Question

Define geitonogamy and xenogamy. Give advantages of self-pollination and cross-pollination. Explain how dichogamy favours pollination.

Answer 1

Hint: Xenogamy and geitonogamy both are the different routes of pollination that are adapted by the plants. The transfer of pollen from anther of a flower to stigma is called pollination. The plant in which pollination occurs are called pollinated plants.

Complete Answer:
- Geitonogamy is the transfer of pollen grains from anther of a flower to the stigma of another flower on the same plant. It functions like a cross-pollination but similar to autogamy genetically. The pollen grains and offspring produce are genetically similar. Example: maize.
- Xenogamy is the transfer of pollen grains from anther of one flower to stigma of another flower of a different plant. It is a type of cross-pollination the pollen grains and offspring produce are genetically different. Example: onion.
- Pollination takes place when male reproductive part i.e. anther transfer to female reproductive part i.e. stigma. There are two types of pollination: self-pollination and cross-pollination.

Advantages of self-pollination:Less wastage of pollen grains and purity of species maintained because genetic diversity does not change. Pollinating agents and external agents like water, wind not involved in self-pollination. Recessive characters are eliminated.

Advantages of cross-pollination:
- High quality of seeds produced. There is a variety of genes within the species. Offspring show better immunity against the diseases.
- Dichogamy is the maturation of sex organs i.e. anther and stigma in the plants at different times. Dichogamy may be interflora and intrafloral. In diclinous species, it exists among flowers. So, that is why floral mechanism favours cross-pollination.

Note: Self-pollination occurs when transfer of pollen from anther to stigma of the same flower. They have stable genetic diversity. Cross-pollination occurs when pollen transfers from anther of one flower to stigma of another flower of different species.