Question

Describe three devices by which cross pollination is encouraged in angiosperms by avoiding self pollination.

Answer 1

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.

Answer 2

Answer:

Three outbreeding devices that flowering plants have developed:

1. Receptivity of stigma and release of the pollen grain is not synchronized, i.e., stigma becomes receptive much before pollens are released or after they are released to avoid self-pollination.
2. Self-incompatibility: A genetic method to prevent pollens from fertilizing ovules of the same flower by inhibiting their germination on stigma or pistil.
3. Production of unisexual flowers: So that the male and female parts will be present on different plants i.e., dioecious or on different flowers in the same plant (monoecious). This prevents both autogamy and geitonogamy.