The different influence of germination and growth inhibitors in aqueous extracts, at the same concentration, of Tamus communis L. leaves, on germinating seeds and seedlings of nigra L., Lactuca sativa L., Medicago sativa L., has been shown. This action, very marked at the experimental concentrations, is not toxic, as the seeds and seedlings, if immersed in deionized water after treatments, recover their germination and growth. This recovery occurs however differently in the plants investigated.