The Botany of Iceland - 01.12.1928, Side 86

410
JOHS. BOYE PETERSEN
P. viridis var. commutata is undoubtedly most widespread in fresh
water (0strup 148 samples). Nevertheless it not infrequently occurs
on land, and in 5 samples I found specimens with cell contents. In
most cases I found it among mosses on rocks or on purely mineral
ground, but also in a few cases near houses (samples 40, 92, 298).
Probably it is among the forms that cannot thrive on soil containing
much organic substance. In this connection I may mention that Kolk-
witz and Marsson (1900, p. 517) regard P. viridis as oligosaprobe.
Pinnularia viridis Nitzsch v. rupestris Hantzsch. Cl. Syn. II, p. 92.
A. S. Atl. Taf. 45, flg. 38-44.
W. Icel. 338.
In the specimens found the apical area seemed somewhat broader
than typical of this form. Found in a sample from a potato íield
near the hot springs at Helgavatn, among Vaucheria.
VII. Gomphonemeæ.
Gomphonema Ag.
Gomphonema acuminatum Ehrb. f. coronata Ehrb. Cl. Syn. I, p. 184.
G. acuminatum V. H. Syn. Pl. 23, flg. 16.
N. Icel. L. 169.
The sample in which this form was found originates from a very
damp locality. It is hardly an aérial alga.
Gomphonema angustatum Kíitz. var. productum Grun. Cl. Syn. I, p. 181.
Van Heurck, Syn. Pl. 24, fig. 52—55.
E. Icel. 8, 41, 77, 78, 112, L.? 113, 123, 125 — N. Icel. 162, 173 —
W. Icel. 297, 336 - S. Icei. 295.
As will appear from the above list of localities, this variety was
found in 13 samples; however, it was not possible to ascertain the
presence of individuals with cell contents. Since there were also only
few specimens in each sample, and since it is common in fresh water
(0strup 87 samples), it is not probable that it is particularly well
suited for an aérial life.
Gomphonema gracile Ehrb. var. dichotomum (W. Sm.) Cl. Cl. Syn. I,
p.182, Van Heurck Syn. Pl. 24, fig. 19.
E. Icel. L. 15.
This otherwise very widespread and common form is evidently not
very common in Iceland (0strup 4 samples). In the sample I found
it living among Prasiola on a wall.
Gomphonema intricatum Kútz. Cl. Syn.I, p. 181. V.H. Syn. P1.24,fig.28.
N. Icel. 256.