THE BRYOPHYTA OF ICELAND 555 



were composed of Brachytheciiim riimlare, Mniobrijiim albicans var. 

 glacialis, Philonotis fontana, Bnjum ventricosiim, Mnium Seligeri and 

 Mniiim affme var. elatiim, which grew in patches intermixed. 



4. Holt (S. Iceland), moss bog below a slope: Acrocladiam 

 cuspidatum, Mniobnjum albicans var. glacialis, Bryum ventricosum f. 

 major, Mnium punctatum, M. Seligeri and Pellia Neesiana grew inter- 

 mixed, sometimes as single piants and sometimes in patches. In 

 the middle Montia rivularis grew among the mosses. 



The majority of the mosses growing near springs form special 

 cold-water forms which are particularly characterized by their 

 highly elongated, slightlj' branched stems of almost equal height, 

 by which feature thej'^ all assume a homogeneous habit. Brachythe- 

 cium rivulare forms a form with long, erects shoots of equal height 

 and with appressed leaves. Philonotis fontana forms, when growing 

 in very cold water, a highlj' elongated, hardly tomentose form with 

 appressed, shortly pointed leaves with short leaf-cells and very broad 

 nerve (formå adpressa). The cold-water form of Bryum ventricosum 

 (f. major) is also higher in growth and more vigorous than is the 

 bog-form, has stems bare of tomentum with large and broad, 

 spreading leaves. Mniobryum albicans var. glacialis is also much more 

 vigorous than the type, with larger and broader leaves. Mnium 

 spp. develop elatum-forms with erect, sterile shoots of equal height. 



The Bryophyte Vegetation of Boggy Soil. 



The bog vegetation is extensively distributed about Iceland, 

 especially in the low land, and in many piaces it occupies almost 

 the whole tract of land between the mountain slopes and the sea. 

 The lower mountain plateaus and slightly inclined slopes up to a 

 height of about 300 — 400 metres are also to a great extent covered 

 with bogs (Sedge-bogs). The mode of formation of these bogs has 

 been described by Helg i Jonsson (^1895, p. 45). They originate 

 partly from the further development of the vegetation of the springs 

 and the banks of streams, and partly from shallow lakes first 

 forming in depressions and afterwards becoming gradually filled up 

 with piants in connection with sand transported by the wind. In 

 the former case a drier bog (myri, pi. m.\rar) is formed, the sedges 

 superseding the mosses ; in the latter case a wet bog (floi, pi. floar) 

 is first formed, which, by gradually becoming overgrown with piants, 

 develops into a "myri"^. 



^ For a description of "myri" and "floi' see also Thoroddsens Ph3sical 

 Geography of Iceland, ante p. 323. 36* 



