LICHENOLOGY OF ICELAND 1(53 



been prepared by the growth of the latter. I have never observed 

 any foliaceous lichens on a quite recently bared surface. The crusta- 

 ceous lichens appear always to be the first to arrive, and are after- 

 wards succeeded and exterminated by the foliaceous lichens. 

 Of Foliaceous rock-lichens Iceland has the following: 



Cetraria Fahlunensis. Leptogium plicatile. 



Collema crispum. Parmelia alpicola. 



flaccidum. encausta. 



pulposum. incurva. 



Dermatocarpon miniatum. lanata. 



Evernia furfuracea. olivacea. 



Gyrophora arctica. physodcs. 



cylindrica. saxatilis. 



erosa. stj'gia. 



hyperborea. Physcia aipolia. 



murina. aquila. 



polyphylla. caesia. 



proboscidea. Xanthoria lychnea. 



vellea. parietina. 



The Fruticose lichens are not numerous. As I have previously 

 shown, they rest almost exclusively on a substratum prepared by 

 other lichens, and consequently are not really true rock-lichens, as 

 they are dependent on the peat-formation, which the first inhabitants 

 of the rocks leave behind them on their decay. Consequently, if we 

 investigate more closely such apparently rock-inhabiting species of 

 Stereocaulon and others, we shall find under them not rock 

 but first a thin layer of peat, and under that, the rock. Consequently, 

 they are in reality earth-lichens. 



A few species are, however, undoubtedly true inhabitants of 

 rocks, for instance Usnea melaxaniha, Roccella, Ramalina and a few 

 Stereocaulon spp. They have at their base a permanent thallus, which 

 is thread-shaped (Usnea) or ribbon-shaped (Ramalina) and isolateral. 

 Formation of haptera between the individuals (see under earth-lichens) 

 is unknown, and would appear also to be rather superfluous, as 

 they do not die away at the base. Consequently, as regards these 

 two points, they appear to differ greatly from their fruticose relatives 

 among the earth-lichens, which is quite in harmony with the 

 different substratum. 



Special modes of propagation - - by detached portions of thallus, 

 etc., are not known. 



With regard to competitive capability the fruticose lichens ge- 

 nerally stand very high. In Denmark species of Ramalina can form 



11* 



