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‘Botanical Geography. , | 437 
species being found at a greater height. ‘The zone of Alpine - 
herbs, or the upper Alpine zone, extends to the limit of 
perpetual snow, 2,800 or 3,000 metres. Of woody plants 
this zone has only the dwarf willows, with perhaps a few 
Rhododendrons, the beautiful mountain heath, 72ca car- 
~ nea, and the single Azalea found in the Alps, 4. procumbens. 
In the zone of Cryptogams, or the snow region, above the 
limit of perpetual snow, all phanerogamic vegetation has 
disappeared ; only Mosses and Lichens are still found, and 
the ‘red-snow,’ Profococcus nivalis, temporarily colours the 
white tracts of snow. 
It will illustrate how the distribution of plants in altitude is modi- 
fied by local circumstances, to mention that in the northern Alps the 
upper limit of the cultivation of the grape-vine is 500 metres, in the 
, central Alps 600, while in the groups of Monte Rosa and Mont Blanc it 
ascends to 900 metres. 
REGIONS OF VEGETATION. 
1. The Arctic Region. 
The Arctic flora embraces those regions of the extreme 
north which le beyond the polar limits of the forests. Its 
character is determined by the shortness of the period of 
vegetation, and the comparatively low temperature during 
this period. The plants belonging to it must be able to 
undergo a period of hibernation of at least nine months 
each year. The portion of them which rises above the sur- — 
face is comparatively small, and their underground stems 
are almost always perennial ; annual plants are almost en- 
tirely wanting. Hepatice, Lichens, Grasses, and Cyperaceze, a 
- few shrubs and sub-shrubs—willows, birches, and Vacciniaceze 
_—as well as evergreen Rhododendrons and Andromedas, 
form the flora characterised [in part] by the size and _bril- 
liant colour of its flowers. ‘There are no cultivated 
plants. In this region occur the ‘Tundren,’ broad plains 
covered with Mosses and Lichens. The Mosses are partial 
to moisture, and hence form the ‘moist Tundren ;’ the 
