18 PYCNOPHYCUS FUCUS. 



IV. PYCNOPHYCUS. Kiitz. [Plate 2, A.] 



Root composed of branching fibres. Frond cylindrical, 

 dichotomous. Air-vessels, when present, innate, simple. 

 Receptacles terminal, cellular, pierced by numerous pores, 

 which communicate with immersed spherical conceptacles, 

 containing parietal spores and tufted antheridia. Name, 

 from TTUXVOS, thick, and Qvxos, a sea-weed. 



1. P. tuberculatus, Huds. ; Grev. Alg. Brit. p. 18 ; Hook. 

 Br. Fl. ii. p. 269 ; Wyatt, Alg. Damn. No. 103 ; E. Bot. t. 

 726 ; Harv. Phyc. Gen. t. Ixxxix. 



In rock-pools left, on the recess of the tide, near low-water mark. Pe- 

 rennial. Summer and autumn. Cornwall and Devonshire. West of 

 Ireland. Jersey. Root fibrous, matted over the surface of the rocky bot- 

 tom. Fronds gregarious, 12 20 inches long, as thick as a goosequill, 

 repeatedly forked : the axils obtuse. Air-vessels frequently absent. Re- 

 ceptacles terminating the branches, cylindrical, obtuse, more or less tuber- 

 culated, composed of compact cellular tissue. Colour, when growing, a 

 clear olive ; when dry, black. Substance brittle when dry. This plant, 

 separated from Fucus by Kiitzing, appears to me to be the type of a dis- 

 tinct genus, known from Fucus by its branching root and the compact cel- 

 lular structure of its receptacles. By Prof. J. Agavdh it is included in 

 what appears to me a very heterogeneous group, which he calls Fucodium. 



V. Fucus. L. [Plate 1, D.] 



Root scutate. Frond linear, either flat, compressed or 

 cylindrical, dichotomous (rarely pinnated). Air-vessels, 

 when present, innate, simple. Receptacles either terminal 

 or lateral, filled with gelatinous matter traversed by a net- 

 work of jointed fibres, pierced by numerous pores, which 

 communicate with immersed spherical conceptacles, contain- 

 ing parietal spores, or antheridia, or both. Name, <puxo$, a 

 sea-weed. 



* Frond Jlat, with a midrib. 



1. F. vesiculosus, L. ; frond plane, coriaceous, thick, linear, 

 dichotomous, quite entire at the margin, midribbed j air-ves- 

 sels globose, mostly in pairs ; receptacles elliptical, terminal. 

 Hook. Br. Fl. ii. p. 267 ; E. Bot. t. 1066 ; Grev. Crypt, t. 

 319 ; Wyatt, Alg. Danm. No. 152 ; Harv. Phyc. Brit. t. 

 cciv. (3. balticus ; very small, densely tufted, with an in- 

 distinct midrib, and destitute of vesicles or receptacles. F. 

 balticus, Ag. ; Grev. Crypt, t. 181. 



