The Botany of Iceland - 01.12.1930, Side 74

64
H M0LHOLM HANSKN'
dalur, at Björk, and at Lækjamót in the north country. The ridge
mýri I have only investigated at Lækjamót, while I had no oppor-
tunitjr of a close study of the fétmýri.
The composition of the swampý mýri in Lyngdalur and at
Björk is shown in table 15 A, 1—11.
Fig. 11 shows the appearance of the mýri at Björk. The soil
is markedly knolly, but the knolls are smaller and more scattered
tlian on the mo.
According to the degree of moisture of the soil it is possible
to distinguish between the following formations. The mýri jaðar
(the margin of the mýri) or the grass mýri is íirst met with on
passing from the mo on to the inýri. Upwards it passes inlo the
moist mo, the Calluna- Empetrum mo. The ground water liardly
ever comes up to the surface, hut the bottom is damp in spring,
winter, and autumn, whereas, in the vegetation period, it is com-
paratively dry. Outwards the jaðar passes into the dry cypera-
ceous mýri, the Salix mýri. The soil is liere considerably more
moist, in wet summers the water will perhaps cover the surface
throughout the vegetation period; normally, however, this vegetation
will not be covered with surface water the greater part of the vege-
tation period, in dry summers perhaps not at all. On the dampest
soil we find the moist cyperaceous mýri or the Betula nana
mýri. The bottom must liere be assumed to be covered with
wafer even in normal summers; in very dry summers dry bottom
may no douht be found in this formation, too. The flói, or
swamp, is met with in spots in this formation. Here the bottom
is ahvays covered with water, even in dry summers. The knolls,
so typical of the mýri, are not present in the llói, and while the
soil of the mýri is firm to the tread, rendered solid by a dense web
of Cyperaceae rhizomes, the ground in the tlói is soft and muddy,
and one moves on it in constant fear of sinking into the slush.
On a gentle slope these 4 belts will succeed eacli olher in the
sequence described above, adjoining Ihe moist mo upwards, while
outwards they will perhaps be succeeded by a collection of water,
a “tjörn” (tarn). Where the surface is more irregular, a compara-
tively moist formation will not rarelv adjoin a comparatively dry
one, while the intermediate formations are not developed.
The Jaðar Vegetation. Table 15 A, 1—5 shows the lloristic
composition of this vegetation in Lýngdalur and at Björk. The