CTIYPTOGAMIA. 379 



and instructive, and are chosen with that accuracy 

 and taste for which Dr. Acharius is conspicuous. 



The aquatic or submersed Algcs form a distinct 

 and peculiar tribe. Some of these abound in fresh 

 water, others in the sea, whence the latter are com- 

 monly denominated sea-weeds. The chief genera 

 are Ulva, t. 419, 420, 1276, well defined by its seeds 

 beinf^ dispersed under the cuticle throughout the 

 membranous or gelatinous substance of the frond ; 

 Fuciis, t. 1066 — 1069, &:c,, whose seeds are collect- 

 ed together in tubercles or swellings, of various forms 

 and sizes ; and Conferva, of which the 24th and 25th 

 volumes oi Engl. Bot., more especially, show various 

 specimens. This last genus is commonly known by 

 its capillary, and, for the most part, jointed frond. 

 The seeds of some species are lodged in external 

 capsules or tubercles ; of others in the joints of the 

 frond ; and hence the ingenious Dr. Roth has formed 

 a genus of the former, called Ceramium. His Rivu- 

 laria, Engl. Bot. t. 1797 — 1799, is perhaps more 

 satisfactorily separated from Conferva^ as we trust is 

 Vaucheria, t. 1765, 1766, a fresh- water genus named 

 after M. Vaucher of Geneva, who has published an 

 elaborate and faithful microscopical work on Fresh- 

 water Confervas. The submersed Alg(e •in general 

 are merely fixed by the roots, their nourishment be- 

 ing imbibed by their surface. Many of them float 

 without being attached to any thing. The genus 

 Fucus has received more botanical attention than the 

 rest of this tribe, and the works of Gmelin, Esper, 

 Stackhouse and Velley have ascertained many spe. 



