STUDIES ON THE VEGETATION OF ICELAND 111 
heidi, and there 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 jadar along the banks of rivers. 
Physiognomically it resembles the jadar further inland, but floristic- 
ally it differs from it by the fact that a number of species such 
as Carex Goodenoughü, Caltha palustris, Geum rivale, Comarum pa- 
lustre, and Menyanthes trifoliata either exclusively or practically ex- 
clusively occur here, and that merely as a narrow fringe only few 
metres wide along both sides of the stream. Since in the lowlands 
the species occur both in the myri far from running water and 
along streams, their predilection for streams in the highlands can- 
not be due to any general property of these, 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 
with 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 Myri and Flöi Vegetation. Cf. figs. 21—22 and table 24 A, 
1—13. i 
The myri vegetation occurs in the dampest hollows and espe- 
cially around the numerous lakes. A depression with myri has the 
following appearance. On somewhat damper ground than the above- 
described jadar with the large knolls, there occurs a Carex myri 
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 they 
communicate to the landscape. The knolly Carex myri may send 
out darker stripes into the myri, while the level myri itself consists 
of yellowish-green patches with Carex rostrata as the dominant, 
white patches in which Eriophorum polystachyum in fruit dominates, 
brown patches with Carex rariflora, and smaller or larger collections 
of water. 
According to the degree of moisture of the soil, three zones of 
moisture may be distinguished; the knolly Carex myri on the least 
