VI THE DISTRIBUTION OF. SPECIES; ‚SPE@E=Z 
GROUPS, AND LIFE-FORMS IN THE FORMATIONS, 
ARRANGED ACCORDING TO INCREASING PREVAL- 
ENCE OF ONE AND THE SAME EXTERNAL FACTOR 
1: the two preceding chapters we have treated in more detail a 
series of Icelandic formations with respect to their environment 
and their floristic and biological characteristics. A very important 
part still remains to be treated, viz. a determination of the areas 
covered by the individual species within the tracts examined. 
The most obvious method of determination would be to map 
the formations within the tracts examined, and determine their areas 
on the basis hereof. But this work would involve too much time 
and trouble if it were to be accomplished in a fairly reliable way. 
A more practical method has been worked out by Thore Fries 
in 1919. The mode of procedure in this method, “the synecological 
line taxation method”, is as follows. A system of definite lines, 
drawn according to more precise rules, is laid down, and the lengths 
of line covering the respective formations, are then measured. If 
the system of lines is correctly laid, that is to say, if the lines are 
laid sufficiently close together, the sum of the lengths of line cover- 
ing a given formation will afford a measure for the area covered 
by the formation within the tract examined, and the proportion of 
the length of line covering a given formation to the total length of 
the line system will correspond to the proportion of the area covered 
by the formation to the total area of the tract examined. (Th. Fries, 
1919, p. 3). 
In my investigations of the Icelandic vegetation I did not em- 
ploy Fries’s line taxation method, a fact which I have often 
regretted during my elaboration of the material, but during inves- 
tigations in Denmark I have often experienced how practical this 
method is compared with the usual mapping of the formations of 
an area. Thus I have the same experience of the line taxalion 
method as has Thore Fries of Raunkiær’s circling method.... 
