Pollination
The process of transfer of pollen grains from anther to stigma is called pollination
Types of pollination
Pollination is a normal natural process, but this process can also be induced, such pollination is called hybridization. Natural pollination is of the following two types-
(i) Self pollination, (ii) Cross pollination
1. Self Pollination
When the pollens of a flower are transferred to the stigma of the same flower or another flower of the same plant, such pollination is called self-pollination . Self-pollination occurs in two unisexual flowers or bisexual flowers present in a plant. Self-pollination is divided into two classes as follows-
(a) Self-coupling or Autogamy: Under this method of self-pollination, the pollen produced in the anther of a flower reaches/is transferred to the stigma of the same flower i.e. the flower is pollinated by its own pollen. There is only one requirement in this type of self-pollination.
(b) Geitonogany Under this method of self-pollination, the pollen grains of a flower of a plant (monoecious flower or bisexual flower) reach/get transferred to the stigma of another flower (female flower or bisexual flower) on the same plant and pollinate it. Such self-pollination is called geitonogamy. This type of self-pollination requires two different flowers present on the same plant. All the flowers of a plant are genetically similar, so according to some geneticists, geitonogamy is a method of self-pollination.
(c) Bisexuality or Hermaphroditism: Both the reproductive organs (male and female) are present in the same flower in bisexual flowers. There are more opportunities for self-pollination in these. Note: Self-pollination does not occur in the flowers of monoecious plants.
Benefits of Self-Pollination
The following are the advantages of self-pollination in angiosperm plants:
1. Self-pollination is a simple and definite process in angiosperm plants, as a result of which the lineage of plants continues.
2. Self-pollinated flowers do not require other flowers for pollination. Hence, the chances of pollination failure are very less.
3. Self-pollination does not depend on any external factor for the transfer of pollens.
4. Self-pollinated flowers do not need to produce colour, fragrance and nectar.
5. Self-pollination does not require large, attractive and fragrant flowers.
6. Self-pollination does not require much pollen and loss of pollen is also less. Hence there is no need for the plant to produce pollen in large numbers.
7. The seeds produced from self-pollinated flowers are of pure breed and their parental characteristics remain the same.
8. In self-pollinated plants, there is no fusion of traits of different parents, hence genetic purity remains indefinitely in self-pollinated species.
Disadvantages of Self Pollination
The following losses occur due to self-pollination:
1. Plants produced from germination of seeds produced through self-pollination are weak.
2. The seeds produced in the process of self-pollination are less in number, light in weight and relatively smaller in size.
3. Seeds produced from self-pollination do not mature quickly. Tight external
4. Seeds produced from self-pollination are not of good quality; there is no possibility of production of new varieties from them.
Adaptation for Self Pollination
Adaptation is necessary for self-pollination, otherwise pollination is not possible in the flower. (a) Cleistogamy These flowers bloom after maturity. Such flowers are called chasmogamous flowers. Their anthers and stigma also get exposed. In some species of angiosperm plants, some bisexual flowers never get exposed after maturity, such flowers are called cleistogamous flowers. Pollen grains are not able to come out of the flowers. Cleistogamy is a special type of adaptation for self-pollination. For the flower to remain closed, the anther bursts due to which the pollen grains get scattered on the stigma of the flower and only self-pollination takes place in them.
2. Cross-pollination
Cross-pollination is a common process in bisexual flowers. In cross-pollination, when the pollen grains of a flower reach the stigma of a flower of another plant of the same species and pollinate it, it is called cross-pollination. In cross-pollination, flowers are located on two different plants.Cross-pollination can occur in both unisexual and bisexual flowers, but cross-pollination is possible only in unisexual flowers. Such cross-pollination is called cross-fertilization. Cross-pollination is very important from a genetic point of view because cross-pollination occurs between flowers present in two different plants and genetic recombination definitely occurs in it.
Agents and types (Methods) of Cross-Pollination
How does cross-pollination take place or the process of cross-pollination. Under cross-pollination, pollen grains of one flower reach/are transferred to the stigma of another flower. Different agencies are required for cross-pollination. The whole process depends on some external factors. As an exception, in the plant Valisneria spiralis, male flowers are completely transferred to the female flowers. Such external factors which help in the process of cross-pollination are mainly divided into two categories as follows-
Types of cross-pollination
1. Inanimate or abiotic factors: This includes air and water.
2. Living or Biotic Agents: This includes insects, birds, bats and snails etc. Based on the above mentioned means, cross-pollination takes place in three ways-
(i) Air pollination,
(ii) Water pollination,
(iii) Animal pollination
[A] Air Pollination or Anemophily
When pollen grains are transferred by wind, it is called air pollination. Flowers that undergo this type of pollination need to produce a large number of pollen grains, because many pollen grains are destroyed in the process of transport from one flower to another.
The following characteristics are found in wind pollinated flowers-
The following characteristics are found in wind pollinated flowers- 1. The flowers of these plants are usually small and unattractive due to being wind pollinated. The perianth in these flowers is either absent or very reduced. The anthers of these flowers are not present in the flowers.
2. Wind pollinated flowers are usually unisexual. Their characteristic is that the inflorescence either grows above the leaf part, due to which it remains in contact with the air, for example- maize or the flowers bloom before the new leaves emerge, for example- poplar.
3.Wind pollinated flowers are usually unisexual. Their characteristic is that the inflorescence either grows above the leafy part, due to which it is in contact with the air, for example- maize or the flowers bloom before the new leaves emerge, for example- poplar. Wind pollinated flowers either lack sepals and corolla or are very small in size so that they cannot create a hindrance/obstruction between the pollen grains and the stigma.
4. Pollens are produced in large quantities in the anthers of wind pollinated flowers, because with strong winds, most of the pollens fall here and there and get destroyed. Only the remaining few pollens take part in the actual pollination process, for example- about 2 crore pollens are produced in maize (Zea mays) and 40 crore pollens are produced in Rumex.
5. Pollens of wind pollinated flowers are small in size, dry and light. As a result, these pollen grains can easily fly from one place to another. Special winged structures are formed in the pollen grains of some flowers which help them to fly, example- Pine (Pinus).
6. Wind pollinated flowers are usually unisexual. Their specialty is that the inflorescence either grows above the leafy part due to which it is in contact with the air, example- maize or the flowers bloom before the new leaves emerge, example- in poplar.
7. In wind pollinated flowers, sepals and corolla are either absent or are very small in size so that they do not create obstruction between the pollen grains and the stigma.Pollination,Cross-pollination