GEOGRAPHY OF PLANTS. 269 



and produce a completely different vegetation. This, how- 

 ever, must be understood rather of the temperate and frigid 

 zones, than of the tropical climates, which, as we have al- 

 ready noticed, are pretty much the same over all the earth. 

 But the summer is shorter in the southern hemisphere, be- 

 cause the motion of the earth in her perigee is more rapid. 

 The summer is there also colder, because the great quantity 

 of ice over the vast extent of sea requires more heat for dis- 

 solving it than can be obtained ; as also, because the sun 

 beams are not reflected in such quantity from the clear sur- 

 face of the sea water, as to afford the proper degree of heat. 

 It hence happens, that in the southern hemisphere, the Flora 

 of the pole extends nearer the equator, than in the northern. 

 Under the 53d and 54th degrees of south latitude, we meet 

 with plants which correspond with the Arctic Flora. In Ma- 

 gellan's Land, and in Terra del Fuego, Betula antarctica cor- 

 responds with Betula nana^ in Lapland ; — Empetrum ruhrum 

 with Empetrum nigrum^'^Arnica oporina with Arnica mon^ 

 tana^ — Geum Magellanicum with Geum rivale, in England, — 

 Saxifraga Magellanica with Saxifraga rimdariSy in Fin- 

 mark. Instead of Andromeda tetragona and hypnoides^ of 

 Lapland, Terra del Fuego produces Andromeda myr smites : 

 in place of Arbutus alpina and Uva Ursi of the Arctic po- 

 lar circle. Terra del Fuego produces Arbutus mucronata^ 

 microphylla, and pumila. Aira antarctica reminds us of the 

 Holcus alpina of Wahlenberg; and Pinguicula antartica 

 recalls to our recollection Pinguicula alpina. 



We must recollect, however, that in South America, the 

 great mountain chains of the Andes stretch from the tropical 

 regions, almost without interruption, to the Straits of Magel- 

 lan, (from the 52d to the 53d degree of S. Lat.) ; and that, on 

 this account, tropical forms are seen in that frigid southern 

 zone, because, as we shall have occasion to remark more fully 

 afterwards, the tract of mountains every where determines 

 vegetation. It is hence that the Straits of Magellan are pro-, 

 lific of CoronariiE, Onagra, Dorstenite, and Heliotropice^ 

 which in other parts of the world grow only within the tro« 

 pics, or in their neighbourhood. 



