STUDIES 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 specific offshoot of 
a series of peculiar Th formations which are met with 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, 
Myosurus minimus, Gnaphalium uliginosum, a number of small Juncus 
spp. J. bufonius, J. tenuis, J. capitatus, and J. pygmeeus, besides Bul- 
liarda aquatica. On slightly damper soil we meet with species such 
as Subularia aquatica, Pilularia globulifera, Elatine hexandra, Montia 
spp., Ranunculus reptans, Juncus supinus, Peplis portula, Limosella 
aquatica. This flora 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., Rhinanthus, 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. supinus, Triglochin 
palustre, Agrostis alba, Equisetum arvense, Sagina nodosa, Parnassia 
palustris, Linum catharticum, Rhinanthus minor, Spergula arvensis, 
Stellaria media, Scirpus pauciflorus. 
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. 
