supply of water and inorganic substances. This is a necessary condition for the normal functioning and development of the aerial part. With the onset of autumn, the leaves die off, and the plant continues to live underground.

Rhizomes are often used for vegetative propagation of some cultivated species. They allow you to create a large amount of planting material. Since many rhizomes are of considerable length, they provide anchorage in sandy soil.

But any modifications have a negative side. The fact is that developed rhizomes are characteristic of many weeds, so it is difficult to deal with them. Their examples are wheatgrass and sow thistle. By pulling out their leaves or individual internodes, you leave most of the shoot in the soil, so after a certain time the ground part begins to develop again.

So, the rhizome is a modification of the shoot that develops underground. Its main functions are the supply of water with a solution of minerals and vegetative reproduction of plants.

Underground shoots, like aboveground ones, are modified, adapting to environmental conditions. Roots can also often take on an unusual appearance.

Shoot modifications

Some plants have underground shoots. An underground shoot differs from a root in the preservation of signs. Like any shoot, the underground one has nodes and internodes, and on the nodes there are leaves (even if they are small and colorless). In the axils of the leaves of the underground shoot there are lateral buds, and on its top - the apical bud.

There are three main types of underground shoots: rhizome, tuber and bulb.

Rhizome outwardly resembles. Adventitious roots grow from it, and above-ground shoots develop from the apical or axillary buds in spring. The rhizome has lily of the valley, coltsfoot, couch grass, nettle.

Tuber- this is the apical thickening of underground shoots (stolons), in which starch is stored. On the surface of the tuber in the recesses there are 2-3 buds, called "eyes". There are more of them at the top of the tuber. Tubers are formed in earthen pears, potatoes.

Bulb- this is a shoot with a very short flat stem, called the "bottom" and succulent with a supply of nutrients, called scales. The outer scales of the bulb are usually leathery. Above-ground green leaves and an arrow develop from the upper kidney of the donets. Bulbs are formed in onions, tulips, daffodils. Most bulbous plants live in the steppes, where in a short wet period they have time to develop green leaves, bloom and form a fruit due to reserve substances in the scales.

Root modifications

Root modifications are very diverse. In some plants, reserve nutrients are deposited in the roots. Such roots grow strongly in thickness and acquire an unusual appearance. If reserve substances accumulate in the main root, root crops are formed. If reserve substances accumulate not in the main, but in adventitious roots, then root tubers are formed.

On swampy, oxygen-poor soils in the tropics, trees form respiratory roots. They rise above the soil surface and supply the underground organs with air through special holes.

Trees growing along the seashores develop stilted roots. They perform a supporting function, help the trees to maintain stability on shaky ground.