Commercial protease and cellulase treatment of dried and milled plant roots decreased their cation exchange capacity to varying degrees, indicating that protein and cellulose contribute to the exchange mechanism in addition to pectin. Membranes isolated from two roots proved to be epidermal cells; these had a significant cation exchange capacity when thought of as an interface between the soil and the root, but not when compared to the root as a whole. Methylation of the membranes reduced their exchange capacity to zero.