Briefly explain secondary meristems.

Explanation

Secondary meristems. These are derived from parenchymatous cells (permanent tissues) by a process called dedifferentiation e.g. cork cambium, vascular cambium in dicot root and interfascicular cambium in dicot stem.
Cork cambium or phellogen forms cork or phellem and secondary cortex or phelloderm.
Vascular cambium forms secondary phloem on its outer side and secondary xylem on its inner side.