What is root apex ? Name the three meristematic regions of it

Root Apex : (a) It is found at the tip of main root and its branches.
(b) It is derived from radicle part of the embryo and its derivatives, in case of tap root system.
© In adventitious roots, it is produced from the derivatives of shoot apex.
(d) The root apex is sub-terminal because it is covered by the root cap.
(e) The root apical meristem (root apex) gives rise to three meristematic regions : (i) Protoderm, (ii) Procambium, (iii) Ground meristem.
(f) Protoderm form epiblema and root cap (calyptra).
(g) However, in monocots, the root cap is derived from a special meristematic region at the end of the root called calyptrogen.
(h) The cells of the root cap secrete a mucilaginous substance that acts as a lubricant.
(i) The root cap cells are parenchymatous and short-lived.
(j) They contain starch grains.
(k) Procambium produces vascular tissues. Ground meristem forms pith, endodermis and cortex.
(l) In many cases, a small region with very low mitotic
activity is present in the centre of the root apex. It is called quiescent centre.