A TEXTBOOK 



OF 



PLANT PHYSIOLOGY 



INTRODUCTION 



Plant physiology is a science that deals with the vital 

 phenomena that occur in plants. Its objects are, first, to sub- 

 divide into separate functions the complex activities that consti- 

 tute the life of a plant; second, to establish the role of each of 

 these in the general behavior of the organism; and, finally, to 

 analyze, as thoroughly as possible, every process into its simpler 

 constituent parts, i.e., into reactions that may be observed even 

 in the inorganic world. 



Plant physiology is an inseparable part of botany. It is closely 

 connected with the study of morphology and anatomy of plants, 

 since without a sufficient knowledge of plant structure an effective 

 study of physiology is hardly possible. Recently plant physiology 

 has been forming connections not only with plant ecology and 

 plant geography but also with taxonomy. Plant physiology is 

 passing gradually from the study of activities common to all plants 

 to a consideration of the physiological distinctions that exist 

 between various groups or even species. 



Though being a part of the botanical sciences, plant physiology 

 is also closely linked with animal physiology. Many essential 

 organic functions, such as respiration, nutrition, and irritability, 

 are exhibited both by plants and by animals. Hence, the numer- 

 ous attempts to create a science of general physiology that should 

 include the study of vital activities manifested by all organisms. 

 Such an approach to the investigation of living beings, however, 

 would leave out of consideration the specific nature of plants. 

 An independent study of the problems that refer particularly to 

 the physiology of plants, therefore, is necessary. 



Plant physiology differs from the other more general biological 

 sciences, in which description plays an important part, in that it is 



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