152 THE CARBOHYDRATES 



this connexion is rare enough to justify their exclusion from 

 the present consideration. 



The above facts are well established, but with regard to 

 the intermediate products, and to the nature of the processes 

 concerned, our knowledge is as yet very incomplete. 



In 1870 Baeyer put forward the hypothesis that the carbon 

 dioxide is split up by the plant into carbon monoxide and 

 oxygen, and that the water is concurrently resolved into its 

 constituent elements. The carbon monoxide and hydrogen 

 thus produced then combine to produce formaldehyde, which 

 undergoes polymerization, and so forms a hexose. 



These changes may be represented in the following equa- 

 tions : — 



Thus, according to the theory, there are two distinct actions ; 

 the first leading to the formation of formaldehyde, and the 

 second to the production of sugar. 



Considering the first part of Baeyer's theory, it is seen 

 that both carbon monoxide and hydrogen are supposed to 

 be produced, but carbon monoxide has not been found in 

 a free state in the living plant, nor is it a substance which 

 lends itself at all readily to constructive metabolism, the 

 evidence as to whether plants are able to make use of it 

 for synthetic purposes being contradictory. Bottomley and 

 Jackson* state that if the carbon dioxide normally present 

 in the atmosphere be replaced by about twenty times as much 

 carbon monoxide — the increase in the amount of the latter 

 being necessary on account of its lesser solubility in water as 

 compared with carbon dioxide — plants of TropcBolunt formed 

 starch and flourished. Preliminary analyses also showed that, 

 in the case of seeds germinated in an atmosphere in which the 

 carbon dioxide had been replaced by carbon monoxide, there 

 was in the seedlings an increase in organic carbon. Further, 

 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 



* Bottomley and Jackson : " Proc. Roy. Soc, Lond,," B,, 1903, 72, 130. 



