40 BRITISH SEA-WEEDS. 



to which species he may safely refer all CysioseireB with 

 knotted stems. 



Cystoseira foeniculacea. 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. 



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

 flattened, as thick as a swan's quill ; branches slender. 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. PYCNOPHYCUS. 



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. 



