Question

Flowering plants have developed many devices to discourage self pollination and to encourage cross pollination .explain three such devices.

Answer 1

First of all what are outbreeding devices n why r they necessary-

Devices that discourage SELF-POLLINATION & encourage CROSS-POLLINATION are known as outbreeding devices.

They r necessary bcuz continued SELF-POLLINATION in flowers causes a downfall in the quality and variety of the products.

There are 4 types of outbreeding devices-

1.) Release of Pollen much before or much after the stigma is ready to accept it (receptiveness of stigma) .

2.) Placement of anther & stigma at such positions so that the pollens do not reach the stigma of the same plant or the same flower.

3.) It is a chemical method in which the stigma inhibits the growth of the pollen tubes into the pistil. This process is known as SELF-INCOMPATIBILITY

4.) Production of flowers or plants that are UNISEXUAL i.e. the plant or flower exhibit dioecy.
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Answer 2

Answer:

(i) Pollen release and stigma receptivity are not synchronized. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen. (ii) Anther and stigma are placed at different positions in such a way that pollen cannot come in contact of stigma of the same flower. (iii) Self-incompatibility which inhibits the pollen germination / pollen tube growth in the pistil of same flower or another flower of same plant. (iv) Production of unisexual flowers. This condition prevents both autogamy and geitonogamy.