VERTICAL RANGE OF VEGETATION. 583 



8. The Polar Zone. This includes all lands from 72 to 82 lati- 

 tude. The mean temperature of one point in this zone, viz., Melville 

 Island, is 1^. In the Old World, the mean temperature is 16^. 

 Summer temperature of the New World, 37^, and of the Old, 38; 

 Winter temperature, 28 in the New, and 2^ in the Old World. 

 No trees nor bushes grow in this zone. Some Saxifrages, and numer- 

 ous Cryptogamic plants, as Lichens, prevail in it. 



1158. Vertical Range of Vegetation. Under this head we consider 

 the changes produced in the physiognomy of vegetation on ascending 

 mountains. It has reference to the distribution of plants in an altitu- 

 dinal or hypsometrical point of view. This geographical range is best 

 seen in the high mountains of tropical countries, where all gradations 

 are met with, from the heat of the torrid zone to the cold of the frigid 

 zone. Humboldt, ha describing South American sceriery, remarks: 

 " In the burning plains, scarce raised above the level of the Southern 

 ocean, we find Bananas, Cycadacea;, and Palms in the greatest luxuri- 

 ance; after them, shaded by the lofty sides of the vallies in the Andes, 

 Tree Ferns; next in succession, bedewed by cool misty clouds, Cin- 

 chonas appear. When lofty trees cease, we come to Aralias, Thibau- 

 dias, and myrtle-leaved Andromedas; 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 sticceeded by large meadows covered 

 with grasses, on which the Llama feeds. We now reach the bare 

 trachytic rocks, on which the lowest tribes of plants nourish. Par- 

 melias, Lecidias, and Leprarias, with their many-coloured sporules, 

 form the flora of this inhospitable zone Patches of recently fallen 

 snow now begin to cover the last eiforts of vegetable life, and then the 

 line of eternal snow begins." 



1159. 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 we gain the ele- 

 vation of the more hardy pines and stunted birches, and tread on 

 pastures fringed by borders of perpetual snow. At the elevation of 

 1,950 feet, the vine disappears; and at a 1000 feet higher, the sweet 

 chestnuts cease to grow; 1000 feet farther, and the oak is unable to 

 maintain itself; the birch ceases to grow at an elevation of 4,680, and 

 the spruce fir at the height of 5,900 feet, beyond which no tree appears. 

 The Rhododendron ferrugineum (the Rose of the Alps) then covers im- 

 mense tracts to the height of 7,480 feet, and Salix herbacea creeps 

 200 or 300 feet higher, accompanied by a few Saxifrages, Gentians, 

 and Grasses, while Lichens and Mosses struggle up to the imperishable 

 barrier of perpetual snow." In central and southern Europe, the pro- 

 portion of Monocotyledons to Dicotyledons, which is as 1 to 4 in the 



