Plants have many mechanisms and devices that they employ to promote cross-pollination, these are called as outbreeding devices.
The outbreeding devices in angiosperm plants that encourage cross-pollination are:
→ Dicliny- Flowers are unisexual so that self-pollination is not possible. The plants may be monoecious, that is, bearing both male and female flowers (example: maize) or dioecious, that is, bearing male and female on different plants (example: Mulberry and papaya).
→ Prepotency: Pollen grains of another flower germinate more rapidly over the stigma than the pollen grains of the same flower (example apple and grape).
→ Self sterility: Pollen grains of a flower do not germinate on the stigma of the same flower due to the presence of the similar self-sterile genes.