THE ALG.E 



231 



growing places. This is true in the case of Sargasmm, some 

 species of which thrive along the shores of tropical oceans. 

 In the North Atlantic Ocean, north of the Canary Islands, 

 is a body of water known as the Sargasso Sea. Its entire 

 area is more or less filled with floating Sargasmm and other 

 forms of plant and animal life. Sargassum, like some other 

 brown algre, is peculiarly fitted 

 for floating by the presence 

 of " air bladders," which are 

 swollen portions of the leaf -like 

 expansions of the plant. In 

 mid-ocean one may see small 

 floating masses of these plants, 

 which have been carried some- 

 times hundreds or even thou- 

 sands of miles from their original 

 homes. 



218. The kelps. The giant 

 kelps belong to the brown algae. 

 The cylindrical, stem-like plants 

 sometimes (as in Macrocystis') 

 reach a length of from 800 to 

 900 feet, while " devil's apron," 

 (Laminaria) grows into strap- 

 like or widely spread, tough, 

 leathery expansions. All of 

 these forms have heavy, root- 

 like holdfasts, which are so strong that the plant will usually 

 break elsewhere before it will pull away from its support. 



At one time the world's supply of iodine was derived from 

 the brown alg;e ; now it can usually be prepared more eco- 

 nomically by chemical means. Soda was formerly secured 

 from these plants, but chemical processes have driven out the 

 laborious methods of securing that substance directly from 

 plants. Gelatinous foods and a sugar known as mannite are 

 secured from some species of brown algae. In some coastal 



FIG. 180. Rockweed (Fucus) 



A, the base of a young plant, showing 

 an early stage in formation of the 

 holdfast, which attached the plant 

 to a piece of wood. B, tip of a plant ; 

 6, air bladders; a, specialized re- 

 gions in which reproductive organs 

 are formed ; c, new leaf-like growth 

 where the plant has been broken. 

 A little less than natural size 



