The Botany of Iceland - 01.12.1928, Qupperneq 71

THE AERIAL ALGÆ OF ICELAND
395
N. Icel. 217. L. 218 - W. Icel. L. 338.
This small species much resemhles Navicula Borrichii, but is smaller
and with Ihinner valves than that species, thc outline of the valves being
also different, but evidently it is not far removed from it. Found on
mossgrown stones and earth near hot springs (Stóra Gjá, Helgavatn).
Naviculœ entoleiœ Cl.
Navicula contenta Grun. Cleve Syn. I p. 132, N. trinodis Van Heurck
Syn. Pl. 14, fig. 31 a. N. c. var. biceps Cl. Syn. I p. 132, Van Heurck Syn.
Pl. 14, íig. 31 b.
E. Icel. 7, 14, 24, L. 68, 69, L. 70, L. 85, L. 99, L. 129, 123 — N. Icel.
133, L. 160, 169, 179, 215, 217, L. 218, L. 219, 241, L. 253, L. 254 -
N. W. Icel. 268 — W. Icel. 337 — S. Icel. 352 — Vestmannaeyjar 400.
The typical form of the species frequently occurs intermixed with
var. bieeps, and all transitional forms betwecn them are found. Hence
I feel convinced that tliese two forms may without harm be included
within one species, merely representing as they rio the extremes in the
series of variations. In a number of samples I have found a form en-
tirely destitute of the gibbosities of the valve, of a regular linear form
which I provisionally associate with this species. It was present in the
following samples: N.Icel. 162 — Vestmannaevjar L.401, I..403, L.408, 409.
The species has long been recognised as an aérial species, thus
by Van Heurck, Cleve, Hoye Petersen,West, Hustedt. In Den-
mark I have found it in several places on rock and on mineral ground
(Boye Petersen 1915, p. 20). West (1916, p. 421) found it in quantity
as an epiphyte on the leaves of trees in thc West Indies, and Hustedt
found it in a rock cave (1922, p. 98). Finally Miss Bristol (1920) pro-
duced it in cultures in samples of earth that had been dried up to
26 weeks. It would seem then to have considerable abilitj' to withstand
desiccation. In Iceland I havc found it on more or less damp rocks,
on purely mineral ground, among inosses, but only rarely near human
habitions. Hence it seems chieíly to thrive well on pure mineral ground
where only few organic substances are present. It was particularly
common in the samples from rocks, thus in samples 68, 70, 85.
Navicula perpusilla Grun. Van Heurck Syn. Pl. 14, fig. 22, 23. Cl.
Syn. I p. 133. Vnn Heurck Types No. 212, 148.
E. Icel. L. 24, 68, 69, L. 70, 78, 85, L. 99, 123. 124, L. 128, L. 129 —
Vestmannaeyjar 400, 401, 408.
Area: Eur., Arct. Amer.
Curiously enough, 0strup has not menlioned this species as a na-
tive of Iceland. I have, nevertheless, ascertained its presencc in several
of the preparations examined bv 0strup. He must. then, have over-
looked it. As regards its habitat my investigations quite confirm what
v. Schönfeldt says as to its occurrence: >Zwischen Moosen an úber-
rieselten Felsen«. 12 of the 13 localities mentioned above are of this