OSCILLATORIACE^E . 219 



the type of a new genus, to which the name Diconia (Jif *wvoj) may be 

 given, in allusion to the form of its ripe spores. 



ORDER XVII. OSCILLATORIACE.E. 



OSCILLATORIE.E, Harv. in Mack. Fl. Hib. part 3, p. 164. 

 Endl. 3rd Suppl. p. 12. Oscillatorieae and Rivularieae, 

 Harv. Er. Fl. J. Ag. Alg. Medit. p. 8, 10. Oscillatorea;, 

 Lindl. Veg. Kingd. p. 18. 



DIAGNOSIS. Green or blue, rarely purplish, marine, or 

 (more frequently) fresh-water Algae, composed of continu- 

 ous, tubular, simple, or rarely branching filaments, which are 

 either free or invested in gelatine. Endochrome annulated, 

 at length separating into lenticular sporidia. 



NATURAL CHARACTER. Root) either simply a point of at- 

 tachment ; or, in most cases, not obvious. Filaments of 

 small size, often exceedingly minute, inarticulated, membra- 

 nous ; each filament formed of a single, slender, filiform tube, 

 which is most frequently simple. These filaments are rarely 

 solitary. In the majority, a great number of filaments lie 

 together, either in bundles or in strata, in the latter case 

 usually surrounded by a slimy matrix. In a few, form- 

 ing the sub-order Rivulariete, the filaments cohere into 

 fronds of definite shape, in which they commonly radiate 

 from a central point, their apices being turned to the circum- 

 ference of the frond. In this sub-order also, each filament 

 springs from a globular cell of small size, the use of which is 

 unexplained, but which is obviously of a similar nature to the 

 cells called " connecting cells" in the Nostochaceae. The 

 filaments are very rarely branched. In some cases where 

 they have the appearance of being branched, the ramose cha- 

 racter is owing to the lateral cohesion of two filaments ; the 

 lower part of one being applied to the side of the other. 

 Such an arrangement is termed appositional branching, and 

 is found in several fresh- water species allied to Calothrix. 



The structure of the plants of this order is very uniform, the 

 chief variety lying in the more or less perfect division of the 

 endochrome into lenticular frustules or cells. In the Oscil- 

 latoriae, and in most others, the endochrome is merely trans- 



