236 OLAF GALLOE 
ability; this, which is simply a special lichenological employment 
of a geographical principle commonly employed in almost all other 
possible circumstances. 
If we want to compare the abundance of species of a certain 
limited area, for instance, that of Iceland with that of other areas 
within the same climate-belt or in others we must naturally first. 
and foremost employ just this last method, that is, we must take 
for comparison areas equal in size to Iceland. 
It is in the nature of the matter, that such investigations in- 
volve considerable difficulties and, in fact, they have not yet been 
made at all. But before they may happen to be made, we must 
help ourselves with less valuable and easier methods, which can 
give us hints with regard to the questions which we wish to have 
solved, and which will presently be more fully discussed. 
If we wish to compare the abundance of species of the 
various plant-associations with one another, several methods 
can naturally be employed, but already here the absolute figure for 
the species is very elucidatory. Thus, for instance, it is very in- 
teresting to ascertain the difference between the number of species 
in a grass-field and in a heath in Iceland (see above). But here also 
it is naturally still more valuable to determine the number of species 
of a certain unit of area in one association, and compare it with 
an equally large area of another association, for instance the number 
of species, let us say in one square mile of heath, compared with 
one square mile of forest, etc. 
But in the main, these statistical investigations are as yet tasks 
for the future, — much still remains to be done in this respect, 
but what we already know for certain as regards Iceland will be 
recorded here. 
Iceland has, according to the list given here, about 285 species; 
a few more may probably be added to this number by latter in- 
vestigations, but judging from what is known — only few. 
Now does this figure represent many or few species in propor- 
tion to the area of the island? 
Let us first compare it with some countries from the Arctic 
regions: Greenland has 287 and Spitzbergen 207 species. In pro- 
portion to its area, Spitzbergen — the smallest of the three coun- 
tries — has consequently the greatest number of species; then comes 
Iceland and — as the one poorest in species — that immense Green- 
land, which has, within its domain, an almost equally great absolute. 
