46 H. MØLHOLM HANSEN 
owing to the fact that polygon-formation and solifluction are be- 
ginning to be prominent. The vegetation appears changed not only 
because species already present occur with greater frequency but 
also because new species have been added. The number of species 
has almost been doubled, the density has increased from c. 2—4 to 
c. 6—9. In table 10, 2—3 and 6—7 show the composition of the 
species on older, more stable tracts of melar. The increase falls 
especially to Ch. Of new species we may particularly mention Dryas 
octopetala, Empetrum nigrum, Cassiope hypnoides, Loiseleuria procum- 
bens, Luzula arcuata, and a number of mo plants. Dryas octopetala 
only occurs in melar on Lyngdalsheidi, not, as is the case in the 
highlands and the north country, in mo. The presence of Loiseleuria 
and Cassiope would seem to show that the localities referred to not 
only differ from the abovementioned in age but also by being more 
snow-covered in winter. 
On Lyngdalsheidi the melar vegetation is not very widespread, 
at any rate compared with the mo. In other parts of Iceland, how- 
ever, it plays a prominent part in the physiognomy of the land- 
scape, not only in the lowlands where it occurs in greatest quantity 
near the sea, but also and especially in the highlands where the 
country for miles is covered exclusively with the melar vegetation. 
At the higher levels it is almost the sole prevailing vegetation. 
The melar vegetation or fell field is an arctic type of vegetation 
and has its greatest distribution north of Iceland, though it occurs 
at high levels in the Faeroes, Scotland and Scandinavia. 
In spite of the great physiognomic differences be- 
tween the melar and the mosathembur vegetation, the 
two types must be included in the same class, charac- 
terised with regard to environment by not being covered 
with snow in the winterandbiologicallybythecompara- 
tively great quantity of Ch and A species, especially A3 
species. Both types have their main distribution in arc- 
tic regions about, above, or north of the 20 p.c. Ch bio- 
chore. The two types show a striking difference in re- 
gard to their biological spectra, the melar vegetation 
having a comparatively high H percentage and a low 
G percentage, the mosathembur vegetation a high G per- 
centage. 
