The Botany of Iceland - 01.12.1914, Síða 118

302
THORODDSEN
unusually large quantity of Viscaria alpina grows at Ulfsvatn (400
metres above sea-level). An old lava-stream, south of Krakatindur
and NE. of Hekla is alniost exclusively overgrown with Oxyria
digyna, which otherwise occurs rather rarely on Iava. The neigh-
bourhood of Eyjafjördur is characterized by a great abundance of
Gentiana, and the neighbourhood of Lake Myvatn by its rich vege-
tation of Nasturtium palustre and Pleurogyne rotata; Erysimum hie-
racifolium, which is otlierwise rather rare, occurs abundantly and
as large specimens on the islands in Myvatn; Succisa pratensis is
very numerous in Sida. A few rare plants have been found only
in very far distant habitats, at opposite sides of the island, thus,
Ophioglossum vulgatum at Gunnuhver at tlie extreme point of Revk-
janes, and at Bjarnarflag near Myvatn. Drosera rotundifotia grows
here and there near Breiditjördur and Faxafjördur and otherwise
only in the extreme north between Eyjafjördur and Skagafjördur,
Cirsium arvense occurs in a few localities which are as far apart
as Grindavik and the Vestmannaeyjar towards the south, and Eyja-
fjördur towards the north.
In Iceland as in other arctic or subarctic countries with a
coastal or insular climate there is comparatively but a slight dif-
ference in the vegetation of the lowlands and of the plateau, of the
mountains and of the valleys; it is very difíicult to arrange the
species according to their altitudinal zone. Almost throughout the
island, and everywhere where plant-life can thrive at all, plant-
formations and plant-associations, with a few modifications, occur
with a gradually increasing or decreasing luxuriance and number
of species according to situation only. With the exception of the
highest situated tracts, close to the snow-line, the distribution of
the plants and the differences in the vegetation appear to be in a
higher degree dependent on local climatic conditions, such as snow
and other atmospheric precipitations, wdnd, conditions of soil, in-
clination, more or less sunny exposure, streams and springs rather
than on the height above sea-level. A luxuriant vegetation with a
lowland character often extends very far upwards on the mountains
on the sunny side, or where a suitable degree of moisture and a
protective snow-covering afford favourable conditions of life for the
vegetation, while in the immediate neighbourhood, and often at a
far lower level, cold sharp winds or sand-drifts have destroyed al-
most all plant-life and laid the land waste. Exceptionally favour-
able localities are aíforded for plants in some places near hot springs