STUDIES ON THE VEGETATION OF ICELAND 123 
"the method, in my opinion, constitutes an ingenious and satisfactory 
solution of the problem.” (Th. Fries, 1919, p. 4). 
I can likewise fully support the author when he goes on to say, 
“Raunkier’s circling method and the synecological line taxation 
method complete each other. By the former we obtain exact 
knowledge of the nature of the units, by the latter of their area and 
distribution. Synecological plant geography should be able to make 
great progress in exactitude by these two methods. Synecology now 
need no more rank last in this respect among the various branches 
of botany, on the contrary, it should soon be able to take up its 
position as one of the first.” 
However, the results which these two methods will be able to 
produce, viz. an exact description of the plant series of the face of 
the earth, only constitute one aspect of plant geography, the geogra- 
phical aspect. For such a description is primarily of importance 
in its bearing on geography. The botanical aspect proper will only 
appear when, in addition, we investigate the external factors which 
determine the distribution of the individual biological or syste- 
matic units. 
If we follow the ordinary scientific method of investigating the 
facts in connection with a given unit by varying only one external 
factor at a time and as far as possible keeping all the other factors 
constant, this means, in the case of the doctrine of formations, that 
we must primarily examine the distribution of the indi- 
vidual species within the formations, arranged according 
to increasing prevalence of one and the same external 
factor. The resulting facts may then be made the basis of more 
detailed ecological considerations. 
In the present chapter we have examined the distribution of a 
series of Icelandic species partly in relation to the Icelandic scale 
of moisture, partly in relation to the scale of snow-covering. The 
material employed is the same which was utilised for the formation 
statistics of the two preceding chapters. On the basis of this ma- 
terial we have further examined the distribution of Raunkiær's 
life-forms and the species groups in relation to the above-mentioned 
two scales. 
The Scale of Moisture. 
Under the treatment of the formations in the localities examined 
the degree of moisture has been more precisely described. 
