Describe three devices by which cross pollination is encouraged in angiosperms by avoiding self pollination.
Answers
Answer:
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:
1. 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).
2. Prepotency: Pollen grains of another flower germinate more rapidly over the stigma than the pollen grains of the same flower (example apple and grape).
3. 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.
Answer:
(1) Unisexuality, dichogany prepotency heteromorphy and herkogamy are the outbreeding devices.
(2) Unisexuality: The plants bear either male or female ilowers. Due to unisexual nature, self-pollination is avoided. Plants are either dioecious, Cg Papaya or monoecious, e-g maze
(3) Heteromorphy: ln same plants different Wpes o lowers are produced. In these TIOWers, sugmas and arthers are situated at different levels. There is heterostyly and heteroanthy. This prevents selfpolinalion e.g. Primrose.
(4) Herkogamy : In bisexual lowers we may come across mechanical device to prevent self-pollination. Natural physical barrier avoids contact of pollens with sigma. E.g. Calotropis where pollinia are situated below ne sigma.