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Fertilization in flowering plants. Ovules in flowering plants develop in the Structure and development of the plant ovule

Fertilization in flowering plants. Ovules in flowering plants develop in the Structure and development of the plant ovule

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Male reproductive cells - sperm - are formed in pollen grains, which develop in the anthers of flower stamens. Typically, pollen consists of many grains of dust (pollen grains) connected in groups. Sperm - male reproductive cells - are formed in dust particles.

Female reproductive cells - eggs - are formed in the ovules located in the ovary of the pistil of a flower (flowering plants have ovaries with one or more ovules). In order for seeds to develop from all ovules, sperm must be delivered to each ovule to the eggs, since each egg is fertilized by a separate sperm.

The process of fertilization in plants is preceded by pollination. As soon as a speck of dust lands on the stigma of the pistil (either by wind or insects), it begins to germinate. One of its walls extends and forms a pollen tube. At the same time, two sperm are formed in a speck of dust. They move to the tip of the pollen tube. Moving through the tissues of the stigma and style, the pollen tube reaches the ovary and penetrates into the ovule.

By this time, in the ovule, in its middle part, one cell divides and greatly elongates, forming the so-called embryo sac. It contains an egg at one end, and in the center there is a cell with two nuclei, which soon merge to form one - the central nucleus. Having penetrated the ovule, the pollen tube grows into the embryo sac, and there one sperm fuses (joins) with the egg, forming a zygote, from which the embryo of a new plant develops.

Another sperm that enters the embryo sac fuses with the central nucleus. The resulting cell divides very quickly, and soon nutritious tissue - endosperm - is formed from it.

The fusion of sperm in the embryo sac, one with the egg and the other with the central nucleus, is called double fertilization.

The process of double fertilization is a phenomenon characteristic only of flowering plants. Thanks to double fertilization, the embryo of a new plant receives very valuable endosperm with nutrients.

There is also this classification:

13. Structure and functions of a flower.

Flower - organ of seed reproduction of angiosperms. A flower consists of a peduncle, receptacle, perianth, androecium and gynoecium.

Fertile parts of a flower (stamen, pistil).

Sterile parts of the flower (calyx, corolla, perianth).

Functions of a flower.

A flower is a modified shortened shoot adapted for the reproduction of angiosperms (flowering) plants.

The exclusive role of the flower is due to the fact that it combines all the processes of asexual and sexual reproduction, while in lower and many higher plants they are separated. In a bisexual flower, micro- and megasporogenesis, micro- and megagametogenesis, pollination, fertilization, and the formation of seeds and fruits take place. The structural features of the flower allow the above functions to be carried out with minimal costs plastic substances and energy.

The central (main) parts of the flower. Most plants have one or more pistils in the center of the flower. Each pistil consists of three parts: the ovary - an expanded base; column - more or less elongated middle part; stigma - the upper part of the pistil. One or more ovules are located inside the ovary. Outside, the ovule is surrounded by integuments through which a narrow channel passes - the pollen passage.

The stamens are located around the pistil (or pistils). Their number in a flower varies among flowering plants: in wild radish - 6, in clover - 10, in cherry - many (about 30). The stamen consists of two anthers and a filament. Pollen develops inside the anther. Individual dust particles are usually very small grains. They are called pollen grains. The largest pollen grains reach 0.5 mm in diameter.

Perianth. In most flowers, the pistils and stamens are surrounded by perianth. In cherries, peas, and buttercups, the perianth consists of a corolla (a set of petals) and a calyx (a set of sepals). This type of perianth is called double. A tulip, lily, or lily of the valley has all the same leaves. Such a perianth is called simple.

Flowers with double perianth

Flowers with a simple perianth

The tepals may grow together or remain free. The tulip and lily have a simple, separate-leaved perianth, while the lily of the valley has a compound-leaved perianth. In flowers with a double perianth, both sepals and petals can also grow together. Primrose flowers, for example, have a fused calyx and a fused corolla. Cherry buttercup flowers have a separate-leaved calyx and a separate-petalled corolla. The bell has a separate-leaved calyx and a fused-petalled corolla.

The flowers of some plants do not have a developed perianth. For example, in willow flowers it resembles scales.

Willow inflorescences and flowers

Flower formula. The structural features of a flower can be noted briefly in the form of a formula. When compiling it, the following abbreviations are used:

Ok - tepals of a simple perianth,

H - sepals, L - petals, T - stamens, P - pistils.

The number of parts of a flower is indicated by numbers in the form of an index (H5 is 5 sepals); if there are a large number of parts of a flower, the sign ∞ is used. If the parts grow together, the number indicating their number is placed in brackets (L(5) - the corolla consists of 5 fused petals). If the parts of the flower of the same name are located in several circles, then a + sign is placed between the numbers indicating their number in each circle (T5+5 - 10 stamens in a flower are arranged 5 in two circles). For example, the formula of the lily flower- Ok3+3T3+3P1, bell- Ch5L(5)T5P1.

Receptacle. All parts of the flower (near the flower bed, stamens, pistils) are located on the receptacle - the overgrown axial part of the flower. Most flowers have a pedicel. It extends from the stem and connects it to the flower. In some plants (wheat, clover, plantain) the pedicels are not pronounced. Such flowers are called sessile.

Flowers are bisexual and unisexual. Usually one flower contains both pistil(s) and stamens. Such flowers are called bisexual. Some plants (willow, poplar, corn) have only pistil or stamens in the flower. Such flowers are called unisexual - staminate or pistillate (Fig. 71).

Monoecious and dioecious plants. In birch, corn, and cucumber, unisexual flowers (staminate and pistillate) are located on the same plant. Such plants are called monoecious. In poplar, willow, sea buckthorn, and stinging nettle, some plants have only staminate flowers, while others have pistillate flowers. These are dioecious plants.

The ovary is the empty lower thickened part of the pistil - female organ plant propagation.

It provides protection and fertilization of the ovules (ovules) from which seeds are formed.

The pistil is located in the flower and consists of a stigma that traps pollen, a style that carries pollen inside, and an ovary where the seeds develop. After fertilization, a fetus is formed from it.

In the central part of the ovule (nucellus) there are eggs; in the case of pollination, they are fertilized and seeds develop from them. In the same place, an embryo sac is formed, from which they will feed.

Functions of the ovary

  • Inside the ovary, the process of fertilization and seed maturation takes place;
  • Protects ovules from external harmful environmental factors (temperature changes, drought, eating by insects, rain, etc.);
  • Maintains the required level of moisture;
  • Provides nutrition to seeds;
  • It is the basis of the future fetus.

Types of ovary

According to the number of nests, that is, existing cavities separated by partitions in which the seeds are located, the ovary can be single- or multi-locular.

I - single-locular ovary, II - two-locular ovary, III - five-locular ovary. In all pictures: 1 - wall of the ovary; 2 - socket; a - ovules, 4 - seed carrier.

Another classification of ovaries is based on their location in relation to the receptacle.

The receptacle is the lower part of the flower, that is, its base, on which the petals, sepals, stamens and pistils are located.

According to the type of location, the ovary can be:

  • Upper or free - located above the receptacle. It does not grow together with other parts of the flower; the flower is called subpistillate (cereals, ranunculaceae, legumes, etc.);
  • The lower one is under the receptacle, the flower is attached to the top of the ovary, therefore it is called suprapistal (Asteraceae, cactaceae, orchids, etc.);
  • Semi-inferior - grows together with the flower, but not at the very top; the flower is called semi-pistillate (saxifrage).

Formation of fruits from the ovary

Fruits, depending on the type of formation from the ovary, are divided into several types: 1. Real - formed only by the ovary. Are divided into:

  • Simple, formed by one pestle (cherry, plum, bird cherry, acacia bean);
  • Complex, formed by several fused pistils (raspberries, blackberries)
  • Fractional fruits are formed by a multilocular ovary with partitions (forget-me-not, basil, lavender, thyme, etc.);

2. False - formed with the participation of other parts of the flower such as the receptacle and perianth, including petals and sepals.

note

It is easy to distinguish false ones from real ones by the remains of parts of the flower (apples, pears).

Causes of damage to the ovary

Damage to the ovary can lead to a lack of further seeds and even fruits. The causes of damage may be:

  • Late spring frosts during flowering, during which flowers and set fruits fall off. If the ovaries are partially damaged, then deformed, small, or unsuitable fruits develop from them;
  • The absence or small number of pollinators, while some of the flowers remain unfertilized and are therefore discarded;
  • Poor soil and lack of watering, when the plant does not have enough substances to grow all the ovaries that appear. In this case, it is necessary to add complex mineral and organic fertilizers and provide watering during drought;
  • Pests (codling moth, apple sawfly, flower beetle, etc.). To get rid of them, you do not need to resort to artificial insect repellents, since they will also have a detrimental effect on pollinating insects. It is better to spray the plants with decoctions of herbs that repel pests (nettle, dandelion, garlic, wormwood, etc.)

  • Leaf diseases. Healthy leaves are necessary to provide the plant with the necessary substances; without them, the ripening of fruits and seeds is impossible;

  • Overload with the number of fruits: with large quantities formed ovaries, the plant cannot feed them all, so it discards some. Timely thinning of flowers will help to avoid this process.

The variety of flowering plants is amazingly large. To understand this diversity, botanists combine all types of plants into groups, which in turn are combined into larger groups. To establish such groups of plants, signs of their similarities and differences are used, by which one can judge the degree of relationship between plants.


Flowering plants have a more advanced structure than other groups. Only angiosperms produce flowers, and flowers produce pistils. The ovaries of the pistils contain the ovules. Flowering plants of different angiosperms differ in size, shape, color, and structure; The flowers of some angiosperms are adapted to pollination by wind, while others are adapted to pollination by insects. But with any method of pollination, pollen grains fall on the stigmas of the pistils, where pollen tubes are formed.


Pollen tubes with sperm grow to the ovules and grow into them, where fertilization occurs, which is characteristic only of flowering plants. In this case, an embryo is formed from the zygote resulting from the fusion of gametes. The largest cell, after merging with the second sperm, grows, divides, and an endosperm is formed, which stores nutrients for the embryo. Seeds develop from the ovules, and the pericarp develops from the wall of the ovary.


So, the seeds of flowering plants develop inside the fruit. That's why flowering plants called angiosperms. Currently, angiosperms dominate among the plants inhabiting the Earth's land.


Let's look at the plants blooming in autumn, For example, pansies, or tricolor violet. This plant, like most others, has organs:

roots and shoots. A shoot is a stem with leaves and buds located on it. Modified underground shoots are rhizomes, tubers and bulbs. Flowers can develop on the shoots. In their place, fruits with seeds ripen. Plants that bloom at least once in their life are called flowering plants.


The same organs of flowering plants can be very diverse in appearance.

A flower is a modified shoot, in the place of which a fruit with seeds or with one seed ripens.

Flower structure

Let's look at the structure of a flower. The flower develops on a peduncle that expands into the receptacle; All other parts of the flower are formed on it.

The brightly colored corolla consists of petals. Below the corolla there is a cup of green leaves - sepals. The corolla and calyx are the perianth that protects the internal parts of the flower from damage and can attract pollinating insects.

The main parts of a flower are the pistil and stamens. The stamen consists of a thin filament and an anther, which produces pollen. In the pistil there is a wide bottom part- ovary, narrow style and stigma. The fruit develops from the ovary. In some plants, other parts of the flower, such as the receptacle, also take part in the formation of the fruit. Only a few plants have flowers solitary. Most flowers are collected in inflorescences.

In summer and autumn, plants ripen in different shapes and colors. fruits Fruits are formed from ovaries. The enlarged and modified walls of the ovary, which has become a fruit, are called the pericarp. There are seeds inside the fruit. Based on the number of seeds, fruits are divided into single-seeded and multi-seeded.

There are juicy and dry fruits. Ripe, juicy fruits contain juicy pulp within the pericarp. Ripe dry fruits do not have pulp.

Plant seeds are distinguished by shape and size. The seed consists of a peel (hull), an embryo and contains a reserve nutrients. The embryo is divided into a germinal root, a stalk, a bud with leaves.

Plants that have one cotyledon in the seed embryo are called monocots. In dicotyledonous plants, as the name suggests, the seed has two cotyledons. The supply of nutrients can be located in the cotyledons or in a special storage tissue - the endosperm. From the embryo of the seed, a new plant develops. A seed is the germ of a future plant.

Plants differ from each other in the color and shape of stems, leaves, flowers and fruits, life expectancy and other characteristics. But no matter how different flowering plants are, each of them can be classified into one of three groups: trees, shrubs and herbs.

Trees are usually large plants with perennial woody stems. Each tree has a trunk, branches, and tree branches form their crowns. Everyone is familiar with birch, aspen, linden, maple, and ash. Among the trees there are real giants, for example eucalyptus trees, reaching a height of more than 100 meters.

Shrubs differ from trees in that their trunk begins almost at the very surface of the soil and is difficult to recognize among the branches. Therefore, shrubs do not have one trunk, like trees, but several trunks extending from a common base. Shrubs are widespread: hazel, lilac, honeysuckle, elderberry.

Herbs, or herbaceous plants, usually have green, succulent stems; they are almost always lower than trees and bushes. But a banana, for example, reaches a height of 7 meters, and some hogweeds are taller than a person. There are tiny herbaceous plants. Duckweed lives on the surface of reservoirs; The size of each plant is several millimeters.

Trees and shrubs - perennials. For example, some oak trees live for more than a thousand years. Among the herbs there are both perennial, annual and biennial.

Among the perennial herbs, lily of the valley, dandelion, coltsfoot, and nettle are well known. The aboveground parts of most of these herbaceous plants die off in autumn. In the spring, they develop anew, since these plants retain roots and other underground organs with buds in the soil under the snow.

Annual plants, such as violets, quinoa, gillyflower, radishes, buckwheat, oats, wheat, develop from seeds in the spring, bloom, form fruits with seeds and then die.

Biennial plants live for almost two years. In beets, radishes, and cabbage, only roots, stems and leaves usually develop in the first year. In the second year, these plants develop new shoots, bloom and produce fruits with seeds, and die off by autumn.

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