1 ( J2 Dl. Al (,ALI.0K 



Such a Glvcerietum is often abundantly mixed with Aqrostis 



d *- \j 



and as regards growth-form, is consequently, on the whole, a grass- 

 land, but differs in many respects so widely from the other grass- 

 areas inland, that its associates are very different from those of 

 these inland grass-areas. 



This example is mentioned here merely to emphasize the com- 

 monly-existing rule which I demonstrated several years ago, that 

 soil containing chloride of sodium is devoid of lichens. Not only 

 would the presence of this substance, poisonous to lichens, but also 

 the very high level of the ground-water undoubtedly, in itself, suffice 

 to exclude lichens. 



When the ground-water is fresh (lakes, etc.) a fixed succession 

 of associations is no doubt developed in Iceland as with us in Den- 

 mark; those of Denmark are excellently set forth in Mentz's 

 (Mentz, 1913) work on the recent vegetation of the Danish bogs, 

 in which he demonstrates the transition from reed-swamp through 

 mud-meadows to grass-bogs or PaludeUa-bogs and on to other vege- 

 tations (Sphagnum-bogs, etc.). With regard to Iceland we have not 

 as yet such exhaustive descriptions ; it is however already known 

 that reed-swamps occur, passing into wet Ci/joeracece-meadows, etc., 

 and thence transitional forms to grassland. 



But whether the ground-water is fresh or salt, it must be em- 

 phasized as a common feature, that lichens are absent everywhere 

 where the ground- water, even during a shorter period of the year 

 only, stands up to the level of the plant-covering or even above it, 

 as in Denmark. I have observed such extensive meadows, devoid 

 of lichens, in several places near Eyjafjordur and elsewhere. 



The drier, lichen-containing grassland will be treated more fully 

 in the following pages. 



There exist no statistical investigations of the frequency-number 

 of the grass species which occur in the grass-carpets, from which 

 the various types of grass-areas could be designated or named. It 

 is mentioned in the literature on the subject that the list of species 

 from the different substrata (level land, mountain sides, home-fields, 

 etc.) differs, but an exhaustive statistical verification is still wanting, 

 ;iiid is also difficult to obtain, as the grasses are usually closely 

 grazed by sheep so that it is a difficult or at any rate a slow work 

 to determine tlu-m in the field. But even now an orientation may 

 be had. It is for instance known that not only highly mixed carpels 

 of both Grdininew and (lyperaceit- are found, but also purer carpets 



