Question

Secondary growth in the cortical region of a dicot stem is due to the activity of

• A. Cambium
• B. Phellogen
• C. Phellem
• D. Phelloderm

Answer 1

The correct option is A Cambium

Secondary growth refers to the growth that results from cell division in the cambia or lateral meristem and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips of stems and roots, causing them to elongate and gives rise to primary tissue. Secondary growth occurs in most seed plants, but monocots usually lack secondary growth. In many vascular plants, secondary growth is the result of the activity of the two lateral meristems, the cork cambium and vascular cambium. Arising from lateral meristems, secondary growth increases the girth of the plant root or stem, rather than its length. As long as the lateral meristems continue to produce new cells, the stem or root will continue to grow in diameter. Thus, option A is correct.

Phellogen is defined as the meristematic cell layer responsible for the development of the periderm. Cells that grow inwards from the phellogen are termed phelloderm, and cells that develop outwards are termed phellem or cork. The periderm is the secondary protective (dermal) tissue that replaces the epidermis during growth in thickness of stems and roots of gymnosperms and dicotyledons.