The Botany of Iceland - 01.12.1928, Side 32

356
JOHS. BOYE PETERSEN
f. Cultwated Soit.
The cultivated area of Iceland is srnall. It may be divided into
»tún« (homefield) and arable land. Every farm has a tún covered
with a dense, luxuriant growth of perennial grass. Undoubtedly
various algæ will always be present there, but evidently the)r rarely
form maeroscopically visible growths. I have collected no samples
from tún. Mr. Molholm-Hansen took a sample in a sterile glass
from the tún at the farm Björk in Árnessýsla. A culture of this
sample in a fluid medium developed the following algæ: Botrydiopsis
minor, Bumilleria exitis, Bumilleriopsis brevis, Hormidium flaccidum,
Tribonema vulgare, Hantzschia amphioxys v. xerophila, Pinnularia
borealis, P. intermedia.
Tilled soil is even less common in the island than grassland.
It is generally used for growing potatoes. I have collected two
samples from potato fields (297, 338), the íirst-mentioned from Geita-
berg where the field immediately adjoined the »hiað«. Here I found
a growth of Phormidium capitatum, Prasiola crispa, besides 7 species
of Diatoms of which Navicula Atomus and N. nitrophila were the
commonest. In the second sample I found Botrydiopsis arhiza,
Vaucheria hamata, Navicula thermicola, Pinnularia appendiculata,
P. molaris, and other Diatoms.
g. Mýri.
With regard to the vegetation of phanerogams on mýri the reader
is referred to Helgi Jónsson (1900, p. 23). According to Molholm-
Hansen’s determinations the soil has a comparatively low pH-value,
viz. from 4.8 to 6.3 (se above p. 353). The surface of the mýri is
often covered with hillocks, and just as there is a difference belween
the higher plants on the hillocks and in the depressions between
them, so also is there a difference in the algal vegetalion. In the
depressions it consists almost entirely of hydrophilous species, but
on the hillocks it grows poorer and assumes more of the character
of an aérial algal association. In a mýri at a height of 300 m above
Seyðisfjörður I collected a sample from a hillock (4), which con-
tained Stiyonema sp., and 7 species of Dialoms, among which were
Anomoeoneis brachysira, Pinnularia borealis, and P. subcapitata, which
must be regarded as good terrestrial Diatoms. Among the mosses
in the depressions between the hillocks (samples 3, 5) I found the
following species: Stigonema mamillosum, Fischerella sp., Mesotœ-
nium sp., Cosmarium sp., Stigonema turfaceum, Gloeothece tepidario-