Introduction. 3 



Although it has been recognised for a long time that this 

 essential transformation of radiant energy into chemical energy 

 was accomplished by means of a pigment, yet even the recent 

 brilliant researches on the chemistry of the leaf pigments has 

 not so far helped in the elucidation of the problem. Nevertheless 

 it is clear that a good knowledge of the pigments concerned is 

 absolutely necessary in order that an attack may be made on the 

 problems of carbon assimilation. 



Further scope for organic chemistry occurs in regard to the 

 products of the assimilatory processes ; those substances at some 

 stage in the formation of which the transference of radiant energy 

 to chemical energy takes place, This seems likely to be a more 

 difficult problem even than the determination of the chemical 

 nature of the pigments. Apart from the inherent difficulties 

 attending all vifork on a group of substances of similar properties 

 such as the carbohydrates, the problem is further complicated by 

 the possibility of intermediate substances between the crude 

 materials and the final product, and also of degradation pro- 

 ducts of this latter preparatory to translocation away from the 

 leaf. Again there is the possibility of " multiple carbon-assimila- 

 tion," i.e. the formation of not one but several final products in the 

 assimilatory processes. 



Room there is undoubtedly for an enormous amount of organic 

 chemical work on these problems, but it must never be forgotten that 

 we cannot expect, nor perhaps should we even aim at getting the 

 processes of the plant pictured by means of simple reactions. For 

 this reason we think that the most promising aspects of carbon 

 assimilation are not those made evident in the contributions of 

 organic chemistry, necessary and valuable as they are, but in those 

 investigations which constitute a struggle towards a clear cut 

 conception of the main problems involved ; no easy matter when 

 these are obscured by a mass of secondary issues due to the com- 

 plexity of the setting provided by organism and environment. 



The investigations to which we refer are those in which an 

 analysis of the various factors concerned in carbon assimilation 

 has been attempted. It was indeed recognised long ago that there 

 were various environmental factors which influenced carbon 

 assimilation, but it was due to F. F. Blackman that the effect of 

 each of these factors and the manner of their interaction was 

 systematically investigated by a careful control of the possible 

 external factors. This same line of investigation has been con- 



