What roots grow from the bottom of the bulb. Practical work “The structure of the bulb. The root system of different types of onions

Plant seeds usually germinate when they fall into the ground at some depth. The very first shoot growing from the bud of the embryo must break through the soil. The first adventitious roots usually grow on this underground part of the stem. They can pull the base of the stem into the soil even deeper than it was originally immersed. Unlike rhizomes and tubers, bulbs have well developed leaves and a very short and flat stem. It is called "donets".

At the top of the bottom, under the cover of scales, there is a bud, from which an above-ground shoot grows. From the axillary buds located below the apical, new "daughter" bulbs are formed. From each daughter bulb - "kids" a new plant can grow.

What to do. Consider external structure bulbs.

• What is the outside of the bulb covered with?
• What does it matter?

What to do. Slice the onion lengthwise with a paring knife.

What to watch. Examine closely pressed to each other juicy scales - leaves.

How are inner scales different from outer ones?

What to do. Find and examine the bottom stem, apical and lateral buds.

What to do. Consider the roots growing from the bottom.

• What are these roots called?
• What root system do they form?

Prepare for a report. Draw a longitudinal section of the bulb and label its parts. Write down signs showing that the bulb is a shoot.

>>Rhizome, tuber, bulb

§ 37. Rhizome, tuber, bulb

Peculiar underground pantries have perennial herbaceous plants. The above-ground parts of these plants die off annually by autumn. AT soil roots and modified underground shoots remain. They don't look like regular overhead ones. It is in these modified shoots that reserves of organic matter are deposited for the winter. Modified shoots are rhizomes, tubers and bulbs.

The rhizome is found in nettle, couch grass, iris, lily of the valley, houseplant aspidistra.

If you dig the rhizome of any plant out of the ground, you can see that outwardly it resembles root. But the rhizome, like above-ground shoots, has apical and axillary buds, as well as membranous scales - modified leaves. Adventitious roots grow from the rhizome 72. From the apical or axillary buds of the rhizome, young above-ground shoots develop in spring. At the same time, they use the nutrients deposited in the rhizome in autumn. If a piece of rhizome with a bud and adventitious roots is planted in the soil, a new, independently existing plant. Some perennial ornamental plants propagate by dividing the rhizome into parts.

Tubers are characteristic of a few plants, for example, for potatoes. Underground shoots, on the tops of which tubers develop, grow from the bases of above-ground stems; these shoots are called stolons. Tubers are apical thickenings of stolons 73 . The tuber has short internodes; it does not contain chlorophyll, but when exposed to light, it can turn green.

Consider a potato tuber.

On its surface, in depressions of 2-3, there are buds, or eyes. There are more eyes on that part of the tuber, which is called the top. The opposite side - the base - the tuber is connected to the stolon. The structure of the potato tuber convinces that the tuber is a modified underground shoot 74 .

Organic matter constantly flows from potato leaves through the stems into stolons and in the form starch deposited at the top.

The tops of stolons grow, thicken and turn into large tubers by autumn. Cut a tuber and put a drop of a weak iodine solution on it. You will make sure that there is starch in the tuber.

Tubers have some wild plants, for example, Corydalis and Jerusalem artichoke fodder plant.

In the lower part of the onion bulb there is an almost flat stem - the bottom.

On the bottom are modified leaves - scales. The outer scales are dry, leathery, while the inner scales are fleshy and juicy. They contain water reserves, as well as sugar and other substances dissolved in it. Buds located in the axils of scales 75 are visible on the bottom. Thus, the bulb is a modified shoot.

If the bulb is planted in the ground, a fibrous root system grows from the underside of the bottom. Sometimes young bulbs, called children, develop from the kidneys. An independent plant can grow from each bulb of a baby.

Bulbs form onions, lilies, tulips, daffodils, wild goose onions. All of them are perennial.

1. What modified underground shoots do you know? Name plants that have a rhizome, tuber, bulb 72, 73.
2. How to distinguish a rhizome from a root?
3. How does a potato tuber develop?
4. Why should a potato tuber be considered a shoot?
5. What is the structure of the bulb?
6. How to prove that the rhizome and bulb are a modified shoot?

1. Place an onion bulb in a jar with a narrow neck so that the bulb does not fall through, but only touches the bottom of the water poured into the jar. After a few days, the bulb will develop adventitious roots and green leaves. Why does the bulb grow, although it is not in the soil, but in the water?

2. With the onset of warm spring weather, watch the flowering of wild bulbous and rhizomatous plants. 3. Watch the development of woody shoots and sprouting tubers 76, 77 . Compare them and draw your own conclusions.

Korchagina V.A., Biology: Plants, bacteria, fungi, lichens: Proc. for 6 cells. avg. school - 24th ed. - M.: Enlightenment, 2003. - 256 p.: ill.

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It is not necessary to be a botanist to understand the biological characteristics of vegetable crops. Knowledge in this area will help you cultivate an onion bed correctly, without making elementary mistakes. Having at least a minimal idea of ​​​​the structure of the plant and its features, the gardener will be able to pay attention to those nuances that will increase the yield. Since the onion fruit is a bulb, a modified root process, in order to increase productivity, you first need to learn more about the root system of this species.

Characteristic

Onions are a biennial crop belonging to the class monocot plants. The homeland of onions is Afghanistan, Iraq and Turkmenistan, with a mountain climate characteristic of these regions (low pressure and air humidity, hard rocks and soil rich in minerals, but devoid of organic matter). Later, breeders bred many varieties adapted to different climatic conditions.

For the onion family, there is no clear distinction between organs. These plants are not divided into root, shoot, leaves. The reason for this is the gradual transition from one morphological part to another. The rhizome, transformed into a bulb, gives rise to a shoot that does not have a main stem, but is represented by a bunch of hard, erect leaves. Grow onions to obtain:

1. Sevka - in order to obtain further planting material. Usually, .
2. Directly onions, the varieties of which are described in.
3. For decorative purposes. Varieties and methods of growing ornamental onions are described.

Generative organs capable of sexual reproduction mature only in the second year of growth.

The root system of different types of onions

Like the entire class of monocots, onions have a fibrous root system. That is, the plant does not have a main root, but instead a lot of adventitious thin filaments-roots. This allows the onion to firmly establish itself in the soil: the roots gradually draw the bulb deeper, penetrate the soil with a dense network, and cling to the rhizomes of other plants.

Onions have a fibrous root system

Onions are still considered a shallow, sedentary crop. For this reason, it requires special loose soil types, especially when propagated by seeds.

Onion roots have a high capacity for chemotropism - the instinctive search for and absorption of dissolved nutrients. Roots are an annual structure and die off after the end of the growing season. Nutrients accumulate in a modified basal shoot - a bulb.

stem structure

The stem of the onion is also modified. It is presented in the form of a simplified plate - the bottom. On this plate is one or more buds, surrounded by leaves of the vaginal type. These kidneys are called buds.

When breeding vegetatively the plant forms a "heel" - dead and hardened remnants of the maternal bottom. The heel protects the bulb from excessive moisture penetration and subsequent decay, which is especially important in the last stages of its development. Therefore, to ensure good keeping quality of the crop, it is more profitable to breed its sets.

Onion cut

The ability of the plant to produce a green crop depends on the number of primordia (the fewer primordia, the more actively the leaves develop).

leaf structure

Onions are characterized by conical, erect, cone-shaped leaves, narrowing towards the end and hollow inside. From frost and lack of moisture, the sheet is protected by a loose wax coating. The color of the leaves depends on the level of illumination: the more sunlight gets the plant lighter color feathers. In general, the color varies from light green to gray-green, dark.

Leaves also vary in size and density. Toward the end of the growing season, the leaves become denser, acquire a pronounced venation (in onions it is longitudinal-transverse). The most dense are the leaves formed from the extreme open scales of the bulb. The multi-tiered onion has a different root system, which can be found.

Onion leaves are cone-shaped, tapering towards the end and hollow inside.

The structure of the bulb

The bulb is called false leaves sitting right on the bottom, protecting the kidney inside. The cross section shows that the scales form concentric circles, and their density and juiciness increase as they approach the center. Bulb-forming scales are divided into:

• closed juicy. Modified cone-shaped leaves that do not assimilate and perform an exclusively storage function.
• open juicy. Thickened, non-photosynthetic parts of the leaf with a succulent base, thinning towards the top.
• dry integumentary scales. They have a different color (depending on the variety -,), dense and smooth, protect the bulb from pests, drying out and help it be stored for a longer time.

The juicy parts of the bulb, depending on the variety, may have a loose granular, fibrous, papery, mesh or membranous structure.

In the center of the bulb, buds are spirally located, from which heterophytes (flowering shoots) or new bulbs are formed in the future . By the number of such primordial buds, the onion primordia and nesting are determined.

The shape of the bulbs are divided into several main types:

• flat;
• rounded flat;
• rounded;
• long (elongated or oblong);
• melon;
• round melon.

The structure of the flower and shoot

The number and size of flowering shoots in onions depend on the variety and growing conditions. . They are formed after new feathers stop growing, at the very end of the growing season. For this reason, the shoot has the ability to photosynthesis, which ensures the maturation of seeds. Seeds are also involved in planting. As a rule, sevok is obtained from them. Growing onions in open ground seeds and sevkom described.

The flower stalks of onion plants are called an arrow, and the process of their formation is called arrowing. The arrow is a hollow thin-walled tube with a slight thickening at the base. Its length can reach from 45 to 130 cm.

Onion flowers can be white, blue, purple or yellowish in color. They form a complex inflorescence-umbrella, which can contain from several pieces to several thousand flowers. On average, the flowering period of an individual flower is 3-7 days, and the entire umbrella is 7-35 days. Symmetrical flowers do not have sepals, but they have a constant set of gametophytes - 6 stamens and 1 pistil.

reproduction

Onions are characterized by both sexual reproduction with the help of seeds and vegetative reproduction with the help of bulbs. Sexual reproduction occurs by self-pollination or pollination by insects. During double fertilization, one seed is formed for each flower. From the receptacle develops a dry multi-seeded fruit - a box. Seeds of irregular pyramidal shape ripen within 40-60 days. After the seeds, covered with a dense black peel (for which the people called them "chernushka"), are ready for assembly . In 1 gram, up to 1000 individual grains usually fit.

When not favorable conditions vital processes freeze, the active formation of primordia and the accumulation of nutrients in the bulb begin.

In this form, the plant is going through a difficult period, and with the onset of heat it gives several arrows at once and does not form bulbs at the second stage of development.

Landing features

Given this structure of the plant, it can be assumed how and where onions should be planted. The most profitable is the breeding of sets, while the onions are buried shallowly in loose, abundantly watered soil. . Early-maturing varieties can be sown with nigella, grooves up to 1 cm deep. It should be planted in a well-lit place, avoid darkening and excess moisture.

Landing occurs at the end of April, when the soil is well warmed up and the longest daylight hours.

Video

findings

The structure of onions allows it to easily survive bad period, but this will significantly reduce its yield. maintenance normal conditions is the key to abundant fruiting, good keeping quality of the bulbs. Knowing the stages of onion development, it is possible to establish a regime for cultivating it as a two-year crop, which will significantly increase its productivity. How to store onions at home is described in this.

Common modifications of shoots of angiosperms are rhizomes, bulbs and tubers. They usually form in perennials. herbaceous plants as organs in which reserve nutrients are deposited. In such plants, green aerial parts die off for the winter, but modified shoots remain in the soil. In the spring, due to the nutrients contained in them, the plants again develop ordinary above-ground shoots.

In addition to storing nutrients, modified shoots perform another function. With their help, plants can reproduce vegetatively.

Rhizome

Modified Escape rhizome found in many perennial plants (nettle, lily of the valley, couch grass, etc.). The rhizome is located in the upper layers of the soil, resembles a root, but spreads horizontally.

The rhizome is a shoot, as it has apical and axillary buds, as well as leaves that are modified into scales. The resemblance to the root of the rhizome is given by adventitious roots that grow from it along the entire length.

During the growing season, the plant deposits reserve nutrients in the rhizome. At their expense next year new young shoots grow from the buds of the rhizome.

With the help of parts of the rhizome containing buds and roots, vegetative propagation of plants is possible.

Bulb

Modified Escape bulb characteristic of onions, tulips, lilies and other plants. At the bottom of the bulb there is a flattened stem called bottom. Leaves of two types modified into scales grow from the bottom. The outer leaves are changed into dry scales that perform a protective function. The inner thick and juicy scales contain spare nutrients (bulbs contain many different sugars among other substances) and water. The bulbs also grow buds from the bottom.

In favorable conditions, adventitious roots grow from the bottom of the bulb, resulting in the formation of a fibrous root system. Buds can grow into shoots, but they can also develop into so-called baby bulbs. Each such bulb can give rise to a separate new plant. Thus, vegetative reproduction is carried out with the help of bulbs.

Tuber

Modified Escape tuber can be observed in plants such as potatoes and Jerusalem artichoke, as well as some others.

The tuber is formed at the top of another modified shoot - stolon. Stolons grow from the lower parts of above-ground shoots and go into the soil. Organic substances synthesized by the green parts of the plant during photosynthesis move along the stolons to their tops, and thus tubers are formed here. Tubers accumulate a lot of starch.

A tuber is at least modified, but an escape. It has short but thick internodes and many buds called eyes. The leaves of the tubers are reduced. The eyes are located in the recesses of the tuber, and in each such recess there may be several bud eyes.

The part of the tuber that is connected to the stolon is called the base of the tuber. On the opposite side of the base is the top of the tuber. Glazkov is closer to the top. Most often, the apical eye-bud develops into a young green shoot.

Question 1. What modified underground shoots do you know? Name plants that have a rhizome, tuber, bulb.
Tubers are formed as terminal thickenings of underground shoots - stolons. Stolons grow from the base of above-ground stems. Tubers develop as a result of thickening of the apical buds of stolons (potato, Corydalis, pear). On them are groups of kidneys, which are called eyes. The tubers are used for vegetative propagation.
The bulb is an underground shortened modified shoot. The stem of the bulb forms the bottom. Leaves, or scales, are attached to the bottom. The outer scales are usually dry, they perform a protective function. They cover the juicy scales, in which nutrients and water are deposited. At the bottom there is an apical bud, from which aerial leaves and a flower-bearing arrow develop. Adventitious roots develop on the lower part of the donut. Bulbs are characteristic of perennial plants (lilies, tulips, onions, garlic, narcissus, wild onions, etc.). Bulbs allow plants to reproduce vegetatively.
The rhizome is also an underground shoot that looks like a root. The rhizome bears scale-like leaves, in the axils of which are axillary buds. Adventitious roots are formed on the rhizome, and lateral branches of the rhizome and above-ground shoots develop from the axillary buds. Rhizomes are found in perennial herbaceous plants (horsetails, ferns, nettles, lilies of the valley, cereals, etc.). The rhizome is an organ of vegetative reproduction.

Question 2. How to distinguish a rhizome from a root?
By appearance the rhizome resembles a root, but differs from it in the presence of scaly leaves, leaf marks (scars from fallen leaves), buds, and the absence of a root cap.

Question 3. How does a potato tuber develop?
From the leaves of the potato through the stems into the underground shoots (stolons), organic substances constantly flow and are deposited in the form of starch in the tops of the stolons. The tops of stolons grow, thicken and turn into large tubers by autumn.

Question 4. Why should a potato tuber be considered an escape?
A potato tuber should be considered a shoot because, like a shoot, it is formed by a stem that performs a storage function, has buds (eyes) and scaly leaves.

Question 5. What is the structure of the bulb?
In the lower part of the bulb, for example, onions, there is an almost flat stem - the bottom. Adventitious roots and modified leaves (scales) depart from the bottom. Outer leaves - scales - dry and leathery, they perform a protective function; internal - fleshy and juicy, nutrients are deposited in them. In the axils of the scales there are axillary buds.

Question 6. How to prove that the rhizome and bulb are modified shoots?
Outwardly, the rhizome resembles a root, but, like a ground shoot, it has apical and axillary buds, as well as membranous scales - modified leaves. Thus, the rhizome has a stem (the axial part of the rhizome, buds and leaves (membrane scales), that is, what is characteristic of the shoot. At the bulb, we can also see all parts of the shoot: the stem (bottom of the bulb), leaves (dry and juicy scales) and buds (between scales) This confirms that the rhizome and bulb are modified shoots.

Question 7. What above-ground modifications of shoots do you know?
Terrestrial modifications of the shoot include thorns (wild apple tree, wild pear), antennae (pumpkin, grapes), lashes (bone, tenacious), above-ground stolons, or mustaches - (strawberries), cactus stems.