40 THE SYNTHESIS OF CARBOHYDRATES 



they found that a negative pressure obtained in the vessels 

 containing the plants assimilating carbon monoxide. This 

 was to be expected if the hypothesis be accepted, for if the 

 carbon monoxide be used up in photosynthesis, then the 

 amount of oxygen set free would be half that evolved in 

 normal photolysis. On the other hand, Kraschennikoff* has 

 come to the conclusion, based on a number of experiments, 

 that green plants cannot make use of carbon monoxide ; he 

 points out, however, that his evidence does not prove that 

 carbon monoxide is not formed in the early stages of photo- 

 synthesis. It may also be remarked that according to the 

 investigations of Sulander,f carbon monoxide acts as an 

 anaesthetic, but is much weaker in its action than chloro- 

 form. He found that 0*5 per cent of this gas was sufficient to 

 inhibit the growth of seedlings of the lupin and the germina- 

 tion of the spores of many Fungi. It does not therefore 

 follow that carbon monoxide is not formed in plants. As is 

 well known, carbon dioxide is itself an anaesthetic if present 

 in a sufficient amount, and possibly it is more potent in this 

 respect than is carbon monoxide, for Sulander found that in 

 many cases the streaming movements of protoplasm were not 

 affected even after several hours' exposure to the last-named 

 gas. 



A modification of Baeyer's theory thus appears to be 

 necessary. Erlenmeyer, long before the experimental work 

 on carbon monoxide just referred to was done, suggested that 

 the carbonic acid in the cells undergoes a reduction which 

 leads to the formation of formic acid and oxygen, and that 

 the formic acid is further reduced to formaldehyde and 

 oxygen : 



T. H 2 C0 3 = CH,(X, + O 

 2. CH 2 O 2 = CH 2 0" + O 



or else that the action is continuous and that the carbon 

 dioxide and water may directly give rise to formaldehyde 

 and oxygen : 



co 2 + H 2 o = CH 2 o + O 2 



According to these views either formaldehyde or formic acid 

 must be produced, 



* Kraschennikoff : "Rev. gdn. Bot.," 1909, 21, 177. 

 f SulancLr : " Beih. hot. Centrbl.," 1909, 24, I., 357. 



