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. 1 ; Hook. Br. Fl. 

 11. p. 264; E. Bot. *. 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. bacciferum, 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. 

 i\.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. Name, aAj, 

 the sea, and 3jjw?, 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 Fucus 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, t. 1 ; Hook. Br. 

 Fl. n.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 



