Question

Non-transfer of pollen from the anther to stigma of the same flower due to a mechanical barrier is
(a) Dichogamy
(b) Herkogamy
(c) Heterostyly
(d) Cleistogamy

Answer 1

Hint: Non-transfer of pollen from the anther to the stigma of the same flower is a method to prevent autogamy or self- fertilization. Prevention of self- fertilization is necessary to bring in variations in the plant which finally leads to evolution.

Complete Step by Step Answer:
Herkogamy is known as the process in which pollination of pollen with the stigma of the same flower is prevented by the means of mechanical separation. This occurs in bisexual flowers. An example of this is hood-like covering found on the stigma of the flower.
So, the correct answer is ‘Herkogamy’.

Additional information: The other terms mentioned in the options are as follows:
- Dichogamy: This is the condition in which the anther and stigma reach maturation at different times.
Protandry: When another matures and releases pollen grains before stigma matures.
Protogyny: When stigma matures before another releases pollen.
- Heterostyly: Some flowers have different lengths of stamens and styles. This is also to prevent the chances of self- fertilization.
- Cleistogamy: Cleistogamy is the term used to refer to flowers that never open i.e. their anther and stigma are never exposed to the outside world. This means that when pollen grains are released they are going to pollinate the stigma of the same flower only. Examples- Oxalis and Commelina.

Note:
- Another reason to avoid self-fertilization is to prevent inbreeding depression.
- Inbreeding depression is a phenomenon in which the fitness of a species decreases due to continuous inbreeding among related individuals or in the case of plants, the same individual.
- Self-fertilization can also be prevented by self-incompatibility. This is a genetic mechanism that involves the flower not allowing the pollen from the same flower to fertilize the egg.