971 



In ravines and crevices where there is little light and miich 

 moisture, we find another special lithophyte association, cliarac- 

 terized by mosses and algæ [Trentepohlia aiirea, Nostoc carnenm, elc), 

 but only a few lichens [Ephebe piibescens, Collema flaccidiim and 

 Leptogiiim spp.); this association I call the wet lithophyte 

 association. 



The hlhophyte vegetation is extensively distributed on the- Fær- 

 oes because so much bare rock is exposed, either in the form of 

 more or less steep walls, or as somewhat flat expanses on the 

 mountain-plaleaux, whence the wind has removed all the loose 

 products of disintegration (see Fig. 182). This kind of vegetation 

 may be said to be exlremely well-developed in this country and 

 is no doubt a result of the high degree of atmospheric moisture, 

 the frequent and abundant rainfall, and the comparatively slight 

 insolation. 



II. The vegetation in crevices and on rock-ledges, 

 the chomophyte vegetation. A. F.W. Schimper (1898, p. 191) 

 has cailed those piants which grow in crevices of the cliffs, Chas- 

 mophytes as opposed to lithophytes. Max Oettli (1905), who 

 studied the ecology of the rock-vegetation in Switzerland, originated 

 the term Chomophytes to include the chasmophytes and the 

 piants of rock- ledges (1. c, p. 15). Chomophytes and lithophytes he 

 includes under the term cliff-plants or Petrophytes: »all those 

 piants growing on rock-faces or blocks, which are in a condition, 

 as the first of their kind, to make the cliffs their habitat, and which 

 in distribution or structure show a more or less marked dependance 

 on the rock as a substratum.« 



Chomophytes he defines as those petrophytes »which are 

 only able to settle amongst the cliffs where det ritus has 

 gat bered, either in crevices or on the sur face of the 

 cliff.« Oettli's conclusions on the peculiarities of rocky substrata 

 as a habitat are equally applicable to areas beyond the district 

 investigated by him. Hence I propose to quote some of his more 

 important inferences, arranging them, however. in a slightly different 

 way : 



1*^ Piaces devoid of a plant-covering will always exist on cliffs 

 because of the hardness and steepness of the surface, and because 

 the higher piants can only find a home on terraces and crevices 

 with loose soil. 



2*^ Each place has its own particular degree of soil-moistness; 



