LICHENOLOGY OF ICELAND 



191 



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 %) 100. But con- 

 sequently the areas contain many other plants besides grasses, for 

 instance a larger or smaller number of chamsephytes, mosses, 

 lichens, etc. 



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. Jonsson's investigations, that low- 

 lying, clayey sea-shores are in many cases covered with Gtyceria 

 maritima provided the ground is occasionally inundated by the sea. 



