STUDIES ON THE VEGETATION OF ICELAND 65 
number of species and density are comparatively high, on an average 
c. 40 species in 25 sq. m. with a density of ec. 14. The southern 
species play a much greater part than the arctic species; of the 
life forms H predominate with an average percentage amount of 
more than 50. Ch attain their minimum here; both above and 
below they constitute a larger percentage amount of the vegetation 
than here. The G percentage is somewhat higher than in the mo. 
With regard to the floristic composition, we find not only a 
number of species from the mo, such as Empetrum nigrum, Vac- 
cinium uliginosum, Salix herbacea, Polygonum viviparum, Thalictrum 
alpinum, Agrostis canina, Festuca rubra, F. ovina, and Carex rigida, 
but also a number of species which must be said to be peculiar 
to the jadar. Of these Deschampsia cespitosa, the typical dominant 
for the jadar, must especially be noted, even though its F.- percentage 
is not always very high. Further Agrostis tenuis, Carex sparsiflora, 
C. capitata, Taraxacum officinale, Cardamine pratensis, and Viola 
palustris, as also the Salix species, S. phylicifolia and S. lanata. Most 
of these species attain their maximum development here. Of plants 
peculiar to the myri Carex Goodenoughü is the only one which 
plays any great part in the jadar vegetation. 
The Salix Myri. Table 15 A—B, 4—6. 
Similarly to the jadar this formation has a large average 
number of species and high average density, though not as high 
as in the jadar. While grasses were dominant in the jadar here 
it is the Cyperaceae, and the result is a great decrease in the H 
percentage and a corresponding increase of the G percentage in the 
biological spectrum. HH are gradually gaining ground and are 
represented by c. 6—8 p.c. in the spectrum. The Ch percentage is 
somewhat higher than in the jadar. The proportion of A and E 
species is practically the same for this and the above-mentioned 
formation, but there is a displacement within the subgroups. The 
E 2 percentage is comparatively high in the former, considerably 
lower in the latter formation. 
Floristically the Salix myri differs from the jadar in that the 
grasses play a very slight part, while the Salix species are the same. 
From the Betula nana myri it is distinct by the absence of the 
characteristic species of that formation, Belula nana, but it has the 
same cyperaceous flora. The dominant species are Garex Goode- 
noughit, Eriophorum polystachyum and the Salix spp. especially 
The Botany of Iceland, Vol, III, 5 
