200 OLAF GALL0E 



\'ficcininm uliginosum (F /o 80), Sali.v lanatd (F /o 60), Geranium 

 silvaticnm (F % 26), Betula pubescens (F % 20), Sali.i- spp. (F % 20), 

 l-:<liiisetum (F /o 20), a little Callnna (F % 7), a little Lycopodinm 

 (F % 7) and some mosses (F /o 13). Consequently, these heaths 

 contain considerable quantities of high, well-grown shrubs, viz. Snli.r 

 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 Fnjoskadalur and Ofjord (North Ice- 

 land) I noted in some places a Dryas-heaih on which the charac- 

 teristic plants were Dryas (F %> 100), Glumiflorcc (F % 100), dwarf- 

 birch (F % 50), Empetrum (F % 40), Salix lanata (F % 20), and 

 Vaccinium nliyinosnm (F % 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 chamsephytes and Nano-phanero- 

 phyles which may dominate so highly that lichen-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 

 lo 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 healhs near Einarslaftir (Adalreykjadalr in North Iceland) 

 were found scattered larger and smaller areas of Dryas-grass- 

 heaths which were easily discernible even from a considerable 



