LIFE HISTORIES OF ALG^ 229 



commonly found attached to rocks between the lines of 

 high and low tide, where they are subjected to alternate 

 submersion and exposure (Fig. 171). The Fucace^ have 

 an added interest because of their economic uses. They 

 serve as food for the inhabitants of the west coast of 

 South America, and in other countries, and are also widely 

 used as fertilizer, and as a source of iodine. They include 



Fig. 172.— Portion of plant of Ascophyllufn nodosum. X %. 



some of the largest plants in the ocean, and one of the 

 genera, Sargassum, floating on the surface, helps to form 

 the well-known - Sargasso Sea," of the middle Atlantic 

 ocean. 



208. Description of AscophyUum.— The plant body of 

 Ascophyllum is a branched thallus, the branches being 



