The Botany of Iceland - 01.12.1930, Qupperneq 145

STUDIES ON THE VEGETATION OF ICELAND
135
now relatively cold water to heat, while in the fór mýri there will
be a constant amount of water to be heated, and the result will
be that in tlie summer the temperature of the fór mýri will
be higher than that of the halla mýri. Which will be best
for the yegetation must depend on the relative lengths of summer
and winter. Where summer is the longer season, the result will
be a relative cooling of the locality in question and a stronger
cooling than that whicli is conditioned by stagnant water. Where
winter is the longer season, the locality in question will offer favour-
able temperature conditions for the vegetation, even though the
summer, short as it is, must also exert its influence.
The former conditions prevail in Denmark, the latter in Iceland.
For Denmark A. Mentz (1912) has shown that the Paludella bog
is tenanled by a series ol' northern-alpine species not found elsewhere
in this country. Thus the Paludella bog offers more favourable
growth conditions to arctic plants than other types of bogs. The
same is the case in Iceland. In the halla mýri at Lækjamót the
quantity of A 2 species is considerably higher than in the corre-
sponding fór mýri zoneá in the south country, wliile tlie quantity of
A 2 + A 1 species is higher in the lialla mýri ol the valley slopes
Iban in the fór mýri of the valley bottom.
Hence the cold water peculiar to the halla mýri in
Ihe summer has even in Iceland a noticeable influence
°n the vegetation and gives it an arctic character.
The elfect on the vegetation of the warm water in winter is,
however, much stronger.
If, in a fór mýri series, we pass from the drier to the more
moist zones, the E 3 percentage lias practically the same value
Hiroughout the zones until we reach the very wettest, when it shows
a very great rise. In the halla mýri series the E 3 percentage has
its lowest value in the drier zones, whence it rises steadily until
it attains its highest value in the dampest zone.
In the fór mýri series E 2 atlains its highest value in tlie driest
moderately moist zones (mo and jaðar), whereas, in the dampest
zones (mýri and flói), it has decreased much or is entirely absent.
in the halla mýri, on the other haud. the E 2 percentage rises on
the passage from dry to moist soil; where there is the highest degree
°f nioisture, the E 2 percentage is highest.
This difference between the halla mýri and the fór
mýri is most naturally explained if we assume that it is