— 164 — 



The divisions of the cells in the monosiphonous filaments begin with 

 a longitudinal, median wall, and each of the two cells, thus produced, are 

 afterwards divided by a wall perpendicular on the first one into two cells 

 (fig. 18, a), and the mother cell is thus divided into four cells, of about 

 the same size, and limited by two plain walls and a curved one (fig. 18, a); 

 each of these four cells is afterwards divided into two cells of different 

 shape and size by an oblique wall between one of the plain walls and the 

 outer wall, and thus there are produced 8 cells, 4 three-sided and 4 four- 

 sided; each of the foursided cells becomes divided by a tangential wall 

 (fig. 18, b) into two cells, and thus we see in the middle 4 central cells 

 and surrounding them 8 pericentral cells (fig. 18, b), of which the former 



usually are divided by horizontal walls, 

 while the latter are divided by tan- 

 gential and radial walls thus forming the 

 plurilocular sporangia (fig. 18, c, d, e, f). 

 I have sometimes seen the 4 central 

 cells also divided by tangential and 

 radial walls, and in such cases they 

 also take part in the formation of the 

 plurilocular sporangia (fig. 18, g). The 

 limits of the mother cells are usually to 

 be seen in the polysiphonous filaments 

 (fig. 19, a -d). 



The plurilocular sporangia are in- 

 definitely expanded in the main axis 

 and the branches of the upper part of 

 the frond, but two or few cells at the 

 apex of the branches are usually sterile 

 (fig. \9,a,b). The spores escape through 



Fig. 19. Isthmoplea sphœrophora 

 (Harv.) Kjellm. 



a, b the uppermost part of two an opening, which is usually found in 



shows a somewhat prominent part of the cell- 

 wall (fig. 19, a, d). 



Regarding the structure and de- 



branches, one of Avhich, a, si 

 the opening of the sporangia; c, d, 

 two portions of the lower part of the 

 branches: d shows the opening of 

 the sporangia; e, a portion of the velopment of the plurilocular sporangia 

 main axis (of Fosliea curta (Fosl.) this species highly resembles Litosiphon 

 Rke.) showing the branching. One filiforme (Rke.) and on account of the 



cell of the right branch shows the 

 small disc-shaped chromatophores. 

 (316:1.) 



structure of the frond it generally agrees 

 much better with the species of Punc- 

 tariaceæ than with the Ectocarpaceæ. 

 The unilocular sporangia of Isthmoplea are also, as well known, partly 

 immersed in the frond and this also agrees better with the Punctariaceæ 

 than with the Ectocarpaceæ. I therefore refer the genus Isthmoplea to the 



