438 
The tetrasporangia occur in the upper ends of the long shoots and in the 
fusiform short shoots. They are situated to the right of the trichoblast in the tri- 
choblast-bearing segments, in the foregoing 
trichoblast-less joints the sporangia are situ- 
ated under the sporangium in the trichoblast- 
bearing joint. The sporangia are covered by 
two secondary pericentral cells. A small peri- 
pheric cell is never found under one of 
these.! 
P. atrorubescens occurs only in waters with 
a high salinity. It grows on stones and shells 
of mollusks at from one to 23 meters’ depth 
or deeper. In the Skagerak it has mostly been 
found near land in 1 to 4 meters’ depth 
growing on stones, in the northern Kattegat 
in 11,5 to 23 meters’ depth or deeper in soft 
bottom growing on Aporrhais, Turritella a. o. 
mollusks. Its non-occurrence in the upper regions of this water is probably due to 
the slighter and more variable salinity. It has only been collected in the summer 
months (June—August) and thus it cannot be stated whether the species is annual 
or perennial on the Danish 
shores. In October it was - 
only met with once in a 
denudate state. GREVILLE and 
HARVEY mention it as annual, 
while BATTERS states that it 
is to be found “all the year”. 
In the Skagerak and the A 
Limfjord it attains a length of 
18 cm, in the Kattegat 13 cm. RUN Fig. 391. N er, 
In the Danish waters it has 0 ysip honia atrorubescens. A, transverse section of stem. > , transverse 
sections of tetrasporiferous joints, C emptied. 200 : 1. 
been found with cystocarps 
and tetrasporangia in June to August, with antheridia in July. It must be supposed 
that the spores germinate in summer and that the plants pass the winter in a feebly 
developed state. 
Fig. 390. 
Polysiphonia atrorubescens. Ripe cystocarp. 150 : 1. 
Localities. Sk: YT? and YT%, Hanstholm 5,5 and 13 meters and YM, Roshage, near land, 2 m; 
Bragerne, YM’, 1,5—2 m; Grønhøj Strand, Miss Ellen Möller; Lønstrup, on stones near land, 1m; 
1 J. Acarpn states (1. c. p. 1037) that he has found two sporangia in each joint in a densely 
branched specimen from Tanger collected by SCHOUSBOE. As this species has not been found near Tanger 
(comp. BORNET, Les Algues de Schousboe. Mém. soc. sc. nat. Cherbourg 1892 p. 315) it must be supposed 
that it has been confounded with another species, f. i. Ophidocladus Schousboei (Thuret). (Comp. DE- 
Toni Syll. Alg. IV, p. 1073). 
