In Vallisneria, pollination takes place by the agency of :

Options

A. Water
B. Wind
C. Birds
D. Insects

Explanation

**Step-by-Step Solution:**

1. **Understanding Vallisneria**: Vallisneria is an aquatic plant that has both male and female flowers. It is important to know the structure of these flowers to understand how pollination occurs.

2. **Identifying Pollination Method**: In Vallisneria, pollination occurs through a unique method due to its aquatic environment. Unlike many terrestrial plants that rely on wind or animals for pollination, Vallisneria uses water as the medium for transferring pollen.

3. **Structure of Flowers**: The male flowers of Vallisneria are typically submerged underwater, while the female flowers have long stalks that extend to the surface of the water. This adaptation is crucial for the pollination process.

4. **Pollen Release**: When the male flowers release pollen grains, these grains float in the water. The water acts as a carrier, transporting the pollen from the male flowers to the female flowers.

5. **Pollination Process**: As the pollen grains drift in the water, they eventually reach the stigma of the female flowers that are positioned at the water's surface. This contact between the pollen and the stigma is what constitutes pollination.

6. **Conclusion**: Therefore, in Vallisneria, the agency of pollination is water. The water facilitates the movement of pollen from male flowers to female flowers, enabling fertilization to occur.

**Final Answer**: In Vallisneria, pollination takes place by the agency of water.

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