LICHENOLOGY OF ICELAND 179 



sification), or the "summer-annuals," "csespitose 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 chamaephytes 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 "E/npe/rum-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, from 

 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-occurrence 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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