PREFACE 



WITH the ever-increasing tendency to regard an organ- 

 ism as a complex of physical and chemical processes which 

 may one day be analyzed and understood, there has neces- 

 sarily gone hand in hand a tendency toward more and more 

 accurate and quantitative investigation of the physics and 

 chemistry of the cell itself. Among the various groups of 

 physical and chemical phenomena that have been found to 

 play important roles in the life-process, and which, there- 

 fore, have been interrogated for answers to physiological 

 questions, none has stood out within the past few years as 

 more fundamentally important than those connected with 

 diffusion and osmotic pressure. This field has thus far only 

 been touched upon, and it would seem, judging from 

 researches which have recently appeared, that the best and 

 most far-reaching work therein is probably yet to come. 



The present volume will deal with the past and present of 

 diffusion and osmotic pressure from the standpoint of plant 

 physiology. It has a double raison d'etre. First, it was felt 

 that there was need of some direct and not too exhaustive 

 account of the essential physical facts and theories of the 

 subject. The interest of the physical chemist here has lain 

 mainly in the light which these phenomena have been able 

 to throw upon the ultimate nature of matter and upon elec- 

 trolytic processes. It has thus been difficult for the student 

 of physiology who is not at the same time well versed in 

 physical chemistry to obtain the information required for 

 the prosecution of work in this field. Secondly, it seemed 

 desirable to bring together in a general review the literature 

 of this subject in its biological aspects, so that the promising 

 and unpromising points for future research might become 



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