Summary.1. A comparative study of the rates of respiration, as measured by the weight of carbon dioxide evolved, has been made with healthy and leaf‐roll infected potatoes at all stages in the life cycle, under anaerobic as well as aerobic conditions.2. Except for a short period covering the end of dormancy of the tuber to the first unfolding of the leaves, the infected plant respires at a much lugher rate than does the healthy one. This is true also when the conditions of light, temperature, and external carbon dioxide approximate to those present in the fiel