(i) Pollen release and stigma receptivity are not synchronized. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen.
(ii) Anther and stigma are placed at different positions in such a way that pollen cannot come in contact of stigma of the same flower.
(iii) Self-incompatibility which inhibits the pollen germination / pollen tube growth in the pistil of same flower or another flower of same plant.
(iv) Production of unisexual flowers. This condition prevents both autogamy and geitonogamy.
