204 HISTORY OF BOTANY 



the sun's rays, an accumulation of acids should take 

 place and gradually be replaced by sugar. So far as I 

 know this has never been observed, and when it is re- 

 membered that, in the plant, sugars and their anhydrides 

 are formed under all circumstances, whereas the presence 

 of acids varies according to the kind of plant, the particular 

 .part of it, and its age, then the opinion already often put 

 forward that the sugar is formed directly from the carbon 

 dioxide increases in probability. Butlerow's discovery 

 provides the key and one may indeed wonder why it is 

 that, so far, it has been so little utilised by plant physio- 

 logists. The similarity which exists between the blood 

 pigment and plant chlorophyll has often been referred 

 to and it is probable that chlorophyll as well as haemo- 

 globin binds carbon dioxide. Now when sunlight strikes 

 chlorophyll which is surrounded by carbon dioxide, 

 the carbon dioxide appears to undergo the same dis- 

 sociation, oxygen escapes and carbon monoxide remains 

 bound to the chlorophyll. The simplest reduction 

 of carbon monoxide is to the aldehyde of formic acid ; 

 it only requires to take up hydrogen, i.e. CO +H 2 =HCOH. 

 This aldehyde is then transformed under the influence 

 of the cell contents as well as by alkalies into sugar. 

 As a matter of fact it would be difficult, according to 

 the other view, by successive syntheses to reach the goal 

 so easily. Glycerine could be formed by the condensation 

 of three molecules and the subsequent reduction of the 

 glycerine aldehyde so produced. The formation of sugar 

 by a more complex method is of course not excluded, 

 and it might be quite possible that plant acids under 

 certain conditions are transformed into sugar which in 

 a thousand different forms helps to build up the body 

 of the plant. How the cell contents act in order to effect 

 the condensation of formaldehyde cannot be settled 

 a priori, but one may assume that the sugar so formed 

 remains bound with the cell contents and later, according to 

 circumstances, splits off as a carbohydrate or glucoside." 



