The Botany of Iceland - 01.12.1928, Qupperneq 109

THE AERIAL ALGÆ OF ICELAND
433
Stichococcus bacillaris Nag. Nageli 1849, p. 76, Tab. IV, G.
N. Icel. 243 — W. Icel. 349 — S. Icel. 287, 395.
In Denmark this species grows on various substrata, but especially
on the bark of living trees and on wood, and bj' preference in places
with very subdued light, e. g. in dense woods. In Iceland it is of much
rarer occurrence which is perhaps due to the fact that suitable habitats
are not common here. In the birch woods the light may possibly be
too strong for it, and all woodwork is as a rule exposed to the light and
wind in Iceland. I have only found it in four localities, viz. 1) in a cave
formed by the action of the waves by the shore near Húsavík (243),
2) on a fence pole at Möðruvellir in Kjós, and 3) on a telegraph pole
at Borgarnes, in both the latter cases quitc near the ground, and finally
4) on the lower part of the wall of the old factory near Reykjafos.
Prasiolaceæ.
Prasiola Ag.
The taxonomy of the genus Prasiola has long been a matter of
controversy and the discussion is hardly closed yet. The tendency has
in the main been towards assembling the numerous forms described
according to two lines. In the first place it has been recognised that
each species could occur in a íilamentous form (Hormidium), a band-
shaped form (Schizogonium), and a flat expanded form (Prasiola). To
these may be added a Pleurococcus-like form, often confused with Pleuro-
coccus vulgaris Men., thus by Chodat (1909), and by Brand (1925).
In this way the numbcr of genera has heen reduced to one, viz. Prasiola.
In the second place various authors havc realised that several of the
species established cannot, in fact, be distinguished from each other,
and so nowadays abt. 4—5 aérial species are taken into account. Even
the justification of certain of these species is sometimes questioned, just
as also the various authors do not quite agree as to what characters
should be employed to distinguish them. I shall not here enter more
fully into the extensive literature, but refer the reader to the thorough
researches of Imháuser (1889) and Brand (1914), who cite the litera-
ture then available.
Prasiola crispa (Lightf.) Men. Brand 1914, p. 308.
Schizogonium crispum Gay 1891, p. 86.
— murale — — - 87.
— radicans Chodat 1909.
E. Icel. 14, 15, 40, 77, 78, 92, 112, 114, 121, 131 — N. Icel. 135,
161, 162, 172, 173, 185, 196, 197, 216, 217, 242, 252 - N.W.Icel. 261,
268 — W. Icel. 297, 298, 307, 309a, 325 — S. Icel. 275, 282, 283, 287,
295, 352, 372, 381 — Vestmannaeyjar 408, 409.
Above I have only given a few of the numerous synonyms of this
species; the reader will be able to find the rest from the citations given.
After it had been established by Imháuser’s investigations that the
Hormidium forms were merely imperfectly developed Prasiolæ, Gay thought
nevertheless (1. c.), that two aérial forms could be distinguished, which