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 Halsskogur the bottom, which is of fine sand, is covered by 

 a carpet consisting af grass, dwarf-birches, V actinium uliginosnm, 

 Empelrum, Rnbns and Galinni , 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 810 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 Hals and EinarstaSir (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. Jons son'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. 

 Biatora Tornoensis. 

 Lecanora svmmicta. 



Pertusaria xanthostoma. 

 Lecanora protuberans. 



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. 

 Cetraria snepincola. 

 Parmelia olivacea. 

 Placodium ferrugineum. 

 P. vitellinum v. octosporum. 

 Lecanora hypnorum. 



Lecanora subfusca (with var. coilo- 

 carpa, albella, glabrata, rugosa). 

 L. varia (with var. symmicta). 

 L. protuberans. 

 L. verrucosa. 

 Pertusaria communis. 



