The phenomenon of transformation of mature cells to the meristematic cells leading to the formation of callus, is called dedifferentiation. These dividing cells of callus have an ability to form entire plant if provided with suitable nutritional and hormonal requirements. Such a phenomenon of the component cells of callus to form whole plants is called redifferentiation. Thus, dedifferentiation and redifferentiation are the basic requirements of cellular totipotency which is the basis of tissue culture and test tube plants.