The Botany of Iceland - 01.12.1928, Síða 49

THE AERIAL ALGÆ OF ICELAND
373
Tetracyclns Ralfs.
Tetracyclus lacustris Ralfs var. emarginata (Ehr.) W. Sm. Van Heurck
Traité p. 358.
N. Icel. 256.
Only a single specimen observed. Tetracyclus Braunii is a common
species on damp rocks in Europe, and the present form may possibly
occur in a similar way. I found it on a mountain slope near Síglufjörður
Denticula Kutz.
Denticula frigida Kiilz. Meister 1912 p. 59, Tab. 5, figs. 5—6.
E. Icel. L. 25, 129.
Area: Eur.
This species is closely allied to D. tenuis Kiitz. and is as a rule, and
perhaps rightly, not distinguished from that species. According to Meister
it occurs chiefly in cold water, both running and stagnant. In sample 25,
originating from moss in a mountain cleft through which water from
the melting snow would no doubt trickle in the spring, I found specimens
with cell contents. In the other sample, from a rocky wall, it occurred
among various Cyanophyceæ, amongst others Desmonema Wrangelii, gene-
rally found, too, in cold mountain streams. It inust then be supposed
that, at any rate in the spring, cold water trickles down this rocky
wall. The two localities thus agree well with Meister’s statements.
The species will then presumably grow up in all the little streams running
down the mountain sides in the spring, and when these run dry in the
course of the summer, it will probably survive for a little while, but
later in the summer most of the specimens will presumably die, except
a few that will survive and reproduce themselves next spring. Hence
the species must probably be classed among those that form a transition
to the terrestrial Diatoms.
III. Fragilarieæ.
Fragilaria Grun.
Fragilaria capucina Desm. Meister 1912, p. 66. Tab. VI, flg. 2.
S. Icel. L. 386.
0strup only found it in 2 samples from Iceland, so it does not
seem to be common in the island. The locality in which I found it
was very damp, so it would hardly be warrantable to conclude from
this occurrence that it may appear as an aerial alga.
Fragilaria construens (Ehr.) Grun. var. pusilla Grun. Meister 1912
p. 67, Tab. VI, fig. 8.
E. lcel. 128.
The Botany of Iceland. Vol. II.
25