Question

Mention two strategies that evolved to prevent self-pollination in flowers.

Explain any four contrivances to prevent self-pollination in plants with an appropriate example of each type.

Answer 1

Continued self-pollination decreases the vigour and vitality of a particular race. Thus, flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination.

1. Unisexuality: Either male or female flowers are borne by plants. For instance, monoecious plants such as maize, mulberry, and papaya are dioecious.
2. Dichogamy protogyny: The gynoecium matures before the androecium. For instance, this is the case with gloriosa.
3. Dichogamy protandry: The androecium matures earlier than the gynoecium. For instance, consider the disc florets of sunflowers.
4. Prepotency: The pollen grains of other flowers germinate rapidly on the stigmas of different flowers. Consider the example of the apple flower.
5. Herkogamy: The anther and the stigma are placed at different positions or have a mechanical barrier so that anthers cannot contact or touch the stigma of the same flower. Consider the example of calotropis.
6. Heterostyly: Styles of the flowers of the same species are at different heights. Consider the primrose as an example.
7. Self-incompatibility (Male sterility): The pollen grains of some plants are not functional. Such plants set seeds only after cross-pollination. Examples of these plants include Tobacco and Thea.