16 H. MØLHOLM HANSEN 
lower and lower, while the winter grows colder and colder. At the 
same time the flora shows a greater and greater paucity of species. 
Unfortunately Stefånsson's “Flöra Islands” gives no upper limit 
for the individual species, and as far as Iceland is concerned, only 
very few authors have stated at what altitudes they have found the 
plants collected by them. Thoroddsen (1914) has given most in this 
respect. By comparing what is found in the literature concerning 
the occurrence of the plants in the highland tracts with my own 
notes, but especially thanks to a long series of flora lists courteously 
left at my disposal by Mr. Pålmi Hannesson, I have been able to 
work out the biological spectra of the highland tracts of Iceland 
given below, divided into zones of 100 m each, from 300 m to 1200 m, - 
the highest locality in which plants have been found. 
While 375 species of vascular plants have been found in the 
whole country, only 224 species have, up to the present, been found 
above the 300 m curve, and only c. 100 species above the 600 m 
curve. Going higher still, we find only 40 species above the 800 m 
curve, and the number is further reduced when we reach the snow- 
line above which all higher plant life is excluded. It applies to 
Iceland as to other arctic regions, the Faeroes, northern Norway 
and Greenland, that only a limited number of species has any lower 
limit, while most of the species decrease as we go upward and 
sooner or later reach their upper limit. The following species are 
of common occurrence right up to the snow-line: — Luzula arcuata, 
Elymus arenarius, Poa glauca, P. alpina, Festuca ovina, Salix glauca, 
S. herbacea, Oxyria digyna, Cerastium alpinum, Silene acaulis, S. ma- 
ritima, Ranunculus glacialis, Arabis petræa, A. alpina, Empetrum ni- 
grum, Saxifraga groenlandica, S. oppositifolia, S. nivalis, and Armeria 
vulgaris. With few exceptions all the above-mentioned species are of 
common occurrence in Greenland right up into the northern parts. 
From considerations of space the species lists are not included. 
The biological spectra calculated from them are given in table 3. 
There is a difference in the occurrence of the individual life forms. 
Some show a decrease as we go upwards, others increase, and others 
again are constant. The H percentage is fairly constant through all 
zones, c. 50. Pt, G, HH and Th decrease strongly as we go upward; 
above the 800 m curve these types have only been noted a few 
times. With respect to their content of these life forms, various 
differences may be shown to exist between the various zones, and 
possibly the highland tracts between 300 and 800 m may by means 
