Text-book of structural and physiological botany / by Otto W. Thomé ... and Alfred W. Bennett.

  • Thomé, Otto W. (Otto Wilhelm), 1840-1925.
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of structural and physiological botany / by Otto W. Thomé ... and Alfred W. Bennett. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

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    species being found at a greater height. The zone of Alpine herbs, or the upper Alpine zone, extends to the Hmit 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, £r/ca car- }iea, and the single Azalea found in the Alps, A. prociinibens. 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,' Pi-otococcus 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. I. The Arctic Region. The Arctic flora embraces those regions of the extreme north which lie 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. Hepaticse, Lichens, Grasses, and Cyperacese, a few shrubs and sub-shrubs—willows, birches, and Vacciniaceae —as well as evergreen Rliododendrons 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 j' the