BRITISH DESMIDIE.E. 53 



Although I had seen sporangia of //. dissiliens at Penzance, I was unable 

 to determine to what plant they belonged until Mr. Jenner sent them from 

 Sussex and suggested that they were its conjugated state. At first the diffi- 

 culty I experienced in recognizing the original cells in their altered condition 

 induced me to hesitate in admitting the correctness of his opinion. But 

 having subsequently gathered this species in all stages near Dolgelley, I have 

 traced its changes, with Mr. Jenner' s assistance, and satisfied my doubts. 



The filaments separate hito single joints, which couple by tubes ; so far the 

 manner of conjugation is similar to the examples I had previously seen in 

 Stanrastrum and Tetmemorus, but in those genera the segments of the cell 

 are completely divided by the growth of the newly -formed portion ; in the 

 present case the cells separate only on the sides opposed to each other. In 

 the cleft is formed the new portion, the enlargement of which, after it has 

 become the connecting tube, by causuig the cell to gape, produces a notch-like 

 appearance on the outer margm. The process would be more evident if the 

 similar texture of the old and new parts did not render it difficult at first sight 

 to detect the joint in its altered form ; and the difficulty is increased, as the 

 couplmg usually takes place in a crossed or twisted position, which thus still 

 farther disguises the joints. 



The sporangium, which is circular, is situated within the connecting tube, 

 and the empty joints are permanently attached to it. 



I have been unable to determine, by my own observation, whether the mu- 

 cous covering remains on the conjugated cells, but Mr. Jenner informs me 

 that in some instances he has observed it, and indeed that its presence led 

 him to the identification of the plant. As in most instances, however, it is 

 either wanting or very obscure, I have thought it advisable to omit it in the 

 figures of the sporangia, and merely to notice its occasional occui'rence. 



Sporangia have been gathered also by Mr. Thwaites, Dr. Dickie, Mr. 

 Broome, and Mr. Sidebotham ; and M. de Brebisson informs me that he has 

 met with them in France. 



Length of joint from ytos ^^ tstt ^^ ^^ i^^^^ ; breadth of filament from 

 XToT ^^ Tzz ; breadth of sheath from -^\-j to ■^\-^. Diameter of sporangium -^\-^. 



Tab. I. f. 1. a, b. portions of mature filaments ; c. portion of a di\'iding fila- 

 ment ; d. empty joint ; e, f. transverse view ; g, cells conjugatmg ; h, i. 

 sporangia. 



2. H. mucosa (Mert.) ; filament scarcely fragile ; joints not constricted, 

 but having at one of the ends a minute bidentate projection on 

 each margin, the adjoining end of the next joint being similar. 



Conferva mucosa, Mert. Dillw. Brit. Conf. t. B. (1809). Hook. Br. Fl. 



V. 2. p. 351. Hai-v. Br. Alg. p. 127. 

 Hyalotheca mucosa, Ehr. Kiirze Nachricht iiber 274 seit dem Abschluss der 



Tafehi des grosser n lnfusorienwerkes% (1840). 

 Gloeoprium mvcosiim, Ralfs, Annals of Nat. Hist. v. 16. p. 11. t. 3. f. 6. 



(1845) ; Trans, of Bot. Soc. of Edinburgh, v. 2. p. 165. t. 18. Jenner, 



Fl. of Tunbridge Wells, p. 192. Hass. Br. Freshwater Algce, p. 346. 



t. 83. f. 5. 

 Hyalotheca Mertensii, Brebisson in lit. (1846). 



E 2 



