6S The Scottish Naturalist. 



It is, however, among the Thallogens that we meet with the 

 most numerous examples of Cryptogams useful or injurious to 

 mankind. The Algae, including the seaweeds (so often brilliant 

 red, purple, or green, though frequently also dull and sombre- 

 browns, or olive-greens, or almost black in colour), are known to 

 every resident by the sea-shore, in some or other of the many 

 forms that these plants assume. They are almost the sole plants 

 of the salt waters, in which they cover the rocks with almost as 

 copious a vegetation as that of our terrestrial pastures ; and the im- 

 mense masses thrown in on many coasts after a storm must be 

 familiar to everyone who has spent a winter on seaweed-fringed 

 coasts. Seaweeds afford, directly or indirectly, the greater part 

 of the food of fishes, and thus are of the greatest value to the 

 fisheries so successfully prosecuted along our coasts. The masses 

 cast up after storms are very largely employed in many seaboard 

 parishes as manure for the fields, and they are found to be most 

 valuable for this purpose, and to increase the produce very largely. 



Another very important use of seaweeds is affording various 

 mineral substances from the kelp, or mass of ashes, that remains 

 after they have been burned. Some years ago the preparation of kelp 

 was a source of considerable revenue to the inhabitants of the Scotch 

 sea coasts, and especially of the Hebrides, and of the Orkney and 

 Shetland Islands. Among the most familiar sights of these coasts 

 in summer were the dense columns of smoke that used to arise 

 along the coast from the numerous heaps of seaweeds while being 

 burned, which required to be done slowly at a low heat. The im- 

 portance and value of kelp has fallen greatly since the progress of 

 chemical discoveries has disclosed more economical methods of 

 preparing carbonate of soda, of which it was formerly the -chief 

 source. Nor is it now used, as it was formerly, in the preparation 

 of crown glass. It is still, however, the chief source of the 

 element iodine, the compounds of which are largely used by 

 chemists, and in medicine. About 8 lbs. of iodine can usually 

 be obtained from a ton of good kelp. Bromine, the com- 

 pounds of which are also much used in medicine, is obtained 

 mostly from kelp ; but in smaller quantity than iodine. 



Seaweeds in considerable variety are employed as food. In our 

 own maritime districts, and indeed by European nations generally, 

 they are used only to a limited extent. The Alga most commonly 

 seen in our markets is the Dulse (Rhodymenia palmatd) ; and of it 



