The Botany of Iceland - 01.12.1928, Side 26

350
JOHS. BOYE PETERSEN
on the woodwork, and I should imagine tliat the brickwork is better
able to absorb moisture from the ground than the woodwork, and
retains it with greater energy. I have had material from 4 localities
(15, 197, 352, 395).
In all four samples Chlorophyceæ as w:ell as Diatoms were
found, though it is doubtful whether these had been alive on one
of the wTalls (197). Prasiola crispa constituted the greater part of the
three samples (15, 197, .352). The other algæ were Rumilleria exilis,
Chlorella ellipsoidea, Hormidium flaccidum, Oocystis rupestris and
Stichococcus bacillaris. The Diatoms wære chiefly represented by
Hantzschia amphioxys, Pinnularia borealis, Navicula Atomus, and
N. nitrophila. For the remainder of the species the reader is referred
to the list of the separate samples.
3. Turf Walls.
On the turf wralls of the old farms a somewhat different com-
munity of algæ is found. Among the green algæ Prasiola crispa
is the commonest, and sometimes Hormidium flaccidum occurs.
Besides these I have found a greater or less number of Diatoms in
all the samples, they were, however, only represented by dead fru-
stules so that in several instances it was quite impossible for me to
find any specimens with cell-contents. Possibly this is due to the fact
that the Diatoms struggle hard 1‘or existence here, so tliat the greater
part of tliem perish in protracted periods of desiccation. It may
also be that most of the Diatoms have been brought to the place
with the turf which may have been cut in bogs where there is
often a great degree of moisture. The frequent occurrence here, for
instance, of Melosira crenulata here must no doubt be explained
in this way. The samples collected from this kind of locality are
Nos. 40, 77, 196, 294, 325.
4. Turf Fences.
Fences around the »tún< or home field, are often made of piled
turf. Froni such fences I have collected a couple of samples (182,
381). It turned out that they contained Diatoms and one of them
Prasiola crispa. Quite otherw ise than on the turf in the house-walls
I found only terrestrial species on the fences, especially Hanlzschia
amphioxys, Navicula Atomns, N. mutica, and Pinnularia borealis.
The two latter kinds of habitats resemble the ground very much