STUDIES ON THE VEGETATION OF ICELAND 71 
pronounced southern (Th) types of plants it is one of the most re- 
markable and interesting vegetations of Iceland. 
The flag occurs as from 2—3 to 15—20 m. wide and often very 
long clayey flats delimited upwards towards the mo by a more or 
less connected slope and outwards towards the myri by a con- 
nected ridge (cf. figs. 11—12). The soil of the flag is level and hori- 
zontal. If covered with water the whole of the summer it is a 
naked clayey flat without any trace of knolls. If such a flat is laid 
dry, the familiar polygonal cracks appear. If the soil is not covered 
with water in the summer, it will always be cracked, and a greater 
or smaller number of small knolls covered with vegetation will be 
spread over the surface. Such is the typical appearance of the flag. 
If the soil grows drier still, the knolls increase in number as well 
as in size and we get the flag mo, though the bare clay surface still 
predominates. 
The flag vegetation seems to comprise a number of for- 
mations. Table 17 A shows the circling results for three such for- 
mations, the Subularia flag, the Koenigia flag, and the flag mo. 
The Subularia flag was examined in a single locality, the 
myri at Björk. Here a long strip of Koenigia flag occurred in con- 
nection with a small brook. The Subularia flag was found at the 
transition from the Koenigia flag to the brook. At the time when 
the investigation was made, (the close of July), the soil was covered 
with water. In the deepest water only scattered specimens of Subu- 
laria aquatica were found (table 17 A, 1), while further in (table 
17 A, 2) it was found in company with some other species such as 
Koenigia islandica, Juncus bufonius, Equisetum arvense. 
From East Iceland a formation has been recorded by Helgi 
Jönsson which must probably be referred to the flag. “Where 
the soil has an admixture of clay little pools are formed in the 
depressions which evaporate in the course of the summer. In these 
places the vegetation varies not a little, consisting now almost ex- 
clusively of Subularia aquatica, now on the other hand only of 
Ranunculus reptans which colours such spots quite yellow. I have 
seen both species occur in such quantities that they coloured the 
whole bottom of the pool white or yellow. In other places I saw 
that the vegetation consisted of Ranunculus reptans, Subularia aqua- 
lica, Alopecurus fulvus and Juncus supinus fairly equally distributed, 
so that neither one nor the other could be designated as the cha- 
racteristic plant.” 
