The Botany of Iceland - 01.12.1928, Qupperneq 67

THE AERIAL ALGÆ OF ICELAND
391
only transition forms between f. Cohnii and f. Göppertiana in some few
samples. I have mentioned f. elliptica in 1915, p. 287; I have not found
it in Iceland.
Of tlie remaining forms the following, which shall now be more
closely described, were found by me in Iceland.
Navicula mutica Kiitz. f. Cohnii Hilse. Cleve Syn. I, p. 129. Van Heurck
Syn. Pl. 10, fig. 17. Van Heurck, Types No. 119.
E. Icel. 8, L. 40, L. 68, L. 69, L. 77, L. 78, L. 92, 99, L. 112, L. 113,
L 114, L. 121, L. 129 — N. Icel. L. 135, L. 137, 140, 160, L. 162, 169,
L. 173, L. 179, L. 184, L. 196, 217, 218, L. 219, L. 241, L. 242, 252,
L. 253, L. 254 — N. W. Icel. 268, L. 269 — S. Icel. 295, L. 381 — Vest-
mannaeyjar 400, L. 403, L. 407, L. 408, L. 409.
This form is characterised by its elliptic-lanceolate often slightly
rostrate valves with rounded apices. As shown in Van Heurck’s figure
(1. c.), the valve is as a rule distinctly asymmetrical, the side on which
the isolated point is found being distinctly smaller than the other one.
The punctation is rather variable, sometimes the puncta are very coarse
(samples 408, 409, forms that approach N. muticopsis West), sometimes fine.
Bristol shows various punctations (1920, p. 68 and p. 69, fig. 9,2, 3, e)
in a nurnber of different specimens which must most probably be re-
ferred to f. Cohnii.
This form, as well as other forms of N. mutica, is stated both by
Van Heurck (Traité p. 206) and Cleve (1. c.) to live chieíly in brackish
water. Judging by my experience this is hardly quite correct. They
are more probably all of them pronounced aérial diatoms, with the ex-
ception, perhaps, of some of the undulate forms which I have not had
an opportunity of observing. The form Cohnii is extremely widespread
in Iceland and most probably over the greater part of the globe, on
the surface, and I have found it in Iceland on very diverse substrata,
but most frequently on the ground near human habitations, both in the
towns and near the farms, on the turf of which the older houses are
built, on fences round the tún, etc. In sucli places I liave often found
it in very great quantity in the samples. This agrees well with my ex-
perience from Denmark (Boye P. 1915, p. 287), wliere I have found it
on the manured soil both of gardens and fields as well as on a purely
mineral substratum. In England Miss Bristol has likewise found the
species in samples chiefly of arable soil. It would seem, however, that
the species thrives best on a substratum abounding in organic and more
especially nitrogenous substances. This form of the species was found
by Moore and Carter (1926, p. 118) in samples of soil taken from a
depth of down to 4 feet.
— — f. ventricosa Kiitz. Cl. Syn. I, p. 129. Meister 1912, Taf. XIX,
fig. 16.
N. Icel. L. 137, 217, 218.
The specimens I have seen from Iceland bear most resemblance to
Meister’s figure cited by me, but are somewhat longer and thus ap-
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