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Preface 



The popularity which the general subject of the utilization of solar 

 energy has enjoyed within recent years has led to much speculation re- 

 garding means of accomplishing this. These speculations have con- 

 cerned themselves not only with mechanical contrivances designed to 

 utilize the energy of the sun, but in many cases have also endeavored to 

 explain the manner in which the green plant plays the role of a converter 

 of radiant energy. In this book only the latter subject is discussed. Un- 

 fortunately much of the speculation regarding the manner in which the 

 green plant utilizes solar energy has not been restrained by a knowledge 

 of certain facts concerning the process. It is quite true that the subject 

 with which this monograph deals is still in a condition of development ; our 

 knowledge of many phases of the subject is fragmentary and incomplete. 

 There are nevertheless certain well established facts which cannot be 

 disregarded in any consideration of the problem. 



In the following pages the results of experimental investigations have 

 been stressed rather than the conclusions which have been arrived at by 

 observations in the field or by empirical methods. There can be little 

 doubt that the greatest advances in our knowledge of the phenomenon of 

 photosynthesis have been made through experimental study, that is, through 

 analysis of the phenomenon by the exact control of the different factors 

 which affect the process. These experimental studies have also served 

 to emphasize the complexity of the subject and to demonstrate that great 

 experimental skill is required in order to penetrate more deeply into the 

 nature of the phenomenon. While the direct object of this book is to give 

 the present status of the subject, it is hoped that it may serve to stimulate 

 the interest of those familiar with allied branches of science and bring 

 other and more refined methods to bear on the problems involved. 



The problem of photosynthesis borders on so many sciences that there 

 have developed a number of avenues of approach. Each of these presents 

 an aspect somewhat different from the other, each sees certain features 

 in relief which from another approach are only vaguely discernible. It 

 is very much like looking at a mountain from different sides. It is as yet 

 impossible to determine which is the surest path of ascent. But of this 

 we can be quite certain, that a single approach will not give us a complete 

 view of our objective. Only from knowledge obtained by a study of the 

 different aspects can we construct a true picture. 



The sciences of chemistry, plant physiology, physics, geology, oceanog- 

 raphy and others have offered a view of the phenomenon of photosynthesis. 

 To many viewing this process from one such restricted field it has ap- 



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