38 BRITISH SEA-WEKDS. 



jointed, divided internally into eel's, pointed at the apex. 

 Fructification in terminal, tuberculated receptacles. 



The name of this genus is derived from the Greek 

 words ah, the sea, and drus, an oak. Of the two species 

 that are known, one has only been found in North 

 American waters, and the other is common on all parts 

 of the British coast and the adjacent shores of Europe. 



Halidrys siliquosa. Podded Sea-oak. 



Frond repeatedly pinnate. Air-vessels oblong, with a 

 bristle-like point. 



This Sea-weed is a perennial, and may be found at all 

 seasons, in pools between high- and low- water mark. It 

 varies in size from a few inches long in shallow water to 

 three or four feet at greater depths. 



Genus III. CYSTOSEIRA. 



E,oot a conical disc. Frond shrub-like, having a woody 

 stem with alternate branches. Air-vessels of one cell in 

 the substance of the branches. Fructification at the ends 

 of the branchlets. 



The name Cystoseira, from the Greek words kustis, 

 a bladder, and seira, a string, has reference to the ar- 

 rangement of the air-vessels. The larger proportion of the 

 twenty species which compose this genus are found in 

 the Mediterranean Sea, and the remainder, with the ex- 

 ception of one or two which grow in America, frequent 

 the shores of Europe. They appear to form the con- 

 necting link between the warmth-loving Sarffassa and 

 the Fuci, which delight in colder climates ; and as in geo- 

 graphical position, so also in structure they are interme- 



