Correct option (a) medullary rays
Explanation
In dicot stems, the cells of cambium present between primary xylem and primary phloem is the intrafascicular cambium. The cells of medullary rays, adjoining these intrafascicular cambium become meristematic and form the interfascicular cambium.
Xylem parenchyma are living and thin-walled and their cell walls are made up of cellulose. In dicot roots the innermost layer of the cortex is called endodermis. Next to endodermis like a few layers of thick walled parenchymatous cells called as pericycle.
