What is pollination ? Sexual reproduction in plants

 

Pollination

The transfer of pollen grains from Anther to stigma is called pollination. Depending upon source of pollen, pollination is of three type-

Autogamy- it refers to the transfer of pollen grains from anther  to stigma in the same flower. It is a type of self pollination.

Xenogamy - It is pollination in which there is a transfer of pollen grains from anther to stigma of different flowers but in the same plant.

Geitonogamy -  it means the transfer of pollen grains from anther to stigma of different plants.

Both Autogamy and xenogamy are discouraged because both do not lead to genetic variability. Geitonogamy leads to genetic variability so  This kind of pollination is encouraged by the plant breeders and nature.

In flowering plants, pollen grains are not motile so they cannot move themselves towards the stigma. To achieve the pollination, pollen grains need biotic and abiotic agents. Biotic agents are animals, insects , birds, bats etc. Whereas Abiotic agents are wind, water etc.

Agents of Pollination

Anemophily is pollination by wind. The plants in which pollination takes place by wind , have some special characteristics. The pollen grains are non sticky and light in weight for easy transportation by wind current. The stigma of these plants are feathery for easily capturing  the pollen grain that is carried by wind current.

Flowers are arranged in inflorescence and have a single ovule in the ovary. Example - Palm, Maize, grasses, etc.

Hydrophilly means pollination by water. Plants like Ceratophyllum, Zostra,Vallisneria whose flowers are generally submerged in water, have the phenomenon of hydrophily. When pollination of flowers takes place below the water called Hypo hydrophily.  In ceratophyllum, stamens are separated from flowers and float upwards. The anthers rupture and pollen grains are liberated.These pollens are trapped by the stigma. In Zostera, pollen grains are needle-like and reach the stigma for pollination.

When pollination occurs at the surface of water it is called epihydrophily. In vallisneria, the  female flowers  are long and reach the water surface to receive the pollen grains carried by water currents. Male flowers are small and submerged in water.

When it releases the pollen, pollen comes to the water surface and reaches the female flower.

The plants in which pollination takes place by water , have some special characteristics. The pollen grains are ribbon shaped  for easy transportation by water current. Pollen grains are covered by the mucilaginous covering for getting protection from wetting.

Entomophily is pollination by insects .The plants in which pollination takes place by insects , have some special characteristics. The flowers are large, sticky and colorful to more visiting insects. Flowers are rich in nectar and fragrances to attract the insect. The flower offers rewards in the form of nectar and pollen grains for insects. In turn, flowers provide a safe place for egg laying insects. 

Yucca plants and moths are both dependent on each other. Both can not complete their life cycle without each other. Yucca provide a safe place for the eggs of moths in the locule of ovaries. When larvae hatch out from the egg then they feed the seeds of the yucca plants. In turn, moths pollinate the yucca plants and carry out the pollination process.

Ornithophily is pollination by the birds like humming birds, sun birds etc. These birds regularly visit the flower silk cotton tree, coral tree, etc. Ornithophilous flowers are cup shaped or urn shaped and produce more nector to make continuity of visit of birds. Ornithophilous flowers are brighter in colour to attract the birds .

Cheiropteriphily is pollination by bats . Tree like Anthocephalus Chinense, kigelia , Bauhinia are pollinated by the bats. The bats visit on these plants to eat the parts of flowers or search of moths and pollinates these plants.