USES OF ALG^E 39 



land. Gracilaria spinosa is used by birds, allied to the swallows, 

 for making their nests the edible nests found in large numbers 

 on the islands of the Indian Archipelago, especially in the caves 

 on the shores of Java, and gathered and sent to China, where 

 they bring large prices and are used in making the famous birds'- 

 nest soup. Gracilaria lichenoides, also a species of the Eastern seas, 

 is the source of agar-agar, a preparation used in laboratories as a 

 culture-medium for bacteria. Fossil diatoms are .ground and 

 used for polishing-powders. Seaweeds are everywhere used by 

 farmers on the coasts as fertilizers. 



