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BOOK III 



PHYSIOLOGY. 



We have now examined the structure, classification, and uses of 

 plants, and have still to consider them in a state of life or action, 

 and to explain, as far as science enables us, the laws which regu- 

 late their life, growth, and reproduction. The department of 

 botany which investigates these phenomena is termed Physiology; 

 and the various processes which go on in the plant, and which 

 are the necessary accompaniments of its life, are called its 

 functions. The different vital actions are naturally divided into 

 two classes, called, respectively, the functions of the organs of 

 nutrition or vegetation, and the functions of the organs of repro- 

 duction ; the former being those concerned in preserving the life 

 of the particular plant, and the latter in continuing the species. 

 Physiology includes the study of the life of the whole plant, 

 when it is termed general; and that of the particular organs, in 

 which case it is called spicial. 



The present state of our knowledge of many points connected 

 with the physiology of plants is so imperfect that there is diffi- 

 culty in arranging a good plan for its study. In examin- 

 ing, therefore, the functions of the different organs, the order of 

 arrangement adopted in treating of their structure and morpho- 

 logy will be followed as far as possible, and a few observations 

 on the phenomena in the life of the whole plant will conclude 

 the subject. 



