PART III, 



PHYSIOLOGY, 



CHAPTER I. 

 PHYSIOLOGICAL ANATOMY OF PLANTS. 



Sect. 1. THE STEUCTUEE or PLANTS. 



The Physiology of Plants is that department of Botany which treats 

 of the phenomena of the Life of Plants, as manifested in a series 

 of changes taking place in the diverse organs of which each plant 

 is composed. These organs, as we have already seen (MOEPHOLOGY, 

 Chap. I.), are not simply fragments, combining to increase the bulk 

 of the object (their size alone having no definite relation to that of 

 the entire plant), but they are instruments, variously occupied in 

 performing the different functions, the continuous operation of 

 which indicates the existence of what we call Life. For morpho- 

 logical purposes it is best to use the word " part " or " member " 

 without reference to physiological function, which may be different 

 in parts of the same morphological nature. For physiological 

 purposes the term organ is now employed. 



The external characters of the parts of plants, generally, have been 

 described in the First Part of this work, and an indication of their func- 

 tions has been conveyed by their classification under the heads of Vege- 

 tative and Reproductive Organs. But the object of the Morphological 

 chapters was to point out the conditions and relations of Form, as pro- 

 duced by the external shapes of the individual organs and their modes of 

 combination. Here we have to examine the phenomena of Vitality, as 

 displayed in the changes they present in the course of the Development, 

 Growth, and Multiplication of Plants. 



The physiological Organs of plants are themselves composed of 

 a number of parts, which again exhibit a kind of completeness of 

 their own, and a relation to the organs analogous to the relation 



