LICHENOLOGY OF ICELAND 229 



Gyrophora arctica, foliaceous lichen. 



hyperborea, 

 Stereocaulon denudatum v. pulvinatum, fruticose lichen. 



Taken as a whole, the liparite impresses one as being a very 

 poor substratum for lichens. This fact is curious, considering that 

 granite, which has the same chemical composition as liparite, is so 

 rich in lichens. It must therefore be presumed, that the difference 

 is due to physical conditions. 



