342 



Some Photochemical Experiments with Pure Chlorophyll and their 

 Bearing on Theories of Carbon Assimilation. 

 By Ingvar Jorgensen and Franklin Kidd. 

 (Communicated by V. H. Blackman, F.B.S. Received June 26, 1916.) 



(From the Department of Plant Physiology and Pathology, Imperial College of Science 



and Technology, London.) 



CONTENTS. page 



Introduction 342 



Chlorophyll Extraction and Purification 345 



The Preparation and Properties of a Colloidal Solution of Chlorophyll 347 



Experiments 349 



Criticism of Previous Theories of the Function of Chlorophyll in Carbon 



Assimilation in view of the Experimental Data obtained in this 



Investigation — 



(a) Theory of Usher and Priestley 355 



(b) Theory of "Wager 357 



(c) Theory of Ewart 358 



Conclusion 359 



Summary 359 



Literature Cited 360 



Introduction. 



The main features of the processes of carbon assimilation are that the green 

 plant under the influence of radiant energy takes in carbon dioxide, evolves 

 oxygen, and in the majority of cases produces carbohydrates. The only 

 aspect of these processes which has been subjected to detailed investigation 

 is the intake of carbon dioxide, our knowledge of which is due to the 

 extensive researches of F. F. Blackman and of R. Willstatter. Blackman has 

 investigated the factors, such as light, temperature, carbon dioxide supply, 

 which influence the intake of carbon dioxide by the ordinary green leaf, 

 while Willstatter has extended Blackman's work by including quantitative 

 investigation of the amount of chlorophyll. 



When we turn, on the other hand, to the question of the actual physical 

 and chemical processes of carbon assimilation we find many hypotheses, but 

 few facts. We are acquainted with the primary facts of the intake of carbon 

 dioxide and the formation of carbohydrates, etc., but we have no definite 

 knowledge of the intermediate processes concerned. 



Since the hypothesis of Baeyer in 1870 it has been generally supposed that 

 carbon dioxide and water are synthesised to carbohydrates under the 

 influence of light and in presence of chlorophyll, and that formaldehyde is an 



