LICHENOLOGY OF ICELAND 203 
I shall describe one more specimen of a Dryas-heath which I 
investigated near Einarstadir. The ground was slightly inclined and 
partially bared in many places. The plant-covering was 8—10 cm. 
high and consisted of Dryas (F °/o 100), Empetrum (F °/o 100), grasses 
(F °/o 100), dwarf-birch (F °/o 64), Azalea procumbens (F °/o 24), Vac- 
cinum uliginosum (F °/o 16), Polygonum viviparum (F °/o 12) and Tha- 
lictrum alpinum (F °/o 4). In this low-growing, open vegetation a 
quantity of lichens was growing (F °/o 100), fruticose and foliaceous 
lichens and Lecanora tartarea. The species were: — 
Alectoria ochroleuca (fruticose lichen). 
— nigricans — 
Cetraria nivalis (foliaceous lichen). 
= aculeata (fruticose lichen). 
Thamnolia vermicularis (fruticose lichen). 
Lecanora tartarea (crustaceous lichen). 
The types of heath described above are characterized by their 
level, partially sloping substratum, their open and low-growing ve- 
getation, and chamæphytes and hemicryptophytes with slight leaf- 
fall which dominate, both physiognomically and ecologically. Con- 
sequently, the conditions are favourable to the lichens, and their 
frequency-percentage is everywhere 100 or thereabout, sometimes 
crustaceous lichens (mostly Lecanora tartarea), sometimes fruticose 
lichens dominating. 
Type II. Dry, knolly heaths with phanerogams on the hori- 
zontal surface of the knolls, lichens on the sides of the knolls, and 
mosses, etc., in the narrow depressions or ruts between the knolls. 
A third type of heath which is common in Iceland is the 
Knolly heath; it has fewer lichens than has the low-lying, level 
Dryas-Empetrum-grass-heath. 
I noted some examples of this type of heath from different 
areas in North Iceland between Einarstadir (in Adalreykjadalur) and 
Myvatn, on Reykjaheidi (south of Axarfjöröur, between the Jökulsä 
and the Laxä), along the left bank of the Laxä (which runs out 
into Skjalfandi) and in a few other places. 
As already mentioned it is peculiar to these heaths that the 
ground is very knolly, i. e. it consists of mounds with deep inter- 
vening depressions. The heaths appear usually or perhaps exclu- 
sively to develop on level (not sloping) ground. 
Between Einarstadir and Myvatn (in the valley of the Laxä) 
heaths were found composed of Empetrum (F °/o 100), grasses (F °/o 
100), dwarf-birch (F °/o 80), and a few other phanerogams with a 
