THE BRYOPHYTA OF ICELAND 621 



of the vegetation of the flats, and that many of the species of the 

 low land are absent. 



Unfortunately there was no opportunity of investigating the 

 lava-fields of West Iceland more closely, since unfavourable atmos- 

 pheric conditions with rain and fog, combined with a want of time, 

 made a longer stay there impossible, but the conditions appear to 

 be essentiallv the same as in South-west Iceland. 



I, 



In his description of Budahraun Helgi Jonsson has also men- 

 tioned some mosses, and, as far as is possible to judge from the 

 lists which, however, are no doubt incomplete, the conditions there 

 are exactly like those in Hafnarfjardarhraun. There also coastal 

 species are found, for instance Ulota maritima, and southern species 

 such as Eurhynchium Stockesii and Lejeunea cavifolia, and the 

 dominant species are quite similar to those in the lava-fields of 

 South-west Iceland. 



In North Iceland the Bryophyte vegetation of the lava-fields has 

 an essentially different composition from that in West and South- 

 west Iceland. All the lava-fields there are situated at a distance 

 from the coast, and at a higher level above the sea, the vegetation 

 is therefore decidedly xerophilous both on exposed surfaces and in 

 clefts and crevices. The immense lava-flats at a great height above 

 sea-level, are deserts almost entirely void of vegetation ; they have, 

 however, been very little investigated. There are to hand only a 

 few collections from Koch's tour across Odadahraun in 1912, and 

 these consist only of Tortilla ruralis, Ceratodon purpureus and Di- 

 cranoweisia crispiila, which grew here and there upon the lava. 



The onlv lava-field which has been investigated is Mvvatns- 



\J *J 



hrauii, which is about 160 years old, and upon which the farm 

 Reykjahlid stands. It was described by Gronlund in 1890 and does 

 not appear to have undergone any great change since that time. 

 The Rhacomitrium heath occurred only scantily in the depressions, 

 while the lava-cones were bare of vegetation or covered with scat- 

 tered moss-cushions and crustaceous lichens. In the intervening 

 space between the farm and the lake the following species were 

 observed : Upon the blocks and on the lava were found Tortala 

 ruralis, Ceratodon purpureus, Rhacomitrium hypnoides, Grimmia Don- 

 iana, Schistidium confertum, Dicranoweisia crispula, Polytrichum pi- 

 losum and Hypnnm revolutum, all of which were very common. In 

 sandy soil, especially in depressions, there grew Desmatodon latifolius 

 and Rhacomitrium canescens. In dark caves and clefts Lophozia 



