Outbreeding devices :
(i) In order to avoid self-pollination, cross-pollination is encouraged in plants as follows:
(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 stigma becomes 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 autogamy.
(c) Self-incompatibility :
It is a genetic mechanism which prevent pollen of one flower to germinate on the stigma of same flower.
(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 papaya, the male and female flowers are present on different plants prevents both autogamy and geitonogamy.
