The characteristic symptoms of what seems a new disease of potato, observed in Alberta, have been outlined, certain observations and preliminary experiments reported, and the name "purple dwarf" suggested for it.Purple dwarf is perpetuated through the tubers, and the symptoms on plants from diseased tubers either appear immediately the plant emerges from the ground or apparently fail to become recognizable during the remainder of the season.Apical growth is checked, the entire plant becomes stunted, the newer leaves develop a purplish hue along their margins and curl upwards, the phloem of the entire plant is disorganized, and a well developed, brown, dendritic necrosis extends from proximal to distal ends of the tuber. First the roots, then the stolons, and later the base of the stem, become brown and soon decay. Usually the central pith in the tuber and upper stem remains normal.Purple dwarf was transmitted to healthy plants by grafting, a result which suggests that the causal agent is a virus.