List any three outbreeding devices that flowering plants have developed for cross-pollination and explain how they help to encourage cross-pollination.

− Self-incompatibility is the genetic mechanism which prevents self-pollination by inhibits the germination of pollen from same flower or different flower of same plant on stigma. − Unisexual flowers have no chance for self-pollination − Receptivity of male and female parts: Pollen release and stigma receptivity are not synchronised. − Position of male and female parts: The anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower. − Unisexual plants have no chance of self-pollination. − Any other correct outbreeding device.