INTRODUCTION 5 



as is the evidence, our existing vegetation can be linked 

 with that of past geological periods: its existing distri- 

 bution is that of the vegetation of the past, modified 

 by changes in the environment perhaps as profound as 

 those seen in the vegetation itself. 



During the second half of the nineteenth century 

 the division of the earth's surface into climatic regions 

 of vegetation was, by the labours of many scientific 

 travellers, very fully accomplished. Species were tabu- 

 lated according to their distribution, and, under the 

 influence of the theory of evolution, it was recognised 

 that neighbouring natural floras are connected together 

 by the migration of species from one to another; and 

 also distinguished from one another by peculiar or 

 " endemic " species which have originated where they 

 occur by the modification of pre-existing forms. This 

 department of the subject has been termed " floristic 

 geography," and deals, it should be noted, mainly with 

 the distribution of species over large areas. 



During the present century the attention of botanists 

 has been more directed to the simultaneous relation of 

 groups of plants (united only in physiological require- 

 ments and not generally by genetic affinity) to their 

 " habitats " or situations as regards soil, drainage, 

 aspect, etc. This study of the homes of plants is termed 

 "ecology"; and this treatment of plants, in groups 

 presenting marked landscape or " physiognomic " 

 characters according to their habitat, has been termed 

 " ecological geography " ; but might rather perhaps 

 be named " ecological topography." It deals with 

 vegetation rather than with individual species; and, 

 though much concerned with such local climatic in- 

 fluences as those due to slope, aspect, and drainage, 

 treats more of plant physiology than of what is usually 

 considered as geography. 



If then we take Phyto-geography, or the geography 

 of plants, to signify the science of the distribution of 

 plant-life over the surface of the globe, we shall deal 

 with it under four heads. We shall first sketch briefly 

 what is known as the evolution of the plant- world and 

 its distribution in past geological periods. Secondly, 

 we shall write of the factors of distribution: climate, 

 soil, the effects of other plants and animals, the response 

 of plants to these influences, the agencies and mechanisms 



