Seeds are used for sexual reproduction of plants. The good thing is that offspring receive genetic material from two different individuals. Combinations of genes become possible, leading to greater diversity than asexual reproduction. One of the main tasks of any individual is the preservation of the offspring, its protection and feeding. Consider the structure of the seed of the plant in more detail to see how these functions are performed.

Seed structure

Angiosperms have a seed peel. The peel protects the fetus from drying out and other environmental influences. It can be thin (peas, beans) or thick (apricot, cherry).

Nutrient reserve - it is necessary to obtain all the substances necessary for the growth and development. They will be used until the plant crawls out of the ground and can not use sunlight for photosynthesis - self-nutrition.

The tissue in which the nutrients are located is called the endosperm. It consists of large cells that contain starch, proteins and oils.

The embryo is the future plant, which is still in its infancy, but it already has:

• germinal root;
• gemmule;
• the stalk.

Angiosperms in the endosperm contain special hormones (cytokines) that regulate the growth and development of individual parts of the embryo.

But in some groups of plants (for example, in orchids), the structure of the plant seed is different from the rest: the small embryo does not yet have differentiated organs. They develop after germination.

In addition to the embryo, the cotyledons are located in the seed. One or two, depending on which plant in front of us: monocotyledonous or dicotyledonous.

In the seed of a monocotyledonous plant, the embryo is located at the base of the seed, separating from the endosperm using a modified cotyledon (scutellum). And during germination it is not carried to the surface of the soil, the sprout comes out of the ground already without seed.

An example of a monocotyledonous plant is wheat.

The structure of the plant seed in dicotyledons is slightly different: the embryo sits between the cotyledons. When germinating, they are carried out from the ground at the top of the sprout. Of course, after they fall off, opening the top of the plant.

A bright representative of dicotyledons is beans.

Seed function

It is important to remember that seeds are the result of a long evolution of plants. And for many years they have successfully performed all their functions:

• embryo protection - so that the offspring does not die from environmental influences, a dense peel is able to withstand changes in temperature and humidity;
• nutrition of the future plant - the endosperm carries all the necessary substances for the development of the embryo;
• distribution - seeds can have a rather intricate shape for flying over long distances, or be surrounded by pulp, so that animals serve as a "transport" for plants.

Seed structure - video

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

What is a seed

A seed is a generative organ. In addition to the function of sexual reproduction, it performs an important function of the settlement of plants. Spread with the help of wind or animals, it is the seeds of plants that germinate and develop new territories. This ability is determined by plants.

External structure of the seed

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

The seed size of various plants varies significantly: from millimeter poppy seeds to half-meter in Seychelles palm.

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

The peel of the seed is formed from the integument of the ovum. This is a reliable seed protection against moisture and environmental hazards.

The protective cover can be painted in different colors. Looking at the concave side of the seed, it is easy to notice the indentation that follows from the placenta. Before the fetus formed, she connected the seed to the pericarp.

The internal structure of the seed

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

Ripened seeds can be at rest 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 protein. Another type of seed is called proteinless.

Seed composition

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

Also in the seeds is 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 - in starch.

In addition to proteins, fats and carbohydrates, seeds also contain inorganic substances. This is primarily the 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 indispensable.

Seeds of monocotyledonous and dicotyledonous plants

The presence of seeds is characteristic only for a certain systematic group of plants - seed. In turn, they are combined into two groups: Gymnosperms and Angiosperms. Plant seeds are located on the scales of cones without coating. Therefore, 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.

Far more likely to germinate are seeds of angiosperms. 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 against cold and nutrition of the embryo.

The belonging of a plant to a certain group is easy to determine. Having examined the structure of a monocotyledonous seed, for example, a wheat grain, we can verify that there is only one cotyledon. The seedling of such a seed forms one germinal leaf.

Beans seeds are arranged in a completely different way. Their structure is characteristic of the seeds of dicotyledonous plants: two cotyledons in the seed embryo 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 root system, the presence of cambium, the structure and venation of leaves, the shape of the leaves. But the structure of the seed is a defining feature.

Seed germination

Surely, every house has many seeds. Beans, peas, lentils, sunflower seeds, and even wheat are frequent guests in the kitchen. But why do not 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 a living embryo.

Important conditions for germination are also access of oxygen, sunlight, 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 feed 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 seeds of sunflower and corn. And the success of the future crop largely depends on the quality of the seed.

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

Seed   - This is the reproductive organ, which in angiosperms is formed from the ovule, usually after double fertilization.

The structure of the seed. Initially, the seed is inside the fruit, which protects it before germination. Each seed consists of a seed peel, embryo, and storage tissue.

Testa   evolving from integument (integument) ovuletherefore, it is diploid (2n). It is multi-layered and is always in the seed. The thickness and density of the seed peel are associated with the characteristics of the pericarp, so it can be soft, leathery, membranous or hard (woody). Seed peel protects the embryo from mechanical damage, drying out and premature germination. In addition, it can contribute to seed germination.

Embryo   is a plant in its infancy and consists of germinal root, stalk, cotyledons and kidneys. An embryo develops from a zygote formed as a result of the fusion of sperm with an egg (2n).

Stocking fabrics   the seeds are endosperm and perisperm. Endosperm   formed as a result of double fertilization at the fusion of the central nucleus of the embryo sac (2n) with the second sperm (1n). Therefore, the endosperm consists of triploid cells (3n). Perisperm   is a derivative of nucellus and consists of cells with a diploid set of chromosomes.

Types of seeds.The classification of seeds is based on the location of the reserve nutrients. Distinguish four types of seeds   (fig. 22):

Fig. 22. Types of seeds:

BUT   - seeds with endosperm that surrounds the embryo (poppy);

B- seeds with endosperm adjacent to the embryo (wheat); AT   - seeds with a small endosperm (surrounds the embryo) and powerful perisperm (pepper); G   - seeds with perisperm (cockle);

D   - seeds with spare substances deposited in the cotyledons of the embryo (peas); 1   - seed peel; 2   - endosperm; 3   - spine; 4   - a stalk; 5   - kidney; 6   - cotyledons; 7   - pericarp;

8   - perisperm

1) seeds with endosperm   mainly characteristic of seeds of the class monocotyledonous, as well as some dicotyledonous (nightshade, celery, poppy); reserve nutrients are localized in the endosperm;

2) seeds with perisperm   characteristic for cloves, haze, in which in the mature seed the endosperm is completely absorbed, and the perisperm remains and grows; the seed consists of the seed peel, embryo and perisperm;

3) seeds with endosperm and perisperm   have black pepper, egg capsule, water lily, in the seeds of which endosperm is preserved and perisperm develops; the seed consists of the seed peel, embryo, endosperm and perisperm;

4) seeds without endosperm and without perisperm characteristic of legumes, pumpkin, asters; in the process of development, the embryo completely absorbs the endosperm, therefore, the supply of nutrients is in the cotyledons of the embryo; in this case, the seed consists of the seed peel and the germ.

The structure of the seed with endosperm.Such seeds are characteristic of monocotyledonous plants, for example bluegrass (cereal). Wheat grain (swollen seeds) are distinguished the ventral side   (from the groove) and the opposite - dorsal. At one of the poles of the seed, on the dorsal side, is fetus. From the opposite pole there are hairs that hold the grain in the soil and facilitate the supply of water to the endosperm of the seed (Fig. 23).

Fig. 23. Wheat grain structure

(longitudinal section):

1 - hairs; 2   - pericarp, fused with seed peel; 3 - aleuron layer;

4 - a layer of spare starch ( 3 –4   - endosperm); 5   - shield; 6 - epiblast; 7 - kidney with leaflets; 8   - coleoptile; 9   - spine;

10   - koleoriza (root vagina)

Outside, the grain is covered with a thin film layer, which is difficult to separate from the inside of the grain. This is the pericarp, fused with the seed peel, since the caryopsis is a single-seeded fruit. The structure of the pericarp and the peel of the seed is clearly visible when considering a micropreparation of the cross section of the grain.

The size of the embryo is small compared to the size of the endosperm. This means that the reserve substances are in the endosperm. It consists of two layers: aleurone and reserve starch.

Embryo   has the following parts:

– germ root with root cap, koleorizu   (root vagina);

– germ stem   and a kidney   with a growth cone;

– coleoptile   (first germinal leaf) in the form of a colorless cap with which it breaks through the soil layers during germination;

– visor   (modified cotyledon) - in its location in the caryopsis forms a septum between the embryo and endosperm; under the influence of enzymes, the scab transfers the nutrients of the endosperm into an assimilable form and transfers them to the nutrition of the embryo;

– epiblast   located on the opposite side of the flap and is the second reduced cotyledon.

The structure of the seed without endosperm and without perisperm.   Such seeds are characteristic of legumes, pumpkin, and aster. Let us consider this type of seed structure using the example of common beans (seeds swollen in water) (Fig. 24).

Fig. 24. The structure of the seed of common beans:

1   - germinal root; 2   - micropile; 3   - scar;

4   - seed suture; 5   - seed peel; 6   - kidney;

7   - germinal stalk; 8   –Cotyledons

Outside, the seed is covered with a thick seed peel. It can be of different colors. On the inner concave side of the seed there is a scar, a micro saw and a seed suture.

Rib- This is the place of attachment of the seed to the placenta.

Micropile   - a hole through which water and gases enter the seed. The micropile is located next to the hem, in one line.

Seed stitch   - This is a trace from the accretion of the ovule with the placenta. It is located on the opposite side from the micropile and also adjoins the scar.

Under the seed peel is embryo.   The following parts are distinguished:

– two large cotyledons   kidney-shaped; they are the embryonic leaves where nutrients are deposited in the reserve;

– germinal root;

– germ stem;

– gemmulecovered with embryonic leaves.

Bean seed does not have endosperm, since the reserve substances are in the cotyledons. It consists of a seed peel and a germ.