214 OLAF GALLOE 
associations, and some by others on Icelandic soil without closer 
notification of the association. : There is hardly a single Icelandic 
earth-lichen which avoids the heath; they certainly all occur there 
occasionally, although those enumerated in the above list doubtless 
form the nucleus of the lichen-vegetation of the heath. 
As may be seen, there have been found 9 fruticose podetia- 
wanderers, 6 fruticose hypothallus-wanderers, 3 erect and 8 procum- 
bent foliaceous lichens, and 19 crustaceous lichens. 
But, as already mentioned, to these must probably be added 
all the other earth-lichens, viz. 12 fruticose, 16 foliaceous and 48 
crustaceous species. 
It is much to be desired that we could compare the lichen- 
vegetation of the Icelandic heaths with that in other countries, for 
instance in Denmark. Our knowledge of the lichens from heaths 
in other parts of the globe, is practically nil. As we know, lichen- 
ecological observations have, up to the present date, played a very 
subordinate part in scientific work. 
Some of the most conspicuous points which there could be 
reason to compare are the agreements or disagreements as regards 
(1) systematic species, (2) growth-forms, (3) frequency-degree and 
(4) mass-occurrence. 
With regard to systematic species there is a very conspicuous 
difference between the Danish and the Icelandic heaths. Whilst the 
Danish heaths — as far as they contain lichens at all — are entirely 
dominated by Cladonia rangiferina, the Icelandic heaths are not 
dominated by any single species. It is true, reindeer moss occurs, 
but only in small quantities. Of far more frequent occurrence 
are Alectoria ochroleuca, Thamnolia vermicularis, Cetraria islandica 
and Lecanora tartarea. Thus the Icelandic heaths cannot be cha- 
racterized by any single species. We shall not, however, go further 
into details as regards the systematic species, it will suffice to refer 
to the list of the Danish Heath-lichens in “Danske Licheners Oko- 
logi” (p. 305) and, as regards the Icelandic lichens, to the list of 
species given above. 
The growth-forms are not exactly the same on the heaths of 
Iceland and Denmark. Whilst Denmark has 21 fruticose lichens 
(57 °/o of the heath-lichens), 3 foliaceous lichens (8 °/o) and 13 cru- 
staceous lichens (35 °/o), in Iceland the proportions of growth-forms 
are distributed as follows: — 15 are fruticose lichens (33 °/o), 11 are 
foliaceous lichens (24.5 °/o), and 19 are crustaceous lichens (42 °/o). 
