192 OLAF GALLOE 
Such a Glycerietum is often abundantly mixed wlth Agrostis alba 
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 Paludella-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 Cyperaceæ-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 Eyjafjördur 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, 
and 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 them in the field. But even now an orientation may 
be had. It is for instance known that not only highly mixed carpets 
of both Gramineæ and Cyperaceæ are found, but also purer carpets 
