Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination result in inbreeding depression.

Flowering plants have developed many devices to discourage self pollination and to encourage cross pollination.

$(i)$ In some species Pollen release and stigma receptivity are not synchronised. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen it. e.g. palms.

$(ii)$ Arrangement of anther and stigma at different positions : The anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower. e.g. Primula. Both these devices prevent autogamy.