2n3 NOTES AND COMMENTS [ocroBEr 1899 
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. 
“Jn 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 hfe depends.” 
