Cellular dedifferentiation and redifferentiation are studied in leaves of the moss gametophore. Changes in the size and number of some cellular constituents as well as changes in their position are observed. Cell division, the plane of new wall formation, and factors affecting them are considered. Isolation of the leaf initiates events leading to the dedifferentiated state of the component cells. These changes include increase in the size of the nucleus and nucleolus and decrease in the size of the chloroplasts accompanied by an increase in chloroplast numbers. Changes in the position of cellular components are initiated by intravacuolar cytoplasmic layer formation leading to systrophe. Systrophe is considered to be an important event in dedifferentiation representing the final topography of the cellular constituents in the dedifferentiated cell. The distribution of clusters is observed, indicating loss of cellular polarity. In order for redifferentiation to take place, a new axis of polarity must be initiated. Redifferentiation leads ultimately to cell division. This division is characterized and the distribution of planes of new wall formation is shown.