102 BRITISH SEA-WEEDS. 



alternate, awl-shaped ; tubes about eight, arranged round 

 a small cavity ; articulations about as long as broad. Spores 

 in ovate, stalked conceptacles ; tetraspores in swollen 

 branchlets. 



This rare and very beautiful species is pretty generally 

 distributed round our coasts. It is only to be found at 

 and beyond extreme low-water mark, where it is parasitic 

 on the Melobesm and Corallines which grow on the per- 

 pendicular sides of ledges of rock. None but floating 

 specimens can, therefore, be obtained except at the 

 lowest spring tides, or by dredging. It is to this cir- 

 cumstance, probably, that its reputed rarity is partly 

 due. 



Polysiphonia variegata. Variegated Polysiphonia. 



Fronds growing in dense tufts, from four to ten inches 

 long, about as thick as a bristle at the base, gradually taper- 

 ing upwards to the size of a hair, much branched ; tubes 

 six, or rarely seven, arranged round a minute central cavity ; 

 articulations, in the lower part of the stems, shorter than 

 they are broad, in the branches and branchlets, varying in 

 length from once to twice their breadth, with three broad 

 tubes distinctly visible in all parts of the frond. Spore- 

 conceptacles on short stalks on the smaller branches and 

 branchlets ; tetraspores small, in slightly swollen branch- 

 lets. 



This species grows on mud- covered rocks, floating 

 timber, Zostera, etc. In the few localities where it has 

 been hitherto found, chiefly on the coasts of Devon and 

 Dorset, it is both luxuriant and abundant. Its distinc- 

 tive characters are the six tubes of its stem and its 

 purple colour. It is annual, and in perfection in sum- 

 mer. 



