77 
/ngvar Jorgensen and Walter Stiles. 
CARBON ASSIMILATION. 
A Review of Recent Work on the Pigments of the 
Green Leaf and the Processes connected with them. 
By Ingvar Jorgensen and Walter Stiles. 
(Continued from p. 45). 
Chapter VII. 
Theories of Carbon Assimilation. 
A. General Remarks. 
It is significant to note that the contributions to the literature 
with which this chapter deals, are not the work of those plant 
physiologists who have built up this branch of their subject: 
de Saussure, Sachs, Pfeffer, F. F. Blackman. It seems as if 
those who by years of experience have obtained most insight into 
the complexity of plant processes have realised that the only way 
for development lay in bringing to light facts, and endeavouring to 
determine the laws underlying these facts. 
It is remarkable that all the theories of carbon assimilation 
have not advanced the state of plant physiology in the least; 
it would not have materially altered our knowledge of plant 
processes if all that voluminous literature had never appeared. 
Thus none of the various aspects of carbon assimilation with 
which we have dealt in the preceding chapters owes anything of 
its development to any theory of carbon assimilation that has ever 
been advanced. 
It is surprising that no protest has been raised by plant 
physiologists against the overwhelming tendency to publish theories 
which have little or no reference to the facts of assimilation by the 
plant. Spoehr’s recent paper, “The Theories of Photosynthesis in 
the Light of Some New Facts” (1916), is indeed a voice raised in 
the desert. We should specially like to draw attention to this 
paper which critically examines one group of theories, those based 
on the formaldehyde hypothesis. Generally speaking, we agree 
with Spoehr’s statement, that “ It can safely be said at the outset 
that, when critically considered from a physiological view point, 
none of the existing theories is even moderately well established 
by observations of facts.” 
In the following we shall cite the theories and suggestions of 
various chemists who have directed their attention to the problems 
of carbon assimilation, namely A. Baeyer, J. H. van’t Hoff, 
M. Siegfried, and R, Willstatter. Only the hypothesis of Baeyer 
seems to have aroused any interest among botanists, as the 
