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

(N/A) Periderm is a collective term for the $3$ layers: phellogen,phellem,and phelloderm.
During secondary growth in dicot stems,the increasing pressure from the vascular cambium causes the outer epidermal and cortical layers to rupture. To replace these protective layers,certain cells of the cortex become meristematic,forming the cork cambium or $phellogen$.
The $phellogen$ consists of narrow,thin-walled,and rectangular cells. It undergoes periclinal divisions to cut off cells on both sides:
$1$. The cells cut off towards the outside differentiate into $phellem$ (cork). These cells become dead and suberized,making them impervious to water.
$2$. The cells cut off towards the inside differentiate into $phelloderm$ (secondary cortex),which consists of living parenchymatous cells.
Together,$phellogen$,$phellem$,and $phelloderm$ constitute the $periderm$.