Read the passage and answer the following question:

In flowering plants, the production of male and female gametes occurs within the pollen grain and embryo sac, respectively. Since both types of gametes are immobile, they require a mechanism to be brought together for fertilization to take place. Pollination is the process that serves this purpose. Pollination refers to the transfer of pollen grains, which are released from the anther to the stigma of a pistil. Flowering plants have developed various remarkable adaptations to accomplish pollination. They rely on external agents to facilitate the process of pollination.

Which of the following agent helps in the pollination of Vallisneria and Hydrilla ?

Water

The correct answer is Option (2) –Water

Pollination by water is quite rare in flowering plants and is limited to about 30 genera, mostly monocotyledons. Some examples of water pollinated plants are Vallisneria and Hydrilla which grow in fresh water and several marine sea-grasses such as Zostera. Not all aquatic plants use water for pollination. In a majority of aquatic plants such as water hyacinth and water lily, the flowers emerge above the level of water and are pollinated by insects or wind as in most of the land plants.

In Vallisneria, the female flower reach the surface of water by the long stalk and the male flowers or pollen grains are released on to the surface of water. They are carried passively by water currents ; some of them eventually reach the female flowers and the stigma. In most of the water-pollinated species, pollen grains are protected from wetting by a mucilaginous covering.