SEAWEEDS. 



291 



identified by the possession of solitary bladders in the centre of 



its rib-less frond, and producing a very gouty appearance at 



intervals. These are air-cells, sometimes measuring two inches, 



which give buoyancy to the plant. Above the bladders the 



frond divides, and from these branches (but not at their 



extremities, as in the Channelled Wrack) the pear-shaped 



reproductive organs are produced. 



Another Wrack that possesses 

 these vesicles, is the so-called 

 Bladder Wrack or Black Tang 

 (Fucus vesiculosus] , though there 

 is little danger of confusing the 

 o species. The Bladder 

 Wrack has a much broader, 

 flatter frond than the Knotted 

 Wrack, and a very distinct mid- 

 rib. The bladders, too, are 

 smaller, and instead of being 

 solitary, are arranged in groups 

 on each side of the mid-rib. 

 The plant is about two feet 



in length, and exceedingly plentiful. 

 Very similar, and equally 



plentiful, is the Saw-edged : 



Wrack (Fucus serratus}> with 



flat, branched fronds and 



mid-rib, the branches mucM 



broader than in Bladder 



Wrack, and the edges cut 



into bold, sharp, distant 



teeth. Its usual length i? 



from two to three feet, but 



it may occur as long as five 



or six feet. The width of 



frond also varies, for it may SAW EDGED WRACK. 



BLADDER WRACK. 



