122 STEPPES AND DESERTS. 



The areas of dry land in the Northern and Southern Hemispheres are 

 to each other in the ^proportion of 3 to 1. > But this inferiority in 

 extent of continental masses in the Southern Hemisphere,^ as com- 

 pared with the Northern, belongs much more to the temperate than 

 to the torrid zone. In the temperate zones of the Northern and 

 Southern Hemispheres, the ratio is as 13 to 1 ; m the torrid zones 

 as 5 to 4. The great inequality in the distribution of the dry land 

 exercises a very sensible influence on the strength of the ascending 

 aerial current which turns towards the Southern Pole, and on the 

 temperature of the Southern Hemisphere. Some of the noblest 

 forms of tropical vegetation, for example the tree-ferns, advance 

 south of the Equator as far as the parallels of 46, and of even 53; 

 whereas north of the Equator they are not found beyond the tropic 

 of Cancer (Robert Brown, Appendix to Flinders' Voyage, pp. 575 

 and 584; Humboldt, de distributione geographica Plantarum, pp. 

 8185.) Tree-ferns thrive extremely well at Hobart Town in Van 

 Diemen Island (lat. 42 53'), where the mean annual temperature 

 is 9 Reaumur, or 52 2' Fahrenheit, and is therefore 1 6' Reau- 

 mur, or 3. 6 Fahrenheit, less than that of Toulon. Rome is almost 

 a degree of latitude farther from the Equator than Hobart Town, and 

 has an annual temperature of 12. 3 R., or 59. 8 Fahr.; a winter 

 temperature of 6. 5 R., or 46.4 Fahr., and a summer temperature 

 of 24 R., or 86 Fahr.; these three values being in Hobart Town 

 8.9, 4.5, and 13. 8 R., or 52.0, 42.2, and 63 Fahr. In Dusky 

 Bay, New Zealand, tree-ferns grow in S. lat. 46 8', and in the Auck- 

 land and Campbell Islands, even in 53 S. lat. (Jos. Hooker, Flora 

 Antarctica, 1844, p. 107.) 



In the Archipelago of Tierra del Fuego where, in the same lati- 

 tude as Dublin, the mean winter temperature is 0.4 Reaumur (33 

 Fahr.), and the mean summer temperature only 8 R., or 50 Fahr. 

 Captain King found the "vegetation thriving most luxuriantly in 

 large woody-stemmed trees of Fuchsia and Veronica;" while this 

 vigor of vegetation, which, especially on the western coast of Ame- 

 rica in 38 and 40 of south latitude, is so picturesquely described 

 by Charles Darwin, suddenly disappears south of Cape Horn, on the 

 rocks of the Southern Orkney and Shetland Islands, and of the 

 Sandwich Archipelago. These islands, but scantily covered with 

 grass, moss, and lichens, "Terres de Desolation," as the French na- 



