The Botany of Iceland - 01.12.1928, Blaðsíða 31

THE AERIAL ALGÆ OF ICELAND
355
d. Bridle-Paths.
The oldest roads in Iceland are the bridle-paths (Icelandic: gata)
which are found all over the island. They are narrow beaten tracks,
only just broad enough for the hoofs of a horse. A low growth of
mosses is often found here, and among tliese algæ, especially Dia-
toms, occur. One would expect the algal vegetation here to be
characterised to some extent by nitrophilous species since there
will of course sometimes fall dung on tlie paths, but at the same
time it might be expected that the original character of the soil
would assert itself. Sample Nr. 28 is derived from a bridle-path
running across mvri, and here it is obvious that the Diatom species
of the mýri predominate, especially Nitzschia amphibia, N. communis,
and N. Palea, further Rhopalodia gibberula and R. ventricosa, as well
as Epitliemia Argus and Eunotia prœrupta f. curta. In the other
samples (219, 254, 373) Navicuta Atomus is present as the represen-
tative of the nitrophilous species; in two of the samples tliere are
also forms of Navicula mutica. For the remaining species the reader
is referred to the list of the individual samples.
e. Roads and Pnrehj Mineral Soil.
Macadamised roads have recently been made in various parts
of the island, and there, too, an algal vegetation is often found,
especially along the margins of the roads. It seems less charac-
terised by nitropliilous species than in the bridle-paths, whereas
the almost purely mineral nalure of the soil seems to be decisive.
Hence I here deal with the algal vegetation of roads in conjunction
with that on purely mineral soil which, by the way, is found in
spots along the roads. These spots correspond in the main to what
I called »new soil« in 1915 (p. 301). A commencing growth of moss
protonema and small mosses are often found here and among these
especially Diatoms and Chlorophyceæ thrive well. The samples
included by me in this group are: naked soil 61, 137, 125, 138, and
roads 264, 269, 336. The Chlorophyceæ here met with were Kerato-
coccus bicaudatus, Vaucheria terrestris, and Botrgdiopsis arhiza. The
Diatom llora is rather variable. The commonest forms are Pinnu-
laria borealis and Hantzschia amphioxys, next come Navicula cincta
v. Heufleri, AchnaiLthes marginulata, and Pmnularia appendiculata
v. irrorata.