The Botany of Iceland - 01.12.1914, Síða 119

PHYSICAL GEOGRAPHY
303
ou the plateau. Sorne plant-formations such as birch-coppices and
heather-moors, do not, however, extend to the highest levels, and
many species disappear on approaching the snow-line; on the other
hand, others, as mentioned above, are distributed in great abund-
ance all over the island, from the sea-level to the snow-line.
The Icelandic climate affords good conditions of life for mosses,
therefore Iceland has a luxuriant moss-vegetation which is not only
shown in the great extent of tlie Grimmia-heaths, but proofs of it
are seen in various other ways in nature. On the interior plateau
in the most barren localities small green oases are often seen, con-
sisting exclu'sively of mosses; on the abrupt faces of rocks they form
bright green cusliions around springs; and at the numerous waterfalls
of Iceland there is a luxuriant moss-vegetation, rich in forms; blocks
of rock and steep rock-faces are often covered with mosses, as also
the numerous cracks in the lava-streams; and the damp rock-clefts
are often rich in different species. Under various conditions of na-
ture, various species of mosses are the dominant ones, and form
various characteristic societies.
A considerable number of lowland species have an upper limit
on mountains and plateau, but this has not as yet been thoroughly
investigated. On the other hand, very few highland plants have a
lower limit; the majority of the plants which grow near the snow-
line thrive just as well in the neighbourhood of the sea. In many
districts, and in some places on the northern peninsulas towards the
North Atlantic, plant-associations with well-marked plateau-characters
are seen in the vicinity of the sea; this is especially the case with
associations of Salix herbacea, Sibbaldia procumbens and Gnaphalium
supinum, which are otherwise peculiar to the plateaus. Of the com-
monly distributed species probably very few occur exclusively on
the plateau; of such plants only Ranunculus glacialis is known; it
grows in many localities near the snow-line and has doubtless only
rarelv been found below 300 metres. Pedicularis flammea has a
similar distribution, but in some places it grows perhaps further
downwards. Otherwise there are only a few rarer species which
have been lound only on mountains and plateau, but it is possible
that on a closer investigation these may also be found at a lower
level. Of these may be mentioned Carex pedata, Poa laxa, Cata-
brosa algida, Sagina nivalis, Draba alpina, Ranunculus pggmœus,
Diapensia lapponica, Campanula uniflora, Antennaria alpina and
Rrigeron uniflorus. Of common plateau-plants which also occur in