Growth curves of Lemna minor are presented in which the fresh weight of the sterile cultures was plotted against time, and as a function of additions to the medium of 1 and 2 ppm of the dormin abscisic acid (ABA) and 0.1 ppm of the cytokinin benzyladenine (BA). The growth regulators were presented alone or in a variety of combinations and time sequences. Growth was halted or greatly inhibited by ABA and resumed upon addition of BA, and vice versa. Lemna plant growth thus can be made to stop or go at will, simply by varying the dormin and cytokinin concentrations.