Question

Annual growth rings are formed due to activity of

• A. Extra-stelar cambium
• B. Intra-stelar cambium
• C. Inter-stelar cambium
• D. All of the above

Answer 1

Answer: (B)

Intra-stelar cambium

Intrafascicular cambium is present between xylem and phloem in dicot stem and roots. Pith rays, present between the edges of intrafascicular cambium, divide to form a new cambium strip between the two vascular bundle i.e., interfascicular cambium. Thus, inter and intra fascicular cambium together forms a complete cambium ring, called as vascular cambium, which forms secondary xylem on inner side and secondary phloem on outer side.

Differential cambial activity during autumn and spring season result in narrow and wide secondary xylem rings respectively, which together forms the annual growth ring. Thus, annual growth ring is derived from vascular cambium, which is the present between xylem and phloem in a vascular bundle and that’s why also termed as inter-stelar cambium. Thus, the correct answer is option B.