msTlMUl tion OP PLANTS. 279 



that they should have conveyed the seeds of plants to so great 

 a distance. — The Andes, in this respect, present a striking con- 

 trast with the mountains of the eastern continent This 

 greal chain of mountains appears to extend, almost uninter- 

 ruptedly, from near, or within, tin' antic circle to Cape Horn; 

 md arctic plants, which in the eastern continent do not reach 

 the European Alps, have been here discovered as low as 40 

 N. lat.. far south of those mountain; — as, Campanula unijlora. 

 Saxijraga nivalis, ix.c. 



Great confusion has been occasioned in our floras by man 

 himself carryine ■with him, in his migrations, a multitude oi 

 plants. In the more settled parts of the United States, the 

 greater portion of the entire surface iscovered with European 

 vegetables : many have even wandered into the woods, so as firi - 

 quently to perplex the botanist in determining, whetherthey 

 have been introduced from Europe, or existed here previous 

 to the discovery of the country. The flora of Pursh, which 

 is usually appealed to as giving evidence of the number ol 

 species common to the two continents, contains upwards of 

 one hundred and fifty species, now generally admitted by 

 American botanists to have been introduced, hut on which 

 that author does nol express an opinion, leaving the foreigner 

 without any means of deciding, except that, being frequently 

 indicated as found about held- and cultivated ground, they art 

 of course liable to suspicion. 



Thus, climate and the ocean are the two greal pow< ra 



which sr) bounds to the diffusion of plant-, and at the -aim 



time, by insulating certain portions of land, divide the surface 

 of the globe into several greal botanical regions. 



In this essay the following division ha- been adopted: 



I. Greenland, Iceland, and the arctic regions of both con- 

 tinent-. 



II. The temperate portion of North America. 



III. Tin' temperate portion of tlw Ka-tern continent. 



IV. The West Indies, and the intertropical regions "i 

 America. 



