question_answer 8)

Mention two strategies evolved by flowers to prevent self-pollination.

Answer:

Continued self-pollination result in inbreeding depression. So flowering plants have developed following devices to discourage self-pollination and to encourage cross pollination: (i) Dicliny (unisexuality): Flowers are unisexual so that self-pollination is not possible. The plants may be monoecious (bearing both male and female flowers, e.g., maize) or dioecious (bearing male and female flowers on different plants, e.g., mulberry, papaya). (ii) Dichogamy: Anthers and stigmas mature at different times in a bisexual flower so as to prevent self-pollination. (a) Protandry – anthers mature earlier than stigma of the same flower. Their pollen grains become available to stigmas of the older flowers, e.g., sunflower, Salvia. (b) Protogyny – stigmas mature earlier so that they get pollinated before the anthers of the same flower develop pollen grains, e..g, Mirabilis jalapa (four o’clock), Gloriosa, Plantago.