Radial conduction is transport of water horizontally within xylem. Ray parenchyma are structures that facilitates lateral conduction of water.

Radial conduction of water in plants refers to the movement of water and nutrients across the radial axis of the plant, from the center of the stem or root towards the outer regions. This process occurs through various pathways in the plant, including the xylem vessels, tracheids, phloem, and ray parenchyma cells.

However, the correct answer to this question is option 'D', which states that radial conduction of water takes place through ray parenchyma cells. Let's understand why:

1. Function of Ray Parenchyma Cells:
Ray parenchyma cells are horizontal cells present in the secondary xylem and secondary phloem of plants. They are responsible for radial conduction of water and nutrients in plants.

2. Structure of Ray Parenchyma Cells:
Ray parenchyma cells are elongated, living cells that run radially across the plant stem or root. They are arranged in vertical rows called rays and are connected to the xylem vessels and phloem. These cells have thin cell walls and abundant cytoplasm, allowing them to transport water and nutrients efficiently.

3. Role in Radial Conduction:
Ray parenchyma cells are involved in both the radial movement of water and the storage of nutrients. They transport water laterally from the xylem vessels towards the cortex or pith of the stem or root. This movement is facilitated by the interconnected cytoplasmic strands present between neighboring ray parenchyma cells.

4. Importance in Plant Growth:
Radial conduction through ray parenchyma cells is crucial for the overall growth and development of plants. It helps in the distribution of water and nutrients to all parts of the plant, ensuring proper functioning and metabolism. It also aids in the healing and defense mechanisms of plants by transporting substances required for wound closure and defense against pathogens.

In conclusion, radial conduction of water in plants primarily occurs through ray parenchyma cells. These cells play a vital role in transporting water and nutrients laterally across the plant's stem or root, ensuring proper growth and functioning.