THE BRYOPHYTA OF ICELAND 58") 



plants and consequently develop better than the latter in loca- 

 lities which are less favourable as regards the light, for instance, 

 on the northern sides of clefts and in caves. In valleys southern 

 slopes are covered with grass or other herbaceous plants, while 

 northern slopes are moss-grown. In the narrow tutT-clefls of South 

 Iceland the sides are often covered with a luxuriant moss carpet 

 consisting of Hylocominm spp., Thnidinm, Polytrichum, etc. Here 

 the snow-covering no doubt also plays an important part, since by 

 remaining until far into the spring, it checks the growth of the 

 higher plants far more than it does that of the mosses. 



Grassland is mostly knolly, and the mosses grow abun- 

 dantly on the ground between the grasses. Here it is especially 

 species such as Hypmim uncinatum, Hylocomium squarrosum , Cli- 

 maciiim dendroides, Polytrichum alpinnm and Rhacomitrium canes- 

 cens which are the most abundant constituents of the vegeta- 

 tion, but in addition to these many other species occur, for 

 instance Catharinea nndulata , Timmia anstriaca, Tortella tortnosa, 

 Dicranum congestum , Ditrichnm flexicaule, Distichium montanum, 

 Bartramia ityphylla, Rhacomitrium hypnoides, Hylocomium spp., 

 Hypmim Lindbergii and Lophozia quinqiiedentata. The* composi- 

 tion of the vegetation varies according to the degree of dampness, 

 therefore, we sometimes find species from boggy soil and sometimes 

 xerophilous species of heathy soil intermixed in greater and smaller 

 quantities. 



Grass-slope and Herb-slope 1 . On the herb-slope the 

 Bryophyta are very scantily represented. On the grass- slope the 

 bottom is covered with a more or less dense carpet of mosses and 

 liverworts in which the chief species are Hylocomium prolifernm, 

 H. parietinum, H. squarrosum, H.rugosum, H.loreum, H. triq uetru /n, 

 Hypmim uncinatum, Climacium dendroides, Camptothecium lutescens, 

 Thuidium delicatulum (S. Icel.), Mninm affme, Timmia anstriaca, Po- 

 lytrichum alpinnm, Pogonatnm urnigerum, Rhacomitrium cauesceus, 

 R.hypuoides, Ditrichnm flexicaule, Lophozia lycopodioides and Pla- 

 giochila asplenioides, but besides these, many other species occur as 

 a more casual admixture. 



On a stony substratum with a thin layer of soil mosses are 

 dominant, and phanerogams grow scattered in the moss carpet. 

 A "moss-slope" is then developed which, as a rule, is composed of 

 the same species as those found on the grass-slope, most frequently 



1 See footnote in Thoroddsen's Physical Geography of Iceland, ante p. 330. 



The Botany of Iceland. Vol. I, part II. 38 



