620 A. HESSELBO 



occurs on lava-blocks and Trichostoiniim littorale on the sides of the 

 clefts. Scapania dentata was frequent on the ground at the bottom 

 of shady, damp clefts. Reboiilia heinisphærica and FriiUania fragili- 

 folia were found in a single spot on the walls of caves. 



On the ground at the bottom of deep, dark caves, shade-forms 

 are often found, especially of Hepaticæ, with greatly elongated shoots 

 and expanded, widely scattered leaves. Here, it was especially the 

 following species which were common : Cephalozia biciispidata, Pleuro- 

 clada albescens var. islandica, Alicularia scalaris and Blepharostoma 

 trichophylhim, occasionally also Preissia commiitata and in a single 

 spot Ditrichum homomaUum and Oligotrichiun hercynicum. 



Svinahraun is situated about 30 km. south-east of Reykjavik, 

 and about 250 — 300 metres above sea-level. The part which has 

 been investigated is situated in the neighbourhood of the farm Kol- 

 vidarhol, and is of block-lava consisting of blocks and flags piled 

 up into wild-looking heaps, some 10 metres high, with numerous 

 clefts and caves. The top part is covered with an unusually thick 

 and luxuriant mat of Rhacomitriiim hypnoidcs from which olher 

 mosses and flowering piants are almost absent. On the walls there 

 grew Amphidiiim MoiigeotliL Tortella tortuosa and Anæctangiiim com- 

 pactiim. In caves and clefts there was a Bryophyte carpet consisting 

 of Hypniim uncinatum, H. callichroiim, Hylocomiiim loreiini, H. proli- 

 fenim, H. parietinnm, Lophozia qiiinqnedentata, L. lycopodioides, L. 

 Flærckei, Plagiochila asplenioides and Ptilidiiim ciliare. Diplophylliim 

 albicans was extremely common everywhere. In addition to the 

 above the following were found more or less abundantly: Polytrichum 

 alpinum, Diphysciiim sessile, Bartramia ityphylla, Conostomum boreale, 

 Mniiim orthorrhynchnm, Pohlia criida, P. commiitata, Mniobryiim albi- 

 cans, Bryiim elegans, Amphidiiim lapponiciim, Rhacomitriiim siideticnm, 

 Schistidiiim gracile, Fissidens osmiindoides, Dicraniim scoparium, Di- 

 stichium montaniim, Sphagnum teres, Lophozia alpestris, L. qiiadriloba, 

 Alicularia scalaris, Anthelia Juratzkana and Blepharostoma tricho- 

 phylhim. 



It will be seen that the lava-fields here described greatly re- 

 semble each other, and that it is essentially the same species which. 

 constitute the bulk of the vegetation in all of them. Svinahraun 

 is situated on the ridge of bilis which extends along the whole 

 length of the peninsula of Reykjanes, and the climate there is ex- 

 tremely cold and damp, which is proved by the faet that it is the 

 Rhacomitriiim lieath which forms the last stage in the development 



