BOTANY. 49 



8. The Polar Zone, This includes all lands from 72° to the pole. The 

 mean temperature of one point in this zone, Melville Island, is 1^°. In the 

 Old World the mean temperature is 16|°. Summer temperature of the 

 New World 37^°, of the Old 38|°. Winter temperature 28° in the New 

 and 2i° in the Old. Spitzbergen, Greenland, the coast of Baffin's Bay, 

 Melville Island, Northern Siberia, and Nova Zembla, exhibit the same 

 species, "with few exceptions. Trees and shrubs Avanting. Small turfy plants 

 with creeping roots. Poor in genera, species, and individuals. Characteristic 

 genera are Phippsia, Colpodium, Dupontia, Pleuropogon, Eriophorum, Juncus, 

 Salix, Pedicularis. Andromeda, Pyrola, Saxifraga, Cochlearia, Cardamine, 

 Parrya, Platypetalum, Eutrema, Papaver, Ranunculus, Silene, Potentilla, and 

 Dryas. Few Monocotyledons, and these not above the grass type. Almost 

 total destitution of Apetala and Monopetala. 



Vertical Range of Plants. 



The relation between altitude and vegetation is best seen in ascending high 

 mountains in tropical regions, where all gradations, from the heat of the 

 Torrid Zone to the cold of the Arctic regions, may be passed through in 

 regular succession. We quote a striking illustration of this circumstance 

 from Humboldt : — 



" In the burning plains, scarce raised above the level of the southern ocean, 

 we find Bananas, Cycadacese, and Palms, in the greatest luxuriance ; after 

 them, shaded by the lofty sides of the valleys in the Andes, Tree Ferns ; 

 next in succession, bedewed by cool misty clouds. Cinchonas appear. When 

 lofty trees cease, we come to Aralias, Thibaudias, and myrtle-leaved Andro- 

 medas ; these are succeeded by Bejarias abounding in resin, and forming a 

 purple belt around the mountains. In the stormy regions of the Paramos, the 

 more lofty plants and showy flowering herbs disappear, and are succeeded by 

 large meadows covered Avith grasses, on which the Llama feeds. We now 

 reach the bare trachyte rocks, on which the lowest tribes of plants flourish. 

 Parmelias, Lecidias, and Leprarias, with their .many-colored sporules, form 

 the flora of this inhospitable zone. Patches of recently fallen snow now begin 

 to cover the last efi"orts of vegetable life, and then the line of eternal snow 

 begins. 



" On the mountains of temperate regions the variety is rather less, but the 

 change is not less striking. We begin to ascend the Alps, for instance, in 

 the midst of warm vineyards, and pass through a succession of oaks, sweet 

 chestnuts, and beeches, till Ave gain the elevation of the more hardy pines 

 and stunted birches, and tread on pastures fringed by borders of perpetual 

 snow. At the elevation of 1950 feet, the vine disappears ; and 1000 feet 

 higher, the sweet chestnuts cease to grow ; 1000 feet further, and the oak is 

 unable to maintain itself; the birch ceases to groAV at an elevation of 4680, 

 and the spruce fir at the height of 5900 feet, beyond Avhich no tree appears. 

 The Rhododendron ferrugi7ietitn {the Rose of the Alps) then covers immense 

 tracts to the height of 7480 feet, and iSalLv herbacea creeps 200 or 300 feet 



ICONOGRAPHIC ENCYCLOP.EDIA. — VOL. II. 4 49 



