What is the function of the Cortex and the central cylander in roots?

Question

central cylander aka stele

Answer 1

The cortex is the area inside the root that sustain the growth of special cells that cause the growth of Xylem and phloem. These cause the transfer of water from the roots to the leaves in the tree top and food made in the leaves to be transported to the roots.
The central cylinder encases these are other parts of the tree.

Answer 2

Cortex -- Its main function is the storage of starch; often, it also provides aeration of cells to allow respiration.
if the central cylinder you are asking about is vascular cambium it helps in secondary growth of plant's stem and root
hope this will help