The ultimate task of a typical flower is the formation of fruits and seeds. This requires two processes. The first is the pollination of plant flowers. After it, the actual fertilization occurs - fruits and seeds appear. Consider further what types of plant pollination exist.
General information
Pollination of plants is the stage at which small grains are transferred from the stamens to the stigma. It is closely connected with another stage in the development of crops - the formation of the reproductive organ. Scientists have established two types of pollination: allogamy and autogamy. In this case, the first can be carried out in two ways: geitonogamy and xenogamy.
Features
Autogamy - pollination of plants by transferring grains from stamens to the stigma of one reproductive organ. In other words, one system independently carries out the necessary process. Allogamy is the cross transfer of grains from the stamens of one organ to the stigma of another. Geitonogamy involves pollination between flowers of one, and xenogamy - different individuals. The first is genetically similar to autogamy. ATIn this case, only the recombination of gametes in one individual takes place. As a rule, such pollination is typical for multi-flowered inflorescences.
Xenogamy is considered the most favorable in terms of its genetic effect. Such pollination of flowering plants increases the possibility of recombination of genetic data. This, in turn, provides an increase in intraspecific diversity, subsequent adaptive evolution. Meanwhile, autogamy is of no small importance for the stabilization of species characteristics.
Ways
Pollination method depends on seed transfer agents and flower structure. Allogamy and autogamy can be carried out with the help of the same factors. They, in particular, are the wind, animals, man, water. The most diverse are the methods for allogamy. The following groups are distinguished:
- Biological - pollination of plants is carried out with the help of living organisms. This group has several subgroups. Classification is carried out depending on the carrier. So, pollination of plants is carried out by insects (entomophily), birds (ornithophilia), bats (chiropterophilia). There are other ways - with the help of mollusks, mammals, etc. However, they are rarely found in nature.
- Abiotic - pollination of plants is associated with the influence of non-biological factors. This group distinguishes the transfer of grains with the help of wind (anemophilia), water (hydrophilia).
The ways in which plants are pollinated are consideredadaptations to specific environmental conditions. In genetic terms, they are less important than types.
Adaptation of plants to pollination
Let's consider the first group of ways. In nature, as a rule, entomophily occurs. The evolution of plants and pollen vectors took place in parallel. Entomophilous individuals are easily distinguished from others. Plants and vectors have mutual adaptations. In some cases, they are so narrow that the culture is not able to exist independently without its agent (or vice versa). Attracts insects:
- Color.
- Food.
- Smell.
In addition, some insects use flowers as shelter. For example, they hide there at night. The temperature in the flower is several degrees higher than that of the external environment. There are insects that reproduce themselves in crops. For example, chalcid wasps use flowers for this.
Ornithophilia
Bird pollination occurs predominantly in tropical areas. In rare cases, ornithophilia occurs in the subtropics. Signs of flowers that attract birds include:
- No smell. Birds have a rather weak sense of smell.
- The whisk is mostly orange or red. In rare cases, a blue or purple color is noted. It is worth saying that birds can easily distinguish these colors.
- A large amount of weakly concentrated nectar.
Birds often do not sit on a flower, but pollinate it, hovering next to it.
Chiropterofilia
Bats pollinate mainly tropical shrubs and trees. In rare cases, they are involved in the transfer of grains to grasses. Bats pollinate flowers at night. Cultural traits that attract these animals include:
- The presence of fluorescent white or yellow-green color. It can also be brownish, in rare cases purple.
- The presence of a specific smell. It resembles the secrets and secretions of mice.
- Flowers bloom at night or in the evening.
- Large parts hang from branches on long stalks (baobab) or develop directly on tree trunks (cocoa).
Anemophilia
Pollination of about 20% of plants in the temperate zone is carried out with the help of wind. In open areas (steppes, deserts, polar territories), this figure is much higher. Anemophilous cultures have the following characteristics:
- Small inconspicuous flowers that have a yellowish or greenish tint, often without a perianth. If it is present, it is presented in the form of films and scales.
- The presence of multi-flowered inflorescences. Such a "bouquet" can be represented by a dangling axis - an earring.
- Presence of anthers on staminate thin filaments.
- Quite large and often feathery stigmas protruding beyond the flower.
- Cultures are single or dioecious.
- The formation of a large amount of pollen. It is dry, small, smooth. The grains may haveaccessories (air bags, for example).
Anemophilous crops often form large aggregations. This greatly increases the chances of pollination. Examples are birch groves, oak forests, bamboo thickets.
Hydrophilia
Such pollination is quite rare in nature. This is due to the fact that water is not the usual habitat for crops. In many plants, flowers are above the surface and are pollinated mainly by insects or with the help of wind. Signs of hydrophilic crops include:
- The flowers are small and inconspicuous. They develop singly or gather in small "bouquets".
- As a rule, the flowers are unisexual. Examples are Vallisneria, Elodea.
- In the anthers, the wall is thin. They lack endothecium. Often the anthers are filamentous. In some cultures, they braid the stigma. This promotes rapid penetration and germination of pollen.
- There is no exine in the grains. This is because the pollen is in the water and does not need to be protected from drying out.
Autogamy
75% of plants have bisexual flowers. This ensures self-transfer of grains without external carriers. Autogamy is often accidental. This is especially the case under adverse conditions for vectors.
Autogamy is based on the principle "self pollination is better than none at all". This type of grain transfer is known to manycultures. As a rule, they develop in unfavorable conditions, in areas where it is very cold (tundra, mountains) or very hot (desert) and there are no vectors.
In nature, meanwhile, there is also regular autogamy. It is constant and extremely important for cultures. For example, plants such as peas, peanuts, wheat, flax, cotton and others self-pollinate.
Subtypes
Autogamy can be:
- Contact. When the filaments move, the anthers directly touch the stigma. Such autogamy is typical for a hoof, a hoof.
- Gravity. In this case, pollen falls on the stigma from the anthers located above. In gravitational autogamy, therefore, the force of gravity acts. This is typical for heather, wintergreen crops.
- Cleistogamous. In this case, pollination is carried out in a bud or a closed flower. Cleistogamy is considered the extreme degree of autogamy. It can be caused by adverse factors (high humidity or drought). Cleistogamy can also be regular, genetically fixed. For example, in the spring time, amazing violets first have normal flowers, but pollination does not occur in them, respectively, fruits and seeds do not appear. Subsequently, cleistogamous reproductive organs appear. They do not open and are presented in the form of buds. Pollen germination occurs directly in the anthers. The tube passes through the wall and reaches the stigma. As a result, a box with seeds is formed.
Cleistogamy is found in different systematic groups of crops (in some cereals, for example).
