THE BRYOl'HYTA OF ICELAND 663 



Cinclidium stygium, Meesea triquetra, Palndellasqnarrosa, Thnidiiim 

 lanatnm, Hijpnnm exannnlatnm, H. Richardsonii, H. sarmentosum and 

 H. alpestre occur far more abundantly in the northern half of Ice- 

 land than in the southern, and are often the most abundant con- 

 stituents of the vegetation. 



Dicranum congestnm, which is one of the most commonly oc- 

 curring species in North and East Iceland and occur there in 

 numerous forms, is far more rare in South and West Iceland, and 

 is evidently absent from North-west Iceland. 



j 



A rather considerable number of species, which are most fre- 

 quent in South and West Iceland, decrease in frequency throughout 

 East Iceland, and are absent from, or are rarer in, North Iceland, 

 for instance Scapania dentata, Anoectangium compactum, Grimmia 

 torquata, Rhacomitrinm heterostichum, R. fascicnlare, Amphidinm Mon- 

 geottii, Mnium Seligeri, Diphyscium sessile, Hijpmun filicinum, H. cn- 

 pressiforme, Hylocomium parietinum and H. triqnetrum. 



South Iceland. The vegetation is primarily characterized 

 by the presence of numerous meridional species, of which those 

 with a frequency of 3 4 constitute an essential part of the moss- 







covering. 



Fegatella conica and Rebonlia hemisphcerica in company with 

 Preissia commntata and Marchantia polymorpha form special Mar- 

 c/?a/i/zaceo?-associations on damp shady tuff-faces. Lejeunea cavifolia, 

 Madotheca Cardoeana, Barbula cylindrica, Mnium serratnm, M. nndn- 

 latum, Catharinea nndnlata, Thnidiiim tamariscinnm, T. delicatulum, 

 T. Philibertii, Eurhynchium piliferum, E. Swartzii, Rhynchosteginm 

 rnsciforme , Scleropodinm pnrnm, Thamninm alopecnnim, Hijpmim 

 mollnscnm and H. commntatnm are the most frequently occurring 

 species in SW. Iceland. Of the boreal Bryophyta Haploiia riparia, 

 Hymenostylinm cnruiroslre, Grimmia torqnata and Plagiobrynm Zierii 

 are most widely distributed in South Iceland; but this is no doubt 

 chiefly due to the fact that a suitable substratum (tuff) abounds. 



The Alpine species Dicranum Andcrsonii, D. fill vellum and Bry- 

 oxiphhim norvegicnm are common in the tuff districts of South Ice- 

 land, but have not been found in other parts of the country. 



Several ubiquists occur more frequently and abundantly in South 

 Iceland than in the other districts, for instance Mninm Seligeri, Anti- 

 trichia curtipendiila, Hypnnm palnstre, H. cnpressiforme, Hylocomium 

 lorenm, H. triqnetrnm and H. parietinum. These species ascend only 

 exceptionally above the limit of the birch. 



