The transfer of pollen grains from the anther to the stigma is called pollination.
It is of two types:-
1. Self-pollination (autogamy)
When the pollen grains of a flower falls on the stigma of the same flower, or of the different flower of the same plant, it is called self-pollination. It occurs not only in bisexual flowers but also in unisexual flowers of the same plant.
Contrivances (adaptations) for self-pollination is of three types:
Homogamy – When the male and female organs i.e. that stamens and carpels mature at a time and some of the pollen grains drop on the stigma of the same flower, either automatically or through the wind or any insect e.g. in Brassiaca (mustard) and Gardenia florida (Cape jasmine).
Cleistogamy – Here bisexual flowers never open therefore the pollen grains may only pollinate the stigma of the same flower, e.g. in Arachis hypogeal (groundnut) and Commelina bengalensis (dayflower).
Geitonogamy – Sometimes transfer of the pollen from the anther of the male or of the bisexual flower to the stigma of female or another bisexual flower occur in the same plant e.g. in Triticum aestivum (wheat).
Transfer of pollen grains from the anther of a flower to the stigma of another flower borne by two different plants of the same or allied species is called as cross-pollination.
It is of two types. Pollination that occurs between flowers of two different plants of the same species is called xenogamy and that occurs between flowers of two different plants of different species is called hybridism.
Plants prefer cross-pollination than self-pollination. Since two different plants are involved in this process and two sets of parental characters are mixed, it results in a better offspring.
This process is performed through various agencies, e.g. wind, water, insects and animals. Depending upon the nature of pollinating agency, cross-pollination is again of various types like anemophily, entomophily, ornithophily, chiropterophily, malacophily and hydrophily.
Difference between the two types of pollination
|1. Pollen grains are transferred to the stigma of the same or genetically similar flower.||1. Pollen grains are transferred to the stigma of the genetically different flower.|
|2. Anthers and stigma mature simultaneously.||2. They mature at the different time i.e. protandry and protogyny.|
|3. It occurs in open as well as the closed flower.||3. It occurs in only open flower.|
|4. It is very economical for plants.||4. It is not economical as the plant has to produce a large number of pollen grains, nectar, scent, and coloration.|
|5. External agencies are not required||5. It is essential i.e. depends on agencies.|
|6. Young ones are homozygous.||6. Young ones are heterozygous.|
|7. It produces pure lines because of the non-occurrence of genetic recombinations||7. It produces variations due to genetic recombinations.|
|8. It cannot eliminate harmful traits.||8. It can eliminate harmful traits.|
|9. Useful characters are preserved.||9. Not preserved.|
|10. No adaptability in the changing environment.||10. It provides adaptability.|
|11. It cannot introduce new traits.||11. It can introduce new traits.|
|12. Disease resistance is low.||12. Disease resistance is optimum.|
|13. There is a decrease in yield.||13. It increases the yield.|
|14. It does not help in the development of new species.||14. Helps in the development of new species.|