The Botany of Iceland - 01.12.1930, Side 89

Sl'UDIES ON THE VEGETATION OF ICELAND
79
The special association of the flag vegetation with the Icelandic
lowlands is, however, probably more apparent than real, for the
flag vegetation seems to be a northerly, highly speciflc oífshoot of
a series of pecnliar Th formations which are met witli in Denmark,
too, on moderately moist soil. These Th formations have not,
however, been more closely investigated though they had early at-
tracted the attention of botanists by their peculiar flora. The fol-
lowing are some of the most characteristic species: Radiola milli-
grana, Linum catharticum, Scirpus setaceus, Centunculus minimus,
Mi/osiiriis minimus, Gnaphalium uliginosum, a numberof small .liincus
spp. J. bufonius, ./. tenuis, J. capitatus, and ./. pggmœus, besides Bul-
liarda aquatica. On slightly damper soil we meet with species sucli
as Subularia aquatica, Pilularia globulifera, Elatine hexandra, Montia
spp., Ranunculus reptans, Juncus supinus, Peplis. portula, Limoselta
aqnatica. This ílora is especially met with on dunes, on damp moors,
or in badly cultivated rye fields, and occurs frequently at any rate
in western Jutland. In meadows, especially littoral meadows, in
addition to a number of species already mentioned, we meet with a
number of Gentiana spp., Rhinantlius, Euphrasia, Odontites, and Sagina
species. Even in damp birch woods Th formations may be met
with consisting of Geranium Robertianum and Impatiens noli tangere.
However, it is not only the characteristic life form that is com-
mon to the Danish Th formations on soil of moderate moisture
and the Icelandic flag, they have also a number of species in common;
thus the following species recorded from the flag are found in Den-
mark in company with the above-mentioned species. Ranunculus
reptans, Subularia aquatica, Juncus bufonius, J. suþinus, Triglochin
patustre, Agrostis alba, Equisetum arvense, Sagina nodosa, Parnassia
palustris, Linum catharticum, Rhinanthus minor, Spergula arvensis,
Stellaria media, Scirpus pauciftorus.
A comparison of these lists may perhaps be of aid in tracing
the forces which give rise to the flag in Iceland. The causes for
the occurrence of the Th formations on moderately moist soil in
Denmark must be sought partly in fluctuations in the level of the
water, partly in the frost phenomena present here and resulting in
crumbling and aeration of the soil. When the moderately moist
Th formations attain their finest development in the Icelandic low-
lands which are sub-arctic and Atlantic in character, this must no
doubt be due to a corresponding increase in these factors, especially
the frost phenomena.