LICHENOLOGY OF ICELAND 233 



essentially dependent on local conditions, i. e. conditions pertaining 

 to soil, competition with other plants, etc., as has been more fully 

 mentioned under the individual association. 



The main question whether the differences in the climate, 

 which prevail at various altitudes, have any other importance than 

 that which they have by indirectly exposing the lichens to the 

 competition of sometimes the one and sometimes the other plant- 

 species (in heaths, coppices, grass, etc.) is best answered by in- 

 vestigating the vegetation at higher levels. Or to put the question 

 more simply : Can any connection be shown to exist between the 

 character of the climate and the mass-occurrence of the lichens? 

 To this we must reply with a fairly certain "Yes." It is to be ex- 

 pected that, when all competition with other plants is absent, and 

 the soil is of suitable composition, the lichens must be abundantly 

 present in great masses, in other words: mountain heights must 

 necessarily be very rich in lichens. Now there is no doubt at all 

 that the lichens, at higher altitudes, are more conspicuous in 

 the landscape, than at lower levels, but on the other hand, neither 

 can it be doubted that the lichens are far, very far, from covering 

 all the soil on mountain-heights, which is bare of all other com- 

 petitors. There can, on the whole, be no doubt at all that, both as 

 regards number of species and mass-occurrence, the mountain-height 

 manifests a poverty, which cannot be due to soil and competition, 

 but must largely be a result of the more severe climate. 



With regard to the rock-lichens, the list of the hardy moun- 

 tain-height-species is given above. With respect to mass-occurrence 

 it can likewise be said that the mass is evidently smaller on that 

 ground, which lies highest even though, as in the case of the earth- 

 lichens, more reliable determinations concerning mass-occurrence are 

 still wanting. It is, however, evident even from a superficial survey, 

 that both as regards number of species and mass-occurrence the 

 highest mountains are poorer than the lower. 



With the Epiphytic lichens the matter is quite simple : they 

 are solely connected with coppices and cease at the alpine limits 

 of the latter, i. e. they are entirely absent from mountain-heights. 



