Somatic segregation and rate of greening after ultraviolet irradiation of Euglena gracilis.

1. During multiplication of irradiated cells, a segregation may take place between bleached cells, whose progeny is unable to green, and green ones. Some of the green cells give progenies exclusively made of green cells; the progeny of others is partly composed of bleached cells. 2. If one assumes that greening results from the activity of functional units endowed with genetic continuity (Plastidial Segregating Units = PSU), segregation of these units seems to occur according to a model involving random sorting out during the three first divisions. During the following divisions, functional units seem to multiply faster than those impaired by irradiation. 3. The greening rate of colonies issued from irradiated cells seems to be conditioned mostly by the number of functional PSU remaining in the mother cell of the colony.