en 



PREFACE. 



The purpose of this work has been primarily to gather data and some 

 necessary facts which could be brought to converge for an attack on the 

 problems of photosynthesis. Experiments which have been in progress in 

 the Desert Laboratory at Tucson for several years have indicated clearly 

 that prerequisite to a rational discussion of the problems concerning the 

 manner in which sugars are formed in the chlorophyllous leaf is a clearer 

 understanding of the conditions governing the equilibria and mutual trans- 

 formations of the various groups of carbohydrates in the leaf, as well as of 

 the fate of these substances in the general metabolism. The complex and 

 manifold character of the phenomenon of photosynthesis has, it would 

 seem, not been very generally realized by workers in this field. The avenue 

 of approach which appears most promising, at this stage at least, is that 

 which employs chemical methods and conceptions. However, in following 

 this line of attack, the dangers of reasoning from knowledge gained purely 

 from in vitro investigations can hardly be overemphasized. Furthermore, 

 consistent and valid results with living material can be gained only by the 

 most careful control of conditions, such as temperature, water relations, 

 light, and the previous history of the plant. While it is, of course, highly 

 desirable to know the behavior of plants in the field and to develop methods 

 for gaining such knowledge, it seems to the writer that a realization of this 

 ideal can be hoped for only after the more fundamental principles of the 

 phenomenon have been learned. In the study of photosynthesis it is im- 

 possible to segregate entirely the activity of sugar synthesis from that of 

 the further metabolic transformations and from the catabolic processes 

 which yield energy to the living organism, glycolysis. This latter phe- 

 nomenon has received attention from many sides, and the application of the 

 chemical point of view to the manner of sugar disintegration and rearrange- 

 ment seems most promising as an aid to a clearer understanding of the 

 nature and mode of the sugar break-down in the living cell. 



This paper comprises the results of investigations carried out during 

 1916-1918. The work consisted largely of the analysis of plants which had 

 been subjected to various experimental conditions. Of the large number of 

 analyses made, only those are discussed here which are pertinent to the 

 immediate subject. It is a pleasure to acknowledge here the assistance 

 rendered in this work by Dr. J. M. McGee and Mr. R. A. Burt. 



DESERT LABORATORY, 



Tucson, Arizona, December 1918. 



