52 BRITISH DESMIDIE^E. 



Gloeoprium dissiliens, Berk, in Annals of Nat. Hist, v. 16. p. 11 (1845). 



Jenner, Fl. of Tunbridge Wells, p. 192. Hassall, Brit. Freshwater 



Algce, p. 346. t. 83. f. 3. 

 Hyalotheca mucosa, Kiitz. Phycologia Germanica, p. 140? (1845). 

 Hyalotheca dissiliens, Breb. in lit. (1846). 



Common. Henfield, Sussex ; and Cwm Bychan, North Wales, Mr. Borrer. 

 Swansea ; Dolgelley ; Bedgelert ; Penzance, &c., J. R. Hampshire and many 

 stations in Sussex, Kent and Surrey, Mr. Jenner. Essex and Herts, 

 Mr. Hassall. Ayrshire, Rev. D. Landsborough. Aberdeen, Dr. Dickie and 

 Mr. P. Grant. Bandon, Professor Allman. JLerr j, Mr. Andrews. Ambleside, 

 Mr. Sidebotham. Yate near Bristol, Mr. Broome. Stoke Hill near Wells, 

 Mr. Thwaites. Rochdale, Mr. Coates. Manchester, Mr. Williamson. 



Germany, Kutzing. Falaise, Br^bisson. West Point, New York, Pro- 

 fessor Bailey. 



Filaments mucous, adhering firmly to paper. The joints are usually 

 broader than long, and as each has a shallow groove passing round it, it re- 

 sembles a small pulley -wheel, and the filament acquires a crenate appearance ; 

 the crenatures are generally very shallow, sometimes nearly obsolete, but I have 

 occasionally seen them deeper, when the plant looks more like the figure in ' Eng. 

 Bot. ;' at all times they may be detected on a careful examination with the 

 higher powers of the microscope. The endochrome is divided into two portions 

 by this constriction, and there is scarcely any depression between the joints. 



The mucous sheath is easily observed, and on each side of the filament is 

 nearly as broad as the central coloured portion. The sheath and filament are 

 alike cylindrical. 



If kept in water for a few days the plant separates into single joints, each 

 of which has a perfect mucous covering. In the Desmidiese in general the 

 filaments separate mto single joints with a facility proportioned to the greater 

 development of the sheath ; but Hyalotheca mucosa in this, as in other re- 

 spects, deviates from the rest of the group. The breaking up takes place 

 more speedily in the present plant, in Didymoprium Grevillii and Sphfsro- 

 zosma vertebratum, than in Didymoprium Borreri or in the genus Desmidium. 

 This circumstance seems to depend upon the elasticity of the mucous covering 

 of the joint. This elasticity is proved by its becoming longer than the joint 

 immediately upon separation, and hence into whatever number of pieces a 

 filament may be broken, the ends of each portion are as perfectly covered as 

 the original end of the filament itself, and with regard to each particular joint 

 the result is the same. 



The transverse view is circular, and shows a mucous border of the same 

 form. In this aspect the endochrome is generally disposed in a stellate man- 

 ner, with six or seven rays, and frequently has a colourless central spot. 



Foreign specimens of " Desmidium mucosum," given me by the Rev. M. J. 

 Berkeley, agree in all points with the above description. 



Hyalotheca dissiliens frequently occurs in considerable quantities, unmixed 

 with other Algae. WTien young it agrees in appearance with many of the 

 Conjugatse, but it may be distinguished by its fragility. It soon becomes of 

 a pale opake green, and is then even more fragile than before. 



