Pollination is a process of transfer of pollen (the male gametes) from anther to stigma (a female part) in the flower of plants.
This is a method of sexual reproduction in plants. There are different methods of pollination in plants.
But this process is facilitated through different agents of pollination.
The pollination agents, in general, include wind, water, insects, birds, cattle and even humans (manual or assisted pollination in farms)
The flowers of a plant, in general, have a single female organ consisting of stigma, ovary and ovule.
While the male part has one or more stamens that bear the male gametes, namely pollen’s in the anthers.
Plants are two types in this regard. Those having both male and female gametes in the same flower.
Those having separate male and female flowers. Due to this specificity, these flowers have only one type of organs, either male or female.
Types of pollination
- Self-pollination. (Autogamy)
- Cross-pollination. (allogamy)
Here, the transfer of pollen occurs within the same flower. Hence the name autogamy (Auto= self, gamy= fertilization).
The pollen grains from male anthers settle on the stigma of the same flower.
This type of pollination requires a closed environment and also, the anthers and stigma should lie close to each other in the particular flower.
To avoid autogamy, the plants practice Dichogamy.
By dichogamy, the male and female parts of flowers mature at different time spans to avoid autogamy.
- Ex: Apple
Here, the transfer of pollen occurs in between two or more flowers. Pollen from one flower falls on the stigma of another flower.
Based on the location of the flower on the plant, this is again of two types.
Here, the transfer occurs in between two flowers of the same plant. That is, pollen from one flower reaches the stigma of another flower on the same plant.
Here, the pollination occurs in between the flowers of two plants. That is, the pollen from one flower reaches the stigma of a flower on another plant.
Based on the agents involved in this method, there are the following two types as
I) Abiotic: Without the involvement of animals, the transfer occurs.
II) Biotic: Due to animal involvement, pollen transfer occurs.
This involves the transfer of pollen by air and water.
- Anemophily: Here, wind acts as a pollinating agent. Pollen grains released into the air are carried over to distant plants.
Hence we can notice allergy of the respiratory system during cropping season if one stays close to farms.
- Ex: Pinus plant
- Ex: Pinus plant
- Hydrophily: Here, pollen grains are transferred by flowing water currents, as seen in rivers.
The pollen in some species travels on the water surface while in others submerged in water, i.e., below the water surface.
- Ex: Hydrilla, vallisneria.
This is the most common and also efficient method.
Many animals are involved in pollen transfer.
A) Zoophily: Here, the pollen grains are transferred from one plant to another with the help of vertebrate animals, bats, birds, etc.
This occurs due to the dependence of animals on plants for food. The transfer happens mostly by limbs and other body parts which come in contact with flowers.
- Ex: cactuses
B) Ornithophily: Here, birds transmit pollen grains from one tree to another. These plants secrete nectar to attract birds.
C) Entomophily: Here, the pollen transfer happens due to insects.
- Examples: Honey bees, beetles are common pollinators.
Even in agriculture, manual cross-pollination is done by farmers to enhance yield.
Read the importance of pollination.