188 LIGHT, VEGETATION AND CHLOROPHYLL 



substances. Actually we find nothing of the sort; all the 

 substances which are carriers of C^^ are at least tricarbonate, 

 and never, during these brief exposures, are dicarbonate or 

 monocarbonate substances found "labelled." Substances are 

 "labelled" by their carboxyl, and this shows that oxygen has 

 hberated only one of the valencies of carbon which has been 

 fixed on a dicarbonate or tricarbonate substance; here we 

 find a reaction similar to that of Wood and Werkmann. 



After five seconds of exposure to hght, 97 per cent of the 

 fixed carbon is found in the carboxyl of two tricarbonate 

 substances, phosphoglyceric acid and phosphopyruvic acid. 

 The fixation has been eff'ected on a dicarbonate substance 

 which has not yet been identified; we can only conjecture its 

 anterior state, as the fiixation of carbon dioxide may have 

 been accompanied by various modifications. 



This substance would doubtless be produced by a special 

 cycle put in operation by photosynthesis. It would be a cycle 

 which is much more rapid than the citric acid cycle and of 

 which the intermediaries are still unknown, for hfe is much 

 more complex and agile than we can imagine. 



Suppose that green algae, provided with carbon dioxide 

 each molecule of which has its atom of carbon radioactive, are 

 illuminated with 100,000 lux and that at the end of five 

 seconds they are plunged in boihng alcohol which kills all the 

 diastases and arrests all the biochemical transformations. If the 

 substances present in the algae are then extracted and analysed 

 by chromatography and radio-autograph, 87 per cent of the 

 radioactive carbon fixed is found in phosphoglyceric acid, 



PO4H2- CHg- CHOH - COOH, 

 with sometimes a trace in glyceric acid, 



CH2OH - CHOH - COOH, 

 10 per cent in phosphopyruvic acid, 



PO4H2 



I 

 CH2-C-COOH 



and 3 per cent in malic acid, 



COOH - CHa - CHOH - COOH 



