Abstract
As well as showing the existence, during the first stages of in vitro bud neoformation, of cell populations in a tissue composed of a single cell layer (stem epidermis of Torenia fournieri Lind), some new physiological characteristics of mitosis are defined. Most of the cells which divide during organogenesis synthesize their DNA between 20 and 48 hours of culture. On an epidermal strip (10 x 2.5 millimeters composed of about 5,500 cells) 20% of the original cells enter the S-phase. The first division takes place at the 20-hour stage after the entry into the S-phase of a cell population of about 25 cells. Almost none of the cells of this population divide. The greatest percentage of divisions occurs in cells which synthesize DNA near the 48-hour stage. The relation [Formula: see text] has a value of about 25 at the beginning of cell division (20 hours) and falls to a value of about 1.4 for cells which synthesize DNA near the 48-hour stage. A hypothesis of the existence of a mitotic stimulant in the epidermis is put forward; this stimulant, at first weak, increases progressively.