BOTANY. 49 
8. Tue Potar Zone. This includes all lands from 72° to the pole. The 
mean temperature of one point in this zone, Melville Island, is 15°. In the 
Old World the mean temperature is 165°. Summer temperature of the 
New World 374°, of the Old 384°. Winter temperature 28° in the New 
and 2}° 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 wanting. 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 :— 
“Tn the burning plains, scarce raised above the level of the southern ocean. 
we find Bananas, Cycadacez, 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 snedesliee by 
large meadows covered with 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 efforts of vegetable life, and then the line of eternal snow 
begins. 
« On the mountains of temperate regions the variety i 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 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 grow at an elevation of 4680, 
and the spruce fir at the height of 5900 feet, beyond which no tree appears. 
The RAododendron ferrugineum (the Rose of the Alps) then covers immense 
tracts to the height of 7480 feet, and Salix herbacea creeps 200 or 300 feet 
ICONOGRAPHIC ENCYCLOP#ZDIA.—VOL., Il. 4 49 
