And protected by the seed coat. The seed serves to disperse plants and survive unfavorable conditions.

The seeds are used in the spring when sowing cucumbers, radishes, beans, peas, beans, and when growing seedlings of tomatoes, peppers and eggplants.

Seeds of different plants vary in shape and size. For example, poppy seeds, turnips, cabbage, parsley, and carrots have small seeds, while beans, beans, and pumpkins have large seeds.

Consists of an embryo, nutrients and seed skin. Nutrients are deposited in the endosperm or cotyledons.

Seed embryo

The main part of the seed is the embryo. It consists of an embryonic root, an embryonic stalk, a bud and cotyledons (Fig. 167). Cotyledons are the first leaves of the embryo. Thus, the embryo is a miniature plant that has all the organs of an adult plant - root, stem, leaves.

Cotyledon

The embryo may have one cotyledon or two. Depending on the number of cotyledons, plants are divided into monocotyledonous (corn, onion, oats, wheat, rye, tulip, etc.) and dicotyledonous (peas, cucumber, pumpkin, beans, etc.).

Seed Nutrients

The seeds contain a supply of nutrients. The main reserve nutrients are starch, proteins and fats. In addition, the seeds contain small amounts of minerals, vitamins and other organic substances. Some plants store nutrients in the endosperm (wheat, rye, barley, poppy, linden, sweet pepper, lilac, etc.). In other plants, endosperm nutrients are spent on embryo growth during seed ripening. Then seeds without endosperm are formed. Reserve nutrients in the seeds of such plants are deposited in fleshy cotyledons (beans, peas, cucumber, pumpkin, beans, etc.). Seeds always contain a small amount of water.

Seed protection products

Testa

The outside of the seed is covered with a seed coat, which is formed from the integument of the ovule.

The seed coat reliably protects the seed from drying out, mechanical damage, temperature changes, and the penetration of bacteria and fungi. The seed coat is often colored in different colors (Fig. 168). In the seeds of wheat, rye, barley and other cereals, the seed coat fuses with the dry pericarp (see Fig. 167).

Toxic substances

The means of protecting the seed is not only the strong seed coat, but also various substances with a pungent odor and taste. The seeds of some plants contain toxic substances that also perform a protective function.

Seed dormancy

Seed dormancy is an important adaptation that allows plants to survive unfavorable conditions and maintain the existence of their species.

During the period of seed ripening, the embryo develops in them and reserve nutrients accumulate. In mature seeds, all vital processes are slowed down, the amount of water does not exceed 10-15% of the total mass of the seed. After maturation on the mother plant and before germination, the seeds of most plants are dormant. Thanks to the state of dormancy, seeds can survive unfavorable conditions and remain alive for a long time. Material from the site

Seed viability is the ability of seeds to retain the ability to germinate. When favorable conditions occur, the seed awakens and germinates. In some plants, seeds very quickly lose their viability - the ability to germinate. Seeds of silver maple, oak, beech, horse chestnut, poplar, willow, and elm remain viable from several days to several months. Seeds of parsnip and celery remain viable for 1-2 years, beans, corn - 5-7 years, cucumbers, squash - 6-7 years. The viability of seeds depends on the biological characteristics of the plant species, as well as on storage conditions. If stored improperly (high temperature and humidity), the seeds quickly lose their viability.

The record for longevity was set by the seeds of Arctic lupine, covered with a thick, almost impenetrable skin. The seeds of this plant were found on the Yukon Plateau in the frozen silt of the Miller Creek River (Canada). They lay in holes dug by lemmings for about 10 thousand years. The sown seeds sprouted after two days, and one of them gave rise to a flowering plant.

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1. A seed is an organ of sexual reproduction of a plant. Seed structure

Seed plants appeared on our planet in the process of a long evolution associated with the establishment of increasingly advanced ways of reproduction, distribution and preservation of offspring. With the advent of seeds, plants not only acquired new methods of dispersal in “convenient packaging,” but also new opportunities for preserving offspring in the least vulnerable form and caring for them in the early stages of development. A seed is the embryonic stage of life of a plant organism.

All angiosperms, despite their diversity, have a common structural plan. Their organs are divided into vegetative and reproductive.

Vegetative(from the Latin word "vegetativus" - plant) organs make up the body of the plant and carry out its main functions, including vegetative propagation. These include the root and shoot.

Reproductive, or generative(from the Latin word “generare” - to produce), organs associated with sexual reproduction of plants. These include flower, fruit and seed.

Today we will talk about the seed from which the plant grows. We will look inside the seed and get acquainted with all its parts and organs.

The life of a flowering plant begins with seeds. In the spring, when the ground is cleared of snow, many people rush to quickly sow various vegetable crops and flowers in the beds and flower beds. What are they sowing? Of course, seeds. A dry, small (and sometimes very tiny) seed is buried into the ground at a shallow depth. Usually, after 2-3 weeks, a small green plant appears in the place where the seed was located under the layer of soil - sprout Miracle? No. It turns out that every seed contains a future plant.

Plant seeds vary in shape, color, size, weight, but they all have a similar structure.

The seed consists of:

• peels,
• embryo
• and contains a supply of nutrients.

An embryo is the rudiment of a future plant. In the embryo there are:

• germinal root,
• stalk,
• kidney
• and cotyledons.

The seed's supply of nutrients is located in a special storage tissue - endosperm(from the Greek words “endos” - inside and “sperm”).

Flowering plants have one or two cotyledons. Accordingly, monocotyledonous or dicotyledonous flowering plants are distinguished. But conifers (gymnosperms) have several of them.

2. Structure of seeds of dicotyledonous plants

Laboratory work “Structure of bean seed” Purpose of the work: to study the structure of the bean seed. Materials and equipment: for each desk - 2 swollen bean grains, 2 dissecting needles, 2 hand magnifying glasses. 1. Examine and verbally describe the appearance of a bean seed (shape, surface, size). Where is the scar located?

2. Take a swollen bean seed and separate the skin from the germ.

3. Attach the peeled skin and the embryo to your notebook (or sketch it). 4. Take the whole embryo, examine it, find 2 ovules, a root, a stalk, a bud. 5. Show the main parts using a schematic drawing. What type of root and bud are there, how can you tell them apart? To which organ of the embryo are the cotyledons attached? .

6. In your notebook, attach (or sketch) 2 cotyledons separately and the remaining 3 parts of the embryo together. Write their names. Which fetal organ is the largest? Why are the cotyledons thick and large? What is the structure of the embryo?

For the first acquaintance, beans are most suitable. For convenience, we will call the slightly curved side of the seed the dorsal part, and the concave side the ventral part.

External structure of a bean seed

. Let's get acquainted with the structure of a bean seed. It is large and all its parts can be easily seen. Let's extract the seed from the fruit, soak it in water and examine it. The bean seed is kidney-shaped, flattened, covered on the outside with a thick

seed coat Peel

- dense, durable outer cover, white or differently colored (depending on the variety). It reliably protects the seed from mechanical damage, drying out, pathogenic microorganisms and prevents it from germinating until favorable conditions are reliably and steadily established. It was not for nothing that we placed the seeds in a wet cloth 1.5-2 days before the lesson, carefully ensured that it did not dry out, and kept them in a warm place. If you get briefly wet, water will not pass inside, because... the dry skin tightly covers the seed. The peel has other functions, we will talk about them later. On the ventral side, the trace of the achene stalk, which attached the seed to the walls of the fruit, is clearly visible. This is a scar, next to it is a small round hole - the spermatic opening.Through it, male reproductive cells - specks of dust - penetrate to the embryonic ovule while still in the flower, and then fertilization occurs. It will still serve well. We squeeze the swollen seed - a drop of water emerges through the seed entrance. What can be concluded?, which means they are part of the embryo. The cotyledons are thick, fleshy, because contain many nutrients. We begin to move the cotyledons apart from the dorsal side, slowly and carefully. If you are lucky, both segments will remain sitting on a small shoot, but in any case it is easy to see where they are attached.

Germinal root already prepared to go outside. Carefully remove the peel. Stop!

Where did the spine stop?

Just opposite the spermatic opening!

Yes, he is supposed to be the first to jump out, fix the seed in the soil and start extracting water. This has already happened with some seeds.

Without a visible border, the root smoothly passes into the embryonic stem, on which the cotyledons sit. In the upper part, the stalk bends, carrying the embryonic bud inside the seed from the gap between the cotyledons.

- Where is the endosperm? What will the embryo eat?

The “well-fed” appearance of the cotyledons suggests:

- What are the cotyledons for?

The fact is that in beans and its other relatives (legumes), the cotyledons turned out to be especially hardworking and caring nannies of the embryo. They pumped all the nutrients from the endosperm into themselves in advance. Surrounded by such care, the embryo formed the rudiments of all the vegetative organs of the future seedling, and under favorable conditions, germination occurs very quickly. (In many other plants the embryo is much less developed.)

Their concern for the embryo does not end there.

In the dense lobules, like in a cradle, the tender bud is securely hidden, and during germination it is the cotyledons that will make a way for the young shoot through the soil, protecting the bud from damage.

And young leaves may not be in a hurry to begin their duties - feeding the plant with photosynthetic products. And this responsibility will be taken on by the cotyledons at first. When they come to the surface, they will noticeably grow, turn green, and we will see numerous veins of the conductive system on them. They will actively feed the young shoot. And when it comes into force, they will shrink, dry out and die. What a wonderful organ this is - the cotyledon!

Let us remember what other plants bring their large cotyledons to the surface. These are cucumbers, pumpkins, zucchini, etc.

But peas are not. Its cotyledons remain underground and support the growing shoot only with the substances contained in them.

Not all plants have cotyledons that absorb nutrients from the endosperm in advance. Some postpone this work partially or completely until germination. Pumping nutrients is a complex biochemical process similar to the digestion of food.

The cotyledons produce special substances that dissolve the endosperm and convert it into easily digestible food for the embryo. This is a special “baby food”, as it should be for babies! Later we learn that the endosperm is not a simple storage of nutrients, it also arises as a result of fertilization, which is why the nutrients acquire special value. Endosperm best contributes to the consolidation and development of all the beneficial properties and qualities of both parents.

Deprive the seed of the endosperm (both the endosperm itself and the cotyledons) - and the embryo will not develop, it will die, and the seed will not produce offspring. All seed plants have cotyledons, but their number, shape and operating time are different.

Thus, the embryo has the same vegetative organs as the adult plant. The embryo has a root and a shoot. The embryonic shoot consists of a stalk, two embryonic leaves (cotyledons) and a bud.

Plants whose embryo has two cotyledons are classified as dicotyledons. These are potatoes, tomatoes, carrots, apple trees, oak trees, cucumbers and many other plants.

Most dicotyledonous plants have seeds with endosperm.

Endosperm is well represented in the seeds of tomatoes, eggplant, lilac, poppy and linden.

Although there is endosperm in flax and apple seeds, it is small, and nutrients are also stored in the embryos, mainly the cotyledons. In pumpkin, sunflower, and seeds, endosperm is practically absent and reserve substances are deposited in the cotyledons.

3. Structure of monocot seeds

Laboratory work “Structure of wheat seed” Purpose of the work: learn to recognize the parts of a wheat seed, study the structure of the seed of monocots. Materials and equipment: for each desk - 2 swollen dry grains of wheat, 2 dissecting needles, 2 hand magnifying glasses. Progress:

1. Examine and verbally describe the appearance of dry wheat seed. Considering the presented material, students answer the following questions: What is the surface, the color of the grain? What is the size? 2. Cut the swollen whole grain along the groove into 2 halves and examine it with a magnifying glass. Find the peel, endosperm, germ. Which part of the grain takes up more space? Where are the embryo and endosperm located?. First we look at the seed through a magnifying glass. The outside is the peel. At the top there is a tuft of thin hairs, at the opposite, lower end there is a barely noticeable tubercle. This is where the embryo is located. Using the prepared preparation, we examine its structure under a microscope. We can easily find an embryonic bud consisting of several leaves, an embryonic root, but the contours of the stem are almost invisible, merging with the cotyledons, but it should definitely be between the bud and the root.

Where is the cotyledon itself?

It, like a shield, separates the named parts of the embryo from the endosperm, which occupies most of the seed, and is called the “scutellum”. The border with the endosperm is clearly visible. The boundary layer of cells has a special structure and consists of transversely elongated cells. When the time of germination comes, these cells extend even more, penetrate the endosperm and, dissolving it, actively absorb nutrients, like a root, pumping them into the embryo.

If we make a longitudinal section of the grain, we will see that the embryo is located at the base of the seed. The main part of the grain is the endosperm.

On a preparation of a longitudinal section of a caryopsis under a microscope, the organs of the embryo, the embryonic root, the stalk and the bud are visible. The cotyledon is located on the side of the embryo at the endosperm border and has the shape of a shield, only very small, which is why the cotyledon is called shield

The germ of wheat, like other grain crops, has a unique structure and differs from other monocotyledonous plants in the lateral position of the cotyledon and a large, well-formed bud.

Plants whose embryos have one cotyledon are called monocots.

Among monocots there are plants, such as arrowhead and plantain, whose seeds do not have endosperm. In such seeds, reserve substances are concentrated in the embryo.

Consolidation of acquired knowledge.

Let's compare a bean seed with a wheat seed. So what do they have in common?

General The structure of bean and wheat seeds is that the seeds have a seed coat, a supply of nutrients and an embryo.

How are they different?

Vary:

• in bean seed two cotyledons, which contain reserve nutrients,
• and in the seed of wheat one cotyledon, A nutrients are found in the endosperm,
• The peel of monocots grows together with the pericarp, so it cannot be separated.

1. What is a seed? What functions does it perform?

A seed is the generative organ of a plant. In flowering plants it is formed inside the fruit. Functions of seeds:

1. Reproduction. Having separated from the mother plant after maturation, the seed can germinate and give rise to a new organism. Consequently, thanks to seeds, plants reproduce.

2. Distribution of plants throughout the territory. For example, poplar and fireweed seeds have numerous hairs on the surface. With their help, seeds are easily picked up by the wind and spread throughout the area.

3. Enduring unfavorable conditions. The seeds of many plants have increased resistance to unfavorable external conditions and are preserved where vegetative organs die. The seed gives the plant the opportunity to endure unfavorable periods: summer heat, winter cold, lack of moisture.

2. What is the structure of a seed?

The seed consists of a seed coat, an embryo and an endos-perm.

The seed coat protects the internal contents of the seed. There may be various formations on it that facilitate the spread of seeds. On the surface of the peel there is a scar from the seed stalk, which connected the ripening seed with the wall of the fruit.

The embryo is an important part of the seed. It consists of an embryonic shoot and an embryonic root. An embryonic shoot has an embryonic stem, embryonic leaves and an embryonic apical bud. The embryonic leaves (two for representatives of the dicotyledonous class, one for representatives of the monocotyledonous class) are called cotyledons. These leaves protect the bud. In many species, nutrients are stored in cotyledons. For example, beans, peas, sunflowers, pumpkins.

Endosperm is a storage tissue in the cells of which reserve nutrients necessary for the development of the embryo are deposited. In some seeds, endos-perm may be absent, and then reserve substances are deposited in the cells of the embryo, often in its cotyledons. Seeds with endosperm in tomato, onion, caraway, persimmon, violet, lily of the valley. Seeds without endosperm in beans, peas, sunflowers, pumpkins.

3. Describe the main types of seed germination.

Ripe seeds begin to grow in the presence of water, air and heat. This is preceded by their swelling. Under the pressure of water-saturated cells, the peel breaks and the root “comes out.” Material from the site

The root grows from the top, anchors the young plant in the soil, and absorbs from it the water and mineral salts necessary for the growing organism. Starts to grow and run. He goes into the air. The stem stretches, leaves grow, and the apical bud unfolds. The growth of the shoot occurs due to the intercalary and apical educational tissues. The seed embryo turns into a seedling.

If the cotyledons are carried into the air, then they speak of “above-ground” seed germination. Such germination occurs in common beans, cucumbers, turnips, cabbage, onions, small-leaved linden, Norway maple and many other plants.

If the cotyledons of the seedling remain in the soil, such seed germination is called “underground” (peas, hazel, oak and other plants).

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Various in size and shape. For example, thousands of small orchid fruits weigh less than a gram, the fruits of some palm trees weigh up to 8-15 kg.

It can withstand unfavorable conditions for a long time and remain dormant. The embryo remains alive. A seed that can germinate is called germinating . For seed germination, favorable conditions (temperature, humidity, air) are required. The seed breathes, so access to air (oxygen) is necessary. During breathing, heat is generated. Water penetrates the seed through the pollen passage.

The seed consists of an embryo and a supply of nutrients covered 5. Show the main parts using a schematic drawing. What type of root and bud are there, how can you tell them apart? To which organ of the embryo are the cotyledons attached? . The surface can be smooth, rough, with spikes, ribs, etc. The seed skin protects the contents of the seed from damage and drying out. On the surface of the seed you can see hem – trace from the seed stalk and pollen passage . The pollen duct is preserved as a small hole in the peel.

Nutrients are usually found in the endosperm. The composition of the seed includes organic and inorganic compounds. In many plants, during the ripening of the seed and the formation of the embryo, the endosperm is completely used. Then the reserve substances are deposited or in first germ layers or cotyledons (potatoes, beans, peas, pumpkin), in other parts of the seed (coll).

The number of cotyledons in a seed determined the name of the classes of angiosperms (Monocots, Dicots). Seeds of dicotyledonous and monocotyledonous plants have different structures.

A dicotyledon seed has two cotyledons, between which is the embryo. The cotyledons contain nutrients. The embryo consists of a germinal root, stem, bud and leaves. During germination, the cotyledons serve as the first leaves.

A monocot seed has a single cotyledon - shield . This is a thin film located between the endosperm and the embryo. The second cotyledon is reduced. The embryo occupies a small part of the seed and has an embryonic root, stem, bud and leaves. When a seed germinates through the scutellum, the embryo absorbs nutrients from the endosperm.

In angiosperms, the seed loses its connection with the mother plant and germinates elsewhere. The spread of fruits and seeds occurs under the influence of various external factors or independently.

Autochory

Autochory (from Greek autos- myself, choreo- to spread) is the ability of plants (lupine, geranium, violet, yellow acacia) to independently spread fruits and seeds. When ripe, the “mad cucumber” is capable of throwing seeds out with force over many meters.

Anemochoria

Anemochoria (from Greek anemos- wind, choreo- to spread) is the spread of fruits with the help of the wind (dandelion, sow thistle, birch, maple). For this, the fruits have a number of different adaptations: winged outgrowths (parachutes, hairs, wing-like appendages, etc.), light seeds. This allows the wind to pick up the seed. Thus, the fruits do not fall out all at once, but gradually. This is a common method among plants.

Ornitochory

Ornitochory (from Greek ornis- bird, choreo– spread) – distribution of seeds and fruits with the help of birds. Birds can eat the fruit, but after passing through the intestines, the seeds of most plants are not digested; the seed is excreted in droppings; or simply move them long distances and lose them. Some birds can hide fruits in hiding places, where the latter sometimes germinate.

Zoochoria

Zoochoria (from Greek zoon– animal, choreo- to spread) is the distribution of fruits and seeds of plants with the help of animals. Animals eat fruits and remove seeds with droppings, bury fruits in the ground or make hiding places that are forgotten or not used, and carry tenacious fruits on the covers.

Hydrochoria

Hydrochoria (from Greek hydro– water, choreo- to spread) - the spread of fruits and seeds using water. Characteristic mainly for aquatic and marsh plants (sedge, water lilies, reeds, etc.).

Anthropochory

Anthropochory (from Greek anthropos- Human, choreo- to spread) is the dissemination of seed and fruit by man. A person carries the fruits on clothing, transport, along with food and goods. Sometimes the fruits are thus transferred even to other continents. Often such plants (elodea, ragweed, cyclochene, etc.) quickly multiply in new places, spread and cause great damage; they are weeds that have no natural enemies.

The meaning of fruits and seeds

People eat a lot of fruits and seeds and feed their pets. People get oil from the fruits and seeds of some plants (sunflower, soybeans). The seeds of oilseed plants contain from 25 to 80% oil.

Seeds and fruits are used in medicine (raspberries, blackberries, viburnum). Sometimes the fruits and seeds of plants (henbane, datura, belladonna, etc.) contain toxic substances. When they are consumed, a person becomes poisoned. Therefore, when consuming fruits, especially unfamiliar ones, you need to be careful. Narcotic substances are made from the fruits of some plants (hemp, poppy). Most drugs are of plant origin.

Seeds in plants arose as a result of a long process of evolution as the organ that most reliably ensures their distribution.

The main part of the seed is embryo future plant. It consists of a rudimentary stem from which leaf primordia and roots extend. At the top of the stem there is a bud. The first leaves of the embryo, usually sharply different from subsequent ones in their structure and function, are called cotyledons. Plants that have a pair of cotyledons in the seed belong to the class Dicotyledons (peas, flax, hemp, cabbage, etc.). If the seed has only one cotyledon, then it is a monocotyledonous plant (iris, lily, etc.).

The seed contains the supply of nutrients necessary for the germination of the embryo, which is either in the embryo itself or in the special storage tissue of the seed. The outside of the seed is protected by a shell. In plants such as beans, peas, and pumpkin, the seed consists of a peel and an embryo. The peel protects it from drying out and damage. The embryo is located under the skin. Most of the embryo is located in the cotyledons, which contain reserve nutrients (fats, carbohydrates). Cotyledons are modified leaves. Between them there is a germinal root, a stalk and a bud (. 18, L).

endosperm

Conditions for seed germination

18, L).

Rice. 18. Structure of the seed. A - bean seed; B - wheat seed (kernel): 1 - peel, 2 - embryo bud, 3 - stalk 4 - root, 5 - cotyledon, 6 - scutellum (cotyledon), 7 - endosperm

In the seeds of other plants, nutrients are stored in specialized storage tissue - endosperm. An example of seeds with endosperm are cereal seeds. Under the skin of their seed, the endosperm and the embryo are easily distinguished (Fig. 18, B). In the embryo, with the help of a magnifying glass, you can examine a single cotyledon - the scutellum, the embryonic root, the stalk and the bud. When the grain germinates, the endosperm nutrients are absorbed by the scutellum cells and used by the embryo. The endosperm contains starch and vegetable protein - gluten. The seeds also contain minerals and water. Dry seeds contain 6-14% water, 2-4% minerals.

The seeds also contain various enzymes. With their help, the reserve substances of the seed are converted into a form that is digestible for the developing embryo.

Conditions for seed germination. Seed germination requires water, air and heat. Water penetrates the seed coat through a small opening called the aperture, causing the seed to swell. The need for water for swelling primarily depends on the composition of the seeds. Seeds rich in fat absorb 30-40% of water, seeds rich in starch - 50-70%, seeds with a lot of protein - about 90% of water. Water is also needed to dissolve the seed's nutrients, which are absorbed by the growing seed embryo.

Seed swelling is accompanied by intense enzyme activity. Reserve nutrients in seeds are in sedentary forms of complex organic compounds. In order for the solid polysaccharide starch to be used by the embryo, it must be hydrolyzed under the influence of the enzyme diastase, which saccharifies starch to the soluble disaccharide maltose. Other substances dissolve under the action of other groups of enzymes. Dissolved and mobile decomposition products can already be used by the embryo. During decay, energy is released, which is used to enhance the physiological functions of the seedling.

Fig. 19. Germination of a bean seed (A, B, C - different stages): 1 - main root, 2 - subcotyledonous knee, 3 - epicotyledonous knee, 4 - cotyledons, 5 - first leaves, b - bud

During the dormant period, seed respiration is very weak, but during germination it increases sharply and the need for oxygen increases. Germinating seeds not only absorb oxygen, but also release carbon dioxide, i.e., they respire. This is natural: after all, plants, like animals, are living organisms. During breathing, heat is generated. Raw seeds breathe more energetically than dry ones. Therefore, folded in a thick layer, they quickly heat up and, as they say, “burn out,” and their embryos die. The seeds become ungerminating. They are stored only dry and stored in dry, well-ventilated areas, while air access to the seeds should be free and constant.

Seeds can germinate only at a certain temperature: for example, winter rye at 2-4 C, and cucumber seeds at 15-16 C. Plants that require heat are sown later, when the soil has warmed up sufficiently.

Sprouts. Young plants that develop from the seed embryo are called seedlings (Fig. 19). At first, the seedlings feed on the reserve substances accumulated in the seed. If the cotyledons are raised above the soil during germination, then this type of germination is called above-ground (for example, cucumber, pumpkin, beans, carrots). In the case when the cotyledons remain underground, germination is called underground (peas, oak, wheat,).

Seedlings of monocotyledonous plants usually have several roots (winter wheat has 3, spring wheat has 5). In dicotyledonous seedlings, as a rule, one root is first formed, which then branches.