Pollination :- Biology

 Pollination:

Pollen grains being non motile, angiosperms have evolved the strategy to use abiotic agents (wind, water) and biotic agents (birds, insects, snails) to their flowers, feeding the visitors and exploiting their mobility for pollination and also seed dispersal. Pollen grains are non-motile and they are usually carried from flower to flower by means of external agents. Pollination is the transfer of pollen grains from anther to the stigma of the flower. It is the pre- requisite for fertilization because both the male and female gametes are non-motile. Moreover gametes are produced at two different sites.

a. Autogamy (self pollination) :

It is a type of pollination in which bisexual flower is pollinated by its own pollen grains. Offsprings are genetically identical to their parents e.g. pea, Clitoria

b. Geitonogamy:

It is the transfer of pollen grain to a stigma of a different flower produced on the same plant. It is functionally similar to cross pollination as it involves pollinating agents, but it cannot bring about genetic variations and is only of ecological significance e.g. Cucurbita maxima. It is similar to autogamy as pollen grains come from same plant.

c. Xenogamy (cross polination/ out breeding):

It is a type of cross pollination when pollen grains of one flower are deposited on the stigma of a flower of different plant belonging to same species, with the help of pollinating agency. It generates genetically varied offsprings.

Majority of flowering plants depend on the transfer of pollen grains. Virtually all seed plants need to be pollinated. Most of the food and fibre crops grown throughout the world, depend upon pollinators for reproduction.

The agents responsible for pollination have been grouped into two main categories:

A. Abiotic agents

B. Biotic agents

A. Abiotic Agents : These are non-living agents which include wind and water.

1. Pollination by wind (Anemophily) :

Most of the important crop plants are wind pollinated. These include wheat, rice, corn, rye, barley and oats. Palms are also wind pollinated.

Adaptations in anemophilous flowers :

The flowers are small, inconspicuous, colourless, without nectar and fragrance (odour).

The pollen grains are light in weight, dry and produced in large numbers to increase chances of pollination considering wastage of pollengrains.

Stigma is feathery to trap pollens carried by wind currents.