THK HIIVOI'IIYTA OF ICELAND 585 



piants and conse(iuently develop beller than Ihe laller in loca- 

 lities which are less favourable as regards llic liglit, Tor inslance, 

 on Ihe northern sides of clells and in caves. In valleys soulhern 

 slopes are covered with grass or olher herbaceous piants, while 

 norlhern slopes are moss-grown. In the narrow lulVclefls of South 

 Iceland Ihe sides are oflen covered wilh a luxurianl moss carpel 

 consisling of Hylocomiiim spp., Tlmidiniu, Pohjtrichiiin, etc. Here 

 the snow-covering no doubt also plays an imporlant part, since bj' 

 remaining until far inlo the spring, il checks the gro^^•lh of the 

 higher piants far more than il does thai of the mosses. 



Grass land is moslly knolly, and the mosses grow abun- 

 dantly on the ground between the grasses. Here il is especially 

 species such as Hypnnm iincinatiim, Hijlocomiiim s(jii(irrosuiu, Cli- 

 maciiim dendroides, Pohjirichum alpinum and Rhacomilrium canes- 

 ceiis which are the most abundanl consliluenls of Ihe vegeta- 

 tion, but in addition to these many olher species occur, for 

 inslance Catharinea undiilata. Timmia austriacn. Tortella tortuosa, 

 Dicramim congesliim , Ditrichiim flexicaule, Distichium montaniim, 

 Bartramia ityphijlla, Rhacomitriiim hijpnoides, Hylocomiiim spp., 

 Hypnnm Lindbergii and Lophozia qninqnedentata. The composi- 

 tion of the vegetation varies according to the degree of dampness, 

 Iherefore, we somelimes find species from boggy soil and somelimes 

 xerophilous species of healhy soil inlermixed in grealer and smaller 

 quanlilies. 



Grass-slope and Herb-slope^. On the herb-slope the 

 Bryophyla are very scantily represented. On Ihe grass-slope the 

 bottom is covered wilh a more or less dense carpel of mosses and 

 liverwort^ in which the chief species are Hylocomiiim proliferiim, 

 H. parietinnm, H. sqiiarrosnm, H. rngosnm, H.lorenm, H. triqnetnim, 

 Hypnnm nncinatnm, Climacium dendroides, Camptothecinm Intescens, 

 Thnidinm delicatnlnm (S. Icel.), Mninm affine, Timmia aiistriaca, Po- 

 lytrichnm alpinnm, Pogonatnm nrnigenun, Rhacomitrinm canescens, 

 R.hypnoides, Ditrichnm flexicaule, Lophozia lycopodioides and Pla- 

 giochila asplenioides, bul besides these, many olher species occur as 

 a more casual admixture. 



On a stony substratum with a thin layer of soil mosses are 

 dominant, and phanerogams grow scatlered in the moss carpet. 

 A "moss-slope" is then developed which, as a rule, is composed of 

 the same species as those found on the grass-slope, most frequently 



* See footnote in Thoroddsen's Physical Geography of Iceland, ante p. 330. 

 The Botany of Iceland. Vol. I, part II. 38 



