:( 



384 



GEOGRAPHICAL DISTEIBUTION AND 



[Ch. XL. 



complete, diversity in the species of plants, De Candolle 

 observed, that, out of 2,891 



3 01 pnsenogamons plants 

 described bj Pnrsh as known in 1820 in the United States, 

 there were only 385 common to northern or temperate Europe. 

 On comparing New Holland with Europe, Mr. Brown as- 

 certained that, out of 4,100 species, then discovered in 

 Australia, there were only 166 common to Europe, and of 

 this small number there Avere some few which may have 



Almost all of the 160 



been transported thither by man. 

 species were cryptogamic, and the rest consist, in nearly 

 every case, of pheenogamous plants which also inhabit in- 

 tervening regions. 



But it is still more remarkable that there should be an 

 almost equal diversity of species, in distant parts of the 

 ancient continent between which there is an uninterrupted 

 land communication. Thus there is one assemblage of species 

 in China, another in the countries bordering the Black Sea 

 and the Caspian, a third in those surrounding the Mediter- 

 ranean, a fourth on the great platforms of Siberia and Tartary, 



and so forth. 



The distinctness of the groups of indigenous plants, in 



parallel of latitude, is greatest, as in the case of 



animals before mentioned, where continents are disjoined 



by a wide expanse of ocean. In the northern hemisphere^ 



near the pole, where the extremities of Europe, Asia, and 



America unite or approach near to one another, a consider- 



same 



same 



to the three continents. But it has been remarked, that 

 these plants, which are thus so widely diffused in the arctic 

 regions, are also found in the chain of the Aleutian islands, 



? 



which stretch almost across from America to Asia, and whici: 

 may probably have served as the channel of communicatioi 

 for the partial blending of the floras of the adjoining regions 

 De Candolle enumerated twenty great botanical provinces 

 inhabited by indigenous and aboriginal plants ; and his son 

 Alphonse, a distinguished living botanist, has made a further 

 subdivision into twenty-seven provinces, between Avliich the 

 lines of demarcation are bv no means ill- defined."^' 



^ Alph. De CaudoUej Monogr. cles Campanulees. Paris, 1830. 



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