Substances extracted with a phenolic reagent mixture form spheroids of volvox carteri f. nagariensis have been shown to induce the formation of sexual spheroids. Analysis of the cultures from which the phenolic extracts were prepared implicated the glycoprotein sex hormone as the inducing substance present in potent extracts. Phenolic extracts were shown to interact with calf-thymus histones such that, when the two were mixed, the extract-histone complex formed and the induction potency increased 100-fold or more. Assays of both effects are described. Differences in the physical properties and activities of the sex hormone present in male sexual fluids and the inducing substance in phenolic extracts are discussed with reference to some effects the extraction process may have on the inducer.