The Botany of Iceland - 01.12.1928, Side 42

366
JOHS. BOYE PETERSEN
In the above-mentioned ravine »Stóra Gjá« near Mývatn (see p. 363)
at the bottom of which there was a hot spring (temp. abt. 28°) there
was an abundant algal vegetation on tlie earth and mud, consisting
of Oscillatoria tenuis and Diatoms in quantity, the commonest being
Achnanthes tanceotata, Navicuta cryptocephala v. veneta, N. thermicota,
Pinnularia mesotepta v. stauroneiformis, and P. subcapitata (215, 218).
On the ground on the bank of a stream issuing from Uxahver
(N. Iceland 241) with water at a temperature of 54° I found Cylindro-
spermum muscicola together with a number of Diatoms (see Boye
Petersen 1923 p. 302). Round a small »hver« (boiling spring) at
Laugarvatn (364) there was a growth of Schizothrix Friesii on the
ground, besides 4 species of Diatoms of which Caloneis fasciata was
the commonest.
At Uxahver (N. Iceland) I liave seen how a true thermal alga
will grow on the siliceous sinter above the surface of the water.
The water of the spring was so hot (near 100°) that algæ could not
grow in it, but on the siliceous sinter above the surface there was
a handsome belt of Hapalosiphon laminosus f. typica (237). I have
previously given a detailed description of the hot spring at Klepp-
járnsreykir (1923, p. 280) where Phormidium Treleasei as well as
Stigonema panniforme grew in a similar way on the siliceous sinter
(315, 316, 317, 318). Tlie latter species also grew at Deildartungahver
(333), while Calothrix thermatis occurred at Sturlureykir (330) under
almost identical conditions. As a rule Diatoms do not occur on
the sinter around the springs. An exception occux-red at the hot
spring near Helgavatn (337) where Symploca Muscorum occurred
(Boye Petersen 1924, p. 286) together with 6 species of Diatoms,
the commonest being Rhopalodia gibberuta. As will appear from
the list of them in the summary of the samples examined, these
species are not especially thermophilous but are usually found on
damp ground or rocks.
An abundant flora of algæ consisting of Cyanophyceæ, Chloro-
phyceæ and Diatoms is also vei'y often found in the luxuriant tufts
of moss growing í'ound the hot springs (Hesselbo 1918, figs. 21 —
23). If the water from a tuft of moss is squeezed into a glass, a
great ({uantitj' of these different algæ will fi'equently appear. Thus,
of Cyanophyceæ I have found Schizothrix Miilleri (Reykholt 322)
(Boye Petersen 1923, p. 290). The Chlorophyceæ are especially re-
presented by sevei'al species of Desmidiaceœ (328, 331, 334). The
Diatoms, however, are most abundantly represented. I shall not