"240 OLAF GALLOE 
But the absolute number itself is greater for Iceland than for 
Denmark! Does this imply that the climate up there in the north 
is more favourable to lichens than down here in Denmark? Does 
not this contradict our general assumption, that lichens are more 
abundant in temperate countries than in Iceland? Anything of this 
kind cannot be deduced from the aforesaid fact. Considering the 
particularly favourable conditions which Iceland can offer the earth- 
lichens as regards competition, the number 121 in proportion to the 
104000 square km. of country is very modest compared with Den- 
mark’s 86 on 38000 square km. 
Still more interesting conditions become apparent when we re- 
gard the sub-divisions of the earth-lichens: the crustaceous, foliaceous 
and fruticose lichens. It is then seen that Denmark and Iceland 
have the following earth-lichens: — 
= | | 
| Crustaceous | Foliaceous | Fruticose 
Denmark Pee wth ce ee a 34 | 21 | 31 
Iceland SER RES så ec ele 67 27 | 27 
These figures are most peculiar, inasmuch as they show that 
Iceland's predominance as regards the number of earth-lichens, is 
due to a greater number of crustaceous lichens, inasmuch as both 
countries have about the same number of foliaceous and fruticose 
lichens, taken collectively, whilst Iceland has very nearly twice as 
many crustaceous lichens as Denmark. Remembering, that this 
growth-form in particular, in order to be able to live at all, de- 
mands either a very moderate competition, or none whatever, on 
the part of other plants, it is easily to be understood, that an Arctic 
country in particular, with a slightly developed phanerogamic vege- 
tation, offers the crustaceous lichens the most favourable conditions 
possible, as regards competition. In reality there is so much un- 
occupied ground, free from other plants, that we might expect a 
much greater number, offering an analogy with the fact, that much 
tree-vegetation (for instance in the Tropics, in Italy, etc.) serves 
greatly to increase the number of species of tree-lichens. When in 
spite of the very slight competition, the number of earth-lichens is 
so limited, this can only be regarded as a direct result of the climate. 
