LICHENOLOGY OF ICELAND 205 



Upon the above-mentioned ReykjaheiSi, over considerable tracts 

 of land, I also observed a very knolly heath, with high mounds 

 (reaching to the knee and upwards). Between the knolls there were 

 deep, narrow depressions. 



The vegetation of the knolls consisted of dwarf-birch (F /o 

 100), Vaccinium nliyinosnm (F % 100), Empetnim (F % 100), Jnni- 

 perus (F % 60), grasses (F % 60) and small quantities of Salix lanata 

 and Callnna and a few other less dominant species. 



Mosses and lichens were found to be equally abundant upon 

 the knolls themselves, viz. about frequency-percentage 40 of each. 



As for the rest, each individual knoll showed a characteristic 

 vertical grouping of the species, in that the horizontal surface of 

 the knolls was covered by Empetnim, dwarf-birch and Vaccinium, 

 whilst Callnna grew further down towards the depressions. All the 

 lichens occurred on the sides of the knolls, none upon the hori- 

 zontal surfaces. 



In the depressions between the knolls, a vegetation was formed 

 consisting of an equal mixture of Empetnim, mosses and grasses, 

 whilst lichens were practically absent. The shade was very deep in 

 the depressions, and this is no doubt the reason why lichens were 

 almost absent there. 



On this very characteristic heath, I noted down the following 

 lichens: 



Cladonia fimbriata (fruticose lichen ; sterile). 



uncialis ( ). 



rangiferina ( ; ). 



gracilis ( ; ). 



Alectoria ochroleuca ( ). 



nigricans ( ; ). 



Stereocaulon paschale ( ; ). 



Sphaerophorus fragilis ( ). 



Cetraria aculeata ( ). 



islandica (foliaceous lichen; sterile). 



Peltigera rufescens ( ; ). 

 Lecanora tartarea (crustaceous lichen; fertile). 



Psoroma hypnorum ( ; ). 



Petusaria xanthostoma ( ). 



Bseomyces byssoides ( ; sterile). 



Buellia scabrosa ( ; fertile). 



Bacidia umbrina ( ). 



In a locality on the left bank of the Laxa, and not far from 

 where it flows into Skjalfandi, I observed a similar tract of heath 

 with large, high knolls (about 60 70 cm.) and with a vegetation 



