18 H. MØLHOLM HANSEN 
zones on the other hand. The above-mentioned facts may, however, 
be utilised to fix one biological line of demarkation in Iceland, viz. 
the 20 p.c. Ch biochore. The lowest zone, the 300—400 m zone, has 
a Ch percentage of 20.1. The Ch percentage in the lowlands is 
below 20, and as it is a rule that species decrease in number as 
we go upward, while only a few or no species are added from 
above, the 20 p.c. Ch biochore may with fair accuracy be put at the 
lower limit of the zone, i. e. at c. 300 m above sea level. 
If we compare the position of the 20 p. c. Ch biochore in Iceland 
with the position of this line in other regions, we shall find very 
good agreement. In Scotland, according to Raunkiær (1908), the 
20 p.c. Ch biochore lies at a height of c. 800 m above sea level, and 
in the Faeroes at c.500 m. In Greenland only the southernmost 
part, 61—60° N., lies south of the 20 p. c. Ch biochore. In other words, 
here the line has come down to sea level. Hence the position in 
Iceland of the 20 p.c. Ch biochore at an altitude of c. 300 m is in 
very good agreement with facts in the surrounding countries. 
That Ch is the life form best adapted to the Icelandic climate 
will also appear from the lists in another way. It is clear from 
the way in which the spectra are calculated that the rarer species 
will easily come to dominate too much. This error may, however, 
be rectified by comparing the spectrum formed for a series of zones 
in the usual way with the spectrum which may be formed from 
the total of the notes for all zones. Below in table 3 this has been 
done for Iceland as a whole, for the highland tracts between 300 
and 800 m, and for the tracts between 800 and 1200 m. It will 
appear from the table with all desirable plainness that Ch show 
the best adaptation, H are indifferent, and Pt, F, HH and Th show 
the poorest adaptation to the Icelandic climate. The geophytes 
present interesting facts. In the lowlands they are best adapted to 
the climate, in the highland tracts between 300 and 800 m they 
are indifferent, while above the 800 m curve, similarly to H, they 
thrive badly. 
Though we must thus suppose from the above that Raunkizr’s 
life forms would afford a convenient basis even for a more thorough- 
going investigation of the flora and vegetation of Iceland, a classi- 
fication of the flora according to other viewpoints will always be 
of interest. Hence I have also divided the flora into groups according 
to the distribution of the species in Europe and the adjacent arctic 
