THE BRYOPHYTA OF ICELAND 



()!;■) 



swamp vegetation niay occur. The Rhacomitriuni heaths are gra- 

 dually transformed into heather moors and birch coppices through 

 the decaying of Ihe mosses and their forming humus. But all these 



Fig. 3C. The suriace of a lava block wilh small moss-cushlons (Andrcira, 

 Griiiiinia spp. and Gi)inn<>n)ilriuin coralloides). 



formations will not be treated of more fully here as the mosses 

 occurring in them have been mentioned in previous sections. Very 

 extensively distributed and very characterislic is the Rhacomitriiiin- 

 canescens formation which often replaces R. hypnoides in flat depres- 

 sions where the ground is somewhat damp, and where some sand 

 has accumulated. It is often abundantly mixed with other Brj'ophyta 

 such as Hylocomiuin spp., Hypniiin iincinatiiin, Dicranum scoparium, 

 Polytrichum alpinum and species of Lophozia. 



