LICHENOLOGY OF ICKLAND 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-carpei or of 

 a poorly-developed chamsephyte-heath. But beyond this, no lichen- 

 heaths proper are known, as they are described from other places 

 in Arctic Regions. 



c. Moss-vegetations. 



Whilst chamaephyte-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- 



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