THE BRYOPHYTA OF ICELAND 625 



pages some examples of the rocky-flat vegetation will be given, it 

 is, however, only in NW., SW. and in a few districts of N. and E. 

 Iceland, that this vegetation has been somewhat closely investigated, 

 whilst the whole of the interior high land is quite unknown as far 

 as bryology is concerned. 



1. South Iceland. Barkarstadr, dry stony flat at an alti- 

 tude of 350 metres: Scattered cushions of Schistidium apocarpum v. 

 rufescens, Rhacomitrium hypnoides, R. fasciculare, Dicranoweisia cris- 

 pula and Andrecea petrophila. 



2. Gravelly flat on Esj a, at an altitude of about 550 metres: 

 Moss carpet, partly torn up by the wind, composed of Hijpmuu 

 uncinatiim and Schisiidium apocarpum, scattered in which occur 

 rocky-flat plants such as Silene acaulis and Saxifraga oppositi folia. 



3. Akureyri, rather dry gravelly flat, at an altitude of about 

 900 metres : Moss carpet composed of Rhacomitrium hypnoides, Hyp- 

 num uncinatum, Hylocomium proliferum, Camptothecium nitens, Aula- 

 comnium turgidum, Dicranum congestum, Didymodon rufus, Eurhyn- 

 chium diuersifolium , Lophozia quinquedentata and L. quadriloba. 

 Flowering plants entirely absent. On a dry slope at an elevation 

 of about 770 metres there grew Lescuraea Breidleri, Brachythecium 

 glacials, B. reflexum, Dicranum Starckei, Lophozia lycopodioides and 

 L. alpestris, and on damp gravelly flats near the snow line there 

 grew Pohlia gracilis (abundantly), P. cuciillata, P. commutata, Poly- 

 trichum sexangulare, Oncophorus virens, Dicranum Starckei, Lophozia 

 alpestris, L. uentricosa, L. quinquedentata, L. quadriloba, Pleuroclada 

 albescens and Anthelia Juratzkana. 



Salix herbacea-Sibbaldia Vegetation (Helgi Jonsson, 

 1900, p. 33) occurs everywhere in damp depressions and on slopes 

 where the subsoil consists of a layer of clay. This vegetation has 

 its main distribution from 300 400 metres to about 700 metres, 

 and here, close to the snow line, it is replaced by pure moss-com- 

 munities, in which Salix herbacea occurs but scantily and at last 

 disappears entirely. The moss community consists of a low, dense 

 carpet of mosses and liverworts, interwoven with creeping stems of 

 Salix herbacea, so that only the tips of the shoots protrude above 

 the carpet. The most abundant constituent of this moss carpet is 

 usually a low-growing form of Hypnum uncinatum or of Dicranum 

 Starckei in association with Rhacomitrium canescens, Dicranum molle, 

 Conostomum boreale, Potytrichum sexangulare, Anthelia Juratzkana, 

 Pleuroclada albescens, species of Lophozia, and sometimes other species. 



