364 Introduction. [BOOK HI. 



causal connection. To this the teleological mode of view was 

 inadequate, and it became necessary indeed to discard it as a 

 hindrance, in spite of the difficulty of explaining adaptation in 

 the arrangements of organisms from any other than the teleo- 

 logical point of view. It is sufficient here to say that this 

 difficulty is satisfactorily removed by the theory of selection. 

 This theory is become as important in this respect to physi- 

 ology, as the theory of descent is to systematic botany and 

 morphology. If the theory of descent finally liberated the 

 morphological treatment of organisms from the influence of 

 scholasticism, it is the theory of selection which has made 

 it possible for physiology to set herself free from teleological 

 explanations. Only an entire misunderstanding of the Dar- 

 winian doctrine can allow anyone to reproach it with falling 

 back into teleology ; its greatest merit is to have made tele- 

 ology appear superfluous, where it seemed to naturalists 

 in former times, in spite of all philosophical objections, to 

 be indispensable. 



If the comparison of plants with animals as well as the teleo- 

 logical conception of organisms promoted the first attempts at the 

 physiological investigation of plants, other influences of decisive 

 importance came into play when the time came for endeavour- 

 ing to conceive and explain the causes and conditions of the 

 functions, which had then been ascertained at least in their 

 most obvious features. Phytotomy was here the chief resource. 

 In proportion as the inner structure of plants was better known 

 and the different kinds of tissue better distinguished, it became 

 possible to bring the functions of organs, as made known by 

 experiment, into connection with their microscopic structure ; 

 phytotomy dissected the living machine into its component 

 parts, and could then leave it to physiology to discover from 

 the structure and contents of the tissues, how far they were 

 adapted to perform definite functions. Obviously this only 

 became possible when the phenomena of vegetation had been 

 previously studied in the living plant. For example, the 



