THI'; MUVOI'HYTA Ol- ICKLAM) 599 



Talus of la lien blocks and débris (Urd). The con- 

 dilions for the developnient ol' [)lanls is far niDre favourable here 

 than on the slony slope, Nvhich is constanlly ex})o.sed to distnrbances 

 through the down-sliding of stones and earlh. The most xerophi- 

 lous species, viz. species of Rhacomitrium and Grimmia, Dicrauo- 

 iveisid crispiila, Orlhotrichum nipestre and Hypiuim revohilum grow 

 on the stones, while on the ground between the stones there are 

 favourable condilions for a number of species which have greater 

 requiremenls with regard to shelter, moisture and shade. The Urd 

 is therefore very rich in species, since lithophilous species are 

 found there on the blocks, and species, which grow on the ground, 

 occur between the stones, and Bryophytes belonging to heathland 

 and grassland, are found on the soil-covered stones and ledges. 



In order to show how hetcrogeneous the coniposition of the 

 Bryophyle vegetation may be, the Urd in Heljusdalur on Vest- 

 mannaey may serve as an example. The valle\' is almost semicir- 

 cular in shape, and open towards the south, and in consequence of 

 this favourable situation combined with the comparatively mild, 

 damp climate of the island , a considerable number of southern 

 species are found there, while species such as Ulota marilima and 

 Schistidiiim maritimum beloken the proximily of the sea. The rocks 

 around the valley are inhabited by numerous sea-fowls, and they 

 often rest on the blocks of the Urd, and on these spots, manured 

 by the birds, it is species of Bryum [B. argenteiim and B. capillare) 

 which particularly make their appearance. 



The fallen blocks are everywhere covered with cushions of 

 mosses and liverworts. The commonest species are Schistidiiim 

 apocarpiim, Ulola maritima, Hijpnum ciipressiforme, H. iincinatiim. 

 Orthotricluim nipestre and Ceratodon purpnreus. The foUowing 

 species were also observed on the blocks: Radiila complanata, Ma- 

 dotheca Cordæana , Plagiochila asj)Ienioidcs, Cephaloziella Hampeana, 

 Didijmodon riibelliis, '^Barbiila cylindrica, Tortella tortnosa, T. fragilis, 

 Tortula siihiilata, ""'T. miicronifolia , Distichiiim montanum, "'Orlhotri- 

 chum anomaliim, Encalypta ciliala, E. rhabdocarpa, Pohlia criida, 

 Bryum capillare, B. elegans, B. inclinatiim, B. (x'neiim , Miiiiim serra- 

 tiim, M. stellare, M. orthorrhynchiim, Myurella jiilacea , Ortholhecinm 

 intricatum, '"Tsotheciiim mynrum, Homalotheciiim sericeiim, Amhlyste- 

 ginm Spriicei, '-'A. serpens, Hypniim hamulosiim and H. revolutum. In 

 the caves formed among the stones, inlo which the light penetrated 

 but scantily, the walls were covered with light-green shining mats 



