240 OLAF (1AI.I.0K 



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: 



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 frulicose 

 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 

 spile 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. 



