620 A. HESSELBO 



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

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

 of shady, damp clefts. Reboulia hemisphcerica and Frullania 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 Hepaticce, with greatly elongated shoots 

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

 following species which were common : Cephalozia bicuspidata, Pleuro- 

 clada albescens var. islandica, Alicularia scalaris and Blepharostoma 

 trichophyllam, occasionally also Preissia commutata and in a single 

 spot Ditrichum homomallum and Oligotrichum 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 Rhacomitrinm hypnoidcs from which other 

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

 grew Amphidium Mougeottii, Tortella tortuosa and Anoectanginm com- 

 pactum. In caves and clefts there w r as a Bryophyte carpet consisting 

 of Hypnum uncinatum, H. callichroum, Hylocomium loreum, H. proli- 

 ferum, H. parietinum, Lophozia quinquedentata, L. lycopodioides, L. 

 Floprckei, Plagiochila asplenioides and Ptilidium ciliare. DiplophyUum 

 albicans was extremely common everywhere. In addition to the 

 above the following w r ere found more or less abundantly: Polytrichum 

 alpinum, Diphyscinm sessile, Bartramia ityphylla, Conostomnm boreale, 

 Mnium orthorrhynchum, Pohlia cruda, P. commutata, Mniobryum albi- 

 cans, Brymn elegans, Amphidium lapponicum, Rhacomitrium sudeticum, 

 Schistidium gracile, Fissidens osmuudoides, Dicranum scoparium, Di- 

 stichium montanum, Sphagnum teres, Lophozia alpestris, L. quadriloba, 

 Alicularia scalaris, Anthelia Juratzkana and Blepharostoma tricho- 

 phyllum. 



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 hills 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 fact that it is the 

 Rhacomitrium heath which forms the last stage in the development 



