40 BRITISH SEA-WEEDS. 



to which species he may safely refer all Cystoseira with 

 knotted stems. 



Cystoseira fceniculacea. Fennel-leaved Cystoseira. 



Stem flattened ; branches long, clothed with blunt spines. 

 Air-vessels small, lance-shaped, placed below the forkings of 

 the branchlets. Spore-receptacles very small, smooth, and 

 without points. 



The South of England and the Channel Islands are 

 the best localities for this species, which is not found so 

 far north as some of its kindred. 



Cystoseira fibrosa. Fibrous Cystoseira. 



Frond two to three feet long, very much branched ; stem 

 flattened, as thick as a swan's quill ; branches sleuder. Air- 

 vessels oval, large, imbedded in the lower part of the branch- 

 lets. Spore-receptacles very long, clothed with bristle-like 

 fibres. 



The only species with which this can be confounded is 

 C. ericoides, from which it differs in its generally large 

 size, more prominent air-vessels, and in the absence of 

 the beautiful iridescence which appears on that plant 

 when growing under water. 



Genus IV. PYCE"OPHYCUS. 



Eoot fibrous, spreading. Frond a straight smooth shoot, 

 entirely without branches for the first few inches, then fork- 

 ing, from rounded axils, into branchlets of unequal length 

 which are again similarly divided. Air-vessels one-celled, 

 in the substance of the frond, always obscure and frequently 

 altogether absent. Fructification in cellular receptacles at 

 the tips of the branchlets. 



