INTRODUCTION. 43 



throughout our planet, according to their different relations 

 of latitude and elevation above the level of the sea, and to 

 climatic influences, which are owing to general and often 

 very remote causes. The ultimate aim of physical geography 

 is, however, as we have already said, to recognise unity in 

 the vast diversity of phenomena, and by the exercise ol 

 thought and the combination of observations, to discern the 

 constancy of phenomena in the midst of apparent changes. 

 In the exposition of the terrestrial portion of the Cosmos, it 

 will occasionally be necessary to descend to very special 

 facts ; but this will only be in order to recall the connection 

 existing between the actual distribution of organic beings 

 over the globe, and the laws of the ideal classification by 

 natural families, analogy of internal organization, and pro- 

 gressive evolution. 



It follows from these discussions on the limits of the 

 various sciences, and more particularly from the distinction 

 which must necessarily be made between descriptive botany 

 (morphology of vegetables) and the geography of plants, that 

 in the physical history of the globe, the innumerable multitude 

 of organised bodies which embellish creation are considered 

 rather according to zones of habitation or stations and to 

 differently inflected isothermal bands, than with reference to 

 the principles of gradation in the- development of internal 

 organism. Notwithstanding this, botany and zoology, which 

 constitute the descriptive natural history of all organised 

 beings, are the fruitful sources whence we draw the materials 

 necessary to give a solid basis to the study of the mutual 

 relations and connection of phenomena. 



We will here subjoin one important observation, by way of 

 elucidating the connection of which we have spoken. The 

 first general glance over the vegetation of a vast extent of a 

 continent shows us forms the most dissimilar gramineaa and 

 orchideaB, conifers and oaks, in local approximation to one 

 another ; whilst natural families and genera, instead of being 

 locally associated, are dispersed as if by chance. This dis- 

 persion is, however, only apparent. The physical description 

 of the globe teaches us that vegetation everywhere presents 

 numerically constant relations in the development of its forma 

 and types ; that in the same climates, the species which are 

 wanting in one country are replaced in a neighbouring one DY 



