106 THE STORY OF LIFE IN THE SEAS. 



that are often found far out in the open ocean 

 the best known is the Sargasso or Gulf-weed of 

 the Atlantic. It forms in some cases great 

 floating patches, of very considerable area, and 

 is, when alive, of a bright yellow colour. The 

 Sargasso patches are, however, of great interest 

 to the zoologist, because they support a consider- 

 able population of animals specially adapted by 

 their form and colour to live among the Sea- 

 weeds. They present us, in fact, with a peculiar 

 Fauna, containing representatives of all the most 

 important groups of marine animals. 



Besides the large conspicuous weeds like the 

 Sargasso, the surface of the sea supports a large 

 Flora of minute plants of very lowly organisation, 

 and it is not at all uncommon for them to be 

 present in such numbers as to cause a distinct 

 discolouration of the water. 



The banks that they form on the coast of 

 Brazil and elsewhere were called " Sea-sawdust" 

 by Sir Joseph Banks. Moseley says that "when 

 tracts of the sea are passed through, which are 

 full of this Trichodesmium, the water lighted up 

 by sunlight, when looked down into, appears 

 as if full of small particles of mica or some such 

 substance, so strongly is the light reflected from 

 the minute bundles of the Algae " ; and again, he 

 says, "so abundant is Trichodesmium in some seas 

 that one of the explanations of the name of the 

 Red Sea is that the term was derived from the 

 discolouration of the water by vast quantities of 

 Trichodesmium erythrceum." 



f In addition to this "Sea-sawdust," Diatoms, 

 the still more minute organisms, the Bacteria, 



