The Botany of Iceland - 01.12.1928, Qupperneq 50

374
JOHS. BOYE PETERSEN
This rarely observed variety was found by 0strup in 1 sample
from fresh water. Like the other varieties of this species it is hardly
an aerial form.
Fragilaria construens var. binodis Grun. V. H. Traité p. 326. Pl. 11,
fig. 452.
N. Icel. L. 169.
0strup 14 samples.
— — var. venter Grun. V. H. Traité p. 325, Pl. 11, flg. 451.
N. Icel. 252.
0strup 53 samples.
— — var. genuina Grun. Meister 1912 p. 67 Tab. VI, íig. 6.
N. Icel. L. 169.
0strup 52 samples.
Fragilaria lævissima Cleve. Cl. 1898, p. 9. Boye Petersen 1924 II,
p. 318, fig. 7.
E. Icel. 99, 128 - N. Icel. L. 179, 252 - W. Icel. 336 — S. Icel. L.?327.
Area: Jan Mayen, Fr. Jos., Murray Isl., Walrus Isl., N. Greenl.
This species which lias only been observed a few times, is pre-
sumably of northern distribution. It occurs in quantity in several of
the samples mentioned above, thus in sample 179, which was collected
on the ground in a lava cave where sheep had sheltered in bad weather,
and where there was consequently some manure on the ground. It seems
especially to thrive well on rocks with dripping water. Not previously
found in Iceland. Probably an aérial species.
Fragilaria mutabilis Grun. Meister 1912, p. 68, Tab. VI, fig. 14.
E. Icel. 85, 99, 128 — N. Icel. 161.
Three of the above-mentioned samples are derived from rocks with
trickling water, so presumably the species is not uncommon in such
localities. However, it appears to be commoner in fresh water since
0strup has found it in 39 samples from such localities.
Fragilaria virescens Ralfs. Meister 1912 p. 66, Tab. V, fig. 26.
E. Icel. 113, 123 — N. Icel. L. 169, 256 — W. Icel. 321, 327, 336,
338 - S. Icel. 295.
0strup has it from 30 samples from fresh water. In most of the
above-mentioned samples I found only a few specimens of the species.
I only found it in greater quantity in samples 169 and 256, both ori-
ginating from places where there is plenty of water, at any rate at times.
Will hardly withstand any very intense desiccation.