The Botany of Iceland - 01.12.1928, Side 40

364
JOHS. BOYE PETERSEN
borealis, and on the ridge between Isatjörður and Flateyri, close to
the highest beacon, on loose blocks of lava, I found several íine
green growths of Prasiola crispa with a little Hormidium flaccidum
and a nuinber of Diatom species, the commonest of which was
Pinnularia borealis (sample 268). It is verv peculiar that such a rich
algal vegetation can be found in these two, evidently very dry,
places, quite open to the wind.
Stones near tl\e sliore liave no doubt a special association of
algæ. As an example I can only niention a large stone near the
shore on Heimaey which was covered witli a green pulverulent
layer of Pseudendoclonium submarinum and Prasiola sp.
e. Iiird Cliffs (406, 407, 408, 409, 410).
The steep rocky walls facing the sea which are so common in
Iceland are generally inhabited by counlless seabirds and are then
called bird cliffs. I liave only been able to examine one such cliff,
on Heimaey (Vestmannaeyjar). Rising steeply from the low neck of
sand connecting Heimaklettur with tlie rest of the island, it forms
a grassy slope to about 50 metres’ height, and thence rises perpen-
dicularly to double tbe height (Fig. 2). On the small ledges and in
the cracks in the perpendicular wall the birds build, and their
droppings manure the rocks and the grassy slope below. The samples
of algæ were gathered at the bottom of the perpendicular wall, thus
at a height of about 50 m. As might have been expected, some
nitrophilous species were found, viz. Prasiola crispa, P. furfuracea,
Phormidium aulumnale, P. snbfnscum, Navicnla Atomus, Navicula
mulica f. Cohnii and f. minima. The presence of some brackish
water species inust presumably be ascribed to the proximity of the
sea. These were: Rhizoclonium lapponicum, Vaucheria synandra,
Navicula cincta, N. gregaria, Nitzschia vilrea v. salinarum. Further
a series of indifferent species were found, such as Desmococcus vnl-
garis, Achnanlhes coarctata, A. lanceolala, Caloneis fasciata, Hantzschia
amphioxgs, Navicula contenta, N. perpusilla, N. pusilla, Nitzschia debilis,
N. Sigma v. Clausii, Pinnularia intermedia, P. parva v. Lagerstedtii
f. interrupta.
3. The Algal Vegetation round Hot Springs.
Hot springs are found in nearly all parts of the island. A very
peculiar algal vegetation occurs in the water itself and often spreads
to the surroundings of tlie spring where it is not directly wetted