LICHENOLOGY OF ICELAND 173 
enough for lichen-vegetation, in that the foliage of the birch casts 
a very light shade, and the trees stand a fair distance apart. Lichens 
are also frequently found on the ground under the trees. 
The wood-floor is sometimes occupied by heather-moor, some- 
times by grass- or moss-vegetation. But a “herb-vegetation” (i. e. a 
vegetation in which dicotyledonous flowering-plants are dominant) 
may also occur. 
In Hälsskogur the bottom, which is of fine sand, is covered by 
a carpet consisting af grass, dwarf-birches, Vaccinium uliginosum, 
Empetrum, Rubus and Galium, with here and there intervening 
patches bare of vegetation covered with fallen birch-leaves. The 
trees stand close together, are 1—3 metres high, and the stems are 
thin, being 8—10 cm. in diameter; the bark is smooth. Both the 
wood-floor and the trees are devoid of lichens. This is probably 
due, as regards the bottom, to the too great competition of other 
plants, while as regards the bark, it is undoubtedly due to its not 
being sufficiently decomposed. 
On the road between Häls and Einarstadir (North Iceland) I 
passed by a coppice, quite similar in appearance, where the stems 
were below or about the height of a man, and devoid of lichens, 
while the ground, in only one spot, bore some Cladonia pityrea. 
In some places, according to H. Jénsson’s observations, a rich 
vegetation of lichens occurs on birches, for instance in South Ice- 
land, and probably also in other places, where the birches are old 
enough to have decomposed bark. Thus, there is frequently found 
a rich vegetation of 
Parmelia olivacea v. aspidota. Pertusaria xanthostoma. 
Biatora Tornoénsis. Lecanora protuberans. 
Lecanora symmicta. 
There is also found a rich lichen-vegetation on the dead top 
shoots of birches. 
Deichmann Branth (D. B., 1903, p. 198) has compiled a list 
of more than 34 species, which have been found on Icelandic birches, 
namely the following: — 
Cladonia pyxidata. Lecanora subfusca (with var. coilo- 
Cetraria szepincola. carpa, albella, glabrata, rugosa). 
Parmelia olivacea. L. varia (with var. symmicta). 
Placodium ferrugineum. L. protuberans. 
P. vitellinum v. octosporum. L. verrucosa. 
Lecanora hypnorum. Pertusaria communis. 
