LIFE HISTORIES OF ALGJS 
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 Fucaceae 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 Ascophyllum 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 Ascophyllum. The plant body of 
Ascophyllum is a branched thallus, the branches being 
