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BOOK, IV. 



Chapter 3, Botanical and Physical Geography, A, D. 1838. 



The correspondence between the vegetable forms of North Ame- 

 rica, and Northern Asia, is curious, particularly when contrasted with 

 the almost total want of correspondence between those of Southern 

 America, and Southern Asia. 



We are at once led to suppose that this is the effect of the relative 

 contiguity of the two first mentioned portions of the world, and 

 of the mutual distance of the two latter. 



Elevation above the sea, produces the same effects as receding from 

 the equator to the poles, or, what is called latitude. Both lessen the 

 influence of solar heat in certain given proportions, subject to various 

 local influences. Elevation, however, determines only the appear- 

 ance of northern forms of particular floras : that is to say, it does not 

 act generally. Thus elevation in south America produces elevati- 

 onal forms, but these are of a different nature from those produced 

 by elevation in Asia. The division of the Globe into various secti- 

 ons, distinguished by the peculiar features of vegetation, is called 

 Botanical Geography. Esch division presenting a certain amount 

 of peculiarity, sufficient to entitle it to a separate and distinct rank, 

 is denominated a Kingdom. Division has been carried to a much 

 too great extent by botanical writers. The writer who has dis- 

 tinguished himself most on this subject, is Schow. The Kingdoms 

 he has sketched out, may be Sub Kingdoms, since they cannot all 

 be of the same rank. 



All those regions in which elevation produces similar northern 

 forms should be included in one great Kingdom. And these may be 

 sub divided according to their characteristic features 



Thus, Africa will form one region, Australia another, Asia ano- 

 ther, and America a fourth. Each of these will pass into one another 

 along the lines of greatest contiguity. Each will differ most from 

 one another along the linos of greatest distance. 



Insular floras can be classed on the same principle with those parts 

 to whose productions they shew a similarity. 



Swainsons views, regulating Zoological Kingdoms are, I think, far 

 morejust than those of Botanists, and the same rules will apply to both. 



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