Question

what is phellem, phellogen, cork cambium casparian strip?

Answer 1

Phellogen(or cork cambium) is meristematic in nature which is responsible for secondary growth in stems and roots. It is responsible for the development of periderm.
Cells that grow inner to the phellogen are termed as phelloderm and cells that develop outer to the phellogen are termed as phellem or cork. Phellem is dead at maturity and it is protective in function.
Endodermis is the innermost layer of cortex in land plants in which there is a deposition of casparian strips. It is a band of cell wall which prevents the flow of water and solutes into the stele of the plant.