232 OLAF GALLØE 
The species here enumerated, which occur on rock and on 
earth, consequently represent what may be called the nival lichen- 
flora of Iceland; they are the most hardy species, and ascend far 
above the coppices, heaths and grass-carpets, right up to the snow- 
line. With regard to the majority of them it may be asserted — 
as already mentioned — that they also descend far into the low 
land; only Solorina crocea and Usnea melaxantha can with certainty 
be regarded as exclusively mountain-height plants. 
But in addition to the species mentioned here, various others 
will no doubt be found in the future, when more mountain sum- 
mits and the interior plateau of Iceland have been better investi- 
gated. 
In the above, when discussing the earth-lichens, those species 
have been mentioned, which are found in the common earth-plant- 
associations, as far as these, taken as a whole, bear lichens. The 
lists of species given there, are consequently also illustrative of the 
vertical distribution of the lichens, inasmuch as the heath with its 
lichens ascends to about 300 metres up the mountains, the birch cop- 
pices to about 550 (more frequently less), the willow-coppices (which 
do not appear to be very widely distributed and are almost unknown 
as regards their lichens) to about 800 metres, the grass-vegetation, 
with the upper limit of which I am not acquainted, and the desert- 
vegetation up to 1000—1400 metres; then comes the ice-region. 
If we now go through the lists, which are given above for each 
individual association — grass, heath, moss, coppice, etc. — we 
shall find that they do not include all the earth-lichens of Iceland, 
inasmuch as they do not contain all the numerous species, which 
have in part been found by other collectors without their having 
stated more closely in which association they were collected. Conse- 
quently, here is a large field left for future investigations, i. e. an 
elucidation with regard to the particular association in which each 
single species lives and — together with this association — at what 
sea-level. 
With regard to the mass-occurrence of the earth-lichens at 
various altitudes, very much is likewise wanting to our possession 
of reliable data as regards the heights, which are most favourable 
to them. This much can only be said as a general fact, that (1) 
close to the sea no lichens live on the earth, if the ground-water 
reaches to the surface of the earth; and (2) from these low altitudes, 
and upwards, the mass-occurrence of the lichens appears to be 
