THE BRYOPHYTA OF ICELAND 663 



Cinclidiiimstijgium, Meesea triquetra, Pahidella sqnarrosa, Thiiidiiim 



lanatiim, Hypnum exaniudatiim, H. Richardsonii, H. sarmentosiim and 



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



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



stituents of the vegetation. 



Dicraniim congestum, which is one of the most commonly oc- 

 curring species in Noiih and East Iceland and occur there in 

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

 is evidently absent from North-west Iceland. 



A rather considerable nuniber of species, which are most frc- 

 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, Anwctangiiiin compactiim. Grimmia 

 torqiiata, Rhacomitrinm heterostichiim, R. fascicidare, Amphidiiim Moii- 

 geottii, Mninm Seligeri, Diphyscium sessile, Hypniim filicimim, H. cii- 

 pressiforme, Hylocomium parietinnm and H. triqiietriim. 



South Iceland. The vegetation is primarily characterized 

 by the presence of numerous meridional species, of which those 

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

 ■covering. 



Fegatella conica and Rebonlia hemisphærica in company with 

 Preissia commiitata and Marchantia pohjmorpha form special Mar- 

 c/ja/}//acecp-associations on damp shady tuff-faces. Lejeiinea cauifolia, 

 Madoiheca Cardæaim, Barbnla cylindrica, Mninm serratnm, M. nndn- 

 latum, Catharinea nndnlata, Thnidinm tamariscinnm, T. delicatnlnm, 

 T. Philibertii, Enrhynchinm pilifernm, E. Swartzii, Rlujnchosteginm 

 susciforme, Scleropodinm pnrnm, Thamninni ahpecnrnm, Hypnnm 

 nioUnscnm and H. commntatnm are the most frequently occurring 

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

 Hymenoslylinm cnrviroslre, Grimmia torqnata and Plagiobrynm Zierii 

 are most widely dislribuled in South Iceland; but this is no douht 

 chiefly due to the faet that a suitable substratum (tufT) abounds. 



The Alpine species Dicrannm Andersonii, I), fnloellnm and Bry- 

 oxiphinm norvegicum are common in the tutT districls of South Ice- 

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



Several ubiquists occur more frequently and abundantly in South 

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

 trichia cnrlipendnla, Hypnnm palnstre, H. cnpressiforme, Hylocominm 

 lorenm, H. Iriqnetrnm and H. parietinnm. These species ascend only 

 ■exceptionally above the limit of the birch. 



