266 VEGETABLE SUBSTANCES. 



rate. A given weight of kelp does not contain so 

 much alkali as barilla, but a larger quantity in pro- 

 portion to its inferiority could be sold at a good profit 

 at a much lower price than the barilla with the duty 

 attached to it. Although inferior to the foreign 

 alkali, it could be used in the manufacture of glass 

 and soap, and it therefore speedily became an article 

 of great consumption. 



This manufacture brought prosperity to the shores 

 of the Orkneys. Small farms of 40 yearly rent 

 speedily rose in value to 300; and it is said that 

 Macdonald, Lord of the Isles, obtained a revenue of 

 .10,000 from his kelp shores alone, which had here- 

 tofore been to his ancestors an unproductive, value- 

 less possession. 



The demand for, and profit on kelp was so great 

 that every expedient was devised to increase the pro- 

 duction of this now valuable weed. In addition to the 

 natural rocks, on which it grows in great abundance 

 about low-water mark, fragments of rocks were rolled 

 into the sea, to encourage its growth on their surface, 

 and these were soon covered with ware, as it is tech- 

 nically termed. 



Sea-wrack, or Fucus vesiculosus, has aflat, radical, 

 branching leaf of about two feet long. The branches 

 are half an inch wide, having a flat stalk or rib di- 

 vided like the leaf, and running in the middle of it 

 throughout all its various ramifications. Hollow sphe- 

 rical, or oval air-bladders, hairy within, appear on 

 the surface of the leaf, growing generally in pairs, 

 but often single in the angles of the branches. The 

 office of these air-bladders apparently is to buoy up 

 the plant in the water. At the different extremities of 

 the leaf there are one or two tumid vesicles, about 

 three-quarters of an inch long, containing a clear 

 viscid mucus. 



