Outbreeding devices :
1. Majority of flowering plants produces hermaphrodite flowers which undergo self-pollination.
2. Continuous self-pollination results in inbreeding depression.
3. In order to avoid self-pollination,cross-pollination is encouraged in plants as follows :
a. In some species, pollen release and stigma recepitivity are not synchronized.
Either the pollen is released before the stigma becomes receptive or stigma become receptive before the release of pollen.It prevents autogamy.
b. Arrangement of anther and stigma at different positions :
In some species, the arrangement of anther and stigma at different positions prevents autogam.
c. Self-incompatibility :
It is a genetic mechanism to prevent pollen from the same flower or other flowers of the same plant from fertilization by inhibitting pollen germination or pollen tube growth in the pistil.
d. Production of unisexual flowers :
In monoecious plants such as castor & maize, the male and the female flowers are present on the same plant prevents autogamy but not geitonogamy. On the other hand, in dioecious plants like papays, the male and female flowers are present on different plants prevents both autogamy and geitonogamy.