THE BRYOPHYTA OF ICELAND 559 



-woven with mosses and hepatics, and dilTerent plants such as 

 Vaccinium spp., Betnla nana, Comanun palustre and several Car ices 

 then establishing themselves upon these cushions. 



The numerous hepatics which occur are everywhere found 

 interspersed in the moss carpet, especially in that upon the knolls, 

 and, as regards all the species mentioned below, doubtless also in 

 the ground vegetation between the knolls. 



The Bryophyte Vegetation of Knolls 1 is dependent upon 

 the varying degree of moisture, which is greatest on the ground 

 between the knolls and least in their uppermost part. Some of the 

 Bryophyta of the ground do not ascend higher than to the base 

 of the knolls, while others, especially many of the pleurocarpous 

 mosses, occur with equal frequency upon and between the knolls. 

 In addition to the latter mosses the following species are found upon 

 the knolls: 



*Hypnum uncinatum *Mnium hornum 



imponens *Rhacomitrium canescens 



*Climacium dendroides hypnoides 



"Hylocomium squarrosum *Ditrichum flexicaule 



parietinum *Dicranum scoparium 

 proliferum congestum 



Orthothecium chryseum (N. Icel ) elongatum 



*Polytrichum alpinum *Lophozia lycopodioides 



strictum *Plagiochila asplenioides 



juniperinum *Ptilidium ciliare, 



*Aulacomnium palustre 



-and besides these, numerous other species which belong to other 

 formations and must rather be regarded as casual visitors. 



The following examples will show the composition of the bog 

 vegetation in the different parts of Iceland : 



1. Skalholt in SW. Iceland. The country here over a wide 

 expanse is covered with vast boggy areas in which small, protrud- 



1 According to my observations these knolls are formed either by soil accu- 

 mulating in tufts of Sphagnum, etc.. in which other plants take root, among 

 others sedges, when soil again accumulates, or by soil accumulating directly 

 around roots of sedge-tussocks. This accumulation of soil and plants continues 

 till big knolls are formed, some 60 70 cm. in height. These knolls occur in all 

 stages of development, from tufts or tussocks with a slight accumulation of soil 

 around their roots to completely rounded knolls in which the tussocks have en- 

 tirely disappeared. In Danish "Tue" stands both for "knoll" and for "tuft" and 

 ''tussock' 1 , which is very convenient when referring to one of the various stages 

 of these "knolls". But the rendering into English has been difficult, though in each 

 case the term most appropriate to the stage of development of the "knoll'" has 

 been carefullv chosen. 



