LICHENOLOGY OF ICELAND 228 



water level as far upwards as the spray of the waves reaches. I have 

 seen it developed very distinctly for instance on the sides of SeyQis- 

 fjorSur, Rey5arfj6r5ur, Eyjafjor5ur and in several other places. Its 

 natural history is in all respects a repetition of what we know from 

 Denmark, Finland, etc. Therefore, there is no special reason to 

 dwell upon it more fully here. 



Foliaceous-lichen-associations are found here and there, 

 fairly well-developed, especially in the low land, where they fre- 

 quently consist of Parmelia saxatilis, P. lanata, P. stygia or of species 

 of Gyrophora (G. cylindrica, arctica, erosa). Sometimes the one, 

 sometimes the other species predominates, whereby several forma- 

 tions may be distinguished ("Parme//a-formation," "Gyrophora-forma- 

 tion," etc.). As far as my observations go these communities are 

 most luxuriantly developed in places where it is light and damp. 

 For instance, they are found well-developed by the waterfalls at 

 the head of Sey5isfj6rdur and by Dettifoss (North Iceland). 



The density of the plants is as a rule high and consequently 

 the competition is keen, but regarding this point no detailed in- 

 vestigations have been made. The crustaceous lichens are however 

 mercilessly exterminated when Parmelia saxatilis puts in its ap- 

 pearance; in many places this process of extermination may be 

 observed in various stages. 



It is more rare for the Gyrophora spp. to dominate so de- 

 cidedly; I did not see them as pure growths, as they may be found 

 in Arctic countries. 



The Fruticose-lichen-association. Helgi Jonsson re- 

 cords that Ramalina cnspidata often occurs abundantly on the rocks 

 of South-west Iceland. He does not, however, state more explicitely 

 whether it actually forms carpets. I myself never saw it occur in 

 such abundance as to make it justifiable to speak of Ramalina- 

 carpets, like those found on the shores of Bornholm. Nor did I 

 come across such a feature on the coastal rocks of Iceland. 



Usnea melaxantha may sometimes be found in tolerable abun- 

 dance near the snow-line on mountain heights, but I did not see 

 this species either actually form carpets. 



Therefore it appears that Iceland has no continuous carpets of 

 pendulous fruticose lichens which are attached to the rock- 

 substratum itself like those we have in Denmark. 



Erect fruticose lichens (Alectoria, Stereocaulon, Cladonia, Cetraria 

 .acnleata, etc.) are frequently found covering the rock-substratum at 



