The plant hormone abscisic acid (ABA) is believed to be a dormacy factor in some seeds and buds; it often inhibits growth of plant organs, We found that ABA had dual effects on a duckweed tested (Lemna gibba L.). In these experiments, Lemna gibba plants were cultured under aseptic conditions on liquid E medium (containing minerals and sucrose) to which graded concentrations of ABA were addcd<4), and incubated in a growth chamber which gave continuous illumination from a bank of fluorescent tubes.