On the basis of observing the continuous process of the first mitosis of normal differ-entiation in vivo and comparing this observed results with the process of the first mitosisof dedifferentiation in vitro in wheat pollen grains, the cytological differences between thetwo kinds of mitosis have been found. These differences are expressed chiefly by the posi-tions of nuclei and cytoplasm as well as the positions and shapes of spindles and new cellwalls. The author considers: (i) The differences exist as soon as cell division begins. Sothe critical moment causing cell dedifferentiation is at the interphase instead of the divisionstage. Therefore, the viewpoint that the cause of dedifferentiating initiation is the altera-tion of the direction of the spindle axis could not be agreed. (ii) The cause producing thesecytological differences can be related to the loss of polarity in the dedifferentiating process. On the basis of observing the continuous process of the first mitosis of normal differ-entiation in vivo and comparing this observed results with the process of the first mitosis of dedifferentiation in vitro in wheat pollen grains, the cytological differences between thetwo kinds of mitosis have been found . These differences are expressed chiefly by the posi-tions of nuclei and cytoplasm as well as the shapes and splines and new cellwalls. The author considers: (i) The differences exist as soon as cell division begins. Sothe critical moment causing cell deiifferentiation is at the interphase instead of the division start. Thus, the viewpoint that the cause of dedifferentiating initiation is altera-tion of the direction of the spindle axis could not be agreed. (ii) The cause producing thesecytological differences can be related to the loss of polarity in the dedifferentiating process.