2 o8 OXYLOPHYTES SECT, vi 



Alps, Polytrichum septentrionale would appear to form carpets of moss 

 on deserted glacier-soil ; for instance, in the Oetzthal one may see large 

 tracts which are composed of sand and talus thrown down from the 

 mountains, and are covered by a soft carpet of Grimmia and isolated little 

 spruces, junipers, and herbs. 



In temperate zones similar plant-communities are found upon perio- 

 dically inundated soil. Especially in the neighbourhood of heaths there 

 are formed small associations that take a position intermediate between 

 heath and moor. Danish botanists * have applied a special term ' Moskar ' 

 to these, and they distinguish Sphagnum - kar, Polytrichum-kar, 

 Dicranum-kar, and Grimmia-kar. Identical associations occur in 

 Ireland, 2 and on the Faroe Isles. 3 Even so far south as Madeira carpets 

 of Grimmia occur on high mountains upon periodically inundated soil, yet 

 there is no sign of any production of raw humus. 4 



CHAPTER LI. LICHEN-TUNDRA OR LICHEN-H^ATH 



LICHEN-HEATH or lichen-tundra is drier than moss-heath ; according 

 to Hult, 5 Cladina-formation, as defined by him, apparently has not more 

 than 40 per cent, of moisture in the soil. Lichen-heath occurs especially 

 in hilly, mountainous countries whose rock occurs at a slight depth. 

 A thin layer of raw humus clothes this and supports lichen-heath. The 

 soil is dry, but lichens are incapable of dispensing with atmospheric 

 moisture ; even when they can endure periodic desiccation caused by 

 transpiration, they can flourish only where mist, rain, and dew are frequent. 

 Lichens can absorb aqueous vapour from the atmosphere. The species 

 vary in hardiness. According to Kihlman 6 there are several forms 

 (associations) of lichen-heath exhibiting various stages of sensitiveness, 

 in particular, to dry winds. Fruticose lichens thrive best where the air 

 is still and moist, and are therefore sparse in the extreme north. Cladina- 

 heath, composed of Cladonia rangiferina, C. alpestris and others, with 

 an admixture of Sphaerophoron corallioides, is the most sensitive ; it pre- 

 fers places where the snow lies long, it endures no dry wind, and therefore 

 especially seeks out depressions in the land ; it is common on all extensive 

 alpine plateaux lying inland in northern Europe and Arctic America. 

 The different kinds of Platysma-heath, including Platysma cucullatum, 

 P. nivale and others, with Cetraria crispa, C. islandica and others, are 

 more hardy. But most hardy is Alectoria-heath, which consists of Alectoria 

 ochroleuca, A. divergens, and A. nigricans, together with more abundant 

 dwarf -shrubs. In accordance with these degrees of hardiness, the habitats 

 of the various lichen-heaths are different. 



On heaths where tall fruticose lichens grow close together there is 

 formed a soft, thick carpet, which gives to the landscape a characteristic 

 yellow-grey tint that is visible from afar. They are to be seen on the 



1 See Borgesen and C. Jensen, 1904 ; Mentz, 1902. 



' Pethybridge and Praeger, 1905. * Ostenfeld, 1908. 



* Vahl, 19046 ; in addition to the works already cited, reference should be made 

 to those by Ramann (1895), Sernander (1898), and Dusen (1905). 



5 Hult, 1 88 1. Kihlman, 1890 ; also see Hult, loc. cit. 



