The Botany of Iceland - 01.12.1930, Blaðsíða 121

STUDIES ON THE VEGETATION OF ICELAND
111
lieiði, and tliere it seemed to be peculiar to hollows, the bottom of
which consisted of large boulders over which Grimmia had spread
a deep dense carpet with scattered specimens of Carex rigida, Pedi-
cularis flammea, Saxifraga Hirculus and several others.
The other type is the jaðar along the banks of rivers.
Physiognomically it resembles the jaðar further inland, but íloristic-
ally il differs from it by the fact that a number of species such
as Carex Goodenoughii, Caltha palustris, Geum rivale, Comarum pa-
lustre, and Menganthes trifoliaia either exclusively or practically ex-
clusivelj^ occur liere, and that merely as a narrow fringe only few
metres wide along both sides of the stream. Since in the lowlands
the species occur botli in the mýri far from running water and
along streams, their predilection for streams in the highlands can-
not be due to any general property of tliese, such as an abundance
of nourishment and oxygen, but must be referred to other causes.
Since all the aforementioned plants are southern species, and since
the presence of water in the highlands also otherwise favours the
southern species, it seems natural to suppose that the more abun-
dant occurrence of more southern plants in immediate association
witli running water is due to the fact that running water warms
the soil more than stagnant water even though water in all cases
acts as a reservoir of heat.
The Mvri and Flói Vegetation. Cf. figs. 21—22 and table 24 A,
1—13.
The mýri vegetation occurs in the dampest hollows and espe-
cially around the numerous lakes. A depression with mýri lias the
following appearance. On soniewhat damper ground than the above-
described jaðar with the large knolls, there occurs a Carex mjrri
with small knolls. The damper central parts have a level surface
without knolls and consist of a mosaic of formations which are
fairly distinct and visible at a distance by the different tinges tliey
communicate to the landscape. The knolly Carex mjrri may send
out darker stripes into the mýri, while the level mjrri itself consists
of yellowish-green patches with Carex rostrata as the dominant,
wliite patches in which Eriophorum polystachyum in fruit dominates,
brown patches with Carex rariflora, and smaller or larger eollections
of water.
According to the degree of moisture of the soil, three zones ol'
moisture may be distinguished; tlie knolly Carex mýri on the least