The Botany of Iceland - 01.12.1928, Síða 105

THE AERIAL ALGÆ OF ICELAND
429
Tréboux advocates the conception that the relationship between
the fungus and the alga in a lichen is one of simple parasitism, especi-
ally on the ground that the alga thrives far better in the open than as
a gonidium. However, this view does not seem to meet the case in
Iceland where lichens thrive well while free living algæ are practically
unknown, and we cannot entirelj7 dismiss the idea that the algæ enjoy
no inconsiderable protection from the fungus against the difficult climatic
conditions.
Trochiscia hirta (Reinsch) Hansg. Boye Petersen 1915, p. 325, Tab. II,
flg. 21-24. West 1904, p. 203, fig. 82 G. H.
Acanthococcus hirtus Reinsch 1886, p. 240?
Pleurococcus vestitus Lagerheim 1882, p. 78?
— — Wittr. et Nordst. Alg. exsicc. No. 446?
N.Icel. 216 — N.W. Icel. 261 — S.Icel. 275,292 — Vestmannaeyjar 400.
The present species has previously been mentioned by me (1. c.) and
on comparing the Icelandic material with my samples from Denmark I
have found the closest agreement. I liave again compared my material
with Wittr. et Nordst. No. 446, but with the specimens in this sample
the agreement is not quite satisfactory, the spines on the surface of the
cells being considerablj7 coarser here than in the Icelandic and Danisli
samples I have had under observation. In the small table below I give
the dimensions of the cells.
Wittr. et Nordst. Nr. 446 Sample 292 from Iceland Sample 216 from Iceland From Denmark: Dyrehaven
Diameter of cells 13—15,4,« 15,4—24,2 /i 20 /i 23 /i
Number of spines in 10 /i abt. 4 7—10 abt. 9 abt. 9
Length of spines abt. 2 /i 5D 7 00 ö abt. 0,6 /i abt. 1 /«
While I have found cells both in the Icelandic and the Danish
material in which the numerous chromatophores could be plainly seen,
this was not the case with the exsiccatum. Hence I am not quite certain
of the identity of these forms though I cannot conclusivelj7 show that
they are not variations due to difference of life conditions. The main point
here is how far the form in Wittr. et Nordst. is furnished with one or
several chromatophores, and whether or not there are pyrenoids. Further
investigations may perhaps clear up this poinl.
In Denmark I have found the species on woodwork, tree-trunks,
and thatched roofs. In Iceland I have also collected it from woodwork
(261, 292), but likewise on large stones, especially in places protected
against intense desiccation. (216, 275, 400).
Oocystaceæ.
Keratococcus bicaudatus (A. Braun) Boye P. n. comb.
Dactvlococcus bicaudatus A. Br. in Rab. Fl.eur. alg. Sect. III, 1868, p. 47.