What is pollination ? Sexual reproduction in plants

Pollination

• The transfer of pollen grains from Anther to stigma is called pollination. Flowering plants have special adaptation to achieve 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. The flower in which anthers and stigma are , exposed, complete autogamy is rare.

• There should be Synchronisation in pollen release and stigma receptivity. Anther and stigma should be located close to each other.

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.

• It is  functionally  a cross pollination because it occurs by involvement of pollinating agents but it  is similar to autogamy because pollen grain come from same plant.

• Both Autogamy and geitonogamy are discouraged because both do not lead to genetic variability.

• Xenogamy 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.

• Majority of plants use biotic agents for Pollination. Some of the plants uses Abiotic agents for the pollination. 

• To ensure the pollination and compensate the loss of pollination, anther produces large amount of pollination.

Agents of Pollination

Anemophily

• It 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.

• The stamen are well exposed for easily dispersal of pollen grain in wind.

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

• Hydrophilly means pollination by water. Water pollination is rare and limited.

• It is found in about 30 species and mostly in Monocotyledons.

• Bryophytes, Algae and Pteridophytes are also uses water for the transportation of male gamete.

• Plants like Ceratophyllum, Zostra, whose both male and female 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.

Remember 👌👌In water hyacinth or Eichhornia and water lily, pollination takes place by wind or insect.

Entomophily

• It 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. 

• Amorphophallus is tallest flower which provide safe place to lay egg of insect. Amorphophallus is  6 feet in height.

• 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

• It 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

• It 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.

Chasmogamous and Cleistogamous flower

• In Viola or Common pansy, Oxalis and Commelina in which two types of flowers  ie   Chasmogamous and Cleistogamous flowers are found. 

• In chasmogamous, Anther and stigma are well exposed and  flowers opens completely.

• In cleistogamous flower,  Anther and stigma are not  well exposed and  flowers  do not open completely.

• Cleistogamous flowers are autogamous flowers and have no  the  chance of cross pollination. 

• Cleistogamy is a disadvantage because it does not lead genetic variation. Cleiostogamous produce seed without the involvement of pollinator