The majority of flowering plants reproduce sexually i.e.,through seed formation. We know sexual reproduction is incomplete without fertilization. The male and female gametes have to meet for fertilization and further developments. Have you ever wondered how plants ensure their continuity on earth despite their immobile nature? Let us answer the same by having a brief discussion on a process called pollination.
Pollination in Plants
Reproduction is the life process which helps an organism to procreate its own offspring. There are a lot of events involved in this. In plants, pollination is one among them. Pollination can be defined as the pre-fertilization event or process where pollen grains from anther are transferred to the stigma of a flower.
Plants are immobile. Unlike animals, both male gamete and female gamete are immobile. They can’t copulate with each other by themselves. They need a vector for this. Pollination is the process that helps to unite the male and female gametes and thus helps in fertilization. It can be broadly classified into two, cross-pollination and self-pollination and this is achieved with the help of a variety of vectors/agents. For successful pollinations, it must occur between same species.
Pollinations can occur either within a flower or between flowers of same plant or flowers of different plants. Depending on this, pollinations are of three types, namely:
It is a type of self-pollination where the transfer of pollen grains from the anther to the stigma takes place within the same flower. Opening and exposure of anther and stigma are necessary for autogamy. There are two conditions for autogamy to takes place:
- Anther-stigma synchronization; when the pollen is released, stigma should be ready to receive it.
- The position of or distance between anther and stigma. Both should be close enough for pollinations.
In chasmogamous flowers, anther and stigma are exposed. The exposed reproductive parts give a chance of cross-pollination in chasmogamous flowers. While in cleistogamous flowers anther and stigma are not exposed but lie close enough for transfer . Thus, chances of cross-pollination in cleistogamous flowers are almost none. In addition, they barely require a pollinating agent.
Geitonogamy is the type of pollinations where the transfer of pollen grains from the anther to the stigma takes place between different flowers in the same plant. Though it seems like cross-pollination and takes place with the help of pollinator, both the gametes have the same plant as their origin.
Xenogamy is the cross-pollination where the pollen grain transfer occurs across flowers of two different plants. In other words, transfer of pollen from the anther of one plant to the stigma of another plant.
Each type has its own merits, like xenogamy, leads to a new variety whereas autogamy helps to preserve parental characters. Plants have various adaptations to accomplish this task. In addition, flowers depend on certain pollinating agents which can either be biotic or abiotic. These biotic and abiotic pollinating agents are collectively termed as pollinators.
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