LICHENOLOGY OF ICELAND 179 
sification), or the “summer-annuals,” “czespitose plants,’ “creeping- 
herbs,” “shrubs,” etc., etc. (according to Warming’s classification). 
It is in reality a hopeless task to try to describe a plant-asso- 
ciation without such an analysis. I have experienced this, time after 
time, during my studies in Iceland when, in my notes, I was to 
give a name to an association. I was often uncertain as to how 
far I was now using the old, long-established terms “heaths,” “fell- 
fields,’ ‘“‘mat-herbages,” etc., etc., with exactly the same meaning as 
the creators of these terms themselves gave to them. I did my best 
to use the correct terms, but I cannot deny that it often occurred 
to me, that it would have been much easier if the terms had been 
defined somewhat more precisely. For instance, had the term 
“heath” been defined as a plant-association in which dwarf shrubs 
or chamæphytes had a definite degree of frequency, it would have 
been far easier for me to have recognized the association in question, 
in the field: also remembering the fact, that the same association 
may perhaps be named sometimes in one way, and sometimes in 
another, according as the investigator in question received a more 
strong, subjective impression of this or the other species: It is pos- 
sible that a lichenologist would occasionally speak of a “lichen- 
heath,” which a bryologist would call a “moss-heath,’ and a pha- 
nerogamologist an “Empetrum-heath” ! 
I see no other solution of the difficulty than that the investi- 
gator — be he bryologist, lichenologist, algologist, phanerogamologist 
or what else, should define the association, as far as possible, fronı 
his own point of view, and then afterwards eventually agree upon 
how the whole association is to be named, and how the divergent 
names given by the investigators, may be reconciled with one 
another. 
In the following pages I shall define the associations according 
to the dominant growth-forms. I shall go through the chief plant- 
associations, adopting in the main the division briefly given by 
Thoroddsen in this work (vol. I, pp. 317 et seq.), from which, 
however, in some points I shall differ. 
Besides this analysis of the association as regards the various 
growth-forms it contains, there are several other matters which will 
be discussed, first among which comes the mass-oceurrence of the 
different species, or growth-forms, contained in the association. 
Various methods have been used for this purpose; they have 
been described and compared by C. Ferdinandsen (1918). Their 
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