LICHENOLOGY OF ICELAND 191 
Fruticose Foliaceous | Crustaceous Number 
lichens lichens |  lichens of species 
Icelandic Grimmia carpets.. 61 %o 28 9/9 11 % 18 
Danish = — .. 100 % 00 00 5 
I have no means of determining with certainty the quantitive 
difference, frequency and mass-occurrence (in weight). But a first- 
hand, direct consideration shows clearly enough, that the Danish 
bogs are very poor in lichens, whilst the lichen-wealth is far more 
considerable in Iceland. 
d. The Grass Vegetation. 
The majority of the grasses of Iceland belong probably to the 
same growth-form and are hemicryptophytes. The grass-covered 
areas — the grass-vegetation — may consequently be defined as 
areas containing a hemicryptophyte-vegetation with a very high 
frequency-percentage, in favourable cases — perhaps even most fre- 
quently — with a grass-frequency percentage (F °/o) 100. But con- 
sequently the areas contain many other plants besides grasses, for 
instance a larger or smaller number of chamephytes, mosses, 
lichens, ete. 
The grass-vegetation occurs abundantly everywhere on the island; 
no horizontal limit (compare wood-limit) towards the Arctic regions 
occurs. 
On the other hand, there is a vertical limit, which, however, 
I cannot state precisely in metres, as I myself have not any definite 
measurements, nor have I seen any in the works of other authors. 
This much however is known, that it is chiefly the low-lying parts 
of the mountains and the lowlands which can support grass-carpets, 
while the high land is devoid of continuous grass-carpets. 
With regard to the relation between the grassland and the 
ground-water level, the investigations published are not exhaustive 
enough to be able to give us a clear view on the subject. It is 
known, for instance from H. J6nsson’s investigations, that low- 
lying, clayey sea-shores are in many cases covered with Gtyceria 
marilima provided the ground is occasionally inundated by the sea. 
