The Botany of Iceland - 01.12.1928, Side 78

402
JOHS. BOYE PETERSEN
these forms, among which transitional forms may no doubt be found,
and the nature of which is on the whole doubtful (cf. Introduction). In
the Icelandic material I myself have found the forms given below. If
in addition the dimensions were considered, a great many more forms
might be set up. I have, however, contined
myself to the following which I name pro-
visionally.
1. f. typica (A. Schm. Atl. Taf. 45, fig. 19,
20). The valve linear, with rounded or less
frequentljr somewhat ílattened apices. Shows
considerable variation in size.
2. f. Sclimidtii (A. Schm. Atl. Taf. 45,flg. l(i).
The valve linear, with more or less rostrate-
truncate apices. The valve often slightly con-
stricted in the middle. This form approaches
P. lata v. Rabenhorstii.
3. f. subcapitata n. f. The valve narrowly
lanceolate, with rostrate-subcapitate apices.
Fig. 23 a.
4. f. ovalis. The valve oval in outline,
about twice as long as broad. Fig. 23 b.
5. f. lanceolala. The valve rhombic-lan-
ceoiate, 3 times as long as broad. Fig. 23 c.
F. lypica is much the commonest of these forms. It occurred in
nearly all the samples cited.
F. Schmidtii occurred in samples 8, 182, 218, 254.
F. subcapitata is the commonest form in Iceland after f. typica, and
forms intermediate between them are often found. It occurred in samples
14, 41, 69, 121, 129, 135, 160, 161, 182, 196, 217, 307.
F. ovalis is perhaps merely abnormal. A few specimens of it were
found in samples 268 and 121.
F. lanceolata is likewise infrequent. It occurred in samples 138.
185, 295.
Fig. 23.
Pinnularin borealis Ehrb.
a. f. subcapilata n. f.
b. - ovalis —
c. - lanceolata —
P. borealis has from olden times been recognised as an aérial spe-
cies and is probably spread practically all over the globe. Being so
common, it Will always be present in small quantitjr in fresh water
samples (0strup found it in 195 samples from Iceland, but never in
great number). It has been found on red snow in Antarctica (Fritsch
1912, p. 321) and on the inland ice of Greenland (Boye Petersen
1924 II, p. 315), further in numerous localities in arctic, antarctic, tempe-
rate, and tropical countries. It will be easily understood that its valves
are common in the atmospheric dust. (0strup 1893, p. 140). This
species may therefore correctly be termed ubiquist.
As regards its occurrence in Iceland I may state that it was found
in the greatest quantity in samples that did not contain much manure,
I have, however, found it in almost every kind of locality. That it
withstands desiccation well will appear partly from Brist.ol’s (1920,
p. 42), partly from my own investigations (Boye Petersen 1915, p. 24),
and partly from mjr observations in Nature which would seem to show
that it majr live in Iceland even on the driest ground.