PHYSICAL GEOGRAPHY IH5 



with the birch region , and it probably rarely extends higher than 

 300400 metres above sea-level as an aggregate plant-formation ; but 

 several of the different species of which the heather-moor is com- 

 posed extend far higher up on the mountains without forming any 

 heath-like associations, occurring as a few individuals only. 1 found 

 Vaccininm uliginosum at the highest level (729 metres) near Sydri 

 Pollar, and also Dryas octopetala at the same place; Empetrnm ni- 

 grnm extends to a similar height, and I came across a stunted spe- 

 cimen even on the top of Botnssulur at an altitude of 1108 metres. 

 Cassiope hypnoides extends to a great height also; it is found, among 

 other places, on Hlidarfjall at 790 metres above sea-level, and may 

 perhaps extend even higher. Loiseleufia procumbens, on the other 

 hand, did not occur at a higher level than 400 500 metres. Cal- 

 luna viilgaris, Arctostaphylus uva ursi and Vaccinum Myrtillns were 

 found near Myvatn at an altitude of about 400 metres, but I do 

 not think they extend higher than the limits of the heather moor. 

 Above the upper limit of the birch region an osier or a wil- 

 low region may be said to occur in the centre of the country 

 at an altitude of 500 800 metres, in other places somewhat lower - 

 where willows are dominant among the woody plants, although they 

 have their greatest distribution at a far lower level, in the birch re- 

 gion itself. At this altitude they do not form any coppice proper, 

 but occur as flat expanses of low prostrate shrubs. Above the birch 

 region it is especially Salix herbacea, S. lanata and S. glauca which 

 are the dominants; Salix phylicifolia retires, although small speci- 

 mens of the latter also are now and then met with even at this al- 

 titude. Salix lanata, and to some extent S. glauca, occupy large 

 areas of the lower parts of the plateau, e. g. in Fjallasveit, Myvatn- 

 soraefi, Sudurarbotnar, and several other places; they are of great 

 importance to sheep-breeding, and in some places quantities of wil- 

 low leaves are gathered as winter- fodder for sheep and cattle; in 

 the lowest part of this zone Betula nana occurs now and then. In 

 the centre of the country above 800 900 metres and up to the 

 snow-line at an altitude of 1000 1400 metres, mosses and lichens 

 are undoubtedly the dominant plants, although a few widely scat- 

 tered phanerogams also occur. Salix herbacea extends also through 

 this region to the snow-line ; here and there, the most hardy of the 

 previously mentioned rocky-flat plants occur as somewhat scattered 

 individuals, but the main vegetation consists of mosses, although 

 these do not occur in any great abundance compared with the vast 



The Botany of Iceland. I. 21 



