The respiration of the green alga Chlorella pyrenoidosa , suspended in Knop's solution, has been studied in the dark as a function of time and of temperature. The rates of oxygen consumption and of carbon dioxide production (at constant temperature) decline for about 25 hours to a low, constant level. From an analysis of the curves it is suggested that two substances, A and B , are utilized, whose respiratory quotients are 1 and 0.65 respectively. The values of the temperature characteristics were found to be: for oxidation of A , 19,500 (0.6 to 11.5°C.) and 3,500 (11.5 to 28°C.); for oxidation of B , 5,600 (23.4 to 0.6°C.).

The temperature characteristic for the rate of O 2 consumption by Chlorella pyrenoidosa suspended in Knop solution containing 1 per cent glucose was studied between 1° and 27°C. with the Warburg technic. The value of µ was found to be about 19,000 ±1,000 cal. There is some indication of a critical temperature at 20°C., with shift to a lower µ above this temperature. The effect of sudden changes in temperature on the rate of respiration and the variation of the latter with time at constant temperatures are discussed. It is concluded that the "normal" respiration (in absence of external glucose) does not appear in the determination of this temperature characteristic.