The Botany of Iceland - 01.12.1930, Síða 186

176
H. M0LHOLM HANSEN
to distinguish between a series of zones, a lower and an upper high-
land zone, and a nival zone.
The lines between these zones can be drawn approximately as
follows. The lower highland zone extends from the 300 m curve
to the 600 m curve and has a Ch percentage of from 20 to 25;
the upper highland zone extends from the 600 m curve to the 800 in
eurve and at its upper limit has a Ch percentage of 40; the nival
zone is the zone between the 800 m curve and the snow-line; it
has a Ch percentage of 40—-50. Even though the position of the
limits of the zones must be taken with some reservation, they agree
well with conditions in the adjacent countries. Thus in Scotland
the 20 p. c. Ch biochore lies at c. 800 m above sea-level, in the
Faeroes at c. 500 m, in Greenland the 20 p. c. Ch biochore lies at
the level of the sea in 60—61° N.
4. An investigation of the peculiarities of the flora in the separate
parts of the country and the altitudinal zones shows that the differ-
ences are especially due to differences in temperature. The differ-
ences in the vegetation are likewise due to this factor.
The temperature of the soil differs according to the degree of
snow-covering and water-covering, though in different ways. In the
winter the geiri vegetation with its constant snow-covering as well
as the flói vegetation with its constant water-covering are protected
from the frost. Hence the result in both cases is a vegetation con-
sisting principally of southern species, even though the two areas
have not one species in common, while the snow-bare vegetation,
melar and mosathembur, which is most exposed to the cold of
winter, consists principally of arctic species, and the intermediate
areas, mo, jaðar, and mýri, both as regards environment and bio-
logical conditions, occupy an intermediate position.
In the summer the flói vegetation has a constant covering of
water, the specific heat and evaporating heat of which does not
allow of so high a degree of heating as an equal amount of heat
produces in the geiri vegetation. The result is, then, that a series
of the most heat-loving species do not occur on water-covered soil,
but only in tlre geiri. Soil with a constant water-covering is warm
in winter, but cold in summer. The soil with a constant snow-
covering in the winter is warm both summer and winter; both these
circumstances are strikingly manifested in the composition of the
vegetation.
The sequence dry, moderately moist, and moist soil, or mo,