1 ( .)S OLA I' GALL0E 



decimetres (dm. 2 ) with intermediate spaces of equal si/.e, viz. about 

 1 metre. 



The majority of the heaths, regarded as landscapes, are easily 

 recognizable in Iceland by their greenish-brown tone of colour, 

 which makes them conspicuous even at a fairly long distance. 

 They occur on mountain-sides up to a height of about 400 metres. 

 It is stated that on slopes (mountain-sides) the ground and hence 

 also the plant-covering is flat, whilst they are knolly and uneven 

 on a horizontal substratum. These features agree exactly with my 

 observations. 



In the following I shall give some examples of the more fre- 

 quent fades of the heath and their lichen-vegetation. 



Type I. Dry heaths on level (not knolly) ground. 



(a) Heaths rich in phanerogams but either poor in or devoid 

 of lichens. 



Near Hals parsonage in Fnjoskadalur (North Iceland) I noted 

 down that there occur extensive heaths the character plants of 

 which are Empctnim, Betula nana and various Glumiflonv, mostly 

 grasses. Each of these occur in all the sample-areas, i. e. they have 

 the frequency-percentage 100. The ground, which is gently sloping, 

 consists of line, reddish sand, and is covered by a continuous carpet 

 of the above-mentioned character-plants and by a few others which 

 have a lesser frequency-degree, e. g. Dryas, Silene acaulis, etc. 



Both the open ground and the birch- clusters are de- 

 void of lichens. 



The reason of this phenomenon merits fuller discussion. As 

 mentioned above, we can, on the whole, point out eight essential 

 factors which determine the presence or absence of earth-lichens in 

 a particular association, viz. the chemical composition of the soil, 

 the size of its grains, thermal conditions, water-contents, drifting 

 soil, burrowing animals, a layer of decaying leaves, snow-covering, 

 and competitive relations with other plants. Among these eight 

 factors we must consider more fully the layer of decaying leaves 

 and the competitive relations with neighbours. It is impossible to 

 believe that all the other factors mentioned above, could have an 

 injurious influence on a lichen-covering on the heath-areas in question. 

 But the two powerfully acting factors just mentioned are without 

 doubt instrumental in the existing want of lichens. The fact is, 

 that dwarf-birches, where they form dense growths, are fairly high 

 in growth, cast rather a deep shade, and shed a considerable number 



