INTRODUCTION 3 



their own science, have studied such phases of physics and chem- 

 istry as were most important for the solution of a particular 

 problem. Pfeffer's famous osmotic investigation is a well-known 

 illustration of such a case. Starting primarily with studies of the 

 mechanism which regulates the motion of the leaves of Mimosa, he 

 finally formulated some of the most fundamental conceptions for 

 the theory of solutions. Similar profitable excursions into the 

 adjoining fields of science, however, are but rare exceptions. One 

 must acknowledge, nevertheless, that progress in the science of 

 plant physiology, as a rule, is closely connected with the develop- 

 ment of the physicochemical sciences. Every important dis- 

 covery in physics and chemistry seems to bring new enthusiasm 

 and activity into physiological investigations by opening new pos- 

 sibilities. A good case was the discovery of oxygen at the begin- 

 ning of the science of plant physiology. This enabled physiolo- 

 gists to understand correctly for the first time the basis of plant 

 nutrition. A similar instance can be observed at present, when 

 the study of the concentration of H + ions has become of great 

 value to physiology. 



A close connection between physiology and chemistry has led 

 to the development of an intermediate science, which has been 

 named physiological chemistry or biochemistry. It consists pri- 

 marily of the study of chemical transformations within the organ- 

 ism or related to it. Many physiological problems at present are 

 being transferred to the field of biochemistry. This has led some 

 scientists to believe that biochemistry will finally replace physi- 

 ology. This, of course, is not true. By transferring to biochem- 

 istry a part of its problems of an analytical nature, physiology will 

 only gain. This will enable plant physiologists to devote more 

 attention than formerly to the very essential problem of establishing 

 a connection between the separate biochemical and biophysical proc- 

 esses and the uniting of these into a harmonious system, called life. 



Plant physiology serves as one of the most important founda- 

 tions for the agricultural sciences. An advance in physiology, 

 therefore, frequently leads to new progress in the art and science of 

 crop production. And, on the other hand, it often happens that 

 agricultural problems serve as stimuli for an increased study of 

 particular phases of physiology. Plant physiology is certainly 

 indebted to the agronomists for their contributions to the theory 

 of plant nutrition. The names of such agricultural scientists as 

 Boussingault, Hellriegel, and Prianishnikov rank among the most 



