168 VEGETABLE PHYSIOLOGY 



acid and hydrogen peroxide, according to the equation 

 C0 2 + 2H 2 = HCOOH + H 2 2 , and that then they are 

 decomposed, yielding formaldehyde and water, and giving 

 off oxygen, HCOOH + H 2 2 = HCOH + H 2 + 2 . 



An hypothesis of a different nature was put forward 

 by Crato many years later. He suggested that the carbon 

 dioxide after absorption becomes orthocarbonic acid, 

 C(OH) 4 , which exists in solution in the cell-sap. The 

 orthocarbonic acid has the structure of a closed benzene 

 ring in which six molecules are linked together. This 

 becomes decomposed, liberating six molecules of water 

 and six molecules of oxygen, and forming a hexavalent 

 phenol : 6C(OH) 4 = C 6 H 6 (OH) 6 + 60 2 + 6H 2 0. This new 

 body then undergoes a molecular rearrangement and 

 becomes glucose, C 6 H 6 (OH) 6 = C 6 H 12 6 . 



This view is purely hypothetical, and cannot claim to 

 be based on experiment. 



The most recent suggestion on this subject is that made 

 by Bach in 1893. He points out that when sulphurous 

 acid, H 2 S0 3 , is exposed to light, it becomes transformed to 

 sulphuric acid, sulphur and water being split off, 3H_,S0 3 = 

 2H 2 S0 4 + H 2 + S, and he argues that a similar process 

 analogous with this reaction takes place in a leaf. The 

 carbon dioxide unites with water and forms carbonic acid, 

 which is then split up in the same way as the sulphurous 

 acid, 3H 2 C0 3 = 2H 2 C0 4 + H 2 + C. The carbon and 

 water are not set free separately, but in combination as 

 formaldehyde. The new acid, H 2 C0 4 , splits up into carbon 

 dioxide and hydrogen peroxide, and the latter is decomposed 

 into water and free oxygen. 



All these views must be regarded rather as ingenious 

 speculations than as sound hypotheses resting upon observa- 

 tion and experiment. 



A theory of a totally different nature was advanced 

 some years ago by Vines. Starting with the observation 

 that a carbohydrate substance (cellulose) is produced or 

 secreted by protoplasm in the process of the thickening of 



