VI PREFACE 



the broader view of the chemistry of photosynthesis obtained by the 

 study of bacteria; and of the discovery of the possibihty of changing the 

 chemical course of photosynthesis in certain algae by substituting new 

 substrates for carbon dioxide and water. The use of flashing light, of 

 heavy hydrogen, and particularly of the isotopes of carbon and oxygen, 

 as well as quantitative study of the fluorescence of living plants during 

 photosynthesis, has revealed many new facts about the mechanism of 

 this process. Together with rate measurements by sensitive physical 

 methods, these new experimental procedures have produced valuable 

 material for comprehensive kinetic treatment. The knowledge of the 

 structure of the photosynthetic apparatus has been advanced by the 

 discovery of the chloroplast grana and laminae; and the application of 

 the electron microscope promises new progress in this field. The long 

 overdue, detailed chemical analysis of the chloroplasts has been brought 

 under way; much progress can be hoped for by its further development, 

 assisted by a more extensive application of the methods of enzyme chem- 

 istry. Further progress of our knowledge of the role of pigments in 

 photosynthesis can be expected from the study of the relationship be- 

 tween their structure and photochemical behavior in vitro. An important 

 development may have been initiated by the reconsideration of the func- 

 tion in photosj-nthesis of the "accessory" pigments — the carotenoids and 

 phycobilins. 



Photosynthesis was last treated in 1926 in the well-known monograph 

 by Spoehr. Since this book, as well as a similar but shorter one by 

 Stiles (1925), contains an extensive presentation of the older literature, 

 no need was felt for a repetition of such a complete review of the early 

 work. Only those of the older investigations which have proved of 

 historical importance or enduring influence are discussed in detail in the 

 present book — and there are more of them than is often thought. The 

 pioneering investigations of Priestley, Ingen-Housz, de Saussure, Sachs, 

 Timiriazev, Reinke, or Engelmann, not omitting the classical work of 

 Willstatter and Stoll, still deserve the study of all who are interested in 

 photosynthesis. The papers which have appeared since 1925 have been 

 considered in greater detail, some probablj^ receiving more consideration 

 than may prove warranted by their lasting importance. No attempt 

 has been made to cover fully the studies of photosynthesis in relation to 

 systematic botany or ecology, or to discuss the organic chemistry of plant 

 pigments beyond its relationship to the mechanism of photosynthesis. 



The present treatise differs from previous books on the subject by an 

 increased emphasis on physical and physicochemical methods and the- 

 ories — a consequence of the newer trends in the study of photos3^nthesis 

 as well as of the inclinations and background of the author. However, an 

 impartial reporting of the work of botanists and plant physiologists has 



