OLAF GALL0E 



The heaths of Iceland and Denmark, regarded from the point 

 of view of a landscape, resemble each other as regards their whole 

 physiognomical feature, besides which there is a great similiarity 

 as regards the frequency- degree of the lichens (as far as this 

 can be decided by a rough estimate). The difference as regards 

 mass-occurrence (stated in weight) is not known (but at a rough 

 estimate it would not seem to be great; the mass -occurrence is 

 greatest perhaps on the Danish heaths). With respect to growth- 

 forms the similiarity also appears to be rather great, but it will 

 probably, on a closer investigation, be lessened by the fact that more 

 crustaceous lichens will be found on the heaths of Iceland, than on 

 those of Denmark. The systematic species of the two countries 

 differ by no means slightly from each other. 



It may therefore be said generally, that the conception "heath," 

 as we know it from Denmark, does not undergo any great funda- 

 mental change through a closer investigation of the Icelandic heaths. 



After having thus dwelt upon the appearance of the lichen- 

 vegetation, it now remains for us briefly to point out the conditions 

 which the lichens find on the heath and which have a determining 

 influence as regards whether they thrive or do not. 



The following are the most essential: 



(1) Nowhere on the heaths did I observe, that the chemical 

 composition of the soil had a detrimental influence on the lichen- 

 vegetation but in other localities, for instance near Solfataras, 

 etc., the conditions were very unfavourable to them. 



(2) Thermal conditions and water contents are so closely con- 

 nected with each other, that it is usually difficult to separate them. 

 Damp, cold soil is generally unfavourable to man}" lichens (compare 

 Bogs), whilst desiccation is not detrimental to them in a climate 

 where the precipitation is as great as it is in Iceland. The greatest 

 degree of moisture which permits the growth of heath-vegetation 

 (i.e. F. o 100 chamaephytes) is however also favourable to lichens 

 (mountain-heaths at higher altitudes). 



(3) Loose, drifting soil frequently bears heath-vegetation, when 

 the soil does not drift very greatly. But such heaths are devoid 

 of lichens. 



(4) Leal-fall, which covers the lichens, does not hamper them 

 greatly on the heaths; luxuriant dwarf-birch growths and in some 

 degree a lew other larger species may, however, by this means 

 prevent the appearance of lichens. 



