Outbreeding Devices:-

The majority of flowering plants produces hermaphrodite flowers that can undergo self-pollination. Continued self-pollination results in inbreeding depression. To avoid self-pollination and encourage cross-pollination, there are some devices in plants:

a.Avoiding synchronization:-

• In some species, pollen release and stigma receptivity are not synchronized.
  Either the pollen is released before the stigma becomes receptive or the stigma becomes receptive before the release of pollen. It prevents autogamy.

b.Arrangement of anther & stigma at different positions:-

• This prevents autogamy.

c. Self-incompatibility:-

• It is a genetic mechanism to prevent self-pollen (from the same flower or other flowers of the same plant) from fertilization by inhibiting pollen germination or pollen tube growth in the pistil.

d. Production of unisexual flowers:-

• If male & female flowers are present on the same plant (i.e., monoecious),
  e.g. castor & maize), it prevents autogamy but not geitonogamy. In dioecious plants (e.g. papaya), male and female flowers are present on different plants (dioecy). This prevents both autogamy and geitonogamy.