J'J 1 OLA I C.ALL0K 



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 0kologi" 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 

 (lenmiatnm, which at least appears to be able to live upon the rock 

 itsell. 1 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 Grzmmia-carpets, which again can develop into heaths, etc. 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 Verrn- 

 c<tri(t- and Cer/o/j/ac-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: 



C r u staceo us-lic hen 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 

 ot crustaceous lichens; in 90 /o of the sample-areas were found 

 a lew foliacrous lichens (1 %), fruticose lichens (40 /o) and moss 

 '."i 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: 



