LICHENOLOGY OF ICELAND 205 
Upon the above-mentioned Reykjaheidi, 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 uliginosum (F °/o 100), Empetrum (F °/o 100), Juni- 
perus (F °/o 60), grasses (F °/o 60) and small quantities of Salix lanata 
and Calluna 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 Empetrum, dwarf-birch and Vaccinium, 
whilst Calluna 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 Empetrum, 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 
= uncialis 
— rangiferina 
= gracilis 
Alectoria ochroleuca 
— nigricans 
Stereocaulon paschale 
Sphærophorus fragilis 
Cetraria aculeata 
(fruticose lichen; sterile). 
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— islandica (foliaceous lichen; sterile). 
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Peltigera rufescens 
Lecanora tartarea 
— u) 
crustaceous lichen; fertile). 
Psoroma hypnorum u a7 ple 
Petusaria xanthostoma — EN à 
Bæomyces byssoides = ; Sterile). 
Buellia scabrosa — ; fertile). 
Bacidia umbrina — UC eens) 
In a locality on the left bank of the Laxå, 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 
