146 RHODYMENIACE^. v. 



but equally differing in fructification ; and tliat in every natural arrangement 

 characters derived from the structure of the fructification are to be preferred to 

 all others. 



All the genera of this Order are widely dispersed. Rhodymenia has species in 

 the Arctic and Antarctic Oceans, as well as in the temperate and tropical zones. 

 Euthora and Rhodophyllls characterise high northern and high southern latitudes. 

 One species of Ploeamium is cosmopolitan, while the rest, fourteen in number, are 

 confined to the southern hemisphere. Rhabdonia, the only remaining genus, has 

 tropical and Australian species. 



Among the useful plants the most remarkable is Rhodymenia palmata, the Dulse 

 or Dillisk of the Irish (see Introd. Fart I, p. 33) ; and among the most beautiful are 

 Euthora cristata, Wormskioldia sanguinea, and the various species of Plocandum, — 

 all highly prized by collectors of " Ocean flowers." 



SYNOPSIS OF THE NORTH AMERICAN GENERA. 



* Frond flat, dichotomous or irregtdarly laciniate or multifid. 

 f Sporiferous nucleus simple, surrounded hy a gelatinous integument. 



I. Rhodymenia. Frond stipitate, leaf-like, dichotomous or palmate. 



ff Sporiferous nucleus compound, formed of several nucleoli more or less confluent. 



II. Euthora. Frond dichotomo-pinnate or laciniate, often very narrow. Tetraspores 



cruciate. 



III. Rhodophyllis. Frond dichotomous, often fringed with marginal lobes. 

 Tetraspores zonate. 



** Frond linear, piano-compressed, pectinato-pinnaie, the ramuli alternately secund in 



threes or fours. 



IV. Plocamium. Tetraspores zonate, contained in marginal spore-leaves. 



*** Frond terete, alternately decompound. 



V. Rhabdonia. Conceptacles half immersed in the branches. Tetraspores zonate, 

 dispersed through the superficial cells. 



