280 BRITISH SEA-WEEDS. 



included in the genus Lyngbya. It grows between the 

 tide-marks during summer, and is annual. It has been 

 found in many localities on the British coast. When 

 growing, the threads are of a grass-green colour; but 

 they become dull dark-green when dry. They adhere 

 pretty well to paper. 



Genus CXVI. RHIZOCLONIUM. 



Frond a simple or imperfectly branched, decumbent, 

 membranaceous thread, of uniform diameter throughout, 

 and composed of a string of thin-walled, oblong cells filled 

 with granular endochrome. — Ehizocloxitjm., from the 

 G-reek rhizoo, to root, and Moon, a shoot. 



The limits of this genus are not yet very exactly de- 

 fined, for Kiitzing includes in it several species which 

 Dr. Harvey refers to Chcetomorpha, and Dr. Gray has 

 added to it what was formerly Lyngbya flacca. So far 

 as the British species are concerned, the characters to be 

 observed are the short root-like branches, and the non- 

 gelatinous substance of the threads. 



Rhizoclonium riparium. The shore Rhizoclonium. 



Threads slender, soft, long, angularly bent, spurred with 

 short, root-like branches, densely woven into flat layers of 

 considerable extent; cells about twice the length of their 

 diameter, filled with pale green endochrome. 



This plant grows during summer on rocks, which are 

 covered with sand, usually near high-tide mark, and is 

 annual. It has been found in several localities round 

 our coast, but is far from common. 



