PREFACE 



Photosynthesis is by far the most important biochemical process on 

 earth because it alone produces organic matter from stable inorganic 

 materials and thus prevents life from becoming extinct. It is also the 

 most puzzling of all biochemical reactions, and will probably remain so 

 as long as all attempts to divorce it from the living cell prove futile. 

 Although many physiologists, chemists, and recently also physicists, have 

 attacked the problem, the progress toward its solution has been slow. 

 The difficulties lie in both the physiological and the physical aspects of 

 photosynthesis. As a physiological phenomenon, photosynthesis is dis- 

 tinguished by a particular sensitivity to all factors which interfere with 

 the normal life processes in the plant. This sensitivit}^ makes it difficult 

 to study the mechanism of photosynthesis by breaking the cells down 

 into their cytological or chemical constituents. From the physical point 

 of view, photosynthesis is distinguished by an extraordinarily large con- 

 sumption of energy, and the consequent necessity for a mechanism which 

 would permit the utilization of the energy of several light quanta for the 

 transformation of a single molecule and prevent back reactions which 

 tend to destroy the unstable intermediate products. Nothing similar to 

 such a mechanism has as yet been realized in photochemical experiments 

 outside the living cell, and this makes it difficult to approach the problem 

 of photosynthesis by the study of model systems in vitro. 



Cooperation of plant physiologists, physicists, and physical chemists 

 is a prerequisite for the better understanding and ultimate mastery of 

 these two fundamental aspects of photosynthesis. It is the hope of the 

 author that this book will enable plant physiologists to judge critically 

 the experimental results obtained by various physical methods and will 

 help them appreciate the usefulness of reaction kinetics and of the theory 

 of fluorescence and sensitization in the analysis of photochemical proc- 

 esses in the living cell. To the physicists and the physical chemists who 

 embark on the investigation of photosynthesis equipped mainly with the 

 knowledge of the recent quantitative work on unicellular algae, this book 

 may be of assistance in the understanding of the broad physiological 

 background of photosynthesis and the realization of its intimate associa- 

 tion with other life processes in the plant organism. 



During the last twenty years, some important new avenues of ap- 

 proach to the study of photosynthesis have been opened. Mention may 

 be made, for example, of ox3^gen liberation by isolated chloroplasts; of 



