Pith and cortex do not differentiate in

Explanation

Cortex is the main zone which lies between the epidermis and pericycle and is made up of primary tissues. This zone varies in thickness from a few layers to many layers. In the dicotyledonous stems the cortex is usually differentiated into the following three sub-zones:
(i) hypodermis,     (ii) general cortex, and       (iii) endodermis.