COSMOCLADIUM. 199 



than broad, subcylindrical, constriction extremely slight, 

 semicells subpyramidate, narrowing slightly towards the 

 apex, with gently rounded outlines ; end view circular. 

 Chloroplast axile, only one in each cell, with a central 

 pyrenoid (occasionally 2 are present), and 4 radiating 

 parietal lobes. Cells united by means of gelatinous fila- 

 ments to form branched colonies of an irregular shape ; 

 cells not only at the ends of the strands but arranged 

 distantly at intervals along them. 



Zygospore spherical, with many short, stout, acute 

 spines. 



Length of cell 16-20 (x ; breadth = thickness = 10-12 y. ; 

 breadth of isthmus 8 "5-9^; diam. zygosp., without 

 spines, 17-20 pi ; with spines, 30^. 



ENGLAND.- -Pilmoor, near Thirsk, N. Yorks ! Plank- 

 ton of Bracebridge Pool, Sutton Park, Warwickshire ! 

 Dartmoor, Devon (Harris). 



SCOTLAND. --" Old Road : and Heughhead, near 

 Aboyne, Aberdeen; Dalbrake in Strachan, Kincardine; 

 Buchanty, Perth (Roy & Biss.). 



IRELAND.- -Dublin and Wicklow (Arch.). 



Geogr. Distribution. Sweden. Finland. United States. 



C. constrictum is an alga which is frequently overlooked 

 because the cells are small and are distantly arranged, so that 

 the colonies are not dense. It is usually found in bogs, and 

 although not frequent, is one of the commonest species of the 

 rare genus Cosmocladium. The specimens found in the plankton 

 of Bracebridge Pool consisted almost entirely of isolated cells. 



It has been shown bv Dr. Lutkemuller that in the cells of this 



/ 



species there are two series of minute pores, arranged closely 

 together on either side of the isthmus. They are only present 

 on one side of the cell that side which is directed towards the 

 centre of the colony, and extend about frds of the distance 

 across the face of the cell when examined in front view. They 

 are only rendered visible by special staining methods. These pores 

 give rise to the gelatinous strands, which, extending from the 

 isthmus of one cell to the next, unite the cells together. 



