HALIDRYS. 15 



1. S. vulgare, Ag. ; stem flat, slender, alternately branched; 

 leaves linear-lanceolate, serrated, dotted with mucous pores ; 

 air-vessels few, spherical, on flat stalks ; receptacles cylin- 

 drical, racemose. Grev. Alg. Brit. p. 2, t. \ ; Hook. Br. Fl. 

 n.p. 264; E. Bat. t. 2114. 



Occasionally cast ashore. Orkneys, Mr. P. Neill. — Stem 12 — 18 inches 

 long, pinnated with simple branches. Leaves very variable in breadth. 

 Colour, when recent, olive, reddish brown when dry. 



2. S. hacciferum, Turn. ; stem cylindrical, slender, much 

 branched, flexuose ; leaves linear, serrated, mostly without 

 pores ; air-vessels abundant, spherical, on cylindrical stalks ; 

 receptacles unknown. Grev. Alg. Brit. p. 3; Hook. Br. Fl. 

 W.p. 264; E. Bot. t. 1967; Harv. Phyc. Brit. t. cix. 



Occasionally cast ashore with the preceding. Orkneys, Mr. P. Neill, 

 Shore of Castle Eden Dean, Durham, Mr. W. Backhouse. — Root un- 

 known. Stems extremely brittle. Leaves 1 — 2 inches long, and about a 

 line wide, of a very pale olive colour when recent. This and the preceding- 

 species have no just claim on our Flora, being natives of the tropics, occa- 

 sionally driven, together with cocoa-nuts and other tropical productions, by 

 the force of the western currents, on our Atlantic coasts. 



II. Halidrys. Lyngb. [Plate 1, C] 



Frond compressed, linear, pinnated with distichous 

 branches. Air-vessels lanceolate, stalked, divided into seve- 

 ral cells by transverse partitions. Receptacles terminal, 

 stalked, cellular, pierced by numerous pores, which commu- 

 nicate with immersed, spherical conceptacles. Naiue, aAj, 

 the sea, and ^^vg, an oak or tree. 



Obs. — In this and the two following genera the internal 

 substance of the receptacle is composed of small, polygonal 

 cells closely packed together into a solid flesh ; a structure 

 technically called cellular. In Fucns and Himanthalia the 

 internal substance is loosely gelatinous, the gelatine traversed 

 by a network of jointed threads. 



1. H. siliquosa, L. ; branches linear, very narrow; air- 

 vessels compressed, linear-lanceolate, slightly constricted at 

 the septa, mucronate. Grev. Alg. Brit. p. 9, #. 1 ; Hook. Br. 

 FL ii. p. 266; E. Bot. t. 474; Wyatt, Alg. Danm. No. 53. 

 Harv. Phyc. Brit. t. Ixvi. — (3. minor; smaller in every part, 

 with fewer vesicles. Turn. Syn. i. p. 61. 



On rocks and stones in the sea, at and below half-tide level. Common 

 on the British shores. Perennial. Winter and spring. /3. in shallow 

 pools left by the tide. — Root an expanded disk, from which spring several 



