Bare areas frequently occur under hackberry trees, although several herbaceous species may grow relatively well under adjacent tree species which cast just as dense shade. No significant differences were found in pH, texture, organic carbon or amounts of any of the mineral elements sampled under hackberry as compared with control soils under plum trees in the University of Oklahoma Grasslands Plots. Percent soil moisture was always significantly higher under hackberry trees than under plum trees. The failure of herbaceous species to grow well under hackberry was not due primarily to physical factors or to deficiencies in minerals, water, or light. Decaying leaves of hackberry, leaf leachate and soil collected from under hackberry trees in January 1970 significantly reduced seed germination and seedling growth of Andropogon gerardi, A. scoparius, Panicum virgatum, and Sorghastrum nutans. Scopolin, scopoletin, ferulic acid, caffeic acid, p-coumaric acid and gentisic acid were identified as the chief phytotoxins produced in hackberry leaves. Thus, it appears that the bare areas associated with hackberry trees are due primarily to allelopathy.