The Botany of Iceland - 01.12.1928, Page 82

406
JOHS. BOYE PETERSEN
Forms of P.lata have previously been found on damp rocks (De
Toni, v. Schönfeldt, Hustedt, Deflandre 1926), hut no doubt the
species occurs most commonly in fresh water. 0strup does not men-
tion v. Rabenhorstii as occurring in Iceland. I dare not infer from this
fact, however, that it was not present in the material. Possibly 0strup
may not have distinguished it from the main species, and perhaps there
is not sufficient reason to do so.
The 4 samples from E. Icel. in which I found specimens with cell
contents were all derived from damp rocks, and precisely from very
moist parts that will hardly ever be quite dry even in summer. The
sample from S. Iceland originates from turf in the wall of a house, in
a place where the water runs down in rainy weather, hence the most
damp place of the wall. Thus this form will not, probably, survive much
desiccation, nor does it probahly need much organic nourishment.
Pinnularia major Kiitz. CI. Syn II, p. 89. A. S. Atl. Taf. 42, flg. 8.
N. Icel. L. 215.
The form found in this sample was somewhat smaller than the one
described by Cleve (1. c.). Its dimensions were: L. 169 /u, br. 28 p,
str. 8,2 in 10 ju. The sample was taken from very damp mud from the
floor of the ravine »Stóra Gjá« near Mývatn, and the species can hardly
be an aérial one.
Pinnularia mesolepta Ehrb. var. stauroneiformis Grun. Cl. Syn. II,
p. 76. Ad. Schm. Atl. Taf. 45, fig. 53.
N. Icel. L. 215, L. 217, L. 218 - S. Icel. 372.
According to 0strup var. stauroneiformis is the most commonly
occurring form of P. mesolepta in Iceland, where he found it in 55 samples.
The 3 above-mentioned samples from N.Icel. all originate from »Stóra Gjá«
where it is probably always moist. This form can therefore hardl}7 be
reckoned among the true aérial algæ. But few specimens were found in
the sample from S. Icel., and possiblv they had not lived on thc spot
(ground in front of the house).
Besides the typical form, another form, shorter, hardly capitate and
with straight lateral walls, was found in samples 215 and 217. Its di-
mensions were: L. 28 p, br. 11 ju, str. 14 in 10 p. This form I have here
included within the present variety, since it forms a gradual transition
to the typical form by intermediate forms. But it might perhaps with
equal correctness be referred to P. microstauron.
Pinnularia molaris Grun. Cl. Syn. II, p. 74. A. Schm. Atl. Taf. 313,
fig. 18.
E. Icel. 7, 8, 125 — N. Icel. L. 215, 217, 218 — W. Icel. L. 307, 309a,
L. 321, L. 336, L. 338 — S. Icel. L. 352, L. 364.
0strup only found the species in 3 samples from fresh water in
Iceland, so according to the data it is probable that it lives chiefly as
a terrestrial species in the island. I have found it several limes (samples