296 THE BIOLOGY OF THE SEA-SHORE 



species were collected and employed by the Japanese for 

 various purposes. 



The chief drawback to a more extended use of seaweeds 

 as manure lies in their bulk and in the difficulty and cost of 

 transport. Instead, therefore, of being employed as a 

 complete manure the algae are frequently burnt for the sake 

 of their ash, which contains a high percentage of potash. 

 The ash obtained from algae is usually known as " kelp," 

 though the same term is sometimes applied to denote the 

 living algae which are utilised for obtaining potash. Until 

 a few years ago, however, even the kelp was only of com- 

 paratively local value, as on the open market it was incapable 

 of competing with potassic fertilisers of other origin. The 

 Americans had already begun to turn their attention to the 

 giant kelp-beds of their Pacific coasts as a source of potash 

 when the loss of German supplies due to the war gave a new 

 impetus to this industry. Large factories sprang into 

 existence on the shores of the Pacific and rendered important 

 service in connection with war needs. The species exploited 

 are chiefly Laminarians of great size, known as giant kelps, 

 which form immense beds a short distance from the coast. 

 As the majority of these are provided with floating organs 

 (pneumatocysts) which support the fronds at the surface, 

 mechanical means of harvesting become possible and result 

 in a considerable reduction of the working expenses. Al- 

 though the financial success of these concerns under peace 

 conditions is not yet assured, already thousands of tons of 

 algae are removed from the Pacific for the extraction of 

 potash and other products (Sauvageau, op. cit.). 



The extraction of iodine from seaweeds is still practised 

 on a small scale in diflferent parts of the world, but this sub- 

 stance is now generally obtained more economically as a by- 

 product of the nitre industry. Iodine was formerly obtained 

 from various seaweeds on the Scottish coasts, but the industry 

 has declined for the reason just stated (Cameron, 191 6). 



The exploitation of littoral algas on a commercial scale 

 opens the question as to how far the supply of alg£e is mex- 

 haustible and as to what effects their removal may have on 



