How does pollination and fertilization take place in flowering plants? What does flowering plants develop from the ovary wall? The structure and classification of plant fruits. The spread of seeds and their significance in nature and human life

Chapter 11 Neighbors in the flesh, true enemies and true friends of a Christian For whoever does the will of My Heavenly Father is my brother and sister and mother. Mt. 12, 50 Honor your father and mother. Mt. 15, 4 But if someone does not care about his own people, and especially about his family, he has denied the faith and worse

Partitions

Partitions In order to divide the entire space of the house into separate rooms, partitions are installed. They can be single, double or triple, with or without soundproofing. For device single partitions use unplaned

Flowering plants are a large and diverse group that dominate most terrestrial ecosystems. Its existence depends on the main flowering plants cultivated by man. But to flowering plants appeared, they must go through the stage of pollination and fertilization. How this happens, read this article.

Pollination

This process is carried out by transferring pollen from the stamens to the pistil. How does pollination and fertilization take place in flowering plants? This is done in two ways: self-pollination and cross-pollination. In the first case, the transfer of pollen grains to the pistil occurs in the same flower. This is how peas or tulips are pollinated. With cross-pollination, the pollen of a flower from one plant is transferred to the pistil of another. most often by insects, in rare cases - by wind (sedge and birch), birds and water.

As a result of insect pollination, bright, well-visible flowers with a pleasant smell and nectaries are formed, which produce a sweet liquid. Such plants also produce a lot of pollen. It is food for insects. They are attracted by the bright color or smell of flowers. When insects extract nectar, they touch the surface of the pollen grains, which adhere to their body, and when flying to a flower of another plant, they remain on the pistil. This is how insect pollination takes place. Many are pollinated only by certain insects: scented tobacco - night butterfly, creeping clover is a bee, and meadow clover is a bumblebee.

Cross-pollinated plants are better adapted to changing environmental conditions. But the pollination process in this case depends on a number of factors. And self-pollination does not depend on anything. For him, the weather conditions and the absence of intermediaries are not scary.

Fertilization

A grain of pollen, falling on the stigma of the pistil, begins to germinate gradually. The development of a long pollen tube occurs from the vegetative cell. Growing up, it reaches the level of the ovary, and then the ovule. At the same time, a pair of sperm is formed, which penetrates the pollen tube. It, in turn, enters the ovule through the pollen duct. Then the tube at the very tip breaks and releases the male sperm, which are immediately sent to the embryonic membrane, it is called a sac. This is where the eggs develop.

Further, the fertilization of the egg with one sperm takes place, and the formation of a zygote, from which a small embryo of a completely new organism of plant origin begins to form. At the same time, the fusion of the second sperm occurs with the nucleus of the zygote or with the polar nuclei. As a result, a triploid cell is formed, from which the endosperm arises. It is called a nutrient tissue, which contains reserves of essential substances for the normal development of the embryo of a future plant. This is how the organs of sexual reproduction of flowering plants are represented.

When one sperm with an egg, and the other, with the polar nuclei, merge together, this process is called It is peculiar only to flowering and is a unique feature of angiosperms. A fertilized ovule grows into a seed. As a result, the pistil ovary grows. In flowering plants, a fruit develops from the wall of the ovary.

Reproduction

Any plant, reaching a certain size and passing the appropriate stages of development, begins to reproduce organisms of a similar species. This is reproduction, which is a necessary property of life. All organisms thus prolong the existence of the species itself. Distinguish between sexual and which occurs with the participation of one individual. When plants develop specialized cells - spores, organisms begin to multiply.

Moss, algae, ferns, moss and horsetails. Spores are special small cells with a nucleus and cytoplasm that are covered with a membrane. They are able to endure bad conditions for a long time. But, getting into a favorable environment, they quickly germinate and begin to form daughter plants, the properties of which do not differ from those of the mother.

During sexual reproduction, female and male germ cells merge, resulting in the formation of daughter organisms that are qualitatively different from the parental ones. The parental organisms of the female and male principles are already taking part here.

As part of the ovule, the dominant role is played by macrosporangium. It is in it that the laying of one mother cell takes place, from which macrospores are formed. Three pieces start to die off and eventually collapse. The fourth macrospore - feminine, lengthens and its core divides. Then the daughter nuclei move to different poles of the elongated cell. Each formed nucleus is further divided twice.

Cells located near different poles have four nuclei. This is called the embryo sac, which contains eight haploid nuclei. Further, from each quartet of nuclei, one of them follows to the center of the embryonic sac. There they merge, as a result of which they form a secondary nucleus - diploid.

Then, in the embryo sac, in the cytoplasm, partitions are formed between the nuclei on cellular level... There are seven cells in the bag. Near one of its poles is the egg apparatus, which includes a large egg and two auxiliary cells. At the other pole there are antipode cells, there are three of them in total. So, there are now six in the bag and one is diploid, with a secondary nucleus. It is located in the center of the embryonic sac.

What is an ovary?

It is called the lower thickened part of the pistil with a closed cavity inside, in which the ovules are located. Pollen enters the ovule from the stigma of the pistil, which is protected from unfavorable conditions by an internal moist cavity. In the ovule, the development of female germ cells - ovules - takes place.

What are the types of ovaries?

The types of ovaries of flowering plants are:

• Upper. It attaches to the receptacle freely, without merging with other sections in the flower. The walls of the ovary are formed from carpels. In flowering plants, a fruit develops from the wall of the ovary. Examples are buttercups and cereals. These flowers are called sub-pest or para-pest.
• The lower ovary is always under the receptacle. It is formed with the participation of other parts of the flower: the base of sepals and stamens with petals, which in many flowers are attached to the top of the ovary. In flowering plants, fruit develops from the wall of the ovary. Examples are Compositae, cactus and orchid plants. The flower is called supra-pistillate.

• Semi-inferior ovary. Its top does not grow together with other parts, so it is free. Flowers of this type are called semi-adipose flowers. These are the types of ovaries of flowering plants.

Flowering plants

They are the most progressive group of plants, numbering two hundred and fifty thousand species, distributed throughout the planet Earth. The smallest plant is the duckweed, the diameter of which is equal to one millimeter. She lives in the water. The largest flowering plants are trees that grow to a height of one hundred meters or more.

The emergence of flowering plants occurs due to the development of a special reproductive organ - a flower. In some plants, it is painted in bright colors, in others it smells wonderful. Flowers are small and inconspicuous in plants that look like grass. Despite the huge variety of flowering plants, they all harmoniously fit into our life: they decorate gardens and parks, give the joy of communication with them.

Flower structure

The flower is a complex organ system that ensures the propagation of plants by seeds. Its appearance led to the widespread distribution of angiosperms (flowering) plants on Earth. The flower has many functions. With its participation, stamens with pollen grains, pistils with ovules are formed. It plays a major role in pollination, fertilization, seed and fruit formation.

The flower is a shortened, modified, limited growth shoot bearing the perianth, pistils and stamens. All have flowers that are similar in structure and different in shape. This is how the adaptation to pollination occurs. different ways.

The flower can end in the main or lateral stems, the bare part of which under the flower itself is called the pedicel. It is greatly shortened or completely absent in sessile flowers. The peduncle passes into a receptacle, which is elongated, convex, concave or flat. All parts of the flower are placed on it. These are sepals with petals, stamens with a pistil, in the lower part of which an ovary is formed, in which ovules or ovules are located. A flower with such an ovary has a concave receptacle. If the ovary forms at the top of the pistil, the receptacle will be convex or flat.

The pistil occupies the apical position in the flower. It consists of an ovary, a column and a stigma. Ovules form and develop in the ovary. With the help of the column, the stigma takes the position most favorable for the ingress of pollen, the pollen tube grows along the column.

The pistil is a hollow organ. It is formed from the fusion of the edges of a carpel or several carpels (carpella).

Ovary- the lower part of the pistil, which forms the fruit after pollination. The ovary cavity may contain one or several nests. The walls of the ovary, external and internal, are covered with epidermis. Stomata in the epidermis are few in number, although they can be on both sides of the ovary, external and internal. The cuticle develops mainly on outside... The walls of the ovary are mesophyll. Its cells are poorly specialized, retain their embryonic character, which explains the significant growth of the ovary after fertilization. Both the mesophyll and the epidermis of the ovary walls contain chloroplasts. After fertilization, the ovary develops into a fetus, and the structure of its walls changes significantly.

Stigma- a specialized part of the carpel that receives pollen. The surface of the stigma is covered with a conductive tissue, which often continues into the canal of the column. Conductive tissue is formed from the proliferation of cells of the epidermis and cells of the subepidermal layer. She performs a secretory role. Its cells are relatively large, thin-walled, rich in protoplasm and nutrients. The conductive tissue creates an environment conducive to pollen germination and pollen tube development.

Column in different plants developed in varying degrees, for some it is absent. The tissues that make up the column are more differentiated than the tissues that make up the ovary;

Ovules develop on the walls of the ovary. This part of the ovary wall is called the placenta. Conductive bundles are suitable for the placenta. The epidermis and deeper tissues grow in this place. The position of the placentas in the ovary, and, consequently, the position of the ovules has a regular character, constant for certain taxonomic units.

Ovule consists of nucellus and integument. Its development begins with the inception of a small parenchymal tubercle. The growth of this tubercle leads to the development of the central part of the ovule - nucellus... The development of integuments lags somewhat behind - integuments... One or two covers are laid in the form of circular ridges and, growing up, envelop the ovules on all sides of the nucellus. In the upper part, the integument does not close, leaving a gap, or channel, called spermatic or micropyle... Accordingly, this part of the ovule is called micropillary. Its opposite pole represents the base and is called chalazoi... Here the ovule is attached by the seed to the walls of the ovary.

The ovule is called straight (atropic) if the micropyle and the seedle are on the same axis. Reverse (anatropic) ovules are rotated 180 ° in such a way that the micropyle is located near the base of the ovule. The ovule is called semi-bent (hemitropic) if its axis is at right angles to the axis of the ovule. There are two more types of ovules, curved to varying degrees. The most common are anatropic ovules.

Nucellus corresponds morphologically and functionally to the macrosporangium. In some plants, it is a well-developed multicellular tissue, in others it is markedly reduced, sometimes to a few cells. Cytologically, nucellus cells are meristematic in nature, but the ability to divide, i.e. to the formation of spores, here only the mother cell of spores preserves.

The formation of spores proceeds by means of reduction division, therefore, four haploid cells are formed - macrospores. Of these, only one remains and develops - the embryonic sac. Shape and dimensions embryo sac different plants are different, and its position in nucellus is also different.

The development of the embryo sac consists in several successive divisions of its nucleus. In typical cases, an 8-core embryo sac is formed. In this phase of development, the embryonic sac corresponds to the female gametophyte.

The nuclei are distributed in the embryo sac as follows: at the micropilar pole - the ovum and two accompanying nuclei - synergies, on the opposite - three cores - antipodes. Two nuclei, one from each pole, converge in the center and then merge to form the secondary nucleus of the embryo sac. This embryo sac is ready for fertilization.

During fertilization, one of the sperm fuses with the egg, forming a zygote. The second sperm merges with the secondary nucleus of the embryonic sac, and a triploid nucleus is formed. This type of fertilization is called.

The development of the ovule into a seed is accompanied by the transformation of the ovary into a fruit. The fruit represents the final stage in the development of the reproductive sphere of flowering plants. Its function is to form, protect and spread seeds. Usually the fetus develops as a result of fertilization, but in some angiosperms it can form without fertilization - parthenocarpic. Such fruits do not have seeds and are most often found in many cultivated plants (banana, cucumber, tangerine, grapes, etc.).

Many plants are monocarpic since in ontogeny, they form fruits and seeds once and then die. These include all annuals, as well as biennial plants that produce fruits and seeds once only in the second year. Some perennials are also monocarpic tropical plants... For example, American agave can live up to 100 years and die off after flowering and fruit formation. Plants that repeatedly form fruits and seeds during ontogenesis belong to polycarpics... This group includes woody and most perennial herbaceous plants.

The morphological basis of the fruit is the gynoecium, and above all the ovary. Often, other elements of the flower (receptacle, base of stamens, sepals, etc.) take part in the formation of the fruit of plants, especially those with a lower ovary. In this case, sometimes they speak of "false fruits" as opposed to "real" ones, formed only by the ovary. Examples of such fruits are strawberries, in which the juicy part of the fruit is formed from a strongly overgrown receptacle; rose hips and apple trees, in which hypanthium takes part in the formation of the fruit. However, the definition of the concept of "false fruit" is not entirely correct, since all fruits formed by the inferior ovary should fall into this category, thus confusing the classification of fruits.

In the definition of fruits, the following concepts are used: simple, complex, or composite, fractional, jointed fruits. A special type of formations are infertility.

Simple the fruit develops from one pistil formed by apocarpous single-membered (cherry, pea) or coenocarpic gynoecium (poppy, tulip, cockle, wheat).

Complicated, or made the fruit is formed from a flower with an apocarpous polynomial gynoecium, when each pistil turns into a separate fruit (marsh marigold, raspberry, blackberry, magnolia). The individual fruits that make up the composite fruit can be different: nuts, drupes, leaflets. Depending on this, the prefabricated fruits are called polynuts (strawberries), polystyrene (raspberries), and many-leaves (magnolia).

Fractional the fruit develops from a multi-nest ovary of the coenocarpous gynoecium, if each nest of the ovary turns into an independent fruit (mallow). The disintegrating cenocarps are called schizocarps. Their individual lobes are called mericarpies. Malvaceous fruits that break up into open mericarps are called kalachiks. Borage and labiate fruits are coenobia - they consist of four nut-like lobes.

Jointed the fruit breaks up into separate segments according to the transverse constrictions available on them (wild radish, multi-colored vazel, sowing seradella, etc.). In this case, the number of segments does not correspond to the number of nests in the ovary.

Fertility develops from the inflorescence in the event that the ovaries of flowers during the formation of fruits do not give separate fruits, but grow together into one common formation (pineapple, figs, mulberry tree, beets, spinach, etc.).

With the formation of the fetus, the walls of the ovary grow, it is formed pericarp, or pericarp... It accumulates nutrients - proteins, starch, sugars, oils, vitamins, etc. The pericarp protects the seed or seeds contained within the fruit. In most plants, the pericarp is differentiated into 3 layers: exocarp (extracarp), mesocarp (intercarp), endocarp (intracarp). Histologically, they correspond to the layers of the carpel. Exocarp(from the Greek. exo - outside) is a derivative of the outer (external) epidermis and consists of tightly closed cells with thickened outer walls. For example, in cherry or plum fruit it is a thin shiny or waxed outer layer that is easily removable, in citrus fruit it is a yellow or orange glandular layer. In immature fruits, the exocarp have stomata, in ripe fruits they are invisible. Sometimes small lentils develop in it, like, for example, an apple.

Mesocarp(from the Greek mesos - middle) is formed from the carpel mesophyll, usually it is more developed in comparison with the exo- and endocarp. In cherries and plums, the mesocarp is the edible juicy pulp of the fruit, while in citrus fruits it is a loose whitish layer that lies directly under the yellow. The mesocarp can be dry and underdeveloped (pod, pod).

Endocarp(from the Greek endos - internal) is formed from the internal epidermis of the carpel. It can be single-layer or multi-layer. In cherry, plum, and other stone fruit cultures, the endocarp is represented by sclerified tissue, which forms a bone covering the seed. The citrus endocarp is highly modified and forms a juicy main part of the fruit. The ratio of the thickness of the layers of the pericarp in different species is not the same and is associated with the peculiarities of their distribution.

In accordance with the functions, the fruits are extremely diverse in morphological characteristics - size, shape, color, pericarp consistency, methods of opening, the presence of outgrowths, appendages, etc. Structural features of the fruit are most often associated with seed dispersal. Their diversity forms the basis of the simplest and most widely used morphological classification of fruits in practice. It also takes into account some of the features of the anatomical structure: the number of carpels forming a pistil, the number of nests in the ovary, the number of seeds, the method of opening the fruit, and some other signs.

Depending on the consistency of the pericarp, the fruits are divided into juicy and dry. Fruits can contain one seed, like cherry plum, nasturtium, hazel, or be polyspermous like dope, carnation, bellflower, petunia and other plants.

Juicy and dry single-seeded fruits do not open, the seeds are released when the pericarp is destroyed or as a result of germination. Dry polyspermous fruits, as a rule, have devices for opening and releasing the seeds. The fruits are opened after ripening or later.

Opening polyspermous dry fruits differ in the number of carpels and nests in the ovary that formed them, in the position of the ovary in the flower and in the type of gynoecium. These include flyer, bean, pod (pod), box.

Leaflet- this is the most primitive fruit, formed by one carpel, unilocular, opened at the place of fusion of the edges of the carpel (along the abdominal suture). The opened fruit resembles a leaf. Leaflets are single (field larkspur) and combined, or multileaf (peony, swimsuit, marigold, catchment, magnolia).

Bean- unilocular fruit, formed by one carpel; opens with two valves - at the place of fusion of the edges of the carpel (abdominal suture) and along the midrib (dorsal suture). Seeds (sometimes one seed - for example, in clover, sainfoin) are arranged in one row and attached along the ventral suture. Fruits are varied in appearance: straight (peas, beans, caragana, gleditsia), spirally twisted (alfalfa sowing), bubble-shaped (astragalus-flapweed), articulated (seradella sowing, multicolored vasel). The bean fruit is typical for plants from this. Legumes (Fabaceae), Mimosaceae (Mimosaceae), Caesalpiniaceae (Cesalpiniaceae)

Pod and pod- These are fruits that develop from the upper ovary of the paracarpous gynoecium, consisting of two carpels. Opened longitudinally along two seams from bottom to top. Between the valves there is a septum formed by the placenta and dividing the fetus into two nests. Seeds are attached along its edge in one or two rows. Such fruits are typical for cruciferous plants (cabbage, turnip, levkoy, etc.). The pod and the pod differ in the ratio of the length and width of the fruit. If the length exceeds the width by 3-4 or more times, the fruit is called a pod (rapeseed, mustard); if the length is slightly more than or equal to the width - in a pod (yarotka, shepherd's purse, lunar). In the common weed of the wild radish, the pod is segmented: it does not open with the valves, but breaks up into parts along the constrictions.

Boxes Is a group of fruits that unites all varieties of opening fruits that cannot be attributed to the three previous groups. The boll can be unilocular or multi-celled, which most often depends on the number of nests in the ovary, but sometimes it is not associated with this trait. There are various ways to open the boxes. They can be opened with denticles at the top (common cockle, cloves, tar, primrose), holes (poppy), lid (plantain, henbane), valves. The valves can diverge at the place of fusion of carpels - the abdominal suture (violet, St. John's wort, large-flowered foxglove), along the midrib of the carpels - the dorsal suture (lily, iris, tulip, Chinese tea bush). Sometimes the baffles remain connected together in the center, and the flaps move away from them (dope). Celandine has a large long, narrow capsule similar to a pod, it opens with two valves. Occasionally there are boxes that open with a lid (henbane is black, full color).

Non-opening single-seeded dry fruits differ among themselves in such characteristics as the thickness and density of the pericarp, the presence or absence of appendages, etc. Some non-opening fruits are enclosed in a special formation - a plyus, which develops from overgrown bracts, as, for example, in a hazelnut.

Dry, non-opening fruits include a nut (nut), achene, lionfish and caryopsis.

Nut and nut- these are fruits that have a dense woody pericarp, inside which a single seed is freely located. Between themselves, a nut and a nut differ only in size. Fruits of this type are found in buttercups (buttercup), buckwheat (buckwheat, highlander), etc. Close to this group of fruits is the acorn, the base of which is covered with a cup-shaped plyus made of overgrown and lignified bracts. The thorny cupule also covers the nuts of beech and sowing chestnut. Numerous strawberry nuts sit on a fleshy overgrown receptacle, forming a kind of fruit called strawberry, or fraga. Another multi-nut is the rosehip fruit, or cinarodia. He has individual fruits sitting inside a pitcher-shaped juicy hypanthium.

Achene- a fruit that has a softer leathery pericarp in comparison with a nut, which is easily separated from the seed. Achene is formed from two carpels. It is widespread in Compositae (sunflower, cornflower, string, etc.) and valerian. In many Asteraceae, the achene has a crest. Fractional achenes are also called droplet; it consists of two achenes, which, after ripening, separate, but remain suspended on special legs (conductive bundles of the fetal septum).

Lionfish- these are achenes and nuts, equipped with pterygoid appendages. They are found mainly in woody and shrub plants, for example, in elm, ash, alder, birch, among herbaceous plants - in rhubarb; the fractional lionfish is characteristic of the maple.

Caryopsis formed as a result of fusion of the seed coat with a thin pericarp. Formed by two carpels from the upper ovary of the paracarpous gynoecium. It is typical for cereals (wheat, rye, barley, oats, corn, etc.). Caryopsis are naked (rye, wheat) and filmy (barley, oats). Films are floral scales that persist and grow after flowering.

Juicy fruits... This group includes fruits with a more or less juicy fleshy pericarp that surrounds one or many seeds. Juicy fruits are formed from one or more carpels. The fleshy part of such fruits is usually formed by the intercarp, which consists of thin-walled cells with large vacuoles. Juicy fruits are brightly colored due to the presence of anthocyanin pigment in the cell sap (cherry, plum, black nightshade) or as a result of the formation of chromoplasts (mountain ash, rose hips, tomato). They are found in species of a wide variety of families. Juicy fruits include berry, a composite group of berry-like fruits (pumpkin, orange, apple) and drupe.

Berry- a multi-seeded fruit with a juicy pericarp, covered with a thin skin. The berry has a variety different structure(blueberries, cranberries, grapes, gooseberries, currants, tomatoes, eggplant, persimmons, etc.). In some plants, for example, in gooseberries and currants, the juicy part of the berry is formed not by the pericarp, but by the juicy covers of seeds, and the thin pericarp is the cover of the fruit.

The structure of the pomegranate fruit is peculiar: the pericarp forms a leathery cover and film septa of the fruit, developing from the ovary, and the seed coat, which arose from the integuments, is juicy. The fruit has a special name for pomegranate.

Pumpkin- a kind of berry, formed from the lower ovary. Differs in the strong development of vascular bundles in the pericarp and hard, often lignified exocarp. Pumpkin is typical for pumpkin (pumpkin, cucumber, melon, watermelon, loofah, etc.).

Apple- formed from the lower ovary. From the walls of the ovary, only the very core of the fruit is formed. The endocarp becomes relatively tough, leathery and surrounds the nests with seeds freely lying in them. The overgrown bases of the stamens, sepals, petals and receptacle also take part in the formation of the pulp of the fruit. The apple fruit is typical for apple, pear, quince, hawthorn, etc.

Orange- a multi-celled, multi-seeded juicy fruit with a thick leathery colored exocarp rich in essential oils. The juicy part of the fruit is formed by the overgrown hairs of the inner epidermis of the ovary, which turn into juice sacs. Typical for citrus fruits (lemon, tangerine, orange).

Drupe- single-seeded fruit, formed from one carpel. It is characterized by a clear division of the pericarp into 3 parts: leathery thin exocarp; fleshy juicy mesocarp, and lignified endocarp, forming a bone. It is found mainly in Rosaceae (apricot, cherry, blackthorn, etc.). In almonds and coconut palms, a dry drupe is formed; in their fruits, the intercarp of a mature fruit becomes fibrous and dry.

Along with the above morphological classification of fruits, there are morphogenetic classifications that reflect the evolutionary development of this plant formation. Morphogenetic classification primarily solves the theoretical problems of evolutionary morphology, in particular carpology (the science of fruits) and can be used in phylogenetic systematics.

Modern morphogenetic classifications are based mainly on the origin of the fetus from of a certain type gynoecium: apocarpous, syncarpous, lysicarpous, paracarpous, as well as the position of the ovary in the flower - upper or lower. The number of nests in the ovary is also taken into account. The most primitive are the apocarpous fruits, and among the cenocarp fruits are syncarpous.

Taking into account this approach to classification, all morphological types of fruits can be classified from morphogenetic positions. So, boxes are: a) upper syncarpous: lily, onion, tobacco, dope, henbane, snapdragon, etc.; b) lower syncarpous: iris, gladiolus; v) lower paracarpous: in orchids - orchis, two-leaved lyubka, etc.; e) upper lysicarp: in cloves - cockle, starlet; in primroses - loosestrife, primrose. Berries: a) upper syncarpous: with many seeds - grapes, tomato, potatoes, lily of the valley, asparagus, kupena; with one seed - fruit date palm; b) lower syncarpous: cranberries, lingonberries, blueberries, honeysuckle; v) upper paracarpous: capers, melon tree; G) lower paracarpous: currants, gooseberries; e) upper lysicarp: berry blister. The apple belongs to the lower syncarpous fruits, the pumpkin belongs to the lower paracarpous ones. Leaflets, beans are always the upper apocarpies. are formed from the upper ovary of the apocarpous gynoecium. In general, it should be noted that the same morphological types of fruits can develop from different types of gynoecium. This indicates a convergent evolution associated with seed distribution methods. The main trend in the evolution of gynoecium and fruits is associated with a decrease in the number of carpels forming a pistil and seeds forming in a fruit.

FLOWER
angiosperms (Angiospermae), the largest division of the plant kingdom, characterized by specialized reproductive organs that form a flower. Flowering plants have been known since the Jurassic period (about 150 million years ago): already at that time they were quite highly developed and widespread, so their first representatives, undoubtedly, appeared much earlier, possibly on lands exposed after the retreat of the sea. Subsequently, flowering plants conquered the entire planet, strongly displacing the former dominants, in particular ferns and conifers. It is flowering plants that dominate deciduous forests that once occupied significant areas in North America, and in the vast tropical forests of Central and South America, Africa and Asia. This division includes grasses that cover the American prairies and pampas, African savannas and Eurasian steppes, as well as cacti and thorny shrubs of deserts, many underwater and floating grasses of rivers, lakes and seas, moss-like species creeping over rocks and hanging from tree branches. Finally, it is the flowering plants that a person cultivates in the fields, in vegetable gardens and orchards, they are the main decoration of greenhouses and parks.

LIFE CYCLE OF A FLOWER PLANT.
The flower, a structure unique to this part of the plant, contains the reproductive organs that give rise to seeds and fruit: stamens and pistils. A series of divisions of certain cells contained in them (maternal cells of the megaspore and microspores), including the so-called. reduction division (meiosis), leads to the formation of sex cells (gametes) with half the number of chromosomes in each. For fertilization, the male gamete (sperm) from the pollen grain (more precisely, its nucleus) must merge with the female (egg), which is located in the ovule, enclosed in the ovary of the pistil. For this, a pollen tube growing through the pistil is formed. During fertilization, a zygote appears with a normal (double) number of chromosomes for the species. After a series of its divisions, an embryo is formed. The tissues surrounding it differentiate into the outer protective membrane of the seed and the nutritive tissue (endosperm). In parallel, the ovary (sometimes together with adjacent structures) is modified, turning into a fetus. After a dormant period, the seed germinates and the embryo develops into a new plant. The life cycle is complete.

STRUCTURE OF FLOWER PLANTS

STRUCTURAL TYPES

SPROUTING BEAN SEED.
a - The seed absorbs water from the soil, an embryonic root and a stalk (hypocotal knee) appear from under the peel. b - The seed coat bursts, the root burrows into the soil. c - The stalk grows upward, pulling out the embryonic leaves (cotyledons) and the bud that has begun to develop. d - The first true leaves unfold above the cotyledons - the seedling turns into a plant capable of independent existence.

LIFE FORMS OF FLOWERING PLANTS. The cactus is a desert plant adapted to water shortages: the fleshy stem is flattened, the leaves are turned into thorns, the root system is powerfully developed. Buttercup is a typical plant living in conditions of guaranteed moisture: the stem, root and leaves are well developed. Tulip is a plant with a fleshy underground stem (bulb) that stores nutrients. Pemphigus is an aquatic insectivorous plant: there are no roots, the leaves float in the water column and carry bubbles that support the stem with flowers in the air and play the role of traps for small aquatic animals that serve as food for the plant.

FLOWERS

TYPICAL BULK FLOWER often five-membered: five sepals, petals, stamens and carpels fused into one pistil with a five-lobed stigma. Longitudinal section: pollen grains are visible in the anthers, and ovules (potential seeds) in the ovary.
Pollination. The reproductive part of the stamen is its head, the so-called. anther. It usually consists of four pollen sacs located side by side. When ripe, they open up with longitudinal cracks or rounded pores and release pollen - many tiny, volatile or sticky pollen grains.

FERTILIZATION

TYPES OF FLOWERING PLANTS.
In flowering ovaries, two types of ovaries are distinguished: the lower one is, as it were, recessed in the receptacle, and the stamens and perianth are attached above it; the upper one is located above the place of their origin. The type of ovary is a characteristic feature of each plant species and determines the characteristics of the fruit that forms from it. The upper ovary is characteristic, for example, of blackberries, cherries and peaches; lower - iris (iris), sunflowers and orchids.

FRUIT

TYPES OF FRUIT.
Orange, or hesperidium, is a special type of berry-like fruit characteristic of citrus fruits, in particular oranges; its peel (zest) and juicy pulp are formed from the walls of the ovary. In the apple, the fleshy part is a derivative of the receptacle; an ovary is immersed in it, which forms only the central part of the fruit with seeds. In the drupe of the plum, both the fleshy pulp and the hard bone are formed by the wall of the ovary; the only seed is inside the seed. Raspberries and strawberries have a composite fruit that develops from one flower with many pistils. Figs and pineapples are not eaten with fruits, but with fruit, formed by many densely packed flowers and the surrounding parts of the inflorescence.

GROWTH AND GROWTH

SOCCETES

TYPES OF FLOWERS.
Sunflower: the inflorescence of the basket consists of two types of flowers - marginal ligulate and tubular forming a central disc. Geranium: dicotyledonous with a five-membered flower.

TYPES OF FLOWERS.
Saffron (crocus) is a monocotyledonous species with a three-membered flower (the number of its different parts is a multiple of three). Sweet pea is a dicotyledonous species with a bilaterally symmetrical flower.

CLASSIFICATION AND EVOLUTION