174 LIGHT, VEGETATION AND CHLOROPHYLL 



which, will be transported by the molecules of phosphoric acid. 

 See Fig. II, 3. 



Oxidation is effected progressively to a remarkable degree. 

 Carbon possesses four valencies of which only one in the 



Citrate (j) 



+ HaO 



Y 



Pyruvate ud) COg ^ Cis-aconitate 



Oxaloacetate @ 



Maiate ® 

 N+HaO 



Fumarate (?) 



Ketoglutarate (S) 



— 2H 



CO, 



— 2H Succinate @ 



Fig. II, 3. Citric acid cycle 



glucose is saturated by the oxygen of the alcohol radical. The 

 first step is the transformation of alcohol into aldehydes or 

 ketones ; two valencies of carbon are saturated by the same 

 atom of oxygen. 



COOH 



CHs 



I 

 HOC -COOH 



CH, 



COOH 



i 

 CH2 



I 

 C-COOH 



II 

 CH 



COOH 



CHa 



i 

 HC-COOH 



COOH 



1. Citric acid 



COOH 



2. Cis-aconitic 

 acid 



CHOH 



I 

 COOH 



3. Isocitric acid 



