STUDIES ON THE VEGETATION OF ICELAND 59 
Some of the types of vegetation recorded from Lyngdalur recur 
here, viz. mo, jadar, myri, and flöi, while melar, mosathembur, 
and geiri were not developed. In addition there occurred the flag 
vegetation. 
The Mo Vegetation. Cf. table 14 A—B. 
In its broad features the appearance and floristic composition 
of the mo around Björk corresponds to the above-described mo at 
the higher levels of Lyngdalsheidi. 
The soil has ihe same knolly surface as that previously decribed, 
but the knolls are less conspicuous on the slopes than on the flatter 
parts. The composition of the vegetation is likewise very similar. 
Almost all the species found in the mo in Lyngdalur recur here 
and in approximately the same proportions. There are, however, 
also typical differences partly between this mo and that at the higher 
levels, and partly between the various parts of the mo around Björk. 
Three mo formations could be distinguished, an Elyna mo, an 
Arctostaphylos mo, and a Calluna-Empetrum mo. These three for- 
mations differ in the following way. The Elyna mo is found on 
the top of the many little mounds and hills which are covered 
at the higher levels of Lyngdalsheidi by the mosathembur vege- 
tation, and have a comparatively thin snow-covering. The Arc- 
tostaphylos mo is found on the sunny slopes of these hills 
below the Elyna mo, and in the drier depressions among them. 
The snow-covering is somewhat deeper here and more persistent 
than in the Elyna mo; it is the normal snow-covering in these 
parts. Transitional between the Arctostaphylos mo and the jadar 
is the third mo formation, the Calluna-Empetrum mo. Like 
the Arctostaphylos mo, this formation has the normal snow-covering 
in winter, but differs from the Arctostaphylos mo by being more 
damp. Here the ground water has an appreciable influence on the 
vegetation. In table 14 A the circling results for these three mo 
formations have been tabulated. 
Plants common to the three mo formations and the mo at 
higher levels and characteristic of the mo are, e. g. Empetrum 
nigrum, Thymus serpyllum, Salix herbacea, Festuca rubra, F. ovina, 
Agrostis canina, Carex rigida, Juncus trifidus, Luzula spicata, Poly- 
gonum viviparum, Thalictrum alpinum, Selaginella selaginoides, and 
Equisetum variegatum. Table 14 A shows the proportion in which 
the various species occur and the good agreement between the 
