Radial

The correct answer is option 'B' - Radial.

Xylem and phloem are two types of vascular tissues found in plants that are responsible for the transport of water, minerals, and nutrients throughout the plant. These vascular tissues are organized into bundles called vascular bundles.

Structure of Vascular Bundles
Vascular bundles consist of both xylem and phloem tissues, and their arrangement can vary depending on the type of plant. In certain plants, such as monocots, the xylem and phloem tissues are arranged in separate bundles, while in others, such as dicots, they are present together in a single bundle.

Collateral vs. Radial
The arrangement of xylem and phloem tissues in vascular bundles can be classified as collateral or radial.

- Collateral: In collateral bundles, the xylem tissue is located towards the inner side of the bundle, while the phloem tissue is located towards the outer side. These bundles are typically found in dicots.

- Radial: In radial bundles, the xylem and phloem tissues are arranged in alternating layers, forming concentric rings. The xylem is located towards the center, while the phloem is located towards the periphery. These bundles are commonly found in monocots.

Significance of Radial Vascular Bundles
The presence of radial vascular bundles in plants offers several advantages:

1. Efficient Transport: The radial arrangement allows for efficient transport of water and nutrients throughout the plant. It ensures that all cells have easy access to these essential resources.

2. Structural Support: The radial arrangement provides structural support to the plant. The xylem tissues, which are responsible for water transport, are located towards the center, providing stability to the plant's stem.

3. Flexibility: Radial vascular bundles allow for flexibility in plant growth. As the plant grows, new layers of xylem and phloem can be added to the existing bundles, accommodating the increase in size.

4. Adaptability: The presence of radial vascular bundles is a characteristic feature of many monocots, which include a wide range of plants, such as grasses, lilies, and orchids. This arrangement has allowed these plants to adapt to diverse environments and thrive in various ecological niches.

In conclusion, separate xylem and phloem bundles are known as radial bundles. This arrangement is commonly found in monocots and offers several advantages, including efficient transport, structural support, flexibility, and adaptability.