The Botany of Iceland - 01.12.1928, Side 72

396
JOHS. BOYE PETEHSEN
kind1). It may seem remarkable that I only have it from E. Iceland
and the Vestmannaeyjar. This, however, is presumably due to accident,
most of my collections of algæ from rocky vvalls and dripping rocks
originating from these two parts of the country.
Thus there can hardly be any doubt that this species is a true
aérial alga whose habitat is chiefly among mosses and on more or less
damp rocks. It seems able to withstand rather strong desiccation, while
apparently it requires little nitrogenous nourishment (Kolkwitz und
Marsson 1908, p. 517, oligosaprobe).
Navicula perpusilla Grun. var. Flotowii (Grun.) Boye P. n. comb.
N. Flotowii Cl. Svn. I, p. 132. Van Heurck Svn. Pl. 14, íig. 41. Van Heurck
Types Nr. 148.
E. Icel. 68, 85, L. 99, L. 128.
If we compare the diagnoses of N. Flotowii and N. perpusilla in
Cleve (1. c.) we are struck bv the slight difference between them. Also
the two flgures which Grunow himself has given of the two species in
Van Heurck’s Synopsis show great resemblance to each other. No
one has therefore been in doubt that they were very closely allied. An
examination of the two preparations in Van Heurcks Types (Nos. 212
and 148) has, however, convinced me that the resemblance is even more
pronounced than could be inferred from the descriptions and illustra-
tions, hence I liave thought it right to reduce N. Flotowii to a variety
of N.perpusilla, and we might perhaps even with justice go so far as
to include the two species within one. The chief difference stated by
Grunow and Van Heurck, (Syn. p.106, Traité p.226) viz. that N.Flolowii
is said to be joined into long bands, whereas this it not the case with
N. perpusilla, cannot very well be given as a character as it has often
been seen tliat the samc species has occurred in chains as well as se-
parately. In Van Heurck, Types No. 148 both ,V.perpusitla and N. Flo-
towii are found. which, strangely enough, is not pointed out in the
corresponding text. In all the samples from Iceland in which I found
var. Flotowii, typical Navicula perpusilla were also present.
Naviculœ bacillares Cl.
Navicula pseudobacillum Grun. Cl. Syn. I p. 137. V. Heurck Syn.
Pl. 13, flg.9.
E. Icel. 14.
Only a single specimen observed. The species is hardly a true
aérial species.
Navicula terrestris Boye P. Boye Petersen 1915, p. 288, fig. 7, 8.
E. Icel. 129 — N. Icel. L. 138, L. 253.
‘) Thus it is evidcntly not by accident that Van ileurck, in Types No. 148,
whlch contains the spccies in grcat <piantity, gives as its hahitat >entre les uious-
ses d’un rochcr«.