The mechanism in secondary growth in the cortical region of dicot stem involves the process of dedifferentiation. Few of the cortical cells (in the form of few layers) become meristematic (cork cambium or phellogen) and cut off new cells - cork or phellem (towards the outer side) and phelloderm or secondary cortex (on the inner side). Periderm includes cork or phellem (suberised cell wall), cork cambium or phellogen and secondary cortex or phelloderm.