STUDIES ON THE VEGETATION OF ICELAND ul 
1—5 show what species are characteristic of the mo, and the F.- 
percentage of the individual species. Passing from the mo to one 
of the vegetation types previously mentioned, a transition zone will 
often be met with in which the frequencies of the species have 
undergone great changes. In table 11, 5, 6, and 7 show such 
transition zones passing into geiri, mosathembur, and jadar respec- 
tively. A comparison of these zones, on the one hand with the 
mo vegetation, on the other with the respective types of vegetation, 
will show that statistically, biologically and floristically, the zones 
occupy this intermediate position. 
No. 5 shows the transition from mo to geiri. The geiri plants 
Vaccinium uliginosum, Luzula multiflora, and Anthoxanthum odoratum 
show a comparatively high F.- percentage, while a mo plant Elyna 
Bellardi is inconspicuous. The proportion of A and E species points 
in the same direction. No.6 is a transitional form between mo- 
sathembur and mo. A number of species which occur commonly 
in the mo, only appear sporadically here: this is the case with 
Deschampsia flexuosa, Galium boreale, Selaginella selaginoides, Thymus 
serpyllum, and Trisetum spicatum. The density of the species is ap- 
preciably diminished, being 8.6, and the character of the environment 
more arctic. The G percentage is comparatively high. 
No. 7 is the moist mo which forms the transition to the jadar 
vegetation. Most of the plants of the mo recur with the same F.- 
percentage, a number of jadar plants such as Deschampsia ceespitosa, 
Luzula multiflora, Salix phylicifolia, Viola palustris, Cardamine pra- 
tensis, and Taraxacum officinale begin to thrive better. 
Nos. 8—9 are typical mo at a somewhat higher level, viz. 300— 
400 m above sea level. The vegetation has assumed a more arctic 
character. Salix herbacea is beginning to predominate in the phy- 
siognomy of the vegetation. 
As previously indicated, the mo is the most widely distributed 
type of vegetation in the Icelandic lowland where it probably com- 
prises a fairly large number of formations. It must be left to future 
plant geographers to classify and characterise these formations with 
regard to environment, biology, and flora, and to correlate them. 
The Jadar Vegetation. 
Between the mo, whose degree of moisture is exclusively de- 
termined by the precipitation, and the myri, whose degree of moisture 
is determined, in addition, by the ground water, there occurs a belt 
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