What is periderm? How does periderm formation take place in the dicot stem ?

Cork, cork cambium and secondary cortex are put together called as periderm.  As the stem increases in girth by the division of vascular cambium, the epidermal layer (or) cortex may break.  A new meristematic layer is formed in the cortex called as cork cambium (or) phellogen.  These cork cambium divides and produces the cells on both the sides. Outer layer of cells formed are called as cork (or) phellem. Inner layer of cells formed are called as secondary cortex (or) phelloderm.