Radon transport through a cool-season grass

²²²Rn released by mature tall fescue (Festuca arundinacea Schreb.) growing on uranium mill wastes in a controlled environment was a direct function of leaf area and essentially unrelated to the quantity of water transpired by the plants. The quantity of ²²²Rn released by the grass blades at maturity was approximately 0·01 Bq m⁻² s⁻¹ (0·3 pCi m⁻² s⁻¹). We suggest that the radioactive gas is transported from the rooting medium to leaves by mass flow in liquid water, but from leaves to the atmosphere by a path generally independent of water, i.e., primarily through the leaf cuticle and epicuticular wax.