14 Introduction 



a relation which depends on the phenomenon of adapta- 

 tion, but it is not true that plant-form runs everywhere 

 pari passu with habitat. The net of adaptation is not so 

 close-meshed, nor is it drawn so closely round the 

 manifold of organic form, as to bring about a rigidly exact 

 correspondence of this kind. In broad outline the cor- 

 respondence exists, and we may classify the sum-total 

 of the plant-formations of the world by the plant-form of 

 the dominant species of their chief associations. Such a 

 classification is the expression of the fundamental climatic 

 zonation of the world and of the great mountain com- 

 plexes. 



But a classification of this kind lies outside the scope 

 of a book devoted to the vegetation of a comparatively 

 small country. Our primary task in the present work is 

 to determine the formations themselves, and if we used 

 plant-form as the basis we should associate units of 

 vegetation which are naturally distinct, and divorce 

 others which are naturally associated. Thus we should 

 bring together all deciduous tree-associations in this 

 country and separate them from the naturally related 

 grass- or heath-associations. Such a classification would 

 be quite barren, leading nowhere, because it would ignore 

 habitat. 



