The Botany of Iceland - 01.12.1928, Qupperneq 111

THE AERIAL ALGÆ OF ICELAND
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points out (1914, p. 297) that P. crispa is a saprophytic species that
only attains its full developraent where there is plenty of organic matter.
Helgi Jónsson, too, mentions (1898, p. 360) that the species is very
widespread in Iceland in places abounding in manure.
I have found very large thalli of this species, thus in sample 121
(earth, Seyðisfjörður) where one specimen had a diameter of 5 cm when
fuily extended.
Prasiola furfuracea (Fl. dan.) Men. Imháuser 1889, p. 266, 287
Heering in Pascher, Siisswasserflora Heft. 6, p. 57.
E. Icel. 113 — S. Icel. 353 — Vestmannaeyjar 406.
This species differs from the preceding one by its thalli which as
a rule are much smaller and attached to the substratum by a more
or less distinct stalk-like part, while the Hormidium forms are very
slightly developed. Thus typically developed it occurred on stones in
fences round a couple of farms, and on rocks below bird-cliffs on the
Vestmannaeyjar.
Pujrmaly maintains (1924, p. 230) that P. leprosa Kutz. is a species
quite distinct from P. farfaracea, while most modern authors following
Imháuser regard the two species as identical. He refers certain pleuro-
coccoid forms from chalk cliffs to Prasiola leprosa, amongst others
Pleurococcas calcarius Boye P. (1915, p. 320). It is probably right that
this species must be regarded as a stage of a Prasiola, a possibility
which I already referred to in 1915. But I cannot see that Puymaly
has pointed out characters by which pleurococcoid stages of the different
Prasiola species may he distinguished from each other, and when these
stages alone occur in a growth without further developmental stages,
I think it is impossible at the present juncture to say what species jrou
have hefore you.
Such a pleurococcoid form I have found on stones near the shore
on the Vestmannaeyjar (sample 405).
H. Jónsson states (1903, p. 354) that he has found P. furfuracea in
several places along the shores of Iceland on rocks, often in company
with P. stipitata.
Chætophoraceæ.
Pseudendoclonium submarinum Wille. Wille 1901, p. 29, Taf. III,
fig. 101-134. Wille 1910, p. 282.
Vestmannaeyjar 404, 405.
The species was originally described by Wille from Dröbak in
Norway where it formed coatings on breakwater stakes and other wood-
work in and near salt water, which macroscopically greatly resembled
Pleurococcus layers. Later on Wille found the species near Trondhjem
in Norway (1906, p. 17) and in France (1910, p. 282). It has besides
been observed bjr Helgi Jónsson (1903, p. 358), in Iceland, (E. lcel.
Djupivogur) and by F. Collins in North America. In all these localities
it grew on woodwork, Wille, however, found it on the brick walls of
an aquarium in F'rance.