Question

Secondary growth in the intrastelar region is due to the activity of

• A. interfascicular cambium
• B. intrafascicular cambium
• C. cork cambium
• D. both (a) and (b)

Answer 1

The correct option is D both (a) and (b)

The intrastelar region comprises all the tissues that are interior to the endodermis. This includes pericycle, vascular bundles, medullary rays and pith.
Stele is only found in dicot stems.

Secondary growth is the increase in the girth of the plant. During secondary growth, intrafascicular vascular cambium (present between the xylem and phloem of a vascular bundle) becomes active and joins with the interfascicular cambium (present between the vascular bundles).
The interfascicular cambium is a secondary meristem which develops from permanent cells of medullary rays. The interfascicular cambium and the intrafascicular cambium join together to form a complete ring of the vascular cambium. The cambium, so formed, produces secondary phloem towards the outer side and secondary xylem towards the inner side. Thus, we see both interfascicular and intrafascicular cambium are responsible for secondary growth in the intrastelar region.


Cork cambium, on the other hand, is formed in the extra stelar region usually in the cortex region. In some cases, it may develop in the epidermis itself. Cork cambium forms cork or phellem towards the outer side and secondary cortex or phelloderm towards the inner side.