200 OLAF GALLØE 
Vaccinium uliginosum (F °/o 80), Salix lanata (F °/o 60), Geranium 
silvaticum (F % 26), Betula pubescens (F °/o 20), Salix spp. (F °/o 20), 
Equisetum (F °/o 20), a little Calluna (F °/o 7), a little Lycopodium 
(F °/o 7) and some mosses (F °/o 13). Consequently, these heaths 
contain considerable quantities of high, well-grown shrubs, viz. Salix 
lanata, some Betula pubescens, etc. The vegetation was very close 
and luxuriant, and the floor was entirely covered with decaying 
leaves. In correlation with this lichens were totally wanting 
in these heaths. 
We have now seen some different examples of how both the 
lower and taller shrubs, which shed an abundance of leaves every 
year, are simply through this peculiarity inimical to the growth of 
lichens. The more frequently low-growing trees occur on a heath, 
the more difficult do the life-conditions of the lichens become. It 
cannot be doubted that there is correlation between the occurrence 
of these two growth-forms. 
Type I. (b) Dry heath with drifting soil; devoid of lichens. 
In the mountains between Fnjoskädalur and Ofjord (North Ice- 
land) I noted in some places a Dryas-heath on which the charac- 
teristic plants were Dryas (F °/o 100), Glumiflore (F °/o 100), dwarf- 
birch (F °/o 50), Empetrum (F °/o 40), Salix lanata (F °/o 20), and 
Vaccinium uliginosum (F °/o 20). Peculiar to this heath was the total 
absence of lichens, which was evidently due to the shifting soil 
of the place in question, strong winds causing it to drift. It was 
evident that the plant covering and other conditions were not de- 
trimental to the lichens, which in other places throve excellently 
among the same competitors which occurred here. 
Thus we have seen two essentially different factors which may 
be instrumental in excluding a lichen-vegetation from heaths; (1) 
certain shade-casting, deciduous chamephytes and Nano-phanero- 
phytes which may dominate so highly that liehen-growth is made 
impossible, and (2) drifting soil which may play exactly the same 
part, even if the plants present are not in themselves any hindrance 
to lichen-growth. 
Type I. (c) Heaths poor in phanerogams and rich in lichens. 
Other heaths may be rich, even very rich, in lichens. We shall 
now mention some specimens of them. 
In the heaths near Einarstadir (Adalreykjadalr in North Iceland) 
were found scattered larger and smaller areas of Dryas-grass- 
heaths which were easily discernible even from a considerable 
