1915] SPOEHR—RESPIRATORY ACTIVITY 367 
noticed the increased carbon dioxide production of the frog under 
the influence of light, and later the same fact was observed in man 
by PETTENKOFER and Vorr’ and others. However, in the higher 
animals the results become complicated by the action of the light 
on the nervous system.* The experiments on plants have been 
made mostly with fungi, but on account of the confusing influences 
of temperature, nutrient media, and sources of light, no definite 
conclusions can be drawn from these investigations.5 
Recently, MEYER and DELEANO® have found that the carbon 
dioxide production of leaves at practically constant temperature 
and in the dark is decidedly higher during the daytime than at 
night. These workers consider the cause of this variation as lying 
within the organism. They say: 
achdem wir wissen, dass die Aufpraegung einer intermittiernden 
chronometrischen Bewegungsstruktur, welche zur periodischen Erhoehung 
der Kohlensaeureproduktion fuehrt, moeglich ist, duerfen wir wohl die Hypo- 
these aufstellen, dass die regelmaessigen Schwankungen der Kohlensaeure- 
produktion an Stunden des Volltages bei normalen Laubblaettern nur durch 
den waehrend des Volltages stattfindenden Wechsel der, Assimilationsinten- 
sitaet und wahrscheinlich erst waehrend ihres individuellen Lebens des Laub- 
blattes hervorgerufen ist. 
In the following experiments (mostly with wheat seedlings), 
the carbon dioxide production in the dark at constant conditions 
of temperature and humidity was measured by drawing air from 
out-of-doors over the plants, and then through a standard barium 
hydroxide solution. It was found that the rate at which carbon 
dioxide was produced during the hours of daytime was regularly 
higher than that produced during the night. It is evident that 
under these experimental conditions the only variable external 
3 PeTTENKoFER, M., and Vorrt, C., Uber Kohlensiureausscheidung und Sauer- 
stoffaufnahme ence des Wachens und Schlafens beim gesunden u. kranken Men- 
_ Schen. Sitzber. Akad. Wiss. Miinchen 2:2 6. 
4 NEUBERG, C., Beziehungen des aces zum Licht. Berlin. 1913 (p. 7). 
5’ Kotwitz, R., Uber ae —— des Lichtes auf die Athmung der niederen 
Pilze. Jahrb. Wiss. Bot. 33:1 1899 
Maxiwow, N. A. Ibid. ey Centralbl. 90:94. 1902. 
° Meyer, A., and DeELEANO, N. T., Die periodischen Tag- und  wacoegioned 
ungen der Atmungsgroes oesse im Dunke In befindlicher Laubblitter und deren vermut- 
liche Bezeihung zur Koblensiureassimilation. Zeitschr. Bot. 3: ery IQIT; 
5+209-320. 1913. 
