98 



PROBLEMS IN PHOTOSYNTHESIS 



restored. In Figure 38 the dark intervals between the illumination periods 

 are indicated on the abscissa. After a dark interval of 30 min the maximum 

 end value is again attained following 1 -minute illumination. In Figure 

 38 this value corresponds to a pressure change of 5.5 mm. When the re- 

 covery period lasts only 20 min, the pressure increase after 1 -minute illumina- 

 tion amounts to 4.7 mm, representing 85% of the maximum end value. 



t 



* r- 

 "= .2 ^ 



« -s 4 

 ^ to 



<J .E 



03 E o 



<D E n 



Q. E 



0- 











0- 



0- 



.0- 

 



— ► 



5.5 



10 



20 



30 145 



mm 



Fig. 38. Regeneration of oxygen capacity in the dark. The values of the dark intervals 

 between the periods of illumination are plotted against the positive pressure changes during the 

 periods of illumination (1 min) (Warburg et al., Zschr. Naturf.). 



Fig. 39. Influence of oxygen on the regeneration of the oxygen capacity. Continuous line: 

 aerobic. Dotted line: anaerobic, "light" indicates that green light (/ = 25.7 yul quanta/ 

 min) has been absorbed (Warburg et al., Zschr. Naturf.). 



Hence, the induced respiration restores the O2 capacity. When Oo is re- 

 moved, this recovery is no longer possible. After saturation with 10 vol % 

 COo and argon the capacity cannot be restored, even after very long recovery 

 periods in the dark. At normal O2 pressures small quantities of HCN 

 (10~^ N) have the same effect as O2 deficit. From this analogous action it 

 follows that it is not the O2 pressure but a chemical action of Oo — induced 

 respiration — which restores the Oo capacity. HCN thus acts on the induced 



