216 BRITISH SEA-WEEDS. 



tinous sac (periderm) ; tetraspores spherical, at length 

 tripartite, attached to the inside of involucral branchlets. 

 — Gbieeithsia, in honour of Mrs. Griffiths. 



This is a large and interesting genus, which is hand- 

 somely represented on our shores. The species are all 

 of delicate structure, and must always be laid out in 

 salt water, as they rapidly decompose in fresh. 



Griflithsia setacea. The bristly GrifHthsia. 



Fronds growing in tufts, from three to eight inches or 

 more long, jointed, forked, tapering gradually from the base 

 to the tips; articulations many times longer than broad 

 below, becoming gradually shorter above. Spore-clusters 

 (favellce) oval, enveloped in a transparent membrane, ar- 

 ranged among short-stalked, globular tufts of forked, in- 

 volucral branchlets ; tetraspores attached to the inner side 

 of involucral branchlets, which form a globular tuft, similar 

 to that containing the favellse. 



This is the most common species of the genus, and 

 grows on all our coasts in more or less abundance. It 

 is of a bright red colour, and very crisp when fresh, but 

 it becomes flaccid on exposure to the air, and when put 

 into fresh water its cells discharge the crimson colouring- 

 matter with which they are filled, and the whole plant 

 assumes the dull orange hue indicative of decay. Dr. 

 Harvey ascribes to this plant a quality which will prove 

 valuable to the possessors of marine aquaria. He 

 writes : — u Delicate as the structure of this plant as- 

 suredly is, no marine alga is more patient of confine- 

 ment, or may be more easily domesticated. A tuft 

 placed in a closed bottle of sea- water in April, 1846, is 

 now, after more than two years' imprisonment^ appa- 

 rently as fresh and healthy as when first taken from the 



