The Botany of Iceland - 01.12.1914, Side 152

THORODDSEN
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slopes of mountains are often grass-covered, especially when the rock
is tuff or breccia; in Soulh Iceland the tuff mountains are often en-
tirely grass-covered, at least on the southern side, and sometimes
they are covered with a thick layer of soil without knolls proper,
which occur only on the clay ground of the lowlands. But some-
times wavy rows of small knolis, or narrow ripple-like ledges occur
in the lowesl part of tlie grass-slope, and sometimes above these,
for a great distance up, the surface of tlie soil is undulating and
wave-like; this is undoubtedly due to mud-ílows in the clayey soil-
covering. On l)asalt mountains the grass-vegetation extends upwards
in tongues or occurs in patches in depressions or on ledges, se-
parated by considerable tracts of stones and gravel. On such a
grass-slope, in addition to the grasses, manv other kinds of herbaceous
plants are more or less numerously represented. In South Iceland,
according to H. Jónsson, the following are the dominant species:
Agrostis vulgaris, A. cartina, Anthoxanthum odoratnm, Festnca ovina,
Poa alpina, P. nemoralis, Geraninm silvaticum, Trifolium repens, Bru-
nelta vulgaris and Leontodon autumnalis; less eommon, but often
occurring iocally in great abundance: Spirœa ulmaria, Linum ca-
tharticnm, Rubus saxatilis, Gentiana campestris, Myosotis arvensis,
Parnassia palustris, and many others; in Fijotshiid Carum carvi is
very common and in Myrdalur and Sida Succisa pratensis. The
vegetation is rich in species and is rather mixed, although grasses
preponderate. In other parts of the country where basalt is donii-
nant the grass vegetation of the mountain-slopes consists of similar
species, but is not so luxuriant as in South Iceland. The following
species are common: Agrostis vnlgaris, A. alba, A. canina, Anthoxan-
thum odoratum, Nardus stricta, Aira flexuosa, A. cœspitosa, Phleum
pratense, Poa alpina, Hierochloa borealis, Festuca rubra, etc. A spe-
cial Nardus-association and an Anthoxanthum-association often occur.
Knolly grassland (Græsmo). By this is understood dry, ex-
tremely knolly strelches of clayey ground intermixed with humus,
occurring on level land and in valleys with a mixed vegetation of
Gramineæ, Juncaceæ and Cyperaceæ; it may therefore differ con-
siderabiy in appearance. according to whicli of these families pre-
dominates. When grasses predominate the “Græsmo” resembies
grassland, but sometimes Juncus trifidus and Elyna fíellardi are so
dominant that large stretches attain a brownish tint like that of a
heather-moor. Usually, the vegetation of the knolls differs from tliat
of the depressions; in the depressions, mosses and some Carices