SELF POLLINATION:It is the transfer of pollen grains from the anther to the stigma of the same flower
CROSS POLLINATION: It is the transfer of pollen grains from the anther of one flower to the stigma of another flower 
pollination is done through insects wind etc............
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Self Pollination vs Cross Pollination

Self Pollination

Cross Pollination

It is the transfer of pollen grains from anther to the stigma of either the same or genetically similar flower.

Cross pollination involves the transfer of pollen from anther of one flower to the stigma of a genetically different flower.

Self pollination can occur even in closed flower.

It occurs when he flowers are open.

External agency is not required for self pollination , except in case of geitonogamy.

An external agent is essential for carrying the pollen grains from anthers to the stigma.

The plants ultimately become homozygous.

The plants remain heterozygous.

Highly useful characters are preserved by self pollination

Cross pollination is unable to preserve all the highly useful characters since they tend to get diluted.

Adaptability to changed environment is absent as self pollination does not produce variability.

Plants are better adapted to changed environment and struggle for existence due to introduction of variations.

It does not help in producing new races, varieties and species.

Cross pollination is a mechanism of producing  new races, varieties and even species.

Self pollination produces pure lines.

It give rise to offspring having variations among thems

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