348 CONSIDERATIONS ON THE GEOGRAPHY" 



fixed habitations rarely pass. The elk, for example, lives 

 in the Scandinavian peninsula almost ten degrees of latitude 

 farther north than in the interior of Siberia, where the iso- 

 chimenal lines, or lines of equal winter temperature, present 

 a form so strikingly concave. Plants migrate in the germ ; 

 the seeds of many species are provided with appropriate 

 organs, by means of which they are wafted through the air ; 

 but when once rooted they become dependent on the soil, 

 and on the temperature of the surrounding atmosphere; 

 animals, on the contrary, having the power of locomotion, 

 can migrate at pleasure beyond the bounds of their usual 

 habitations ; and they do so more particularly where the 

 isotheral lines are greatly inflected, and where hot sum- 

 mers follow severe winters. The royal tiger, perfectly iden- 

 tical with the Bengal species, makes incursions every sum- 

 mer into the North of Asia, as far as the latitudes of Berlin 

 and Hamburgh, a fact which Ehrenberg and myself have 

 fully established in another work. ( 43 ) 



The associations of different species of plants, to whicli we 

 are accustomed to give the name of " floras," do not appear 

 to me, from what I have myself seen of the surface of the 

 earth, to manifest that predominance of particular families, 

 which would justify us in distinguishing geographically the 

 regions of the umbellatee, of the solidaginae, of the la- 

 biatse, or of the scitaminese. In this respect my individual 

 opinion diners from the views of several of my friends who 

 are among the most distinguished botanists of Germany. 

 It appears to me, that the character of the floras of the 

 highlands of Mexico, of New Granada and Quito, of 

 the plains of European Russia, and of Northern Asia, 



