Question

Name the phenomenon of two flowers, one having long stamens and short styles, and other having short stamens and long style.
A. Allogamous device
B. Heterostyly
C. Dicliny
D. Herkogamy

Answer 1

As we know that flowers are produced by the phenomenon called pollination which can be of two types that are self-pollination and cross-pollination. And in order to prevent the inbreeding depression or loss of genetic variation from self-pollination, some outbreeding devices or features are known that discourage self-pollination.

Complete answer:
We are very well aware of the pollination phenomenon of flowers that involves the transfer of pollen grains from anther to the stigma. It can be of two types: self-pollination which is basically the pollination within the same plant and the cross-pollination which is the phenomenon of pollination in two different plants or two different flowers of the same plant.
Self-pollination can result in loss of genetic variation or what is commonly called inbreeding depression so to prevent it, some outbreeding devices or features are known which discourage self-pollination and encourage cross-pollination.
These devices includes: Unisexuality meaning formation of unisexual flowers having both the sexes in same flower, Dichogamy, Heterogamy, Herkogamy, Heterostyly etc.
Let us talk about Dichogamy which is the phenomenon of different maturation times of Androecium and Gynoecium of a flower. For instance: Saxifraga where the anthers dehisce much before the stigma of the same flower, hence no pollination is possible.
Then comes Herkogamy which involves the development of a natural barrier between androecium and gynoecium of a flower to check self-pollination. For instance: Salvia.
Next we will talk about Heterostyly which prevents self-pollination and the flowers may be two or more than two and differ in stamen and pistil lengths and pollen from a flower can bring about the effective pollination in flowers of different types and not within its own type. For instance: Primrose
Therefore from the above explanation we can say that Heterostyly is the phenomenon in which two flowers, one having long stamens and short styles, and other having short stamens and long style.

Hence, the correct answer is (B).

Note:
Flowers in Heterostyly become incompatible to each other and thus no self-pollination is possible because the anther will not be able to reach the style. Pollens from one flower can pollinate the flower on another plant so it is a category involving cross-pollination of flowers.