The Botany of Iceland - 01.12.1928, Side 101

THE AERIAL ALGÆ OF ICELAND
425
I have only been able to ascertain the presence of this species with
certainty on two palings in Reykjavík. It is, beyond doubt, much rarer
in Iceland than in Denmark and other European countries where it
occurs habitually almost everywhere on tree trunks and branches, wood-
work, stones, and thatched roofs.
By its peculiar chromatophores without pyrenoids, its cell nucleus
visible already in the living state, and above all by its zoospore forma-
tion it differs so much from the other Pleurococcus species that it may
beyond doubt correctly be referred to a distinct genus. This was first
done by Printz who (1. c.) refers it to Chodat’s very doubtful genus
Pleurastrum (Cliodat 1894, p. 612). Printz says himself (1. c. p. 22)
tliat he only »provisionally« refers it to the genus Pleurastrum and to
me it does not seem correct to choose this generic name, since the
characters which Chodat points out as the essential ones in his diagnosis
of the genus Pleurastrum are not found at all in P. lobatum Printz. Chodat
writes about Pleurastrum (1894, p. 613) »Algue unicellulaire se reproduisant
par tétrades de cellules dans l’intérieur de la membrane primitive, munie
á I’état parfait de sculptures sur la membrane, formant des tétrades
compliquées pouvant se résoudre en états gleocystis et produisant des
zoospores á deux cils«. The onlj7 one of the characters mentioned in
this diagnosis which agrees with Pleurococcus lobatus is the last-men-
tioned one, that it forms zoospores. Reproduction does not take place
hy tetrade formation within the wall of the mother cell, but b}' simple
bipartition, it has never anj' sculpture on the membrane, and does not
form any Gtoeocystis stage. On the whole the genus Pleurastrum is of
doubtful value, as Chodat himself points out (1909, p. 163), saying
about it »genre tout aussi mal déíini et qui est á réétudier«. In Engler-
Prantl’s I)ie naturlichen Planzenfam. 2. Aufl. Bd. III, p. 208, Printz
gives a diagnosis dilfering greatly from the original one given by Cliodat
This also does not agree with the present species, it being given as a
generic character that there is a pyrenoid present in the chromatophore,
which is not the case in Apatococcus lobatus. Brand (1925) took no
account in his paper of the investigations of more recent authors, hence
lie evidently did not recognise the alga before him as Plcurococcus lobatus
Chod. He therefore descrihes it afresh both under a new generic and a
new specific name, calling it Apalococcus vulgaris. The description, however,
agrees exactly with Pleurococcus lobatus (Printz, too, arrived at this result
(1. c.)), and by staining living material of tliis species from the Botanical
Gardens in Copenhagen with Brillant blue I have convinced myself that it
shows precisely the wreath of grains round the cell nucleus (»vacuola
centralis« scq. Brand) mentioned hy Brand. There is, however, no reason
whatever to reject the specific name tobatus, while Brand’s new generic
name Apatococcus is fullv justified. Hence in my opinion the species
sho.uld now rightly be called Apatococcus lobatus (Chod.;.
Desmococcus vulgaris (Nág.) Brand. Brand 1925, p. 344.
Pleurococcus vulgaris Nág. 1849.
— Nágelii Chod. 1902, p. 281.
Protococcus viridis Wille 1913, p. 7.
E. Ieel. 40 — N. Icel. 261 — S. Icel. 275, 276, 292 — Vestmannaevjar
400, 408.