List three strategies that a bisexual chasmogamous flower can evolve to prevent self-pollination (autogamy).

A bisexual chasmogamous flower can evolve the following (three) strategies to prevent self-pollination (autogamy).
(a)  Dichogamy In this mechanism, pollen release and stigma receptivity are not synchronised. In sunflower, the pollen is released before the stigma becomes receptive (protandry). In Datura, Solanum, the stigma becomes receptive much before the release of pollen (protogyny) leads to cross-pollination.
(b)  Herkogamy The male and female sex organs are placed at different positions or in different directions is called Herkogamy. In these plants, the pollen cannot came in contact with the stigma of the same flower. It has undergone cross pollination, e.g., Hibiscus, Gloriosa.
(c) Self-sterility It is a genetic mechanism which prevents the self-pollen from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil, e.g., Abotilon.