Question

Arrange the below four layers in proper order starting from the outermost to the innermost layer after secondary growth has already occurred in a dicot stem:
I. Phellem
II. Wood
III. Phelloderm
IV. Vascular cambium

• A. $I \rightarrow II \rightarrow III \rightarrow IV$
• B. $I \rightarrow III \rightarrow II \rightarrow IV$
• C. $IV \rightarrow III \rightarrow II \rightarrow I$
• D. $III \rightarrow II \rightarrow I \rightarrow IV$

Answer 1

Answer: (B)

The meristematic tissue called cork cambium or phellogen develops, usually in the cortex region. Phellogen is a couple of layers thick. It is made of narrow, thin-walled, and nearly rectangular cells. Phellogen cuts off cells on both sides. The outer cells differentiate into cork or phellem while the inner cells differentiate into secondary cortex or phelloderm. Internal to the secondary cortex lies the xylem (wood), then the vascular cambium and then the phloem is the innermost.