Which type of meristem brings about secondary growth, causing stems and roots to become thicker?

The correct answer is Lateral meristem.

Meristematic tissues are regions of actively dividing cells in plants. Based on their location and function, meristems are classified into different types:

• Lateral meristem: Located along the longitudinal axis of stems and roots, lateral meristems are responsible for secondary growth. Division of these cells leads to an increase in the diameter, girth, or thickness of the plant body. Examples of lateral meristems include the vascular cambium (which produces secondary xylem and phloem) and cork cambium (which forms outer protective periderm/bark).

• Apical meristem: Situated at the growing tips of roots and shoots, it is responsible for primary growth, leading to an increase in plant height or root length.

• Intercalary meristem: Located at the base of leaves or internodes (commonly in grasses), it facilitates the elongation of stems and leaves.

• Protective tissue: Tissues like the epidermis and cork protect the inner structures of the plant from physical damage and water loss; they are not growth-inducing meristematic tissues.

Therefore, the tissue that brings about secondary growth and causes stems and roots to grow thicker is the Lateral meristem.