STUDIES ON THE VEGETATION OF ICELAND 147 
I a, (mosathembur); from here its value decreases until it attains 
its minimum together with the maximum of the E per- 
centage in the class with the deepestsnow-covering. The 
proportion of the average F.-percentages of the two species groups 
in the class most bare of snow is as 83 to 17, in the class with 
the deepest snow-covering as 34 to 66. 
The variations in the distribution of the individual sub-groups 
are closely correlated to the variations in the distribution of the 
main groups. Å 3 attains its highest value in the highest class and 
thence the F.-percentage decreases steadily as we pass downwards 
through the classes. It shows the following change: 70 >48 — 35 — 20. 
The maximum of the A 2 species lies lower in the scale, 
that of the Al species still lower. 
The maximum of the latter group is in class II, corresponding 
to the normal snow-covering of the country. In this class the E 
species, too, attain their maximum, though not a very pronounced 
one. The lower E sub-groups, E 3, E 2, and E 1 all have their 
maxima in class III, corresponding to the fact that the species 
thrive best where there is a deep and constant snow-covering 
throughout the winter. Here E 3 is most abundant, E 2 is somewhat 
less dominant, and E 1 occurs only sparsely. 
Thus to the 3 classes of snow-covering there corresponds a 
vegetation quite definitely stamped by its environment. In class I 
it consists chiefly of A 3 species, less of A 2 species, in class II of 
A 2, A 1, and E 4 species, and in class III of E 3, E 2, and 
E 1 species. 
The snow- bare vegetation of Iceland thus consists of 
species with a pronounced northern distribution, the 
vegetation with a constant snow-covering of species with 
a pronounced southern distribution, and the vegetation 
with a normal snow-covering is composed of species be- 
longing to tracts the climate of which corresponds to 
that of the country. 
Conditions in the individual localities entirely confirm the facts 
stated above, both in respect of the quantitative distribution in the 
main groups and the position of the maximum in the individual 
subgroups. A decrease in the amount of snow will always tend to 
render the vegetation more arctic, an increase will render it more 
southern, 
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