980 



scree or talus of fallen blocks and débris which is found at the 

 base ol" steep mountain precipices (see Fig. 186). They offer ex- 

 tremely good conditions for the growth of mosses, as the piants 

 are well sheltered among the blocks from excessive insolation. The 

 »Ur«, like the cliff-face, has a scanty amount of loose soil lodged 

 among the blocks; it is also not easily accessible for sheep. An 

 »Ur« in its earlier stages is completely dominated by mosses, later, 

 as it becomes older and more overgrown, soil accumulates chiefly 

 by the decay of the large moss-cushions; the higher piants may 

 then become dominant and lead to the formation of other plant- 

 associations, for example the grass-slope. The unstable character 

 of the »Ur« must not be forgotten as an important factor which 

 operates against this development. Fresh fragments and blocks 

 are constantly falling down to destroy the existing vegetation, and 

 at the same time to form a fresh terrain. An example of the ve- 

 getation of the »Ur« will show, how much it resembles that of the 

 »Gjov«. 



On the east-side of Nolso an extensive »Ur« (see Fig. 186) 

 has formed at the base of the mountain-mass (200 — 800 m. in heighl) 

 constituting the larger southern part of the island. Part of this 

 »Ur« inhabited by sea-fowl has that type of plant-covering described 

 in more detail in other paris of this papcr as the vegetation pecu- 

 liar to sea-fowl-cliffs (see p. 894 and p. 1004). The part of the »Ur« 

 not used as a nesting-ground carries a very luxuriant moss-carpet from 

 which the species recorded below were taken. Growing in the 

 moss-sward there w^as also a rich flora of higher piants, Oxyria, 

 Rumex acetosa and Festuca rnbra being the more dominant. 



The following species were nlso noled: Poa trivialis, Saxifraga 

 caespitosa, Cerastium vulgare, Cystopteris, Draba incana, Polypodium 

 valgåre, Sagina procumbens, Stellaria media, Taraxaeum sp., Epilobium 

 alsinifolium, E. lactillorum, E. montanum, Cardamine silvatica, Poa glauca. 

 Agrostis vulgaris, Sedum rhodiola, Poa alpina, Veronica serpyllifolia, 

 Festuca ovina vivipara, Alchimilla fdicaulis, Poa annua, Euphrasia sp., 

 Veronica officinalis and Cerastium tetrandrum; allogether 25 phanero- 

 gams and 2 ferns. 



Among the mosses coUected, the following species were most 

 common: FruUania tamarisci, Metzgeria fnrcata, Spbagmim subnitens, 

 Pohjtrichiim iirnigenim , Grimmia hypnoides, Isotheciiim teniiinerve, 

 Hylocomiiim squarrosiini, H. triqiietnim, H. prolifenim, Stereodon 

 ericetorum. 



The less common species were Diplophyllum albicans, Jungermannia 



