TRANSIENTS FOR CARBON DIOXIDE 



437 



intermediates takes for a while precedence over the oxidative de- 

 carboxylations. 



A very simple proof for the causal connection of these transients with 

 the oxidative metabolism can be given. When air is replaced by nitrogen 

 or hydrogen these transients disappear until enough photosynthetic 

 oxygen has been produced to reverse at least part of the anaerobic 



^ 



^- 



xinnsGE 



^MUi. 



Fig. 8. Prolonged compensation of respiration brought about by 2 seconds of 

 light given everj' 40 seconds. Chlorella, 0.9% cell volume in 0.002 M bicarbonate, 

 pH 7.3. The curves a, b, c, d are consecutive parts of the same recording. See text. 



conditions. Figure G (in which the lower curve is the direct continua- 

 tion of the upper one) shows how a succession of dark and light 

 periods (the light being rather strong) gives nothing but straight- 

 forward photosynthesis without conspicuous transients as long as the 

 algae remain under anaerobic reducing conditions in hydrogen. 

 But the eventual appearance of oxygen causes a most peculiar sequence 

 of aftereffects in the dark, which can be seen enlarged in Fig. 7. 



The question arises whether compensation reactions occur only 

 when they last long enough to be seen so easily or whether they always 

 are present at the start of photosynthesis in the light and must be 



