64 THE SYNTHESIS OF CARBOHYDRATES 



assimilatory ratio ; this ratio is obtained by dividing the 

 volume of carbon dioxide supplied to the plant by the volume 

 of oxygen evolved ; according to theory, the complete reduc- 

 tion of carbon dioxide, i.e. the removal of both oxygen atoms, 

 might proceed through successive stages of oxalic, glycollic and 

 formic acids down to the formaldehyde stage, but in that 

 case the assimilatory ratio would be respectively 4, 2, or 1-33 

 for each of the acids mentioned, whereas formaldehyde alone 

 requires the value 1 which is the figure actually obtained in 

 a number of experiments in varied conditions. This argu- 

 ment is not based upon the actual experimental demonstra- 

 tion of formaldehyde isolated from assimilating leaves, and, 

 with regard to this particular question, these authors have 

 revised many of the statements made by previous workers. 

 It will be remembered that repeated attempts have been made 

 to demonstrate the formation of formaldehyde by the action 

 of chlorophyll upon carbon dioxide outside the plant. The 

 earlier work of Usher and Priestley, demonstrating the for- 

 mation of this substance in films of chlorophyll exposed to 

 an atmosphere of carbon dioxide in sunlight, was shown by 

 Wager * and Warner f to be faulty, inasmuch, as Wager 

 showed, that no formaldehyde was produced if oxygen was 

 excluded, whilst Warner showed that carbon dioxide was 

 unnecessary and took no part in the production of the for- 

 maldehyde. Warner concluded that the formaldehyde was in 

 fact an oxidation product of the chlorophyll since oxygen 

 was actually absorbed in the process. The experiments of Will- 

 statter and Stoll, show that no formaldehyde at all was formed 

 if pure chlorophyll in colloidal solution was employed, the 

 colloidal solution being considered to approximate most closely 

 to the condition of the chlorophyll in the chloroplast. The 

 formaldehyde described by the earlier workers is attributed 

 to the oxidation of impurities accompanying the samples of 

 chlorophyll used by them. 



The failure to obtain any trace of formaldehyde from pure 

 chlorophyll in vitro is attributed by Willstatter and Stoll to 



* Wager : " Proc. Roy. Soc," B, 1914, 87, 386. 

 f Warner : id., 378. 



