`star` Pollination
`star` Types:
A) Autogamy
B) Geistogamy
C) Xenogamy
`star` Agents of Pollination


● The male and female gametes in flowering plants are produced in the `color{Violet}"pollen grain"` and `color{Violet}"embryo sac"`, respectively.

● As both types of gametes are `color{Violet}"non-motile"`, they have to be brought together for `color{Violet}"fertilisation"` to occur.

● `color{Violet}"Pollination"` is the mechanism to achieve this objective.

● Transfer of pollen grains (shed from the anther) to the stigma of a pistil is termed `color{Violet}"pollination"`. Flowering plants have evolved an amazing `color{Violet}"array of adaptations"` to achieve pollination.

● They make use of `color{Violet}"external agents"` to achieve pollination.


`color{Brown}"Kinds of Pollination"` : Depending on the source of pollen, pollination can be divided into `color{Violet}"three types"`.


● This type, pollination is achieved within the `color{Violet}"same flower"`.

● Transfer of pollen grains from the `color{Violet}"anther to the stigma"` of the same flower.

● In a normal flower which opens and exposes the anthers and the stigma, `color{Violet}"complete autogamy"` is rather `color{Violet}"rare"`.

● Autogamy in such flowers requires `color{Violet}"synchrony"` in pollen `color{Violet}"release"` and stigma `color{Violet}"receptivity"` and also, the anthers and the stigma should lie `color{Violet}"close to each other"` so that self-pollination can occur.

● Some plants such as Viola (common pansy), Oxalis, and Commelina produce two types of flowers –

`star` `color{Brown}"Chasmogamous flowers"` which are similar to flowers of other species with `color{Violet}"exposed anthers and stigma"`.

`star` `color{Brown}"Cleistogamous flowers"` which do not open.
● In such flowers, the anthers and stigma lie `color{Violet}"close to each other."`

● When anthers dehisce in the flower buds, pollen grains come in `color{Violet}"contact with the stigma"` to effect pollination.

● Thus, cleistogamous flowers are `color{Violet}"invariably autogamous"` as there is no chance of cross-pollen landing on the stigma.

● Cleistogamous flowers produce `color{Violet}"assured seed-set"` even in the absence of pollinators.


● Transfer of pollen grains from the anther to the stigma of `color{Violet}"another flower"` of the `color{Violet}"same plant."`.

● Although geitonogamy is `color{Violet}"functionally cross-pollination"` involving a pollinating agent, genetically it is `color{Violet}"similar to autogamy"` since the pollen grains come from the same plant.


● Transfer of pollen grains from anther to the stigma of a `color{Violet}"different plant"` .

● This is the only type of pollination which during pollination brings `color{Violet}"genetically different"` types of pollen grains to the stigma.


● Plants use two abiotic (wind and water) and one biotic (animals) agents to achieve pollination. Majority of plants use biotic agents for pollination.

● Only a small proportion of plants use abiotic agents.

● Pollen grains coming in contact with the stigma is a chance factor in both wind and water pollination.

●To compensate for this uncertainties and associated loss of pollen grains, the flowers produce enormous amount of pollen when compared to the number of ovules available for pollination.