The Botany of Iceland - 01.12.1914, Side 144

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THORODDSEN
flats; tliey have a characterislic vegetation consisting of Koenigia
islandica, Sedum villosnm, Juncus alpinus, J. biglumis and J. triglu-
mis; moreover, Epilobium palustre, Spergula arvensis, Sagina pro-
cumbens, S. nodosa, Stellaria crassifolia, Polygonum aviculare, Equise-
tum palustre, Triglochin palustris, Agrostis alba, Luzula spicata and
some other species occur frequently, whic.h are distributed according
to the water content, etc. of the clayey flats
The vegetation of mountain-slopesis often only an extension
of that of the rocky flats, with the difterence that greater variations
occur at the base of the mountains, the conditions there being more
highly diversified: the stony tracts alternating with bogs, springs,
grass-slopes, heather-moors, coppice-woods, etc. But frequently moun-
tain slopes consists mainly of downward-gliding gravel-masses or an-
gular rock-fragments, with little or no vegetation, the stone-covering
being too unstable to pennit plants to gain foothold; in other places
are heaps of loose blocks of rock (urd) or solid rock-terraces or
-faces; in many places mountain-streams excavate channels or deep
ravines, and at the base of mountains they cause the formation of
broad gravel-cones with branching streamlets with mosses and other
plants connected with springs, or with transitions to bog-formations.
On the rock terraces there is sometimes a soil-layer which, accord-
ing to the conditions of moisture, supports either Gramineæ or
Cyperaceæ. Therefore, on mountain-slopes, many different plant-
formations are found in patches close to one another in many transi-
tional stages. In the rock-detritus on mountain slopes which are
not too steep, plants common on rocky flats occur, but none that
are really characteristic; the following have been noted: Silene acaulis,
S. maritima, Alchimilla alpina, Dryas octopetala, Thymus serpyllum,
Cerastium alpinum, Armeria maritima, Saxifraga ccespitosa, S. hyp-
noides, S. stellaris, Potentilla maculata, P. anserina, Sedum acre, Erige-
ron alpinus, Veronica saxatilis, Poa glauca, P. alpina, and several
others. Nor are there many characteristic plants in the vegetation
of the rock-faces. Tuff and breccia mountains are generally richer
in plants than basalt mountains, their surfaces having many more
crevices and hollows in which plants can gain foothold. The fol-
lowing plants occur on steep mountain-sides: Archangelica officinalis,
Rhodiola rosea, Haloscias scoticum, Polypodium vulgare and Woodsia
ilvensis, also Cochlearia officinalis, especially on sea-fowl cliffs; Saxi-
fraga Cotyledon grows only on rocks in south-eastern Iceland. More-
over, in rock-clefts various ferns occur, most frequently Cystopteris