The phenomenon  by which interfascicular cambium and cork cambium are formed  from fully differentiated parenchyma cells is known as 

 Some meristematic cells lost the capacity of division , undergo differentiation and reach to maturity to perform a specific function.Under certain conditions, such cells  regain the capacity of division .This phenomenon is termed as dedifferentiation. For example, formation of meristems – interfascicular cambium and cork cambium from fully differentiated parenchyma cells. Interestingly  dedifferentiated  tissue divide further and produce cells that once again lose the capacity to divide but mature to perform specific functions.