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 algse. 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. IHoralis. 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, cj'lindrical 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 jn. With the exception 

 of the hair-cells, all the cells are rich in granular, equally distributed endochrome 



(fig. 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 — 3). 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 greater 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: DunS and Musselbay on the coast of Spitzbergen. 



The Siberian Sea: rather abundant in Actinia Bay. 



-Baffin Ba,y: Hunde Island on the west coast of Greenland, in case Ectocarpus 

 Landsburgii Dickie belongs to the present species, as is most probable. 



