(a) The pollen grains represent the male gametophytes. When the pollen grains mature, it contains two cells-generative and vegetative cells.
The generative cell is distinguished from vegetative cell:
| Generative cell |
Vegetative cell |
| Smaller in size |
Bigger in size |
| Spindle shaped with dense cytoplasm and a nucleus |
Large irregularly shaped nucleus. |
| It floats in cytoplasm of vegetative cell |
It has abundant food reserves. |
(b) (i) In the given diagram, method 1 is representing the "autogamy" type of pollen transfer as pollination is achieved within the same flower.
Method 2 is representing "Geitonogamy", in which transfer of pollen grains from anther to stigma of another flower of the same plant occurs.
Method 3 represents "Xenogamy", where transfer of pollen grains from anther to stigma of a different plant occurs.
(ii) In water lily, the flowers emerge above the level of water and are pollinated by insects or wind.
In Vallisneria, the female flower reaches the surface of water by the long stalk and male flowers or pollen grains are released on to surface of water. They are carried passively by water currents, some of them eventually reach the female flowers and the stigma.
(iii) Method-3
Xenogamy: It is the only type of pollination in which pollination brings genetically different types of pollen grains to the stigma.
It enables creation of new variants, so that survival advantage is enhanced.
