The Botany of Iceland - 01.12.1928, Qupperneq 99

THE AERIAL ALGÆ OF ICELAND
423
Tribonema bombycinum (Ag.) Derb. et Sol. Heering 1906, p. 131.
E. Icel. 55 c, 84, 86, 88, 91, 100.
The species was extremely common on dripping rocks. Sample 55 c
was collected in a small rocky cave with constantly trickling water. It
was only found at the mouth of the cave, not in the interior where
the light was fainter. All the samples mentioned above originate from
E. Iceland, but there is no doubt that the species is just as common on
irrorated rocks in other parts of the island, but it was only in E. Ice-
land that I had the opportunity of examining this kind of locality. In all
the samples it occurred as forma genuina Wille with a filament thickness
of 6—8 fi.
As regards the common occurrénce of the species as an aérial alga
I refer the reader to Puymaly 1924 p. 177. I shall merely add that
frequently it occurs in cultures of soil-samples in nutrient media con-
taining mineral substances, as carried out by Bristol (1920). I myself
liave found it in similar cultures of soil from Iceland. It further appears
from Miss Bristol's investigations that it will survive strong desiccation,
viz. up to 24 weeks. It is probahly its aplanospores or zygospores that
have this great power of resistance to desiccation. In the soil in Nature
the spores will no doubt be able to survive very long and will easily
develop into »formations passagéres«. (Comére 1913, p. 10). I found it
in Denmark in such a locality. (1915, p. 313).
Tribonema tenerrimum (Gay) Heering. Heering 1906, p. 130.
E. Icel. 91.
The threads found of tbis species had a thickness of 4—5 ju, and
the cells were 4—5 times as long as broad. It occurred in company
with T. bombgcinum on a rocky wall with water trickling down it.
Isokontæ.
Protococcales.
Protococcaceæ.
Coccomyxa Schmidle.
The genera Gloeocgstis Nageli (1849) and Coccomgxa Schmidle (1901)
are, in the opinion of most authors, closely related, and in recent times
several authors have united them, Wille under Coccomgxa (1909, p. 38),
and Puymaly under Gloeocystis (1924, p. 212 ff.). In the diagnosis of the
genus Glococgstis the following are the chief features »Zellen kugelig
. . . in . . . . Familien vereinigt, die von einer Blase umschlossen und im
Innern in der Regel aus wiederholt in einander geschachtelten Blasen
gebildet sind«.
As characters pertaining to the genus Coccomgxa in contrast to
Gloeocyslis Schmidle gives 1) tlie lack of a pyrenoid in the chromato-
phore and 2) a diíferent mode of division. The first-named difference
will in many cases be difficult to demonstrate with certainty. Thus I
am not convinced that it will be possible in the long run to keep Coc-
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