Write short note on Heterostyly.

Explanation

It is a contrivance of cross pollenation. Some plants produce two or three different forms of flowers that are different in their length of stamens and style. Pollination will take place only between organs of the same length
(a) Distyly:
(i) The plant produces two forms of flowers, Pin or long style, long stigmatic papillae, short stamens and small pollen grains, Thrum-eyed or short style, small stigmatic papillace, long stamens and large pollen grains.
Example: Primula
The stigma of the Thrum-eyed flowers and the anther of the pin lie in same level to bring out pollination.
Similarly the anther of Thrum-eyed and stigma of pin ones is found in same height. This helps in effective pollination.
(b) Tristyly:
(i) The plant produces three kinds of flowers, with respect to the length of flowers, with respect to the length of the style and staments.
(ii) Here, the pollen from flowers of one type can pollinate only the other two types but not their own type.
Example: Lythrum.