From the moment of inception to full ripeness, when it becomes capable of producing a normal sprout, a seed goes through a series of complex transformations from one state to another, more perfect one, that is, what happens is what is defined by the concept of “seed development”.

This whole complex process can be divided into several periods and phases that characterize individual stages in the life of seeds.

Each phase has a completely definite state of the seed, and therefore the diagnosis of the phase must be distinguished by the utmost clarity and simplicity. However, now there are only scattered descriptions of individual phases, most often on any one basis.

The classification of periods and phases of seed development is especially important. To build a classification of this or that phenomenon, it is necessary to generalize the accumulated experimental material and sum up the results of the research and suggest a way for further development of this phenomenon. Naturally, such a classification can only be developed by the collective efforts of researchers.

The basis for constructing a classification of periods and phases of seed development should be a set of features: morphological, morphogenetic and biochemical.

The phases have been studied in the most detail and classifications by grain crops have been developed. The best classifications for grain crops were proposed by N. N. Kuleshov, for legumes - by V. A. Vishnevsky, for sunflowers - by V. K. Morozov.

Periods of seed development

The period of seed development is characterized by some significant qualitative change, as well as its duration.

For grain crops, six characteristic, clearly defined periods can be distinguished: seed formation(embryonic), formation, filling, maturation, post-harvest ripening, full ripeness. As we will see later, all these periods in a general form are inherent in all other cultures, although, naturally, each culture will have specific differences in the nature of the period, in its phases.

N. N. Kuleshov divided the process of grain development into three periods (phases): formation, filling And maturation. We perceive the last two periods in the interpretation of N. N. Kuleshov, and we divide the first period into two qualitatively different periods: seed formation and his formation. In addition, we include in a single process of seed development the period post-harvest ripening and period full ripeness.

All these periods can be briefly characterized as follows (on the example of winter wheat).

Period of seed formation begins after fertilization (from the beginning of the postgamous phase) and continues until the moment when the seed, separated from the mother plant, is able to sprout. This indicates that the seed has already been formed and in the future a period of its strengthening, its formation begins. This embryonic period begins with the formation of the zygote and ends with the formation of the growth point of the embryo. In this state, the embryo is able, under optimal conditions, to give a weak, but still viable sprout.

This period lasts 7–9 days for winter wheat, 7 days for soft spring wheat, 10 days for hard spring wheat, 10–15 days for corn, etc.

Formation period continues until the final grain length characteristic of this variety is reached. By the end of the period, the differentiation of the embryo is basically over. During this time, the content of the grain turns from watery to milky (starch grains appear in the endosperm tissue), and the color of the shell changes from white to green (chlorophyll accumulates). The moisture content of the grain is 65–80%, and the dry weight of 1000 grains reaches 8–12 g. This period in grain development is characterized by a high water content (especially free water) and a low dry matter content. The period lasts 5-8 days.

Filling period begins with starch deposition in endosperm cells and continues until starch deposition ceases. The period is characterized by an increase in the width and thickness of the grain to the maximum size, the complete completion of the formation of endosperm tissue, which first has a milky, then pasty, and waxy consistency by the end of the period. The weight of water in the grain remains constant, but the moisture content of the grain is reduced to 38-40% (due to the constant increase in dry matter). This period lasts an average of 20–25 days, but in wet and cool weather it can take up to 30 days, and in dry and hot weather it can be reduced to 15–18 days or less.

seed maturation period begins with its detachment from the mother plant, when the flow of plastic substances, enzymes and even water stops. In grain there are processes of polymerization and drying. Humidity at this time decreases to 12-18%, and sometimes up to 8%. The amount of free water is sharply reduced, and by the end of the period it may disappear completely.

Such a division into periods is correct from the point of view of marketable grain - the latter matures and is considered suitable for technical use, that is, it becomes a raw material for industry.

From the point of view of the seed grower, the development of seeds has not yet been completed by this period. As we will see later, a new qualitative period is beginning, which is associated with the further transformation of chemicals and the emergence of a new and most important property of seeds - full normal germination. Although the morphological formation of seeds ends in the third period, but the physiological processes proceed in the subsequent time, therefore, we consider it necessary to supplement the process of seed formation with the fifth period - the period post-harvest ripening.

IN period post-harvest ripening complex biochemical transformations of various chemical compounds take place in the seeds, although the morphological characters remain the same as in the previous phase.

During this period, the synthesis of high-molecular protein compounds continues and ends, the conversion of free fatty acids into fats, the molecules of carbohydrate compounds grow larger, the processes of transformation of substances - germination inhibitors into other forms take place, the activity of enzymes fades, air and water permeability of the seed coats increases.

Seed moisture is in equilibrium with the relative humidity of the air. Seed respiration is fading. At the beginning of the period, the seeds do not germinate or their germination is very low, at the end it becomes normal. The period lasts depending on the culture and external conditions from one day to several months.

full ripeness period begins with the onset of full germination of seeds, that is, the seeds are ready to begin a new cycle in the life of the plant. There is a slow aging of colloids, which is accompanied by weak breathing. In this state, the seeds are until the beginning of germination or until complete death due to aging during long-term storage.

In some cases, these periods are divided into smaller stages of seed development - phases . Phases are distinguished according to different features, most clearly reflecting their peculiarity. In one case, this may be a special state of the endosperm, in another, the nature of physiological processes, etc.

The filling period is divided into the following phases of development according to the state of the endosperm: watery, pre-dairy, dairy, pasty. During the ripening period, ripeness phases are distinguished: waxy(often distinguish between beginning, full and end of waxy ripeness), hard(sometimes mark the beginning of the solid phase of ripeness).

Watery phase- the beginning of the formation of endosperm cells. The grain is filled with a watery liquid. The shell is white or whitish. Grain moisture is 75–80%, free moisture is 5–6 times more than bound moisture, dry matter is 2–3% of the maximum amount. The duration of the phase is on average about 6 days.

Pre-milk phase- the liquid, watery contents of the grain acquire a milky hue, as the process of deposition of starch grains in the endosperm begins. Shell greenish. Grain moisture content is reduced to 70-75%, free moisture contains 3-4 times more than bound, dry matter by the end of the phase accumulates about 10% of the weight of a ripe grain. The duration of the phase is 6–7 days.

Milk phase- the grain has the consistency of a milky white mass, the shell is green. Grain moisture by the end of the phase drops to 50%, the ratio of free water to bound water is approximately 1.5:1. The amount of water in 1000 raw grains remains approximately constant. In this phase, dry matter intensively accumulates, its amount is about 50% of the weight of a mature seed. The duration of the phase is 7–10 days, sometimes 10–15 days.

Pasty ripeness phase- the endosperm acquires the consistency of a dough; when crushed, strands stretch. In the shell, chlorophyll gradually disappears (preserving in the groove). Grain moisture is reduced to 35–42%, the ratio of free water to bound water is 1:1. The dry matter content reaches 85–90% of the maximum. The duration of the phase is 4–5 days.

Waxy phase- the endosperm becomes waxy, elastic. Shells turn yellow. The chlorophyll in the groove disappears. The amount of water is reduced to 30%. The grain reaches its maximum volume. At the beginning of the phase, a slight increase in dry matter in the grain continues, and by the end it stops completely. The duration of the phase is 3–6 days.

- the endosperm becomes hard, powdery or glassy when broken. The shell also takes on a dense leathery appearance. The color is typical for this culture and variety. Water is contained, depending on the zone and conditions, 8–22%, including 1–8% in the free state. The duration of the phase is 3–5 days, and then a gradual process of substance loss (expiration, etc.) begins.

The duration of each period and phase is determined not only by species characteristics, but also by the conditions in which the development of the seed takes place. The environment can change not only the duration of a period or phase, but also their nature (physiological processes can proceed intensively, or they can be largely suppressed), which affects the sowing and yield properties of seeds.

If the weather is hot and dry during the formation of seeds or the soil is not moist enough, that is, the grain falls under fuse or capture, then the duration of the period is reduced, the seeds do not have time to reach their normal length and are shortened (a very rare occurrence).

In some cases, the process of inhibition of the plant and seed can go further (at high temperature and lack of moisture): severe dehydration of the seeds sets in, the normal physiological state of the cells is disturbed, and the biochemical processes in the seed change. The result is puny seeds with a small weight of 1000 grains, often with a high content of nitrogenous compounds.

Humid weather with a favorable temperature, the provision of nutrients contribute to the lengthening of the period of formation and formation of long seeds, which, under favorable subsequent conditions, turn into large seeds.

The weight and size of the seeds depend on the conditions during the filling of the seeds. Under normal conditions of nutrition, water supply and the absence of physical drying of seeds, the filling process continues for a longer time and many organic substances are deposited in the grain. Seeds under such conditions acquire a large weight, size, smooth surface, bright, fresh color, they have high sowing and yielding properties.

In rainy conditions, the loading is delayed, synthetic processes are weakened, the chemical composition changes, because some substances do not turn into final products. Such seeds have reduced yield properties, have a long post-harvest ripening period, and are poorly stored.

A high temperature with a sufficiently complete water supply shortens the filling period and accelerates the pace of biochemical processes. The seeds are of high quality. If the water supply is insufficient, then, due to the shortening of this period, the seeds can be puny to varying degrees. However, this frailty affects the quality of the seeds less negatively than the frailty that arose during the period of their formation, when unfavorable conditions are also reflected in the development of the embryo.

The conditions that develop during the period of seed maturation affect their quality less than the conditions of previous periods, but they are also important for obtaining high-quality seeds. During this period, there should be a constant, uniform drying of the seeds, which contributes to the conversion of reserve nutrients into final forms. Drought in the phase of waxy ripeness, if it causes rapid drying of the seeds, leads to an increased content of easily mobile carbohydrates (sugar, etc.), which do not have time to turn into starch. Such seeds have high sowing qualities, especially high germination energy, but require special attention during storage. An increased content of sugars, even with a slight increase in humidity, can cause intensive respiration, and later damage to the seeds.

Rainy and cold weather during the ripening period slows down this process, and the seeds are obtained with poor sowing qualities and low germination. Cold but dry weather, although it causes a lengthening of the period, but the seeds are of satisfactory quality.

The considered periods of seed development related to cereal crops, but they are fully applicable to other crops, although some phases may be different.

V. A. Vishnevsky studied in detail the process of development of lupine seeds and established six phases of ripeness: A) cotyledons are dark green, germ root is green; b) the cotyledons are green, the beginning of the whitening of the root of the embryo; V) cotyledons light green, complete whitening of the root of the embryo; G) cotyledons whitish, early yellowing of the root of the germ; e) yellowed cotyledons, yellow root of the embryo; e) the cotyledons are yellow, the root of the embryo is light yellow. According to the author, the filling period ends in the phase of complete yellowing of the root of the embryo, when the moisture content of the seeds becomes below 50% and the flow of plastic substances into the seeds stops. Such a division into phases of periods of filling and ripening is possible for other legumes, although there will be some differences.

The process of development of sunflower seeds is significantly different from the process of development of caryopses. According to the scheme of V. K. Morozov for sunflower the following phases are set:

The phase of achene volume formation(pericarp) begins long before flowering and ends 6–14 days after fertilization. The pericarp of the achene grows in length for about 6 days after fertilization, and in width and thickness - 8–14 days.

The phase of the formation of the volume of the nucleus begins after fertilization. Noticeable growth in all three dimensions begins after the fourth day and ends on the 12-14th day.

Filling phase begins at the end of the previous one, and ends when the supply of dry matter and the accumulation of fat in the achene cease. This usually occurs when the moisture content of achenes decreases to 38–40%.

IN ripening phase the process of drying, removing moisture. Seeds go into a state of post-harvest ripening.

Within the maturation phase, the author also distinguishes degree of ripeness (ripening): harvesting– seeds have a moisture content of 18–20%, economic– humidity of achenes 12–14% and overstay– moisture content of seeds is less than 12%.

As we can see, this division of the process of development of achenes is based on their humidity, and only in the first two phases are other characters taken.

It would be possible to continue the analysis of the phases of development of other cultures, but all of them will reflect only their specificity, and the general pattern remains the same.

The seed is the link between two generations of plants. Being a part of the maternal organism, it simultaneously contains the germ of the child. In the structure of seeds there are common features characteristic of any seed, and differences that divide flowering plants into two large classes.

seed development

The seed is formed from the ovule, which is located inside the ovary of the pistil. The ovule looks like a sac and contains several cells. The most important of these are the ovum (female sex cell) and the central cell.

After pollination of the flower, two spermatozoa (male sex cells) penetrate the ovary. One sperm fuses with the egg and forms a zygote. The other sperm fuses with the central cell and forms the endosperm. This process is called double fertilization.

Rice. 1. Scheme of double fertilization.

General features of the structure of seeds

The seed has the following parts:

• germ;
• endosperm;
• testa.

The embryo develops from the zygote - this is the main part of the seed. The embryo is clearly visible in leguminous plants (beans, peas, beans). It looks like a miniature plant and has:

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• spine;
• the escape;
• cotyledons.

The radicle is the first to start growing when the seed germinates and forms the main root. The shoot is a rudimentary stem with a bud. The cotyledons are attached to the shoot and are the first pair of leaves of the future plant.

Endosperm consists of large cells of storage tissue. Its purpose is to nourish the embryo until it switches to self-feeding through photosynthesis.

The seed coat protects the seed from drying out, damage and premature germination. To penetrate the seed of water, the peel has a hole (micropyle).

The heaviest seed is the Seychelles nut seed, its weight reaches 25 kg.

monocot and dicot plants

If the embryo of a plant has two cotyledons, as in legumes, then it belongs to the class of dicots. Approximately 75% of flowering plants are dicots. The remaining 25% are monocots, they develop only one cotyledon.

Features of the structure of monocot seeds

The cotyledon of monocots is called the scutellum. Its function is to transfer nutrients from the endosperm to the embryo. The endosperm occupies most of the seed.

Rice. 2. The structure of the seed of a monocot plant.

Differences in seed structure are not all that separate the two classes of flowering plants. Dicotyledonous and monocotyledons have different leaf venation, the structure of the root system and the stem.

Endosperm

Endosperm is present in about 85% of flowering plants. Its presence or absence is not a sign of dicots or monocots. Endosperm is found in both.

Most often it contains oily substances, because fats contain the most energy. Some seeds (legumes) are rich in proteins.

Most monocots have an endosperm that contains carbohydrates. These are, first of all, cereals, from the grain of which flour is obtained and bread is baked.

Features of the structure of dicotyledonous seeds

Typical dicot seeds have peas and beans. Under a thick skin, they have two large symmetrical cotyledons, which, during germination, are carried out with an escape to the light, and soon dry up.

Rice. 3. The structure of the seed of a dicotyledonous plant.

The embryo is sandwiched between the cotyledons.

The peel of beans and peas is dense. The seed can be dormant for a long time. But, when it enters a humid environment, water penetrates through the micropyle and the seed swells. The cells of the embryo begin to divide and the root breaks through the peel.

Seeds in nutrition

Seeds of flowering plants are of great importance in the nutrition of animals and humans.

The nutrients of the endosperm, or cotyledons, are what a person grows plants for. The seeds of cereals and legumes play the most important role in human nutrition.

What have we learned?

When studying this topic in biology (grade 6), the student should understand the following: the structure of the seed of a flower and fruit has common features in all flowering plants. The seed consists of three parts: germ, endosperm, seed coat. The structure of the seeds of monocots and dicots has some differences. The seed of many dicots does not contain an endosperm, in which case the nutrients are concentrated in the cotyledons.

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The seed is a plant reproductive organ that develops after fertilization from the ovule.

During the formation of a seed and a fetus, one of the sperm fuses with the egg, forming a diploid zygote. (fertilized egg). Subsequently, the zygote divides many times, and as a result, a multicellular embryo of the plant develops. The central cell, which has merged with the second sperm, also divides many times, but the second embryo does not appear. A special tissue is formed - the endosperm. The endosperm cells accumulate reserves of nutrients necessary for the development of the embryo. The integuments of the ovule grow and turn into a seed coat.

Thus, as a result of double fertilization, a seed is formed, which consists of an embryo, a storage tissue (endosperm) and a seed coat. From the wall of the ovary, the wall of the fruit, called the pericarp, is formed.

Seed types

1. with endosperm (seed consists of three parts: seed coat, endosperm and embryo. Seed with endosperm is inherent in monocotyledons, but can also occur in dicotyledons - poppy, solanaceous, umbellate);

2. with endosperm and perisperm (usually a rare type of structure, when the seed contains an embryo, endosperm and perisperm. It is typical for lotus, nutmeg);

3. with perisperm (the endosperm is completely consumed for the formation of the embryo. Seeds of this type are characteristic of cloves);

1. without endosperm and perisperm (the embryo occupies the entire cavity of the embryo sac, and reserve nutrients accumulate in the cotyledons of the embryo. Together, the seed consists of two parts: the seed coat and the embryo. This structure of the seed is characteristic of legumes, pumpkin, rosaceous, walnut, beech, etc.)

Perisperm - Storage diploid tissue of the seed, in which nutrients are deposited. Arises from nucellus.

Endosperm - Large cell storage tissue, the main source of nutrition for the developing embryo. First, it actively transfers the substances coming from the mother's body to the embryo, and then serves as a reservoir for depositing nutrients.

Rice. seeds

16. Classification of fruits. infructescence .

The fruit is an organ of reproduction of angiosperms, formed from a single flower and serving for the formation, protection and distribution of the seeds enclosed in it. Many fruits are valuable foodstuffs, raw materials for the production of medicinal, coloring substances, etc.

Fruit classification

In most classifications, fruits are usually divided into real(formed from an overgrown ovary) and false(other bodies also take part in their formation).

Real fruits are divided into simple(formed from one pistil) and complex(arising from a polynomial apocarpous gynoecium).

Simple are divided according to the consistency of the pericarp into dry And juicy.

Among the dry distinguish single-seeded(for example, grain, nut) and polysperms. Multi-seeded fruits are divided into open (bean, box, pouch, pod, etc.) and non-open. Non-opening dry multi-seeded fruits are divided into articulated (articulated bean, articulated pod) and fractional (vislocarp, two-winged, etc.)

Among the juicy fruits are also distinguished multi-seeded ( pumpkin, apple, berry) and single-seeded(drupe).

Complex ones are called based on the names of simple fruits (multi-drupe, multi-nut, etc.).

Unlike the fruit (simple or complex), the infructescence is formed not from one flower, but from the whole inflorescence or its parts. In any case, in addition to flowers, the axis of the inflorescence takes part in the formation of the inflorescence. The infructescence is a product of modification (after fertilization) not only of flowers, but also of the axes of the inflorescence. In typical cases, the seed imitates the fetus and corresponds to it functionally. A classic example is the fruit of a pineapple.

17 Vegetative propagation of plants and its biological meaning Vegetative propagation of plants(from lat. vegetativas- vegetable) is the reproduction of plants with the help of vegetative organs (root, stem, leaf) or their parts. Vegetative propagation of plants is based on the phenomenon of regeneration. During this method of reproduction, all properties and hereditary qualities in the offspring are fully preserved.

There are natural and artificial vegetative reproduction. Natural reproduction occurs constantly in nature through the impossibility or difficulty of seed reproduction. It is based on the separation from the mother plant of viable vegetative organs or parts capable of restoring the whole plant from its part as a result of regeneration. The whole set of individuals obtained in this way is called clone. Clone(from the Greek. clon - sprout, branch) - a population of cells or individuals, which is formed as a result of asexual division from one cell or individual. Vegetative propagation of plants in nature carried out by:

Divisions (unicellular);

Root sprouts (cherry, apple, raspberry, blackberry, wild rose);

Corenebulbs (orchid, dahlias);

Layering (currant, gooseberry);

Mustache (strawberry, buttercup creeping);

Rootstocks (wheatgrass, reed);

Tubers (potatoes);

Bulbs (tulip, onion, garlic);

Brood buds on leaves (briofilum).

The biological significance of vegetative propagation: a) one of the adaptations for the formation of offspring where there are no favorable conditions for sexual reproduction; b) the genotype of the parental form is repeated in the descendants, which is important for preserving the traits of the variety; c) one of the ways to preserve valuable varietal characteristics and properties; d) in case of vegetative reproduction, the plant can be stored under the conditions of impossibility of seed reproduction; e) the preferred method of propagating ornamental plants; f) when grafted, resistance to external conditions increases in the graft. The disadvantages of vegetative propagation should also be noted: a) negative traits are transmitted b) diseases of the mother's body are transmitted.

18. Asexual reproduction, its role and forms Reproduction is a universal property of all living organisms, the ability to reproduce their own kind. With its help, species and life in general are preserved in time. The life of cells is much shorter than the life of the organism itself, therefore its existence is supported only by cell reproduction. There are two types of reproduction - asexual and sexual. During asexual reproduction, the main cellular mechanism that provides an increase in the number of cells is mitosis. The parent is one individual. The offspring is an exact genetic copy of the parent material. 1) The biological role of asexual reproduction Maintaining fitness enhances the importance of stabilizing natural selection; provides fast reproduction rates; used in practical selection. 2) Forms of asexual reproduction In unicellular organisms, the following forms of asexual reproduction are distinguished: division, endogony, schizogony and budding, sporulation. Division is typical for amoeba, ciliates, flagellates. First, the mitotic division of the nucleus occurs, then the cytoplasm is divided in half by an ever deeper constriction. In this case, daughter cells receive approximately the same amount of cytoplasm and organelles. Endogony (internal budding) is characteristic of Toxoplasma. With the formation of two daughter individuals, the mother gives only two descendants. But there may be internal multiple budding, leading to schizogony. It occurs in sporozoans (malarial plasmodium), etc. There is a multiple division of the nucleus without cytokinesis. From one cell, a lot of daughters are formed. Budding (in bacteria, yeast fungi, etc.). At the same time, a small tubercle containing a daughter nucleus (nucleoid) is initially formed on the mother cell. The kidney grows, reaches the size of the mother, and then separates from it. Sporulation (in higher spore plants: mosses, ferns, club mosses, horsetails, algae). The daughter organism develops from specialized cells - spores containing a haploid set of chromosomes. 3) Vegetative form of reproduction Characteristic of multicellular organisms. In this case, a new organism is formed from a group of cells that separate from the parent organism. Plants reproduce by tubers, rhizomes, bulbs, root tubers, root crops, root shoots, layering, cuttings, brood buds, leaves. In animals, vegetative reproduction occurs in the lowest organized forms. Ciliary worms are divided into two parts, and in each of them the missing organs are restored due to disordered cell division. Annelids can regenerate an entire organism from a single segment. This type of division underlies regeneration - restoration of lost tissues and body parts (in annelids, lizards, salamanders)

19 Sexual reproduction - associated with the fusion of specialized sex cells - gametes with the formation of a zygote. Gametes may be the same or different morphologically. Isogamy - fusion of identical gametes; heterogamy - the fusion of gametes of different sizes; oogamy - the fusion of a motile spermatozoon with a large immobile egg.

For some groups of plants, alternation of generations is characteristic, in which the sexual generation produces germ cells (gametophyte), and the non-sexual generation produces spores (sporophyte).

Fertilization - this is the union of the nuclei of male and female germ cells - gametes, leading to the formation of a zygote and the subsequent development of a new (daughter) organism from it.

Gamete is a reproductive cell with a single (or haploid) set of chromosomes involved in sexual reproduction. That is, in other words, the egg and sperm are gametes with a set of chromosomes of 23 each.

Zygote is the result of the fusion of two gametes. That is, a zygote is formed as a result of the fusion of a female egg and a male sperm. Subsequently, it develops into an individual (in our case, into a person) with the hereditary characteristics of both organisms of the parents.

isogamy

If the merging gametes do not morphologically differ from each other in size, structure and chromosome set, then they are called isogametes, or asexual gametes. Such gametes are motile, may carry flagella or be amoeboid. Isogamy is typical of many algae.

Back in school in the course of botany (grade 6), the structure of the seed was a fairly simple and memorable topic. In fact, this one arose as a result of a long evolutionary process and has a complex and unique structure. In our article, we will consider the features of its structural parts, the structure of a dicot seed, and also determine the biological role of plant seeds.

The appearance of the seed in the process of evolution

Plants were not always capable of forming seeds. It is known that life arose in water, and algae were the first plants. They had a primitive structure and reproduced vegetatively - by parts of the thallus and with the help of specialized mobile cells - zoospores. Rhinophytes were the first to land on land. They, like their future successors - higher spore plants, reproduced with the help of spores. But water was necessary for the development of these specialized cells. Therefore, when environmental conditions changed, their numbers also decreased.

The next evolutionary step was the appearance of the seed. This was a huge step forward for the adaptation and spread of many plant species. The external and internal structure of the seed determines the reliable protection of the embryo, surrounded by a supply of water and nutrients. This means that they increase the viability and species diversity of the planet's flora.

The process of seed formation

Consider this process on the example of a group of plants, which is dominant in the modern world. These are representatives. All of them form a flower - the most important generative organ. In its pistil is the egg, and the anthers of the stamens contain sperm. After the pollination process, i.e. the transfer of pollen from the anther of the stamens to the stigma of the pistil, the spermatozoa move along the germ tube to the ovary of the stamen, where the process of gamete fusion occurs - fertilization. As a result, an embryo is formed. When the second sperm fuses with the central germ cell, a reserve nutrient is formed. It is also called the endosperm. The structure of the seed is completed by a strong outer shell. This structure is the basis for the development of the future plant organism.

External structure of seeds

As already mentioned, the outside of the seed is covered with a peel. It is dense enough to protect the embryo inside from mechanical damage, temperature changes and the penetration of harmful microorganisms. But the color of the seeds varies widely: from black to bright red. This structure of the seed is easy to explain. In some plants, the color serves as a camouflage. For example, so that birds cannot see them in the soil after planting. Other plants, on the contrary, are adapted to disperse seeds with the help of various animals. Together with undigested food residues, they excrete them far beyond the parent plant's habitat.

The internal structure of the seed

The main part of any seed is the embryo. This is the future organism. Therefore, it consists of the same parts as an adult plant. These are the germinal root, stalk, leaf and bud. The structure of the seed of different plants can vary significantly. In most of them, reserve nutrients accumulate in the endosperm. This is a shell that surrounds the embryo around, protecting and nourishing it throughout the entire period of individual development. But there are cases when, during the process of maturation and germination of the seed, it completely consumes the substances of the endosperm. Then they accumulate mainly in the fleshy parts of the embryo. They are called cotyledons. Such a structure is typical, for example, for pumpkins or beans. But in the shepherd's purse, the supply of substances is concentrated in the tissue of the embryonic root. The seeds of different systematic groups of plants also differ.

Features of the seeds of gymnosperms

The external and internal structure of the seed of this group of organisms is characterized by the fact that the process of formation and development of the embryo occurs on the surface of the seed coat. In addition to the main parts, the seeds of gymnosperms have a pterygoid membranous outgrowth. It helps the seeds of these plants to spread with the help of the wind.

Another feature of gymnosperms seeds is the duration of their formation. For them to become viable, it should take from four months to three years. The process of seed maturation takes place in cones. It's not fruit at all. They are specialized modifications of the escape. Some coniferous seeds can be stored in cones for decades. All this time they retain their viability. In order for the seeds to fall into the ground, the scales of the cone open on their own. They are picked up by the wind, sometimes carrying them over considerable distances. If the cones are soft, outwardly resembling nuts, they do not open themselves, but with the help of birds. Especially like to feast on seeds, various types of jays. This also contributes to the resettlement of representatives of the Gymnosperms department.

The very name of this systematic unit indicates that the embryo of the future plant is poorly protected. Indeed, the presence of endosperm guarantees only the development of the seed. But the cones of many plants open during adverse developmental conditions. Once on the soil surface, the seeds are exposed to low temperatures and lack of moisture, so not all of them germinate and give rise to a new plant.

Features of seeds of flowering plants

Compared with Gymnosperms, representatives of the Flowering department have a number of significant advantages. The formation of their seeds occurs in the ovary of flowers. This is the most expanded part of the pistil and gives rise to the fruit. As a result, the seeds develop inside them. They are surrounded by three layers of pericarp, which differ in their properties and functions. Consider their structure using the example of a plum drupe. The outer leathery layer protects against mechanical damage, ensuring integrity. Medium is juicy and meaty. It nourishes and provides the embryo with the necessary moisture. The inner ossified layer is an additional protection. As a result, the seeds have all the necessary conditions for development and germination, even under adverse circumstances.

Monocot Seeds

The structure of the seed of a monocot plant is very easy to determine. Their embryo consists of only one cotyledon. These parts are also called germ layers. All onion and lily plants are monocots. If you germinate the seeds of corn or wheat, soon one leaflet is formed from each grain on the surface of the soil. This is the cotyledons. Have you tried splitting a grain of rice into several pieces? Naturally, this is impossible. This is because its embryo is formed by a single cotyledon.

Dicot Seeds

Seeds of Nightshade, Aster, Bean, Cabbage and many others differ somewhat in structure. Even based on the name, it is easy to guess that their embryo consists of two cotyledons. This is the main systematic feature. The structure of the seeds of dicotyledonous plants is easy to see with the naked eye. For example, it is easily divided into two equal parts. This is the cotyledon of its embryo. The structure of the dicotyledonous seed can also be seen from young seedlings. Try to germinate the seeds at home and you will see two carpels that will appear above the ground.

seed germination conditions

The structure of the seeds of dicotyledonous plants, as well as representatives of other systematic units of this kingdom of wildlife, determines the presence of all the necessary substances for the development of the embryo. But other conditions are necessary for germination. For each plant, they are completely different. First, it is a certain air temperature. For heat-loving plants, this is +10 degrees Celsius. But winter wheat begins to develop already at + 1. Water is also needed. Thanks to it, the grain swells, which speeds up the processes of respiration and metabolism. Nutrients are converted into a form in which they can be absorbed by the fetus. The presence of air and a sufficient amount of sunlight are two more conditions for the germination of the seed and the development of the whole plant, since photosynthesis is impossible without them.

Seeds and fruits

Each fruit contains higher plants almost identically. But the fruits are more diverse. Allocate dry and juicy fruits. They differ in the structure of the layers that are located around the seed. In succulent, one of the layers of the pericarp is necessarily fleshy. Plum, peach, apple, raspberry, strawberry... These delicacies are loved by everyone precisely because they are juicy and sweet. In dry fruits, the pericarp is leathery or ossified. Its layers usually fuse into one, reliably protecting the seeds inside. A box of poppies, a mustard pod, a grain of wheat have just such a structure.

The biological role of seeds

Most plants on the planet use seeds for reproduction. The structure of the seeds of modern plants is the result of a long evolution. These contain the germ and a supply of substances that ensure its growth and development even under adverse conditions. Seeds have adaptations for dispersal, which increases their chance of survival and dispersal.

So the seed is the result of the process of fertilization. It is a structure consisting of an embryo, reserve substances and a protective peel. All its elements perform certain functions, thanks to which the group of seed plants has taken a dominant position on the planet.

It is from the seed that the life of many plants begins. A miniature chamomile or a spreading maple, a fragrant sunflower or a juicy watermelon - they all grew from a small seed.

What is a seed

The seed is in addition to the function of sexual reproduction, it performs an important function of the resettlement of plants. Spreading with the help of wind or animals, it is the seeds of plants that germinate and develop new territories. This ability determines the structure of the plant seed.

The external structure of the seed

As a result of the process of fertilization are formed which determines the functions performed.

The size of the seeds of various plants varies considerably: from millimeter poppy seeds to half a meter in the Seychellois palm.

The shape of the seeds is also varied, but more often it is round. Usually which is typical, serve as an example of the study of this generative organ.

The seed coat is formed from the integument of the ovule. This is a reliable protection of the seed from lack of moisture and dangerous environmental factors.

The protective cover can be painted in different colors. Looking at the concave side of the seed, it is easy to notice the depression, which is a trace from the seed stalk. Before the formation of the fetus, she connected the seed with the pericarp.

The internal structure of the seed

The second most important part of every seed is the germ. It is the forerunner of the future leafy plant, therefore it consists of its miniature parts. They are the germinal root, bud and stalk. The nutrient reserve of the embryo is in the cotyledons. There is also another plan for the structure of seeds in nature, when the embryo is inside the endosperm. This is the supply of nutrients.

Ripe seeds can be dormant for a long time, which gives them advantages over spores that germinate immediately after ripening and die if there are no conditions necessary for development.

In nature, all organs, including seeds, are quite diverse. The structure determines their classification. Seeds that are in the endosperm are called proteinaceous. Another type of seed is called protein-free.

Seed composition

Studies have shown that all seeds are composed of organic matter, most of which is vegetable protein or gluten. Most of this substance is found in cereal plants, from which I make flour and bake bread.

The seeds also contain fat and carbohydrate starch. The percentage of these substances varies depending on the type of plant. So, sunflower seeds are rich in oils, wheat grains are rich in starch.

In addition to proteins, fats and carbohydrates, seeds also contain inorganic substances. This is primarily water, necessary for the development of the future plant, and mineral salts.

Regardless of the quantity, each substance has its own significance for the development and growth of seeds and is irreplaceable.

Seeds of monocots and dicots

The presence of seeds is characteristic only for a certain systematic group of plants - seed plants. In turn, they are combined into two groups: gymnosperms and angiosperms. Seeds of gymnosperms of conifers are located on the scales of cones without coating. That is why they have such a name. In February, seeds fall on bare snow, the structure of which does not provide for additional protection of the embryo from adverse conditions.

Seeds of angiosperms are much more likely to germinate. Representatives of this group occupy a dominant position due to the presence of fruits that protect their seeds. The structure of each fetus provides reliable protection from the cold and nutrition of the embryo.

The belonging of a plant to a certain group is easy to determine. Having considered the structure of a monocotyledonous seed, for example, a grain of wheat, one can be convinced that there is only one cotyledon. The sprout of such a seed forms one germ layer.

Bean seeds are completely different. Their structure is characteristic of the seeds of dicotyledonous plants: two cotyledons in the embryo of the seed and two. In addition to the structure of the embryo, there are other signs that determine the group of plants. This is the type of the root system, the presence of cambium, the structure and venation of the leaves, the shape of the leaves. But the structure of the seed is the defining feature.

seed germination

Surely, every house has a lot of seeds. Beans, peas, lentils, and even wheat are frequent guests in the kitchen. But why don't they form seedlings? The answer is simple: certain conditions are necessary for their germination. The most important of these is water. When it penetrates, the seed swells and increases several times in volume, and the nutrients of the endosperm of the embryo dissolve. In this state, they become available to the cells of the living embryo.

Important conditions for germination are also access to oxygen, sunlight, and optimal air temperature. Usually it is above 0 degrees. But the seeds of winter cereals are specially treated with cold, and a negative temperature is a necessary condition for the development of their seeds.

The role of seeds in nature and human life

Seeds are of great importance both for the plants themselves and for animals and humans. For plants, they are a means of reproduction and settlement on the earth's surface. With a supply of starch, fat and protein, the seeds serve as an excellent nutritious food for animals and birds. For humans, they are also a food product. It is impossible to imagine the life of people without bread made from cereal seeds or without vegetable oil from sunflower and corn seeds. And the success of the future harvest largely depends on the quality of the seed.

Seed plants are the most highly developed, complex in structure, life processes, and occupy a dominant position in the plant world. They achieved such development precisely due to the presence of important generative organs - seeds.