969 



part of the plant covering in the associations hitherto considered, 

 it is necessaiy on the cliffs to include the hchens and to some 

 extent the algæ. 



My notes on the cryptogamic groiips are unfortunately very 

 fragmentary because of my insufficient knowledge of them, so that 

 the following sketch is incomplete and defective in many respects. 



When a survey of the constituents of the cHff vegetation is 

 being made, it is necessary lo recognise, that the vegetation seen 

 on a chff-face, a cHff-slope and a cHff-terrace, respectively, is made 

 up of piants which live under widely differing conditions. Pri- 



Fig. 182. On the Kirkeborejii on Stromo (300 m. above sea-level), the solid rock is exposed almost 

 everywhere, and is covered by a typical lithophyte vegetation, mostly lichens. (From photo. by author). 



marily they may be arranged under two main groups: I. Lichens, 

 algæ, and mosses attached to the surface of the bare rock(Schim- 

 per's Lithophytes). II. Lichens, mosses and higher piants which 

 grow in crevices, on terraces, or in other piaces where loose soil 

 has accumiilated through weathering of the cliffs and the decay of 

 plant-remains (Oettli's Chomophytes). 



L The surface-vegetation of the bare rock (Litho- 

 phyte formation). This consists entirely of cryptogams, prin- 

 cipally of a great number of lichens witli some mosses clingiilg 

 to them, and also some algæ in wet piaces. The »black stripes« 

 so frequently seen on the Færoese cliffs, are formed by different 

 algæ {Stigonenia spp., etc), which have become more or less incor- 

 porated into lichen-forms. The majority of the mosses also prefer 



