ZONING OF SEAWEEDS 



73 



water mark, an abundance of the tubular, wavy, pale 

 green Enteromorpha intestinalis, varying from one to 

 many inches in length, and fading through yellow to 

 white in decay. This Alga is well suited to brackish 

 water, and is sometimes found in inland waters. In the 

 same zone we also get the Sea Lettuce {TJlva lactuca), 

 light green in colour, becoming yellowish in decay. 

 The delicate, nearly transparent thaUus of this plant, 

 when mature, is flat, ribless, wavy, and somewhat 

 rounded at its margin. It is from 3 to 6 inches long, 

 and broad. This mature form arises from the rupture 



Fig. 21.— Holy-Wback (Pelvetia canaliculata). 



of a puckered, inflated, saclike thallus — the immature 

 from. Descending to the zone of the brown Seaweeds, 

 we first encounter the Holy- Wrack {Pelvetia canalicu- 

 lata), which is depicted in Fig. 21. The thallus of this 

 species is from 2 to 6 inches long, olive-brown or -yellow 

 in colour, and it is repeatedly forked in its mode of 

 branching. Every part is grooved on one side; hence 

 the name " Chajinelled- Wrack." It is said that cattle 

 are fond of this plant, and browse on it in winter when it 

 is left exposed by the tide. It is sometimes given as 

 a medicine to sheep and cattle. PeZvei^m grows in bushy 



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