SIPHONACE^E. 191 



ORDER XIV. SIPHONACEJ5. 



Siphoneae, Grev. Alg. Brit. p. 183. J. Ag. Alg. Medit. 

 p. 17. Endl. 3rd SuppL p. 16. Due. Class, p. 32 (also 

 Halymedeae and Acetabularieae). Siphoneae, Lindl. Veg. 

 Kingd. p. 18, and Vaucherieae (in part), p. 22. Vauchevieae, 

 Codieas, Anadyonieneae, Polyphyseae and Dasycladeae, Kiltz. 

 Phyc. Gen. pp. 302, 308, 311, 312. Caulerpeae, Grev. et 

 Auct. (?) 



DIAGNOSIS. Green, marine or fresh-water Algae, composed 

 of continuous, tubular, simple or branched filaments, free or 

 variously combined in cylindrical or expanded fronds. 



NATURAL CHARACTER. Root, where obvious, consisting of 

 a mass of fibrous threads interwoven together or entangled ; 

 rarely of different character from the threads constituting 

 other parts of the frond. Frond in the simplest genera ( Vau- 

 cheria, Bryopsis) consisting of a single, very long, branching 

 cell or membranous tube, filled with granular colouring mat- 

 ter, without any partition or dissepiment from the base to the 

 apex of the branches. Thus, if a whole frond of Bryopsis 

 plumosa be placed on a piece of glass, under water, and the 

 tip of one of its branches be wounded, the contents of the 

 frond may be pressed out through the lacerated part, leaving 

 nothing but an empty skin, and showing that there is no in- 

 ternal diaphragm in any part of the tube. This filiform cha- 

 racter of the cells distinguishes the genuine members of the 

 order, the more compound among which are made up of 

 thread-like cells, resembling those of Bryopsis, variously 

 united together. In Vaucheria the threads remain separate, 

 but are densely tufted together, and variously interwoven, so 

 as, in many instances, to form spongy, cushion-like tufts. 

 In Codium there is a closer connexion, the tips of the threads 

 lying close together, or slightly cohering, and the filaments 

 disposed in a definite order, so as to form fronds with a de- 

 termined outline. In Halimeda the union is still more inti- 

 mate, the spaces between the tips of the filaments being 

 closed up by carbonate of lime, and thus the frond cased in 

 a sort of epidermis, and all its parts built up into a common 

 structure. If a piece of Halimeda be placed in acid, so as 

 to dissolve the lime, its parts may readily be dissected, and 

 it will then be seen to consist of branching cells, resembling 

 those of a Codium or Bryopsis. 



