LICHENOLOGY OF ICELAND 215 
The Growth-forms of the Heath-lichens. 
| KR 2. | Number 
| -Fruticose Foliaceous | Crustaceous ; 
| | of species 
Danish heaths ............. Haat. || 8 % 35 % 37 
Icelandic heaths............ 33 % 24.5 0/0 42 9/9 45 
Of these numbers the Danish will scarcely be altered to any 
extent, whilst the Icelandic, through more numerous and more de- 
tailed investigations, will probably undergo a very radical alteration 
in favour of the crustaceous lichens. On riding across the heaths 
in Iceland it strikes one that the crustaceous lichens are more do- 
minant there than in Denmark. This agrees closely with the fact 
that the chamephytes are, as a rule, obviously poorer and less well- 
developed there than on Danish heaths, and are consequently more 
hospitable towards lichens, than are the taller, well-grown species. 
With respect to the frequency-number of the lichens, none are 
to hand from Denmark. Those from Iceland are given above. 
Judging from what I remember, and compared with what I wrote 
on the subject in “Danske Licheners Økologi” (p. 301 et seq.), I am, 
however, inclined to believe that in Denmark all possible frequency- 
numbers occur, from 0 to 100, as in Iceland, in that we have in 
Denmark Calluna-heaths, which are sometimes very rich in lichens 
and sometimes almost devoid of them. In this respect there is 
scarcely any difference worth mentioning between the Danish and 
the Icelandic heaths. 
It is as difficult or, properly speaking, still more difficult to state 
anything about the mass-occurrence of the lichens in Denmark com- 
pared with Iceland. I must, however, enter somewhat more closely 
into this question, as it is, in addition, of more far-reaching eco- 
logical importance. 
If we are briefly to compare Iceland and Denmark as regards 
their lichen-vegetation on heaths, as far as this can be done on the 
basis of the investigations hitherto made, which in a high degree 
require to be more detailed as regards both countries, especially 
with reference to the mass-occurrence of the species, it may be 
stated that: — 
