STUDIES ON THE VEGETATION OF ICELAND 129 
In the 4 moisture series examined so far, the life-forms show, 
in the main, the same sequence. 
If the biological spectra are based on species lists alone, we 
get the same sequence. 
This distribution must be regarded as more specific to the life- 
forms than to conditions in Iceland. 
In Denmark the vegetation of Nørholm Heath has been ex- 
amined with the same minute graduation of the external factors as 
in Iceland. The sequence of the maxima of the life-forms in the 
scale of moisture was the same on Norholm Heath (which, however. 
had more than 7 grades) as in Iceland, viz. HH. G, H, and Ch 
from below upwards. The rise in the Ch percentage in the lower 
section of the scale is not found here, however; on the other hand, 
there is a rise of the H percentage. 
Raunkiær (1909, 1912), C. Olsen (1914, 1921), and Grontved 
(1927) examined the vegetation on solid soil exposed to the sun. 
From their researches it will likewise appear that, if biological 
spectra for the various (more diffusely limited) zones of moisture 
are worked out on the basis of the circling results, the sequence will 
se HH,G,H, Ch, and Th. 
If biological spectra for the various zones of moisture from sunny 
open solid soil were worked out on the basis of the species lists 
alone, the sequence of life-forms was still seen to be the same. 
The correlation between moisture of soil and life-form pointed 
out above must be said, therefore, to be generally valid. In con- 
sidering the physical causes active in the formation of life-forms, 
a knowledge of this correlation is indispensable. 
The Species-Groups. Their Distribution in the Scale of Moisture. 
On the basis of particulars of the presence and quantitative 
distribution of the individual species in northern Europe and the 
adjacent arctic regions we have, in a previous chapter, divided the 
Icelandic flora into groups according to the temperature requirements 
of the species. 
The flora was first divided into two large groups: the A group 
which has its main distribution in arctic regions to the north of or, 
in mountain regions, above, the tree limit, the 20 per cent Ch bio- 
chore; and the E group which has its main distribution in the 
The Botany of Iceland. Vol. III, 9 
