Interfascicular cambium and cork cambium are formed due to cell dedifferentiation.
Differentiation: The process which leads to maturation of cells is called differentiation. During differentiation, a few or major changes happen in protoplasm and cell walls of the cells.
Dedifferentiation: A differentiated cell can regain its capacity for cell division under certain conditions. This phenomenon is called dedifferentiation. Formation of interfascicular cambium and cork cambium from fully-differentiated parenchyma cells is an example of dedifferentiation.
Redifferentiation: A dedifferentiated plant cell once again loses its capacity to divide and becomes mature. This phenomenon is called redifferentiation.