secund, sometimes alternate branches, which are once or twice similarly 

 branched, all the branches and ramuli being very straight and erect, filiform, 

 with very narrow axils. The mature frond is more stipitate, and its upper 

 branches become panicl-ed or dendroid, dividing into many virgate"and sub- 

 patent secondary branches, which are set throughout with sliort, multifid, 

 corymbose ramuli. The ceramldla are ovate, sessile, and borne toward the 

 end of the branches, on specimens which, though much divided, are not fur- 

 nished with the corymbose ultimate ramuli; they contain a tuft of linear cla- 

 vate spores. The tetraspores are in the tips of the corymbose ramuli, very 

 few in each tip, which is then somewhat swollen or distorted. The colour 

 is a very dark purple or brownish, becoming darker in drying, but after ex- 

 posure or long sleeping in fresh-water, it becomes more red. The substance 

 is very rigid and wiry, and in drying the frond very imperfectly adheres to 

 paper. 



This wiry species grows in situations where it is exposed to 

 the full dash of a pretty constantly boisterous surf, and where few 

 other Algae compete with it in " the struggle for life." Its matted 

 roots take very firm hold on the rock, and it spreads in patches 

 of many yards in length, or else borders the thin edge of the reef 

 for a much greater extent. The young plants are remarkably 

 different from the mature, — so much so, that, if separated, they 

 might pass for different species. The cystocarpic and tetrasporic 

 plants also differ in ramification, as takes place sometimes with 

 other species, and adds greatly to the difficulty of distinguishing 

 one from another, I fear the species of Laiirencia have been too 

 much multiplied. 



Fig. 1. Laurencia heteroclada, — tlie natural size. 2. Branch, with cera- 

 midia. 3. Tuft of spores. 4. Branchlet, with tetraspores in the tips. 5. 

 A tetraspore. 6. Cross section of the stem : — the latter figures variously 

 magnified. 



