The Botany of Iceland - 01.12.1928, Side 92

416
JOHS. BOYE PETERSEN
Nitzschia communis Rabenhorst. Cl. et Grunow, Arct. Diat. p. 97.
Van Heurck Sjrn. Pl. 69, íig. 32.
E. Icel. 25, 28, 99 - N. Icel. 217 — S. Icel. 386.
0strup does not niention this species. I have not been able to
find specimens with cell contents in any of the samples which all origin-
ated from places with a fair amount of moisture. Hence the species
will not, probably, withstand much desiccation.
----var. abbreviata Grun. Cl. et Grun. Arct. Diat. p. 97. Van Heurck
Syn. Pl. 69, fig. 35.
E. Icel. 7, 28, 121 — N. Icel. L. 133, L. 137, 217, L. 218 - W. Icel.
L. 307, L. 337 - S. Icel. 352.
I have previously observed this short variety of N. conmuinis on
eartli in Denmark. In Iceland it has not been observed before, but
seems to be fairly common on earth. It was frequent in samples 133
and 137. In several of the localities mentioned there was plenty of
manure (28, 133, 307).
Nitzschia debilis (Arnott) Grun. Van Heurck, Traité, p. 385, Pl. 15,
flg. 497.
E. Icel. 7, L. 25, 128 — N. Icel. 217, 218, L. 253 — Vestmannaeyjar
L. 399, 410.
I have previously found this species in Denmark on earth of various
kinds. In Iceland 0strup only found it in one sample from fresh water,
hence it must be assumed to be a true aérial species. Judging from
the occurrences here observed it would seem to thrive best on a purely
mineral ground. It is only in sample 410 (bird-cliff) that large amounts
of nitrogenous organic substances may be supposed to have been present.
Nitzschia Denticula Grun. Cl. und Grun. Arct. Diat. p. 82. Van H.
Svn. Pl. 60, fig. 10.
E. Icel. L. 7, L. 85 — N. Icel. 217 — W. Icel. 338.
The species, which was found by 0strup in 28 samples from fresh
water, evidently only occurs occasionally on land where, however, it
will thrive well when it is not too dry. It does not seem to require
much organic matter in the substratum.
Nitzschia dissipata (Kiitz.) Grun. Cl. und Grun. Arct. Diat. p. 90.
Van Heurck, Syn. Pl. 63, fig. 3.
E. Icel. 7.
A few specimens were found in the sample of a Nitzschia with almost
central carina and the following dimensions: L. 24/<, br. 3,6/í, carinal
dots abt. 10 in 10 /i, striæ very fine. I take these to belong to N. dis-
sipata though the dimensions do not quite agree with those given by
Cleve and Grunow (1. c.). Tbe species has previously been found on
damp rocks and in similar localities (v. Schönfeldt 1913), also in a
rocky cave (Hustedt 1922, p. 100).