question_answer 57)

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

Answer:

                  A bisexual chasmogamous flower can evolvethe following (three) strategies to preventself-pollination (autogamy). (a) Dichogamy In this mechanism, pollen release and stigma receptivity are notsynchronized. In sunflower, the pollen is released before the stigma becomes receptive(protandry).InDatura, Solarium, the stigma becomes receptive much before therelease of pollen (protogyny) leads to cross-pollination. (b)HerkogamyThe male and female sex organs are placed at different positions or indifferent directions is called Herkogamy. In these plants, the pollen cannot came incontact with the stigma of the same flower. It has undergone cross pollinatione.g., Hibiscus Gloriosa. (c)Self-sterilityIt is a genetic mechanism which prevents the self-pollen from fertilizingthe ovules by inhibiting pollen germination or pollen tube growth in the pistil, e.g., Abotilon. Note Another device to prevent self-pollination is the production of unisexual flowers, but this is not beneficial as above mentioned strategies. It prevents auto gamy but notgitonogamyin monoecious plants such as castor and maize.