224 OLAF GALL@E 
almost all altitudes. But it must be remembered that all the lichens 
belonging to this group, are more or less dependent upon the pre- 
sence of other plants, for — as I have fully explained in my 
“Danske Licheners Økologi” — they always follow an initial vege- 
tation of other lichens (crustaceous or foliaceous lichens) or of mosses 
and live so actually on the soil formed by them that they are not 
even attached to the rock-substratum, but on the contrary, in some 
cases die away at the base. This circumstance has also been con- 
sidered more fully in the present treatise under the heading “Earth- 
lichens” and will not be discussed further here. 
An exception to this rule is formed, it appears, by Stereocaulon 
denudatum, which at least appears to be able to live upon the rock 
itself. I have not found it, however, upon basalt, but in great 
abundance upon recent lava, and shall treat of it under the heading 
“Lava.” 
b. Lava. 
The post-glacial lava is black, with many small cavities and 
vesicles, and sometimes of an appearance similar to cokes. When 
it gradually becomes covered with vegetation, this usually consists 
of Grimmia-carpets, which again can develop into heaths, ete. But 
those areas which do not immediately become moss-covered, fre- 
quently become first lichen-covered. The lichens may occur on the 
rock-substratum itself, at first crustaceous lichens, then foliaceous 
and fruticose lichens. The latter are, however, probably most fre- 
quent in places where moss had first been growing. 
I have not had the opportunity of seeing lava at all altitudes, 
and therefore I am not prepared to say how far it supports Verru- 
caria- and Caloplaca-associations near the sea-shore, which it is 
evidently able to do. My observations are made from lava-streams 
in rather low-lying land, up to a height of about 300 metres above 
sea-level, and there I found the following associations: — 
Crustaceous-lichen association. By way of example I 
quote such associations from a lava-field near Havnefjord. I found 
growing here, on sloping surfaces, a vegetation which consisted mainly 
of crustaceous lichens; in 90 °/o of the sample-areas were found 
a few foliaceous lichens (1 °/o), fruticose lichens (40 °/o) and moss 
(90 °/o). The latter did not cover the rock to such an extent, as 
might be expected, judging by the high frequency-number. On the 
whole, the substratum was visible everywhere between the lichens. 
The following species were found: — 
