THE SHORES OF BRITAIN. 43 



equal state of fusion. It is then allowed to cool, 

 and having been taken out and broken to pieces, 

 it is carried to the storehouse to be shipped for 

 market. The general yield of this alkali is one- 

 fifth of the weight of the ashes from weeds pro- 

 miscuously collected ; but from one species, the 

 Sea- wrack, or Black-tang (Fucus vesiculosus), one of 

 the most abundant on our coast, the ashes yield 

 half their weight of alkali. The Sea- wrack is of a 

 dark-green hue, bearing long, flat, and narrow 

 fronds, resembling leaves, divided into branches, 

 and having a midrib running through the centre; 

 the leaf-like branches terminate in large yellow 

 oval receptacles, containing many seeds, enveloped 

 in a thick mucus. But its chief peculiarity is, that 

 the substance of the frond swells at irregular in- 

 tervals into oval air-cells, always arranged in pairs, 

 one on each side of the midrib. The Dutch use 

 this sort, # and another called Black- wrack (F. ser- 

 ratus), to pack their lobsters ; the latter, how- 

 ever, is preferred, on account of its containing less 

 mucus, and therefore being less liable to ferment- 

 ation. 



Scarcely inferior in its alkaline properties to the 

 Sea- wrack is the Knotted- wrack (F. nodosus). The 

 fronds look like slender stems, swelling at intervals 

 into oval bulbs or air-vessels. Boys amuse them- 

 selves occasionally by cutting off these nodules in 

 a diagonal direction, to make them into whistles. 

 They are too tough to be burst \>j the pressure of 

 the fingers, like those of the Sea-wrack; but if 

 stamped on, or put into the fire, they explode 



