LICHENOLOGY OF ICELAND 163 
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 arclica. == physodes. 
— cylindrica. = saxatilis. 
— erosa. = sty 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 melaxantha, 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 
als 
