Theories of Carbon Assimilation. 153 



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, PfeflFer, P. P. 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 

 literature of the subject sufficiently indicates, and it is not unusual 

 to find Baeyer's hypothesis almost accepted as an axiom in 



