KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 20. N:0 5. 283 
of a dark olive-brown, lying free on the bottom or hanging on larger alga. I have not 
found attached specimens. ‘The frond is repeatedly racemosely branched with distinct 
main axis with branches of at least four orders. The branches are of two kinds: long 
branches with many cells and short ones with from one to ten cells. The former are 
few in number and issue partly alone partly in pairs opposite to each other. The 
short branches are numerous; by these the present species is easily recognized from 
P. litoralis. In long parts of the frond such a branch issues from every cell. They 
are always isolated, and issue at a right or nearly right angle. The long branches 
are somewhat attenuated towards the tip and generally end in some long hair-cells. 
The short branches are cylindrical or slightly claviform, with an apical cell rich in 
endochrome, which cell is finally transformed into a zoosporangium. 
The cells of the frond are usually short, cylindrical or slightly tun-shaped, equally 
or even twice as long as thick. Those cells which give rise to a long branch are 
commonly short. If a short branch issues from a cell which is more long than thick, 
as is often the case, the branch is almost always placed at the middle of the longer 
wall. The thickness of the principal axis amounts to about 50“. With the exception 
of the hair-cells, all the cells are rich in granular, equally distributed endochrome 
(ig. 1): 
The development of the zoosporangia and their arrangement dependent thereon 
are subject to very great variations. I have represented the most common of these 
modes of development fig. 2—12. The zoosporangia are sometimes arranged as in P. 
litoralis (fig. 2—8). A modification of this type is exhibited by fig. 4, in which all 
the cells, not only the ultimate ones, are transformed into zoosporangia. Sometimes 
it is only the apical cell that becomes a zoosporangium, the branch be composed of 
one or more cells (fig. 9). It also happens often that a vreater or less number of cells 
are divided by longitudinal or oblique walls, and that it is the secondary cells, pro- 
duced by this division, that are developed into zoosporangia (fig. 5, 7, 8, 10, 12). In 
this case the division of the cells and the development of the zoosporangia takes place 
sometimes in such a manner that the zoosporangia become arranged in whorls (fig. 11). 
I have not observed the bursting forth of the zoosporangia. 
Habitat. This alga is found sublitoral in 2—3 fathoms on exposed coasts. It 
occurs sometimes at Norway in considerable masses, and has been collected here with 
almost ripe zoosporangia at the beginning of August. 
Geogr. Distrib. It belongs both to the Atlantic and the arctic region of the Polar 
Sea and appears to have a wide range in the latter. It is most abundant however in 
the Norwegian Polar Sea. Its most northern point is Musselbay on the north coast of 
Spitzbergen Lat. N. 79° 53’. 
Localities: The Norwegian Polar Sea: Finmarken pretty common and plentiful 
at Maaso. 
The Greenland Sea: Dund and Musselbay on the coast of Spitzbergen. 
The Siberian Sea: rather abundant in Actinia Bay. 
Baffin Bay: Hunde Island on the west coast of Greenland, in case Ectocarpus 
Landsburgii Dickie belongs to the present species, as is most probable. 
