Question

The allogamy is best favoured by
(a) Chasmogamy
(b) Cleistogamy
(c) Dicliny
(d) Homogamy

Answer 1

Hint: When the fertilization of an ovum in a flower occurs by the spermatozoa of another flower, such a mechanism is called allogamy. It is facilitated in conditions where the flower has only one type of gamete, be it male or female.

Complete answer:
Allogamy is best favoured by dicliny. To understand what is chasmogamy, cleistogamy or homogamy, let's first know what is pollination.
- Transfer of pollen grains from the anther to the stigma of a pistIl in a flower is termed as ‘pollination’. It is needed because both male and female gametes of a flower are non-motile.
Now, let’s see different kinds of fertilization.
Autogamy:
- It is a type of fertilization that occurs within gametes of the same flower.
- This type of fertilization is rarely seen in open and exposed anthers and stigma.
- In some plants like Viola, Oxalis, and Commelina, two types of flowers are produced namely, chasmogamous and cleistogamous.
- ‘Chasmogamous’ flowers: Flowers that possess exposed anther and stigma.
- ‘Cleistogamous’ flowers: Flowers that have closed anther and stigma.
- Cleistogamous flowers are invariably ‘autogamous’ so have an assured seed set even in the absence of a pollinator.
Homogamy: It is a condition where anther and stigma of a flower mature at the same time, leading to self-pollination.
Regarding the arrangement of reproductive structures in a plant; plants may have both male and female reproductive structures in the same plant (bisexual) or on different plants (unisexual).
In some organisms only one of the gamete (male or female) is present, this unisexual condition is described as heterothallic, ‘dicliny’, and dioecious.
So, the correct answer is “dicliny”.

Note: In several fungi and plants, terms such as homothallic, ‘monocline’, and monoecious are used to denote the bisexual condition. These are the organisms that bear both the gametes in the same body.