The effects of oxygen and of dinitrophenol on the respiratory activation of potato tuber slices. —It is well known that thin slices from storage organs show, in the first period following preparation and washing, a transition from a low to a high level of metabolic activity. In the potato tuber discs (and similar materials) this transition is characterized by:a)a several fold increase of oxygen uptake;b)an increase of the capacity of dissimilating to CO2the carbon 1 of glucose;c)a decrease of the sensibility of oxygen uptake to the uncoupler 2,4 dinitrophenol(DNP); d)an increase of the capacity of ion and sugar uptake;e)the development of marked capacity of protein synthesis;f)and increase of the activity (as determined in homogenates) of several enzymes involved in the directs oxidation of glucose-6-P or — possibly — in the reoxidation of the TPN reduced by the pentose phosphate pathway reactions. The two latter responses appear with some delay respect the activation of oxygen uptake, which suggested(Marrè et al.)that they are probably rather a consequence than a primary cause of the activation of respiration.