LICHENOLOGY OF ICELAND 174 
(8) The snow-covering has a very great influence, especially 
in the mountains. Where there is a perpetual snow-covering, lichens 
naturally cannot live. But lichens can live even on soil which is 
free from snow for only a few weeks during the summer. Thus I 
observed in several places on the mountains around Ofjord that 
lichens grew abundantly at considerable elevations, which are not 
freed of snow until July. Taken as a whole it may be said, that 
the snow-covering in Iceland, by shortening the annual growth- 
period, plays a far greater rôle than it does in Denmark. 
(9) The competitive relations with other plants are, on the 
whole, more favourable to the lichens in Iceland than in Denmark, 
because the higher plants — in consequence of the soil and climate 
— are not generally of so quick a growth there as in Denmark; 
but this I must naturally discuss more fully under each particular 
plant-association. For the present I shall only point out that the 
lichen-vegetation in Iceland plays physiognomically a more dominant 
role than in Denmark, more particularly because the competition 
on the part of other plants is not so keen there as it is in the 
more temperate regions. 
The combined result of all the factors, climatic and edaphic, 
which we have been considering above, shows itself in the form of 
plant-associations as they occur in nature. I shall therefore go 
through these one by one, and, as far as our present knowledge of 
the subject makes it possible, occupy myself more closely with 
what has given them their appearance. 
With regard to the plant-associations of loose soil, it is difficult 
to carry out any single logical systematization — merely to find 
proper names for them, such as are characteristic and to the point, 
is difficult. To do this we can proceed in any one of three essenti- 
ally different ways: we can (1) name the association after the soil 
(e. g. “sandy shore,’ “dunes,” etc.), or (2) after the conspicuous, 
dominant plants found therein (e. g. “beech wood,” “birch coppice,” 
etc.), or lastly (3) we may combine these two, as ecologists frequently 
do, and as people do in common language, naming some associa- 
tions after the characteristic features of the soil, and others after 
conspicuous, characteristic plants. 
In reality it is extremely difficult to decide upon one of these 
methods in particular, for the following reasons: If there existed 
The Botany of Iceland. Vol. II. 12 
