A survey of the course of carbon dioxide output of potato tubers upon transfer from air to nitrogen shows that the form of drift in nitrogen undergoes metamorphosis with the lapse of time between harvest and the anaerobic experience. A stable form is attained about three months from harvest.On restoration of air after nitrogen a temporary outburst of carbon dioxide occurs, and both form and magnitude of this after-effect change with time elapsed after harvest. The magnitude is also influenced by the duration of anaerobiosis. At any season, increased time in nitrogen produces an increased after-effect of more than proportionate magnitude. The rate of carbon dioxide output in air after nitrogen ultimately becomes steady, but is not necessarily equivalent to that preceding anaerobiosis. For the space of about three months, subjecting a tuber to nitrogen for two days or more at 22 °C. causes the ultimate rate of carbon dioxide output in air to remain well above that preceding anaerobiosis, while it bears a constant ratio to the final rate in nitrogen before air was restored. This permanent displacement of the rate in air is not at any time brought about by an anaerobic period of only one day.The nature of the drifts in metabolic state of the tubers that underlie these metamorphic changes in response to a period of anaerobiosis is still under investigation.