Examples of which plants have same-sex flowers. Same-sex and bisexual flowers

Same-sex relationships The Orthodox Church strongly condemns homosexuality as a mortal sin. This is not a normal sexual orientation, but a damage to human nature. When Elder Paisius of Athos was asked whether homosexuality has hereditary roots, he

The flower is a conspicuous, often beautiful, important part of flowering plants. Flowers can be large or small, brightly colored and green, odorless and odorless, single or collected together from many small flowers in one common inflorescence.

The flower is a modified shortened shoot that serves for seed reproduction... The main or lateral shoot usually ends in a flower. Like any shoot, a flower develops from a bud.

Flower structure

A flower is a reproductive organ of angiosperms, consisting of a shortened stem (flower axis), on which the cover of the flower (perianth), stamens and pistils, consisting of one or more carpels, are located.

The axis of the flower is called receptacle... The receptacle, expanding, accepts different shape flat, concave, convex, hemispherical, cone-shaped, elongated, columnar. The receptacle at the bottom turns into a peduncle connecting the flower with the stem or peduncle.

Flowers without pedicels are called sessile. On the peduncle, many plants have two or one small leaves - bracts.

Flower cover - perianth- can be dissected into a cup and a rim.

Cup forms the outer circle of the perianth, its leaves are usually relatively small size, Green colour... Distinguish between separate and systolic calyx. It usually serves to protect the inner parts of the flower before the bud opens. In some cases, the calyx drops when the flower opens, and most often it persists during flowering.

The parts of the flower located around the stamens and pistil are called the perianth.

The inner leaves are the petals that make up the corolla. The outer leaves - sepals - form a calyx. The perianth, consisting of a calyx and a corolla, is called double. The perianth, which is not subdivided into a corolla and a calyx, and all the leaves of the flower are more or less the same, is simple.

Corolla- the inner part of the perianth, differs from the calyx in its bright color and larger size. The color of the petals is due to the presence of chromoplasts. Distinguish between separate and joint-petal corollas. The first consists of individual petals. In spliced ​​corollas, a tube is distinguished and a bend perpendicularly located in relation to it, which has a certain number of teeth or blades of the corolla.

Flowers are symmetrical and asymmetrical. There are flowers that do not have a perianth, they are called naked.

Symmetrical (actinomorphic)- if many axes of symmetry can be drawn through the rim.

Asymmetrical (zygomorphic)- if only one axis of symmetry can be drawn.

Double flowers have an abnormally increased number of petals. In most cases, they result from the splitting of the petals.

Stamen- a part of a flower, which is a kind of specialized structure that forms microspores and pollen. It consists of a filament by means of which it is attached to the receptacle, and an anther containing pollen. The number of stamens in a flower is a systematic feature. Stamens are distinguished by the method of attachment to the receptacle, by the shape, size, structure of the filaments, the binder and the anther. The collection of stamens in a flower is called androecium.

Filament- the sterile part of the stamen, bearing the anther at its apex. The filament can be straight, curved, twisted, twisted, broken. In shape - hair-like, conical, cylindrical, flattened, clavate. By the nature of the surface - naked, pubescent, hairy, with glands. In some plants, it is short or does not develop at all.

Anther located at the top of the filament and attached to it by a binder. It consists of two halves, interconnected by a liaison. Each half of the anther has two cavities (pollen sacs, chambers, or nests) in which pollen develops.

As a rule, the anther is four-celled, but sometimes the partition between the nests in each half collapses, and the anther becomes two-celled. In some plants, the anther is even unicellular. Very rare in three-celled. By the type of attachment to the filament, there are stationary, mobile and swinging anthers.

The anthers contain pollen or pollen grains.

Pollen grain structure

The dust particles formed in the anthers of the stamens are small grains, and they are called pollen grains. The largest ones reach 0.5 mm in diameter, but they are usually much smaller. Under the microscope, you can see that the dust particles different plants are not at all the same. They differ in size and shape.

The surface of the dust grain is covered with various protrusions and tubercles. Once on the stigma of the pistil, the pollen grains are retained by outgrowths and sticky liquid released on the stigma.

The nests of the young anther contain special diploid cells. As a result of meiotic division, four haploid spores are formed from each cell, which are called microspores for their very small size. Here, in the cavity of the pollen sac, microspores turn into pollen grains.

It happens as follows: the microspore nucleus is mitotically divided into two nuclei - vegetative and generative. Around the nuclei, areas of the cytoplasm are concentrated and two cells are formed - vegetative and generative. On the surface of the cytoplasmic membrane of the microspore, a very strong shell is formed from the contents of the pollen sac, insoluble in acids and alkalis. Thus, each pollen grain consists of vegetative and generative cells and is covered with two membranes. A lot of pollen grains make up the pollen of the plant. The pollen matures in the anthers by the time the flower blooms.

Pollen germination

The beginning of pollen germination is associated with mitotic division, as a result of which a small reproductive cell is formed (sperm develops from it) and a large vegetative cell (a pollen tube develops from it).

After the pollen in one way or another gets on the stigma, its germination begins. The sticky and uneven surface of the stigma helps to retain pollen. In addition, the stigma secretes a special substance (enzyme) that acts on the pollen, stimulating its germination.

The pollen swells, and the restraining effect of the exine (the outer layer of the pollen grain shell) causes the contents of the pollen cell to break one of the pores through which the intina (the inner, poreless shell of the pollen grain) protrudes outward in the form of a narrow pollen tube. The contents of the pollen cell pass into the pollen tube.

Under the epidermis of the stigma there is a loose tissue into which the pollen tube penetrates. It continues to grow, passing either through a special conductive channel between the mucous cells, or tortuously along the intercellular spaces of the conductive tissue of the column. In this case, a significant number of pollen tubes usually move simultaneously in the column, and the "success" of one or another tube depends on the individual growth rate.

Two sperm and one vegetative nucleus pass into the pollen tube. If the formation of sperm cells in the pollen has not yet occurred, then the generative cell passes into the pollen tube, and here, by its division, sperm cells are formed. The vegetative nucleus is often located in front, at the growing end of the tube, and sperm cells are sequentially located behind it. In the pollen tube, the cytoplasm is in constant motion.

Pollen is rich in nutrients. These substances, especially carbohydrates (sugar, starch, pentosans) are intensively consumed during pollen germination. In addition to carbohydrates in chemical composition pollen includes proteins, fats, ash and an extensive group of enzymes. The pollen contains a high content of phosphorus. Substances are in a mobile state in pollen. Pollen is easy to carry low temperatures up to - 20Cº and even lower, for a long time. High temperatures quickly reduce germination.

Pestle

The pistil is the part of the flower that forms the fruit. It arises from the carpel (leaf-like structure, bearing ovules) after the fusion of the edges of the latter. It can be simple, if it is composed by one carpel, and complex, if it is composed of several simple pistils, fused together by the side walls. In some plants, pistils are underdeveloped and are represented only by rudiments. The pistil is dismembered into an ovary, a column, and a stigma.

Ovary — Bottom part pistil, in which the seed buds are located.

Having entered the ovary, the pollen tube grows further and enters the ovule in most cases through the pollen duct (micropyle). Infiltrating embryo sac, the end of the pollen tube bursts, and the contents are poured onto one of the synergids, which darkens and quickly collapses. The vegetative nucleus is usually destroyed before the pollen tube penetrates into the embryonic sac.

Flowers are right and wrong

Tepals (single and double) can be arranged so that several planes of symmetry can be drawn through it. Such flowers are called correct. Flowers through which one plane of symmetry can be drawn are called irregular.

Flowers bisexual and dioecious

Most plants have flowers that contain both stamens and pistils. These are bisexual flowers. But in some plants, some flowers have only pistils - pistillate flowers, while others - only stamens - staminate flowers. Such flowers are called dioecious.

Plants are monoecious and dioecious

Plants on which both pistillate and staminate flowers develop are called monoecious. Dioecious plants have staminate flowers on one plant and pistillate flowers on another.

There are species in which bisexual and unisexual flowers can be found on one plant. These are the so-called polygamous (polygamous) plants.

Inflorescences

Flowers are formed on the shoots. Very rarely, they are located alone. More often flowers are collected in notable groups, which are called inflorescences. The beginning of the study of inflorescences was laid by Linnaeus. But for him, the inflorescence was not a type of branching, but a way of flowering.

In inflorescences, the main and lateral axes are distinguished (sessile or on pedicels), then such inflorescences are called simple. If the flowers are on the lateral axes, then these are complex inflorescences.

Inflorescence type	Inflorescence scheme	Peculiarities	Example
Simple inflorescences
Brush		Separate lateral flowers sit on an elongated main axis and at the same time have their own pedicels, approximately equal in length	Bird cherry, lily of the valley, cabbage
Ear		The main axis is more or less elongated, but the flowers are without legs, i.e. sedentary.	Plantain, orchis
Ear of ear		It differs from the spike in the fleshy, thickened axis.	Corn, calla
Basket		The flowers are always sessile and sit on the strongly thickened and widened end of the shortened axis, which has a concave, flat or convex appearance. In this case, the inflorescence outside has a so-called wrapper, consisting of one or many successive rows of bracts, free or accrete.	Chamomile, dandelion, aster, sunflower, cornflower
Head		The main axis is greatly shortened, the lateral flowers are sessile or almost sessile, closely spaced to each other.	Clover, scabiosa
Umbrella		The main axis is shortened; lateral flowers emerge, as it were, from one place, sit on legs of different lengths, located in the same plane or domed.	Primrose, onion, cherry
Shield		It differs from the brush in that the lower flowers have long pedicels, so that, as a result, the flowers are located almost in the same plane.	Pear, spirea
Complex inflorescences
Complex brush or broom		From the main axis there are lateral branching axes, on which flowers or simple inflorescences are located.	Lilac, oats
Sophisticated umbrella		Simple inflorescences extend from the shortened main axis.	Carrots, parsley
Complex ear		Individual spikelets are located on the main axis.	Rye, wheat, barley, wheatgrass

The biological significance of inflorescences

The biological significance of inflorescences is that small, often inconspicuous flowers, collected together, become noticeable, give the largest number pollen and better attract insects, which carry pollen from flower to flower.

Pollination

In order for fertilization to take place, it is necessary that the pollen gets on the stigma of the pistil.

The process of transferring pollen from the stamens to the stigma of the pistil is called pollination. There are two main types of pollination: self-pollination and cross-pollination.

Self-pollination

During self-pollination, pollen from the stamen enters the stigma of the pistil of the same flower. This is how wheat, rice, oats, barley, peas, beans, and cotton are pollinated. Self-pollination in plants most often occurs in an unopened flower, that is, in a bud, when the flower opens, it is already completed.

During self-pollination, germ cells that have formed on one plant and, therefore, have the same hereditary characteristics, merge. This is why the offspring resulting from the self-pollination process is very similar to the parent plant.

Cross pollination

With cross-pollination, a recombination of hereditary characteristics of the paternal and maternal organisms occurs, and the resulting offspring can acquire new properties that the parents did not have. Such offspring are more viable. In nature, cross-pollination is much more common than self-pollination.

Cross-pollination is carried out using various external factors.

Anemophilia(wind pollination). In anemophilous plants, flowers are small, often collected in inflorescences, a lot of pollen is formed, it is dry, small, when the anther is opened, it is thrown out with force. Light pollen from these plants can be carried by the wind over distances of up to several hundred kilometers.

Anthers are located on long thin filaments. The stigma of the pistil is wide or long, feathery and protruding from the flowers. Anemophilia is characteristic of almost all cereals and sedges.

Entomophily(transport of pollen by insects). The adaptation of plants to entomophilia is the smell, color and size of flowers, sticky pollen with outgrowths. Most flowers are bisexual, but the maturation of pollen and pistils does not occur simultaneously, or the stigma height is greater or less than the height of the anthers, which serves as protection against self-pollination.

In the flowers of insect pollinated plants, there are areas that emit a sweet aromatic solution. These areas are called nectaries. Nectars can be found in different places of the flower and have different shapes... Insects, flying up to the flower, reach for nectaries and anthers and get dirty with pollen during the meal. When the insect moves to another flower, the pollen grains carried by it adhere to the stigmas.

When pollinated by insects, less pollen is wasted and therefore the plant conserves substances by producing less pollen. The pollen grains do not need to stay in the air for long and can therefore be heavy.

Insects can pollinate sparsely located flowers and flowers in calm places - in forest thickets or thicker grass.

Typically, each plant species is pollinated by several species of insect, and each species of pollinator serves several species of plants. But there are plant species whose flowers are pollinated by insects of only one species. In such cases, the mutual correspondence of the ways of life and the structure of flowers and insects is so complete that it seems miraculous.

Ornithophilia(pollination by birds). Typical for some tropical plants with brightly colored flowers, abundant nectar secretion, strong elastic structure.

Hydrophilia(pollination with water). Observed in aquatic plants... The pollen and stigma of these plants are most often filamentous.

Bestiality(pollination by animals). These plants are characterized by large flower sizes, abundant secretion of nectar containing mucus, mass production of pollen, when pollinated. bats- bloom at night.

Fertilization

The pollen grain enters the stigma of the pistil and attaches to it due to the peculiarities of the structure of the shell, as well as the sticky sugary secretions of the stigma, to which the pollen adheres. The pollen grain swells and grows into a long, very thin pollen tube. The pollen tube is formed as a result of division of the vegetative cell. First, this tube grows between the cells of the stigma, then - of the column, and finally grows into the cavity of the ovary.

The generative cell of the pollen grain moves into the pollen tube, divides and forms two male gametes (sperm). When the pollen tube enters the embryo sac through the pollen duct, one of the sperm is fused with the egg. Fertilization occurs and a zygote is formed.

The second sperm is fused with the nucleus of the large central cell of the embryonic sac. Thus, in flowering plants, two fusions occur during fertilization: the first of the sperm fuses with the egg, the second with a large central cell. This process was discovered in 1898 by a Russian botanist, academician S.G. Navashin and named it double fertilization... Double fertilization is typical only for flowering plants.

The zygote formed during the fusion of gametes is divided into two cells. Each of the cells that arose in this process divides again, and so on. As a result of multiple cell divisions, a multicellular embryo of a new plant develops.

The central cell also divides, forming endosperm cells, in which reserves accumulate nutrients... They are necessary for the nutrition and development of the embryo. The seed coat develops from the ovule cover. After fertilization, a seed develops from the ovule, consisting of a peel, an embryo and a supply of nutrients.

After fertilization, nutrients flow to the ovary, and it gradually turns into a ripe fruit. The pericarp, which protects the seeds from adverse effects, develops from the walls of the ovary. In some plants, other parts of the flower are also involved in the formation of the fruit.

Dispute formation

Simultaneously with the formation of pollen in the stamens, a large diploid cell is formed in the ovule. This cell divides meiotically and gives rise to four haploid spores, which are called macrospores, since they are larger in size than microspores.

Of the four formed macrospores, three die off, and the fourth begins to grow and gradually turns into an embryonic sac.

Embryo sac formation

As a result of three-fold mitotic division of the nucleus in the cavity of the embryonic sac, eight nuclei are formed, which are clothed with cytoplasm. Cells devoid of shells are formed, which are arranged in a certain order. At one pole of the embryonic sac, an egg apparatus is formed, consisting of an egg and two auxiliary cells. At the opposite pole there are three cells (antipodes). One nucleus (polar nuclei) migrates from each pole to the center of the embryo sac. Sometimes the polar nuclei merge and form the diploid central nucleus of the embryo sac. The embryonic sac, in which the nuclei have differentiated, is considered mature, it can perceive sperm.

By the time the pollen and the embryo sac ripen, the flower opens up.

The structure of the ovule

The ovules develop on inner sides the walls of the ovary and, like all parts of the plant, are composed of cells. The number of ovules in the ovaries of different plants is different. In wheat, barley, rye, cherry, the ovary contains only one ovule, in cotton - several dozen, and in poppy, their number reaches several thousand.

Each ovule is covered with a cover. At the top of the ovule there is a narrow channel - the pollen passage. It leads to the tissue that occupies the central part of the ovule. In this tissue, as a result of cell division, an embryonic sac is formed. Opposite the pollen passage, there is an ovum in it, and the central part is occupied by a large central cell.

The development of angiosperms (flowering) plants

Seed and fruit formation

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

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

Sexual reproduction

Sexual reproduction of angiosperms is associated with the flower. Its most important parts are stamens and pistils. Complex processes associated with sexual reproduction take place in them.

In flowering plants, the male gametes (sperm cells) are very small, while the female gametes (eggs) are much larger.

In the anthers of the stamen, cell division occurs, as a result of which pollen grains are formed. Each pollen grain of angiosperms consists of vegetative and generative cells. The pollen grain is covered with two shells. The outer shell, as a rule, is uneven, with spines, warts, and outgrowths in the form of a mesh. This helps the pollen grains stay on the stigma of the pistil. The pollen of the plant, which matures in the anthers, by the time the flower blooms, consists of many pollen grains.

Flower formula

For the conditional expression of the structure of flowers, formulas are used. To draw up a flower formula, the following designations are used:

An example of a cherry blossom formula:

* H 5 L 5 T ∞ P 1

Flower diagram

The structure of a flower can be expressed not only by a formula, but also by a diagram - schematic illustration flower on a plane perpendicular to the axis of the flower.

A cross-sectional diagram of unopened flower buds is plotted. The diagram gives a more complete idea of ​​the structure of a flower than a formula, since it also shows the relative position of its parts, which cannot be shown in the formula.

Same-sex plant species are those in which flowers of both sexes are placed on the same tree or shrub, therefore they are also called bisexual species. Sometimes there are polygamous cultures, which have male bisexual and same-sex flowers at the same time on a single individual.

Monoecious species, in which flowers of two sexes immediately grow, are very common in nature.

Examples of monoecious plants

Hazel

Watermelon

Hazel

Birch

Corn

Walnuts

Pumpkin crops

Flowers of plants with monoecious

Monoeciousness is a special device, which consists in the fact that flowers of both sexes live in the same "house". On the same tree or shrub, both staminate and pistillate inflorescences are found. Sometimes there are flowers in which the perianths are not fully formed. In this case, pollen is well sprayed by the wind over long distances, and bees carry it, but their main advantage is that they have a self-pollination mechanism (entomophilia), therefore, do not depend on external factors. This happens when pollination occurs in one flower: pollen from some inflorescences falls on others. It should be noted that in stressful situations for plants, they turn from monoecious. This is seen in cannabis.

How is pollination of monoecious plants

Various monoecious species have their own pollination characteristics. For this, it is better to consider a few examples. So the walnut is considered a wind-pollinated tree. The fact is that bees sit only on male inflorescences, and female ones do not visit, therefore insects take practically no part in pollination of flowers. walnut... This also happens because the male and female flowers do not bloom on the tree at the same time. In this regard, the inflorescences are pollinated due to the activity of the wind.

An interesting pollination mechanism in hazel. This is a genus of shrubs and trees (in rare cases) in which the male flowers are in the earrings, and the female flowers are in the middle of the buds, so they are not easy to reach. Pollination is due to the wind.

Thus, in nature, the monoecious mechanism is most often found, when both male and female flowers grow on the same plant. So the plants have a much better chance of pollination. First, bees do not need to fly long distances to deliver pollen from male flowers to female flowers. Secondly, if insects take little part in the pollination process, then the wind will always scatter the pollen, and it will fall from male flowers onto female flowers, which will subsequently ensure the appearance of fruits.

Bisexual they call a flower that has both pistils and stamens (androecium and gynoecium). Sometimes the terms are also applied to a bisexual flower perfect or monoecious flower.

A flower that has only stamens (androecium) or only pistils (gynoecium) is called same sex... Unisexual flowers with stamens are staminate, or male flowers; accordingly, flowers only with pistils - pistillate, or female flowers.

Male and female same-sex flowers can grow on the same plant, then the plant is called monoecious, or bisexual, for example: oak, birch, spurge, corn... In this case, pollination can occur between flowers within the same plant.

If male and female flowers grow on different plants, then we are dealing with dioecious plant. A dioecious plant with staminate flowers is called male , and with women - female a plant, for example: poplar, willow, hemp, nettle... For the fertilization of dioecious species, it is necessary to have at least two heterosexual plants - male and female.

A plant on which both bisexual and unisexual flowers are found is called polygamous, for example, such a neighborhood is found in the inflorescences of Compositae.

Flowers devoid of spore-bearing organs are sterile, or asexual flowers, such as ligulate flowers in Compositae inflorescences.

An example of a polygamous plant: in the gerbera inflorescence in the photo there are male flowers (with yellow anthers), female (with white pistils) and sterile reed flowers along the edge.

Flowers of cereals, sedges.

Flowers of cereals, sedges.

Cereal flowers are usually small and inconspicuous. They are adapted for wind pollination, and therefore lack a perianth, since they have no need to attract insects. Flowers of cereals are located on the lateral shoots of a spikelet and consist of stamens and ovaries with stigma branches ... The flower is protected by the top and bottom flowering scales ... Above the flowering scales, two small colorless scales grow - the so-called flower films , or lodicules ... During flowering, long stamens protrude beyond the scales, spreading pollen downwind. Flowers of cereals can be bisexual or unisexual, sometimes within the same inflorescence.

Sedge flowers are also small and inconspicuous, collected in a variety of spikelets and sit in the axils of the bracts, called covering scales ... The sedge flower itself consists of stamens and saviazi with stigma branches ... Flowers are bisexual and unisexual, with or without perianth. The perianth of sedges may consist of a set of scales, hairy or fringed bristles or silky hairs, and is more often present in bisexual or female flowers.

ANDROECIUM

(Greek. "Man's house"): collection microsporophylls, stamens consisting of a filament, divided into two halves anther containing four microsporangia (pollen sac). The stamens are arranged in one or two circles. Stamens are divided into free and accrete.

Exists different types androcea, distinguished by the number of accrete groups of stamens:

-one-brother(stamens in one group, lupine, camellia),

-double-breasted(two groups of stamens),

-plural(several groups, magnolia, St. John's wort),

-fraternal(non-accrete stamens).

Also, the stamens vary in length: equal, unequal, double-strength(out of four stamens, two are long), three-strength(out of six stamens, three are long), four-strong(of six stamens, four are long).

Stamen comprises staminate tissue, at the upper end of which is located anther, and the lower end is attached to the receptacle. The main fabric of the filament is parenchyma... Important processes take place in the anther - microsporogenesis(formation of microspores in microsporangia) and microgametogenesis(formation of male gametophyte from microspores). The sterile stamen is called staminode.

Fig. 3 Stamen and anther development

Anther consists of homogeneous cells surrounded by an epidermis.

Diagram Is a schematic projection of a flower on a plane, in which the flower intersects across, perpendicular to its axis. The rule for the design of the diagram: the inflorescence axis is at the top, the cover leaf at the bottom. Symbols Diagrams: arcs indicate parts of the perianth, sepals - with a protrusion in the middle of the arc, petals - without a protrusion. The stamens are indicated in the form of a cross-section of the anther or filament. Gynoecium - in the form of a cross-section of the ovary. If individual members grow together, this is indicated on the diagram by arcs.

Androecium

Androeum is a collection of stamens in which microsporogenesis, microgametophytogenesis and the formation of male spores occur.

In ontogeny, stamens can be laid in the form of tubercles of the growth cone, as in acropetal(i.e. from the base to the top), and in basipetal(top to bottom) sequence. In the first case, the youngest stamens are located closer to the center of the flower, and the oldest ones are closer to its periphery, and in the second, vice versa. The stamens can be free or grow together in various ways and in varying degrees... For example, in the tropical family of Meliaceae, all 10 stamens grow together with their filaments into a tube ( one-brother androecium). In St. John's wort, the stamens grow together in bunches; for Compositae, gluing of anthers is characteristic. In many members of the legume family, 9 stamens grow together, and one remains free (the so-called double-breasted androecium).

Each stamen consists of a narrowed filamentous or rarely ribbon-like or petal-shaped part - a filamentous filament and usually an expanded part - an anther. The boot has two halves connected to each other messenger, which is a continuation of the filament. The binder is sometimes extended into the binder, visible as a small projection above the anther.

Filament formation begins later than the anther, and its further elongation occurs due to intercalary growth. The number of tubercles forming sometimes less number stamens, later the tubercles are split, and there can be quite a lot of stamens (mimosa). The length of filaments varies from plant to plant. Most often they are more or less equal in length to the perianth, but sometimes they are much shorter or many times longer, as, for example, in the famous tropical medicinal plant kidney tea, or cat's whiskers, from the labiate family. On a transverse section through the filament, it can be seen that most of it consists of parenchymal tissue, and one vascular bundle passes in the center.

Each half of the anther carries two (rarely one) nests - microsporangia... Anther nests are sometimes called pollen sacs. In the mature anther, the partitions between the nests mostly disappear. Outside, the anther is covered with epidermis. Directly under the epidermis is a layer of cells of the so-called endothecium, having a secondarily thickened cell membranes. When the endothecium membranes dry out, the anther nests are opened. 1-3 layers of medium-sized thin-walled cells lie deeper. The innermost layer lining the cavity of the pollen sacs is called tapetum... It is believed that the contents of its cells serve as food for the developing mother cells. microspore(microsporocytes) and promotes their differentiation. Anther nests are usually filled with microspore mother cells, microspores and mature pollen. Microspores are known to arise from microsporocytes as a result of meiosis, and microsporocytes themselves arise from a few archesporic cells (educational tissue functioning at the early stages of anther nest development). The matured anther is opened in a variety of ways: longitudinal cracks, holes, valves, etc. In this case, the pollen spills out.

Signs of the structure, shape, position, number of stamens, as well as the type of androeus itself have great importance for the taxonomy of flowering plants and knowledge of their phylogeny.

In some species, some of the stamens lose their original function, become sterile and turn into the so-called staminodes... Sometimes anthers are transformed into nectaries - secretory parts of a flower that secrete nectar. Petals, their parts, parts of the pistil, and even outgrowths of the receptacle can also turn into nectaries or osmophores. Nectars are of various shapes, usually located in the depths of the flower, and often stand out for their shiny surface.

Gynoecium.

The set of carpels of one flower, forming one or more pistils, is called gynoecium... Carpels, or carpella, Are structures that are believed to be related in origin to the sheet. However, functionally and morphologically, carpels correspond not to vegetative leaves, but to leaves bearing megasporangia, i.e., megasporophylls. Most morphologists believe that in the course of evolution from flat and open carpels, folded along ( conductively) carpels. Then they fused together at the edges and formed a pistil with its most essential part - the ovary carrying the ovules. Thus, a unique structure, which is not found in any other group of plants, resembles a closed vessel, in which reliably protected ovules develop. The structure of the pistil is ideally suited for pollination and fertilization. In the ovules in the ovary, the processes of megasporogenesis and megagametophytogenesis are carried out.

The pistil, or rather the ovary, acts as a wet chamber that protects the ovules from drying out. This made the angiosperms almost independent of moisture levels. environment and was one of the factors of their widespread development of arid territories. In addition, the pistil reliably shelters the ovules from being eaten by insects and partly from temperature fluctuations.

A pistil formed from one carpel is called simple, from two or more accrete carpels - complex. The simple pistil is usually unilocular; complex can be divided into nests or it can also be single-nested. Multi-nesting occurs either as a result of fusion of carpels, or as a result of the formation of additional partitions - outgrowths of the walls of the ovary.

The stigma of the pistil is a structure, unique and characteristic only for flowering plants, intended for the perception of pollen. It develops at the apex of the column or directly on the ovary - a sessile stigma; less often (in archaic species) - along the fused edges of the carpel. The shape and size of the stigma is different in different species. The surface of the stigma is very often uneven, lumpy and covered with a sticky liquid, which contributes to more effective fixation and trapping of pollen. In addition, the stigma surface bears a thin protein layer - the pellicle, which, interacting with the proteins of the sporoderm of the pollen grain, ensures the germination of the pollen tube or prevents it.

The column consists of loose parenchymal tissue. He kind of raises the stigma up, which is necessary for some mechanisms of the pollination process. The morphology of the columns is quite diverse and serves as an important systematic feature. Many archaic families (especially those from the subclass Magnolids) are characterized by the absence or weak development of the column. Columns are often undeveloped in many specialized wind-pollinated forms, for example, in many cereals. In large, wind-pollinated flowers (in some species of lilies), the columns reach a considerable length, the stigma is carried high upward, and thereby facilitates pollination. However, this significantly lengthens the path of the pollen tube.

The ovary is the most essential part of the pistil, bearing the ovules. It is diverse in shape and outward appearance, which is largely determined by the type of gynoecium.

The place of attachment of the ovules in the ovary is called placenta... The placenta usually has the form of a small swelling, outgrowth or protrusion formed by the tissues of the ovary.

Depending on the peculiarities of the attachment of the ovules to the wall of the ovary, several types of placentation are distinguished.

· Mantle, or pariental, when the ovules are located inside the ovary along its walls or in the places of fusion of carpels.

· Axial, or axial, when the ovules are located on the central column of the ovary, divided into nests according to the number of carpels.

· Free central placentation, when ovules develop on a free central column, not connected by septa to the wall of the ovary.

· Basal, when the only ovule is located at the very base of the unilocular ovary.

Types of gynoecium:

1.apocarpous - carpels do not grow together with each other, and each carpel forms a separate pistil (buttercup, rose)

a) monomeric - gynoecium consists of 1 pistil, and it is formed by 1 carpel (peas, plums, cherries)

b) polymer - there are many pistils, but each consists of one carpel

(buttercup, strawberry, rosehip)

1.coenocarpous - the pistil is formed from intergrown carpels

a) syncarpous - carpels grow together with lateral surfaces, several rings are formed (tulip). Several nests are formed inside the fruit.

b) paracarpous - the carpels grow together at the edges and form one ring (poppy), or the central chamber.

c) lysicarpous - the carpels grow together at the edges, forming one chamber or cavity, and a column protrudes from the bottom of the ovary, on which the ovule is located, and then the seeds (clove).

13. Ovule - a relatively complex formation, consisting of a seedle (funicular) bearing nucellus, enclosed in one or two integuments. Depending on the species, from one to many ovules develop on the placentas. The developing ovule initially consists entirely of nucellus, but soon one or two integumentous layers (integuments) with a small hole, micropyle, appear at one end (Fig. 6).

Rice. 6. Scheme of the formation of the ovule and embryo sac.

1, 2, 3, 4 - development of nucellus, isolation and meiosis of the archesporic cell, death of three megaspores; 5, 6, 7, 8 - development of the (remaining) female gametophyte from the megaspore - the embryo sac.

At an early stage of development of the ovule, a single diploid megasporocyte appears in the nucellus. It divides mitotically, producing four haploid megaspores, usually arranged in a linear tetrad. This completes megasporogenesis. Three megaspores are usually destroyed, and the fourth, farthest from the micropyle, develops into the female gametophyte.

The functional megaspore soon begins to increase due to nucellus, and its nucleus divides mitotically three times. At the end of the third mitosis, eight daughter nuclei are arranged in four in two groups - near the micropilar end of the megagametophyte, as well as at the opposite, chalazal, end. One nucleus from each group migrates to the center of the eight-nucleus cell; they are called polar. The three nuclei remaining at the micropilar end form the egg apparatus, which consists of an egg and two synergid cells. At the chalazal end, the formation of cell membranes around the nuclei located here also takes place, and the so-called antipode cells arise. The polar nuclei remain in the binucleated central cell. This eight-core, seven-cell structure is the mature female gametophyte called the embryo sac.