LICHENOLOGY OF ICELAND 187 
This is by no means an exhaustive list of the earth-lichens of 
the plateau; it must be supplemented by several other species, the 
occurrence of which is not known very accurately, and also by 
some which will be mentioned under the description of the moss- 
carpets of Iceland; these, as we know, partially extend upwards 
into the most desolate wastes of mountain heights, and are there 
found interspersed with various species of lichens. 
b. Lichen-heaths 
of wide extent do not appear to occur in Iceland. In the above a 
couple of instances have been mentioned showing that lichens can, 
in patches, dominate the physiognomy of a Grimmia-carpet or of 
a poorly-developed chamæphyte-heath. But beyond this, no lichen- 
heaths proper are known, as they are described from other places 
in Arctic Regions. 
c. Moss-vegetations. 
Whilst chamæphyte-heaths, grass-areas and coppices all have 
their own fairly distinct horizontal limits, this is not the case as 
regards the moss-areas. These are found at all altitudes, right up 
to the snow-limit, both in the low land and in the highest plant- 
bearing high land. The moss-vegetation itself has been exhaustively 
described elsewhere in this work (Hesselbo, 1918). I shall there- 
fore occupy myself exclusively with those parts of it which are of 
importance to lichen-growth. 
Mosses differ (in a higher degree than do lichens) in their re- 
quirements as regards moisture, in that several are hydrophytes 
(Fontinalis, Sphagnum spp., etc.), whilst others suffice with intermit- 
tent supplies of water, and some are distinctly xerophytic. 
The vegetation of all areas of perpetual water-containing mosses, 
(in bogs and the like) is always devoid of lichens. 
Here therefore, only that vegetation will be discussed which, 
during a shorter or longer period of the year, is dry and contains 
lichens. This refers, consequently, almost exclusively to the Grimmia- 
vegetation in both the high and low land. But before mentioning 
these more closely I shall say a few words about the Philonotis- 
bogs on the mountain slopes. They are seen in the landscape as 
bright-green patches on mountain declivities, where springs appear 
on the surface of the ground, and are extremely common every- 
