RHODOMELACEJ]:. 



Order I -RHODOMELACE^. 



Harv. Man. Ed. 2, p. 75. Rhodomelece., J. Ag. in Linn. XV. p. 23. Alg. Medit. p. 

 116. Endl. Gen. 3rd Suppl. p. 44. Earv. Ner. Austr. p. 9 ; /. Ag. Sp. Gen. and 

 Ord. Ahjarum, 2, Syn. p. xi. Rytiphla'ce, Dne. Class, p. 62, also part of 

 Ceramiece, Chondriece, Thamnophorece. and Anomalophyllece, Dne. I. c. Dasyece, Poly- 

 siphoniea;, Chondrieoi (in part), Botryocarpece {in part), Amansiece, Rijtiphkeacea^, 

 Carpoblepharidece (partly) and Claudiece, Kiitz. Pliyc. Gen. p. 414-4.51. 



Diagnosis. Red or brown-red or purple seaweeds, with a leafy or filiform, 

 areolated or articulated frond, composed of polygonal cells ; the inarticulate filiform 

 species having an articulated axis composed of cells radiating round a central cell. 

 Sporiferous nucleus contained in ovate or urceolate, perforate conceptacles ; spores 

 pyriform, formed in the terminal cell of unbranched, tufted spore-threads radiating 

 from a basal placenta. Tetraspores generally seriated, lodged either in distorted 

 ramuli or in proper receptacles (stichidia or sporophylla). 



Natural Character. Root either a simple disc, or accompanied by creeping 

 fibres ; sometimes, in densely tufted filiform kinds, the primary fronds are prostrate, 

 attached by lateral discs issuing along them at intervals, the secondary ones or 

 branches erect. i'^rt)?jj very variable in habit, either leaflike or filiform ; or rarely 

 formed into an anastomosing net-work. In the numerous forms found in various 

 parts of the world all gradations between a perfectly developed, nerved, expanded 

 leaf, and a capillary, articulated filament, finer than human hair, may be traced. 

 In the flat, leaf-like species, the frond is sometimes (as in Odonthalia) thick, opaque, 

 with minute surface cells, and either destitute of midrib or obsoletely ribbed ; 

 sometimes (as in Amansia) it is delicately membranaceous, translucent, composed 

 of regular twelve sided cells of equal length, arranged in transverse lines. Similar 

 varieties occur in the cylindrical fronds, some of which are opaque, with small 

 surface cells (Alsidium, Acanthophora, Rliodomela) ; others (as many Polysiphonia') 

 are pellucidly articulate. This latter character, in several Polysiphonia;, distin- 

 guishes all parts of the frond at all ages; in others only obtains in the young 

 frond, or in the younger branches and ramuli of older fronds. In such the articu- 

 lations arc gradually coated over by successive rows of smaller cells of unequal 

 size and shape, and can only be discovered by making cross and longitudinal sec- 

 tions of the stems. A cross section being made, vox articulated axis composed of 

 several cells disposed like the spokes of a wheel round a central cell may be 



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