Secondary growth is absent in

• A. Hydrophytes
• B. Mesophytes
• C. Halophytes
• D. Xerophytes

Secondary growth refers to the increase in thickness of stems and roots in plants, primarily through the activity of the vascular cambium. This type of growth is typically absent in certain plant groups. In the context of your question, the correct answer is:

Hydrophytes

Hydrophytes are plants that thrive in aquatic environments. They generally do not exhibit secondary growth because their growth patterns are adapted to their water-rich habitats, where the need for thickening stems and roots is minimal.

Other Plant Types

• Mesophytes: These plants grow in moderate environments and can exhibit secondary growth.
• Halophytes: These salt-tolerant plants may also show secondary growth.
• Xerophytes: Adapted to dry conditions, they often have secondary growth to support their structure.

In summary, hydrophytes are the group where secondary growth is typically absent due to their unique environmental adaptations.