Botanists counted more than 360 thousand species among flowering plants. And this account is not over. Flowers are found from the tropics to the tundra - in all climatic zones of the planet. They are everywhere: in deserts, in forests, steppes, swamps and lakes, on sea coasts and in high mountains. This flowering constitute the bulk of the plant matter of the biosphere. Thanks to them, plant foods are formed - cereals, most vegetables and fruits, berries and nuts.
The most important element of angiosperms (the second name of flowering) is the flower. The main parts of the flower are the pestle and stamens. Thanks to the complex processes of pollination and fertilization with their participation, seeds are formed - the continuation of the life and evolution of plants on the planet.
Flower: structure and functions
Higher plants consist of a root, a stem with leaves and flowers, which are shortened and modified stems. The root, stem and leaves are the vegetative parts that are responsible for the growth of the plant. A flower is a generative element, a reproductive organ. Typically, flowers are attached to the pedicels - the so-called sophisticated part of the stem without leaves. Some plants have no pedicels or they are hardly expressed. These are sedentary flowers. The pedicel expands, passing in the receptacle.
We list from the bottom up, starting from the pedicel, the main parts of the flower. This is the receptacle, which is the foundation for the remaining elements of the flower. The receptacle can be of various shapes: from conical, as in magnolia, to flat (chamomile) and even concave (dog rose), starting with a cup formed by sepals. Usually they are green, but can be brightly colored. The calyx may be single-row or with a sub-base formed from the second circle of sepals. Next is a flower whisk composed of petals. The variety of flower corollas is great: in color, color intensity, size, quantity, shape, relative position, cleavage of the petals.
Together, sepals and petals make up the perianth - the cover of a flower. Some flowering plants have no petals or they are no different from sepals. In such cases, the perianth will be simple; it is called double if there is sepals and petals. Perianth is a sterile flower appendage. The functions of the flowers assigned to the perianth are the protection of the carpel (pistil or peduncle) and the guarantee of pollination. The bright colors of the corolla and the attractive smell provide visits to plants by insects.
In the perianth there are spore-bearing, no less main parts of the flower. This is gynoecium, it’s simpler - a pestle, in which ovules develop with a reservoir for the gametophyte (megaspore). It is the female genital organ of the flower. In the perianth there is also a male genital organ, the structural unit of which is the stamen. Collectively, the stamens are called androecium. Microspores are formed in the stamen anthers. From them pollen grain is obtained - male gametophyte.
The main parts of the flower
Pestle and stamens are essential elements, as they are suppliers of female and male reproductive cells. These are gametophytes, substances from the merger of which the seed and fruit of the flowering are born. The pistil (it is more correct to call it carpel) consists of an ovary, a column (some flowering ones have none) and a stigma. In the ovary there is an embryonic sac with blocked ovules. The top of the column ends with a stigma, on which pollen lingers. It is formed in the stamens (microsporistics). A typical stamen consists of two parts: a stamen filament (sterile, sterile part) and anther with fertile (fertilizing) function.
Monoeciousness and dioeciousness
About 75% of the species of angiosperms have bisexual (hermaphroditic) flowers - they contain stamens and pistils. These plants are monoecious (for example, corn). There are plants in which some individuals - only with stamen flowers, and others - only with pistil flowers. They are called dioecious (an example is hemp).
Pollination process
The essence of pollination is getting pollen from stamens on the stigma. This can be self-pollination, a classic example of which is observed in unopened flowers (some types of violets, peanuts, barley). The second method is cross-pollination, which occurs in most flowering plants. Some carriers of pollen: wind, water, insects, ants, birds.
Double fertilization
When the male gamete (sperm) merges with the female gamete (egg), fertilization occurs. For this, it is necessary that on the stigma of a pestle moistened with a sticky sweet liquid, pollen of stamens sprouted. A sprouted speck of dust begins to grow a pollen tube - very long and very thin. It penetrates into the ovary close to the ovules. Two sperm are attached to the end of the tube.
Ovules consisting of cells develop inside the ovary. The ovum is located close to the pollen passage through which the dust tube penetrates. Another cell, secondary, is located in the center of the ovary. The dust tube bursts and both sperm come out of it. One of them penetrates the cytoplasm and merges with the nucleus of the egg cell, and the other penetrates the secondary cell. Fertilization occurs, and the egg begins multiple division, due to which the embryo of the plant develops. The secondary cell is also fertilized and begins to divide with the formation of the endosperm - a storehouse of food supply for the embryo. So the seed is formed.
