Difference : In geitonogamy, transfer of pollen grains from anther to the stigam of another flower of the same plant while in xenogamy, transfer of pollen grains grom another to the stigma of a different plant.
Similarity : Both help in pollination by transfer of pollen grains to the stigma.
(b) Continued self pollination result in inbreeding depression. Flowering plants have developed many devices to discourage self pollination and to encourage cross pollination. In some species, pollen release and stigma receptivity are not synchronised.
In some other species, the anther and stigma are placed at different positions so that the pollen cannot come in contract with the stigma of the same flower. Both these prevent autogamy.
The third device to prevent inbreeding is self- incompatibility. This is a genetic mechanism and prevents self-pollen from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
