STUDIES ON THE VEGETATION OF ICELAND 119 
species is likewise less, 10.0 as against 14.3. The dominant or typi- 
cal species are Salix glauca, S. herbacea, Sibbaldia procumbens, and 
Gnaphalium supinum. Vaccinium uliginosum, Empetrum nigrum, and 
Salix phylicifolia have entirely disappeared. Of more or less do- 
minant species we may mention Equiselum arvense, Carex rigida, 
Deschampsia flexuosa, Agrostis canina, Festuca rubra, Rumex acelosa, 
Viola palustris, Taraxacum and Leontodon. 
Table 25 A, 5 shows the circling results for a smaller snow patch 
having a northern exposure. In its broad features this locality 
corresponds to the bottom vegetation of the large snow patches. 
Floristically there is the difference that Vaccinium uliginosum and 
Empetrum nigrum are present in the small snow patches, while 
Sibbaldia procumbens and Gnaphalium supinum are only present in 
the larger ones. 
Just as, within the myri formations, the flöi forms the extreme 
point in a sequence of changes conditioned by the length of the 
period when the ground is covered with water and the depth of 
the water-layer, so also, in the formations lying above the ground- 
water, the geiri shows a succession of changes conditioned by the 
length of time that the ground is covered with snow and the depth 
of the layer of snow. Passing from melar by way of the mo to 
geiri, the depth and duration of the snow-covering increases more 
and more. Melar is without snow or almost without snow through- 
out the winter, the mo has the snow-covering normal to the area, 
while the geiri is already covered at the first snowfall in the autumn, 
retains a deep and constant snow-covering throughout the winter, 
and only becomes bare again when the snow melts far on in the 
spring. 
Now these conditions have the following effect on the vegetation. 
Where the snow-covering is slight, it consists principally of arctic 
species and life-forms, whereas, where it is deep, it consists of 
southern species and life-forms. 
Thus melar has a Ch percentage of 52, an H percentage of 
36, an A percentage of 81 and an A 3 percentage of 55. The E 
percentage is 0. 
The mo (the knolly mo) has a Ch percentage of 38, an H 
percentage of 47, the A percentage is 71, the A3 percentage 39, and 
the E3 percentage 4. 
The geiri (the Geranium silvaticum belt) has a Ch percentage 
