The Botany of Iceland - 01.12.1930, Page 162

152
H. M0LHOLM HANSEN
Subularia flag, the water-covered vegetation rich in Th, corresponds
closely to that of the flói: concentration of the species in the central
part, and preponderance of the E species.
The treatment of the distribution of the species groups and the
life-forms in the scale of moisture showed that moderately moist
soil (jaðar) caused a relative maximum of E species, hemicryp-
tophytes and therophytes. This was tlie case with the vegetation
on a gently sloping surface with even transitions from one type of
vegetation to another. However, on moderately moist soil there
occurs a series of types which, physiognomically, are rather different,
both mutually and in relation to the jaðar, but which, on close in-
spection, prove to be possessed of the pecularities of the jaðar vege-
tation, though in varying degree, viz. a relatively high H percentage
and Th percentage. Of these types the valllendi and flag vegetations
have so far been examined. The first of these types develops on
the flat cones deposited by the rivulets of melting snow on flat
ledges. The valllendi soil is thus saturated with water until the last
snow has melted, i. e. until the geiri is bare of snow. In the flag,
conditions are otherwise. If it receives any water at all while the
snow is melting, it is at most as long as there is snow on the mo.
The bare soil of the flag is thus exposed to the effects of the frost
(night frost) much longer than the valllendi, which is furnished with
fresh water daily. Hence it is hardly accidental that the E species
are more dominant in valllendi than in flag. The E percentages for
valllendi, jaðar, and flag are respectively 75, 53, and 42.
The Distribution of the Life-Forms in the Scale of
Snow-Covering.
Since differences in respect of snow-covering only appear in
areas not affected by ground-water, where, as previously mentioned,
Ch, H, and Th are the dominant life-forms, it is principally the re-
lation of the snow to these which is of interest. Table 30 shows
the biological spectra of the various classes of snow-covering in the
localities examined by me. At the bottom of the table are given
the mean values for all the iuvestigations.
It appears from the table with all desirable plainness that Ch
are more abundant on snow-bare soil than on soil with
a normal snow-covering, and more abundant there than where
the soil has a constant snovv-covering. For H the case is re-