LICHENOLOGY OF ICELAND 207 



had just disappeared from the greater part of the heath, but it was 

 still lying in many small patches in the depressions. It was evident 

 that both climate and soil here were distinctly wetter and colder 

 than in those places where the heath-types discussed above, usually 

 develop. 



The substratum was very knolly moraine soil, with knolls 

 reaching up to the knees, and with deep, narrow moss-grown de- 

 pressions between the knolls. Lichens were abundantly present; 

 they occurred chiefly on the sides and on the horizontal surface of 

 the knolls. The latter phenomenon I have only met with on this 

 type of heath, and it is no doubt to be explained as a result of 

 the fact that, owing to the difficult conditions of vegetation, well- 

 developed phanerogams do not occur on the top- surfaces of the 

 knolls, as they occurred on the heaths situated on lower levels on 

 the mountains. 



The following phanerogams occurred on the knolls: Dwarf- 

 willow' (F % 90), Cyperacece (F % 90), Polygonum vwiparum (F % 90), 

 Empetrum (F % 40), Silene acanlis (F % 70), Cassiope hypnoides (F % 

 40), Salix lanata (F % 20), and lastly there occurred, also on the 

 knolls, 100 F /o of lichens (i. e. 90 F % of crustaceous lichens, 60 

 F % of foliaceous lichens and 60 F % of fruticose lichens). 



In the depressions between the knolls there grew dwarf-willows 

 (F % 100), Polygonnm vwiparum (F % 100), a small amount of Em- 

 petrum and grasses (F /o 40), a small amount of Cyperacece, large 

 quantities of mosses (F % 100), but no lichens. 



The reason of this absence of lichens must undoubtedly be 

 sought in the fact that the depressions keep very wet during the 

 short period of summer in which the heath is free from snow: 

 this creates unfavourable conditions for the lichens. 



The following lichens were found upon the knolls : 



Stereocaulon paschale (fruticose lichen; sterile), 



Cladonia turgida ( ; ). 



cocci fera ( ; ). 



pyxidata ( ; ). 



fimbriata ( ; ). 



rangiferina ( ; ). 



Cetraria islandica (foliaceous lichen; sterile). 



hiascens ( ; 



Dermatocarpon hepaticum ( ; fertile). 



Peltigera aphtosa ( ; sterile). 



rufescens ( ; ). 



lepidophora ( ). 



