252 NOTES AND COMMENTS [octobee1899 



nearer to an explanation of the first processes of the reduction of carbon 

 dioxide in the living plant. The hypothesis of Baeyer (that the first 

 act of assimilation is the reduction of carbon dioxide and water to the 

 state of formaldehyde) still occupies the position it did when it was 

 first put forward nearly thirty years ago, although it has, it is true, 

 received a certain amount of support from the observations of Bokorny, 

 who found that formaldehyde can, under certain conditions, contribute 

 to the building up of carbohydrates in the chloroplasts. . . . 



" The view which Timiriazeff has put forward, that there is a mere 

 physical transference of vibrations of the right period from the absorb- 

 ing chlorophyll to the reacting carbon dioxide and water, is, I think, 

 far too simple an explanation of the facts. Chromatic sensitisers have 

 been shown to act by reason of their antecedent decomposition, and not 

 by direct transference of energy, and the same probably holds good 

 with regard to chlorophyll, which is also decomposed by the rays which 

 it absorbs. We must probably seek for the first and simplest stages 

 of the assimilatory process in the interaction of the reduced constituents 

 of the chlorophyll and the elements of carbon dioxide and water, the 

 combinations so formed being again split up in another direction by 

 access of energy from without. 



" The failure of all attempts to produce such a reaction under 

 artificial conditions is, I think, to be accounted for by the neglect of 

 one very important factor. We are dealing with a reaction of a highly 

 endothermic nature, which is probably also highly reversible, and on 

 this account we cannot expect any sensible accumulation of the pro- 

 ducts of change, unless we employ some means for removing them from 

 the sphere of action as fast as they are formed. 



" In the plant this removal is provided for by the living elements 

 of the cell, by the chloroplasts, assisted doubtless by the whole of the 

 cytoplasm. We have here, in fact, the analogue of the chemical 

 sensitisers of a photographic plate, which act as halogen absorbers, and 

 so permit a sensible accumulation of effect on the silver salts. 



" When we have succeeded in finding some simple chemical means 

 of fixing the initial products of the reduction of carbon dioxide, then, 

 and then only, may we hopefully look forward to reproducing in the 

 laboratory the first stages of the great synthetic process of nature, on 

 which the continuance of all life depends." 



