156 H. MØLHOLM HANSEN 
forms, it will be of interest to have another system of indicators of 
environment. In the present treatise the geographical distribution 
of the individual species has been employed as an indicator of en- 
vironment. A species with a pronounced southern distribution will 
more certainly indicate a high temperature than a more northern 
species. The more southern species there occur in an area, and 
the more prominent the role they play, the more probable will it 
be that the temperature conditions are favourable. Reversely, it 
must be supposed that a preponderance of arctic species indicates 
severe cold. The proportion of southern and arctic species 
in an area will therefore indicate the temperature con- 
ditions of that area. 
In a previous chapter the species groups were dealt with in 
more detail. At the outset it might be anticipated that the species 
groups would be more sensitive indicators than the life-forms, and 
it might be claimed that the two systems of indicators should lead 
to the same result. An inspection of the tables will show to how 
great an extent this is the case. A change of environment causing 
an increase of the Ch percentage will likewise cause an increase of 
the A percentage, and numerically this increase will be greater than 
the Ch increase. 
Table 31 shows the life-form and species group spectra for a 
series of areas in which the conditions of environment are most 
clearly illustrated. The localities are arranged in groups of 3 each. 
The top group 1, comprises the land spectra for Denmark, Iceland, 
and North Greenland, group 2 the Icelandic zone spectra for the 
lowlands and the upper and lower zones of the highlands respec- 
tively, group 3 various zone spectra from Vestfirdir, for the 0— 
100 m zone, the 2—300 m zone, and the 3—400 m zone respec- 
tively, group 4 shows vegetation spectra for snow-bare, normally, 
and constantly snow-covered vegetation in the same locality, and 
group 5, finally, gives the mean values for the formation spectra 
of the various classes of snow-covering. Within each group the 
coldest area, a, is given first, the warmest, c, last. 
A closer inspection of the table will show that, compared with 
the b spectra, all the a spectra have a high Ch percentage, A 3 per- 
centage, and especially a high A percentage, while the c spectra, on 
the other hand, have a high (Ph + K— Th) percentage and (E3 + 
E2 + E1) percentage. The amount of H and (A2+A1+E4) 
species is relatively unaffected by changes in temperature in any 
