. STUDIES ON THE VEGETATION OF ICELAND 181 
The forest ground vegetation resembles the geiri vegetation 
in external factors and in its main features. The density, the number 
of high-arctic plants, and the quantity of Ch are less in forest ground 
than in geiri, while the quantity of H is higher. The cause for this 
may perhaps be found in the differing illumination and the more 
constant protection from frost in the forest ground than in the geiri. 
Each of the types of vegetation discussed above comprises a 
great number of formations which have not, as yet, been more closely 
examined. 
7. Our knowledge of the quantitative distribution of the indi- 
vidual types of vegetation in the various parts and altitudinal zones 
of Iceland is as yet rather deficient. Of the percentage of types in 
the individual altitudinal zones, the following particulars may be given. 
I. In the lowlands, below the 20 p. c. Ch biochore, the 300 m 
eurve, the dominant features of the landscape are forest, mo (espe- 
cially heather mo), jadar, littoral meadow, flag, myri (för myri, halla 
myri, and fét myri), flöi, dy and fen, and lowland melar. 
II. In the lower highland zone, 300—600 m above sea-level, 
the types of vegetation are melar (highland melar), mosathembur, 
mo (level and knolly), jadar, myri (för myri), flöi, dy, and geiri (in- 
cluding the Salix herbacea and the Sibbaldia vegetation). 
III. In the upper highland zone the vegetation is either melar 
or geiri (especially Anthelia crusts). 
IV. In the zone between the 800 and 1200 m curves, the nival 
zone, a very scattered melar vegetation is recorded. The larger or 
smaller accumulations of snow are another feature of the landscape. 
Above the 1200 m curve, the snow line, we come to the 
V. zone, the jökulls, where all higher vegetation is excluded on 
account of the continuous snow-covering. 
The forces that go to form the various types of vegetation are, 
in the lowlands, especially the differences in moisture, in the high- 
lands, the differences in snow-covering. 
8. The investigation of the distribution of species, species-groups, 
and life-forms in the formations according to increasing prevalence 
of one and the same external factor has brought to light the fol- 
lowing facts. 
In a given scale of one and the same external factor the indi- 
vidual species attain maximum frequency, i. e. minimum distance 
between individuals, at some point in the scale. Passing from this 
point towards either greater or less prevalence of the factor under 
