Taking into account the source of pollen, there are two types of pollination : self-pollination and cross-pollination. In addition, self-pollination can be subdivided into autogamy and geoglycemia.
Pollination is the process whereby the pollen grains of some anther - the male portion of a flower - are transferred to the female part of the flower, known as stigma.
In order for pollination to be successful, the transferred pollen grains must be from a flower of the same species.
Self-pollination is the kind of pollination in which the pollen of the anthers of a flower is transferred to the stigmas of the same flower.
Cross-pollination involves the transfer of pollen grains from the flower of a plant to the stigma of the flower of another plant. This is the only type of pollination that brings different genetic types of pollen grains to stigma during pollination.
Depending on the pollination agent, cross-pollination can be classified into abiotic pollination and biotic pollination.
Types of pollination
1- Self-pollination
It is the most basic type of pollination because it only involves a single flower. This type of pollination occurs when the pollen grains of the anther fall directly into the stigma of the same flower.
Although this type of pollination is simple and rapid, it results in a reduction of genetic diversity, because the sperm and eggs of the same flower share genetic information.
This mechanism of self-pollination can be observed in some legumes, such as peanuts and soybeans. Most plants that self pollinate have small, discrete flowers.
These flowers spill the pollen directly into the stigma, even before the bud blossoms.
Plants that follow self-pollinating processes often have the same amount of stamens and carpels. The plants are pollinated and can produce offspring that are self fertile.
Some plants that exhibit this type of pollination include peaches, figs, roses, tomatoes, orchids, and violets, among others.
Self-pollination can be divided into autogamy and geoglycemia.
- Autogamy
It refers to the fusion of two gametes that come from the same individual. Autogamy is predominantly observed in the form of self-pollination.
It occurs when the pollen sperm of a plant's worm reaches the carpels of that same plant and fertilizes the present egg. In this type of self-pollination, the sperm and ovaries that came together came from the same flower.
- Geitogamy
In flowering plants, pollen is transferred from one flower to another flower on the same plant. In animal pollinator systems, this is achieved when a pollinator visits multiple flowers from the same plant.
This process is also possible in species that are pollinated by air, and can be a common source of seeds that self fertilize in self-compatible species.
Although geitogamy is functionally a cross-pollination involving a pollinating agent, it is genetically similar to autogamy, since pollen grains come from the same plant.
Maize is a plant that shows geitogamy.
Advantages of self-pollination
- The plants that self pollinate spend less energy in the production of attractive pollinators.
- They can grow in areas where organisms that could help pollination, such as insects and other animals, are absent or scarce. This includes arctic regions and regions with very high elevations.
- This process allows the plants to be distributed beyond the range of available pollinators, or produce offspring in regions where there is a reduction in the population of pollinators.
- There is less chance of pollination failure and, therefore, help maintain the purity of your species.
Disadvantages of self-pollination
- There is no possibility of producing new species.
- The descendants show less vigor.
- Unwanted characteristics can not be eliminated.
- The ability to resist disease is decreased.
- It does not help evolution.
- New features are not introduced.
2- Cross-pollination
It occurs when the pollen grains are transferred to the flower of a different plant. Plants that go through this process often have stamens longer than their carpels.
These plants use mechanisms to ensure that the pollen grains are spread to other plant flowers.
The process of cross-pollination requires the help of biotic or abiotic agents such as air, water, insects, birds, and other animals that act as pollinators.
- Abiotic pollination
Pollination is carried out without the intervention of other organisms. The most common form is wind pollination; pollination by water exists in aquatic plants.
- Biotic pollination
This pollination requires pollinators to transfer pollen grains from an anther to the receptive part or stigma of carpels or pistils.
There are many forms of biotic pollination. Pollination by insects, pollination carried out by birds or bats, and that carried out by humans are the most common variations.
Plants that use this type of pollination usually have characteristics in their smell, color and shape to attract pollinators.
Insect pollination occurs in plants that have colored petals and strong odors to attract insects; plants that are pollinated with aerial vertebrates generally have white petals and flashy smells. The flowers pollinated by the birds have tubular corollas of showy colors.
Advantages of cross-pollination
- The descendants are stronger, more viable and more resistant.
- There is the possibility of obtaining new desirable characters.
- Help in evolution.
- The unwanted characters of the plant can be eliminated.
Disadvantages of cross-pollination
- Pollination may fail due to a distance barrier.
- The flowers must be totally dependent on external agents for pollination.
- You can enter unwanted characters.
- There is more wastage of pollen.
References
- What is pollination in plants? Definition and types. Recovered from study.com
- Pollination. Retrieved from wikipedia.org
- Pollination: types and agents. Retrieved from biologydiscussion.com
- Allogamy. Retrieved from wikipedia.org
- Types of pollination. Retrieved from biology.tutorvista.com
- Disadvantages of cross pollination. Retrieved from biology.lifeeasy.org
- Geitonogamy. Retrieved from wikipedia.org
- Advantages of cross pollination. Retrieved from biology.lifeeasy.org