200 INTEODUCTION TO CEYPTOGAMIC BOTANY. 



Derbfes and Solier figure many of them with a delicate appen- 

 dage, but Thuret has in vain sought for such an appearance. 

 There can, however, be little doubt that they are truly impreg- 

 natory organs. The flagellrform appendage cannot certainly 

 be considered as essential to their functions. They will pro- 

 ■bably be found in many other genera than those indicated by 

 Derbes and Solier,* but their abundance in Polysiphonia &nd 

 GalUthamnion, and their apparent rarity in so many other 

 cases, present great difficulties. At present it does not appear 

 that zoospores have been found in a single genus. 



14, RHODOM:ELACE.ffi;, Harv. 



Frond areolate or reticulate, filiform or variously leafy, 

 articulate or inarticulate. Nucleus contained in an urn- 

 shaped conceptacle ; spores radiating from a basal placenta. 

 Tetraspores mostly seriate, in the frond or in proper concep- 

 tacles (stichidia). 



179. The species of this division, as the name implies, often 

 assume a very dark tint, so as to present a rich red brown 

 rather than a florid red. They vary in external appearance 

 very greatly ; some genera, as Polysiphonia, Bostrychia, and 

 Dasya, being composed of slender, often elegantly branched 

 and distinctly articulated, threads ; others, as Rytiphlwa, 

 resembling them in form, but inarticulate, except occasionally 

 in the alternate ramuli, while others, as Ainansia and Odon- 

 thalia, have a flat and pinnatifid frond. They agree in pos- 

 sessing free areolate hollow conceptacles perforated above, from 

 the base of which, short tufts of threads arise, bearing each a 

 large obovate spore at its apex, while the tetraspores are for 

 the most part in rows either on the distorted fronds, or in dis- 

 tinct elongated receptacles. They occur not only in salt or 

 brackish water, but some of the Bostryclviw are found in 

 mountain torrents, in tropical countries, out of the reach of 

 the spray, while others affect the brackish waters of the mouths 

 of rivers, where they are found entangled in phsnogamous 

 plants. Many species of Dasya, Polysiphonia, and Chondria 

 are common on our coasts, and analogous forms occiu- in the 



* See Thuretj 1. c. DerbSs and Solier, Ann. d. Sc. Nat., s6r. 3, vol. 14, 

 and Supplement aux Comptes Bendus de I'Acad. des So, vol 1, 



