The effect upon enzyme activity of various factors, such as temperature, light, and different concentrations of salts, acids, and alkalis, has been studied in considerable detail, and the behavior -of the enzymes, with respect to these factors, has thrown much light upon physiological processes. One phase of this question, however, has been touched upon only to a slight extent, that is, the relation of enzyme activity to the various stages of growth of plant organs. For this reason, it was thought that a study of the activity of the enzyme diastase, in relation to tuber growth in Solanum tuberosum,. might prove profitable. At the same time, it was dee med of interest to follow the changes in starch and sugar content at the different stages, and thus determine whether any correlation exists between diastase activity, growth, and carbohydrate content.