The girth of stem increases due to the activity of

• A. Lateral meristem
• B. Apical meristem
• C. Intercalary meristem
• D. Apical and intercalary meristem

The girth of a stem increases primarily due to the activity of the lateral meristem.

Understanding Lateral Meristem

Lateral meristems are responsible for secondary growth in plants, which leads to an increase in thickness or girth. This growth occurs in two main types of lateral meristems:

• Vascular cambium: Produces new vascular tissue (xylem and phloem).
• Cork cambium: Produces the outer protective layer of the stem.

Other Meristems Explained

While apical meristems are involved in the elongation of stems and roots, and intercalary meristems contribute to growth at specific regions (like nodes in grasses), they do not significantly affect the girth of the stem.

In summary, the correct answer is A. Lateral meristem, as it plays a crucial role in increasing the girth of the stem through secondary growth processes.