In tissue experiments, leaf mesophyll cells are put in a culture medium to form callus. This phenomenon may be called as:

[Image showing the process of callus formation from tissue explants]Differentiation: When cells lose the ability to divide and specialize for a function.Dedifferentiation: When living differentiated cells regain the capacity to divide under specific conditions. In tissue culture, differentiated mesophyll cells "revert" to an undifferentiated mass of dividing cells called callus. This is a classic example of dedifferentiation.