194 BRITISH DESMIDIE^. 



the frond consists of only a single pair of cells so connected, but sometimes of 

 two or even three of these pairs, which however are remote from each other : 

 in this case, as the connecting mucus is colourless, they look hke distinct 

 plants, and their relation can be detected only by moving the frond. If kept 

 in water for a few days, the cells separate from each other. 



Professor Kiitzing formed his genus Rhaphidium for the reception of the 

 plant above described and a species of Ankistrodesmua ; but I beheve the 

 proper position of the former is in this genus. 



Tab. XXXIV. fig. 17. a. frond with dividing cells ; b. cell with the division 

 more advanced. 



