STUDIES ON THE VEGETATION OF ICELAND 151 
temperature appears especially in the E group spectrum in that the 
lower E sub-groups occur abundantly on snow-covered soil, but 
are entirely absent from water-covered soil. The E 2 and E 1 species 
are such as require a high temperature to be able to thrive, and 
this requirement is only satisfied in geiri and forest. 
The A group spectrum shows a peculiar difference between the 
two types of vegetation. The A percentage is 34 in the geiri, 28 in 
the flöi. In the flöi 20 p. c. of these species are A 1 species, and 
only 8 p.c. are A 3 and A 2 species, while in the geiri the A1 
percentage is only 4, and the sum total of the A 3 and A 2 per- 
centages is no less than 30. 
The high A 3 percentage in the snow-covered vegetation and 
the low A 3 percentage in the water-covered vegetation must be 
assumed to be a consequence of difference of stability in the covering 
medium. In the flöi the water is always present, hence the vegeta- 
tion is never exposed to severe cold. Thus a condition necessary 
for the growth of A 3.species is not present. 
Compared with the water in the flöi, the snow in the geiri is 
less stable. A hard frost may set in before the first snowfall, and 
frost in the night may affect the vegetation after the snow has 
melted. This provides a possibility for the growth of the A 3 
species, hence compared with water-covered soil the A 3 percentage 
is high, but compared with snow-bare soil or a vegetation with a 
normal snow-covering, it is comparatively low. The A 3 percentage 
is higher in geiri than in forest, respectively 23 and 14, which further 
confirms the above considerations. 
Thus the difference between the species group spectra 
for water-covered and snow-covered vegetation is as fol- 
lows. The species in the species group spectrum of the 
water-covered vegetation are largely concentrated in the 
central part of the spectrum with a marked dominance 
of E species, corresponding to a favourable and fairly 
stable winter temperature, and only a slight difference 
between the winter and summer temperatures, The spe- 
cies in the species group spectrum of snow-covered soil, 
on the other hand, though also showing a preponderance 
of E species, are distributed over the entire scale in con- 
sequence of a relatively high winter and summer tempe- 
rature, and greater instability in the winter. 
As previously mentioned, the species group spectrum for the 
