453 



From the observation that the steady rates of carbon 

 dioxide evolution in dark are not affected by oxygen, while 

 those in lip;ht are, it has been concluded that evolution of 

 carbon dioxide in light and in dark is the result of two 

 different processes. While steady rates of carbon dioxide 

 evolution in the dark represent true respiration, evolution 

 of carbon dioxide in the light does not. Tentatively it can 

 be called either a "photorespiration" or still better simply 

 "carbon dioxide evolution in the light". 



1000 



100 200 300 400 500 600 700 

 Time (sec) after releose of c'^'Oo 



800 



Fig. 1. Absorption and evolution of 

 CO2 and 01^^02 by a detached to- 

 bacco leaf in light and dark. 



,/- 



^. 



\y 



Fig. 2. Typical records 

 of CO2 production by 

 tobacco leaf during 

 the dark periods fol- 

 lowing illumination 

 with different light 

 intensities . 



