LICHENOLOGY OF ICELAND 211 



Type III. 



(Wet mountain heaths; level or knolly; snow-covering of long persistence; 



on the whole rich in lichens). 



Ex. 1. Vadlaheidi; the vegetation upon the knolls 



(North Iceland). 



Dwarf willow F % 90 Cassiope hypnoides.. . . F % 40 



Cyperacese F /o 90 Salix lanata F /o 20 



Polygonum viviparum . . F /o 90 Mosses F % 100 



Empetrum F % 40 Lichens F % 1 00 



Silene acaulis F /o 70 



Ex. 2. Vegetation upon the knolls on a heath on 

 Husavikrfjall (North Iceland). 



Empetrum F /o 1 00 Salix spp F % 40 



Cyperacese F /o 100 Grasses F /o 20 



Vaccinium uliginosum . . F /o 80 Alchemilla alpina F % 20 



Azalea procumbens. . . . F /o 80 Lichens F % 100 



Ex.3. Not knolly, level heath on Va31ahei5i 

 (North Iceland). 



Dwarf willow F % 95 Alchemilla alpina F % 25 



Cyperaceae F % 85 Lichens F % 45 



Cassiope hypnoides F % 45 



As may be seen from the above description, the conception 

 "heath" is rather comprehensive, in that many kinds of vegetation 

 of fairly different physiognomy can be comprised under this name. 

 Heaths however - - as defined by me here have one feature in 

 common: they are all dominated by chamaBphytes (about F % 100), 

 in that sometimes one, sometimes another chamaephyte predominates, 

 and sometimes they occur fairly equally mixed. In the meantime 

 all chamsephytes are not equally hospitable towards lichens, for 

 some, e. g. Salix lanata, dwarf birches and a few others, sometimes 

 when they are well-developed, cast a deep shade and cover the 

 ground abundantly with fallen leaves, and so they prove detrimental 

 to the lichen-vegetation. Consequently the latter, partly from this 

 reason and partly from others, vary as regards frequency-degree 

 and mass-occurrence without its being possible to understand this 

 fact by simply regarding the frequency-number (F %) of the chamas- 

 phytes in the tables. Other peculiarities, viz. the special specific 

 peculiarities (high or low growth, small-leaved or large-leaved, etc.), 

 luxuriant or stunted growth and similar features, cannot at all be 



14* 



