PREF ACE 



In writing a modern scientific monograph, the writers must choose be- 

 tween a detailed treatment of the Hterature and a brief exposition of the 

 facts and principles of the subject. In this volume, we have attempted to 

 cite most of the relevant literature; in Chapter 1, the broader reviews; 

 within the subsequent chapters, the more specialized papers. From these, 

 we have repeated the minimum of material essential to a connected discourse 

 on the subject, feeling that interested students will refer back to the original 

 papers for details. 



Thus, whereas this is intended as a reference work, it is hoped that its 

 reading will not be so tedious as to preclude its use in the classroom. If 

 any part seems needlessly long, it is because we deem the material of particu- 

 lar concern to certain workers in the field, or because it pertains to our own 

 research. For this, our only excuse is that one usually reports most accu- 

 rately that subject in which he is personally interested. 



One further choice that must be made in treating so broad a subject is 

 that of vocabulary. One could use the loose and rather indefinite termi- 

 nology of two or three decades ago; or he may employ the more accurate 

 wording of the modern plant physiologist; or he might adopt the highly 

 technical language of the physical chemist. Again we have compromised. 

 This volume has been written for use by present day botanists and plant 

 physiologists ; hence, we have used their language. At the same time, we 

 have cited several recent treatises that employ, almost entirely, the vocabu- 

 lary of physical chemistry. We realize the need for more accuracy in the 

 definition and use of technical terms ; also the desirability of a universal 

 language for all scientists. On the other hand, the writing of a monograph 

 for a certain group in a language with which they are not familiar is futile. 



If the language of physical chemistry is to be adopted by physiologists, 

 and most modern students will agree that it should be, two changes must be 

 made. First, physical chemistry must become a required course for all 

 undergraduates in physiology, and its terminology should be introduced 

 and used relatively early in their careers. Second, physical chemists must 

 develop a deeper appreciation for certain fields of physiology which, up to 

 the present, have been somewhat or even totally neglected. Although many 

 of the living systems with which the physiologist deals may be so complex 

 as to offer little hope for thermodynamical analysis by present methods, 

 their tremendous importance with respect to the well being of man, both 

 through his own physiology, as well as that of the plants and animals upon 

 which he depends for food and clothing, demands constant and sympathetic 

 study. And the exact vocabulary of physical chemistry must be adapted to 

 these complex functions if it is to be of use in their study. Though the 

 thermodynamicist may be content to treat only the initial and final states 

 of a system, the physiologist is interested in every mechanical detail of its 



