THE BRYOPHYTA OF ICELAND 547 



Orthotrichum Blyttii occurs here and there on coast rocks, or at 

 any rate in the immediate neighbourhood of the coast. Pottia Heimii 

 is commonly distributed along all flat coasts and Amblystegium 

 littorale occurs here and there on damp sandy soil. 



Besides these littoral species proper, there are several others 

 which occur especially abundantly on the coast, but are also distri- 

 buted in many other localities. Bryum argenteum and B. capillare 

 grow especially below cliffs inhabited by sea-fowl , but their pre- 

 sence there is, no doubt, as much due to the abundant supply of 

 organic manure at to the proximity of the sea. Desmatodon lati- 

 folius, Leptobryum pyriforme and Tortilla rnralis are also typical of 

 damp sandy soil and Hypnum polygamum of saline, boggy soil. 

 On damp sandy soil on the beach low, scattered moss-cushions 

 consisting of stunted individuals of many different and more casual 

 species are often met with, for instance, Distichium montannm, Di- 

 dymodon rubelliis, Ceratodon pnrpiireus , Encalypta rhabdocarpa, 

 Myurella julacea, Bryum spp., etc. 



Hydrophilous Bryophyte Formations. 



The water originating from rain and mist or from melting 

 snow will, according to the local conditions and the inclination, 

 either spread out over the ground and if it consists of humus 

 or sand - - sink into it, or seek outlets in brooks and rivers. Where 

 the water remains standing without being able to find a sufficient 

 outlet, a bog vegetation is developed, or, in deeper hollows, a lake 

 is formed. Part of the water which sinks down to the solid rocky 

 substratum continues its way downwards along the latter until it 

 sooner or later issues as a spring. Stagnant water contains humus 

 substances, is not w r ell aerated, and is warmed by the sun, while 

 running water, both in streams and springs, is pure and clear and 

 contains oxygen and carbonic acid. Running water has a very low 

 temperature during the summer, at the most 4 6. Therefore 

 the composition of the vegetation on boggy ground differs entirely 

 from that on ground along streams and near springs, inundated or 

 saturated by the pure water. 



The hydrophilous formations may be classified as follows: 



