616 



A. HESSELBO 



Lava-clefts. The caves, clefts and cavities which occur eveiy- 

 where in the lava-fields contain a Bryophyte vegetation very rich 

 in species. In the broader clefts and in the lava-vesicles (Helgi 

 Jonsson's "Herb-cavities", 1900, p. 90) the bottom is often covered 



Fig. 37. Lava-clel't near Tliiiigvellir ( Almannagja). The lava-blocks are 

 quite covered with Rhacoinitriiun Itijpnoides. 



with ferns and flowering piants, and especially in deeper clefts, or 

 where the bottom is covered with loose blocks, Ihere is also found 

 a continuous carpet of mosses and liverworts in which Hylocominm 

 spp. (H. proliferinu , II. parietiniim , H. loreiim, H. sqiiarrosum and 

 H. triquetriinij together with species of Rhacomitriinn, Hypnuni and 

 Dicranum play a prominent part, and are usually much interwoven 

 with liverworts such as Lophozia lycopodioides, L. quinqiiedentata, 

 L. Knnzeana, Cephalozia spp., Aliciilaria scalaris, Ptilidiiim ciliare, etc. 



