INTRODUCTION. 



The object of Physiological Plant Anatomy is twofold. It consists 

 first, in the recognition of the physiological functions pertaining to the 

 tissues of the plant and to the structural units, or cells, of which these 

 tissues are composed ; and, secondly, in the discovery of the connection 

 that exists between the several functions and the anatomical arrange- 

 ments required for their proper performance. The study of the 

 various cells and tissues of the plant body clearly demonstrates the 

 fact that physiological activity depends upon the general structure of 

 the organism and upon individual anatomical features, just as the 

 special manner of action of every machine is the result of its particular 

 mode of construction. 



Physiological anatomy is an explanatory science, because it sets 

 out to discover the relation between structure and function ; for the 

 discovery of relations between distinct phenomena constitutes " ex- 

 planation " in the scientific sense of the term. Since, however, any 

 particular physiological function appears to the observer to be the aim 

 and object of the correlated structural features, every demonstration 

 of a connection between structure and function naturally assumes a 

 teleological aspect. 



The value of a teleological explanation depends entirely upon the 

 philosophical attitude of its author. In some cases such an "explana- 

 tion " merely serves as a pregnant mode of expressing the relation 

 between structure and function, whereas an objective significance may 

 be ascribed to it by those who recognise the existence of purpose as 

 a final cause, not only in human actions, but also in all the workings 

 of Nature. 



The preceding definition of the scope of physiological anatomy 

 at once raises the following question : Is there no exception to the rule 

 which almost amounts to a postulate from the anatomico-physiological 

 standpoint that each individual cell is endowed with some special 

 function, and that a definite physiological value must be assigned to 

 every morphological feature ? 



A 



