THE AIM OF PHYSIOLOGY 9 



information derived from existing species, we are justified in neglecting 

 the problems connected with phylogeny and descent. Neither is it within 

 our province to describe the relations subsisting between the plant and 

 its environment, or its struggle with the variable and varying external 

 conditions presented to it. In order to determine the relative importance 

 of particular factors, the experimental physiologist must work under con- 

 ditions which he holds in more complete control than he can the varying 

 and multifarious influences operating in nature. The true scientific observer 

 must, however, always submit the results obtained within the narrow 

 walls of the laboratory to the test of nature, our great and inexhaustible 

 mistress and teacher, in order to find out how far the knowledge thus 

 obtained agrees with, and explains, the manifold phenomena which she 

 presents to us. 



The sum of our knowledge with regard to the vital economy of the 

 plant, and its relations with, and adaptations to, its dead and living, organic 

 and inorganic surroundings, may be termed plant economy or Bionomy^ . 

 It is permissible to ignore such relationships when our attention is directed 

 only to the aims and purposes which the plant has in view. Owing to our 

 ignorance of the exact causal relationship of the different phenomena observed, 

 a teleological explanation becomes rnore and more necessary, and if pro- 

 perly used it is in its way not only perfectly justifiable, but also capable 

 of aiding discovery and stimulating inquiry, when applied to natural 

 phenomena. 



It must, however, never be forgotten that the purpose of any given 

 phenomenon can only be determined by an external observer on the 

 basis of the facts which come under his notice. Ideas of purpose being 

 abstract mental conceptions, are not and can never be the direct causes 

 of anything that takes place in the plant. It is therefore always the 

 object of Physiology to investigate the ways and means by which, under 

 certain external conditions, and with varying internal dispositions, some 

 particular final result is produced 2 , and to trace the chain of causes 

 which lead to this result. 



The different changes and processes which go on in a living organism 

 must necessarily have a purposeful character. A plant can only live 

 and continue its development when the external conditions are suitable 



1 In former times Aristotle, and nowadays Spencer and others, use the term ' Biology ' to 

 include the whole of the phenomena with which life confronts us. It seems worth while to retain 

 for the word this general meaning, and to call, as Haeckel does (Generelle Morphologic, 1866, 

 Bd. I, p. 8, Bd. II, p. 236; Systematische Phylogenie, 1894, Bd. i, p. 386), the principles of plant 

 economy, to which the name of Biology is sometimes given, Oecology or Bionomy. From an historical 

 point of view, Physiology and Biology are identical terms. Nevertheless, it is justifiable to restrict 

 the term 'Physiology' as applying only to the attempts at a causal explanation of vital phenomena. 



2 On these questions, see B. Lotze, Mikrokosmos, Bd. I ; Lange, Geschichte des Materialismus, 

 2. Aufl., Bd. I, p. 13; Wundt, System der Philosophic, 1869, p. 318. 



