The Algae 



463 



years been used as a source of potassium salts and of other chemi- 

 cals. It has been estimated that they are capable of furnishing 



Fig. 283. Parts of a red alga, Polysiphonia, showing vegetative branch {A, B) and re- 

 productive structures ; C, antheridium ; D, cystocarp and carpospores ; E, branch forming 

 tetraspores. 



all the potassium needed for agricultural fertilizers in the United 

 States, and more iodine than we now annually use. In Europe 

 and Asia the kelps were formerly the chief source of iodine. 



RED ALG^ OR RHODOPHYCE^ 



The red algae, noted for their beautiful colorings and graceful 

 forms, reach their greatest development in the warm temperate 

 and tropical seas. Many species occur in shallow water, but 

 some likewise grow at great depths. The red pigment found in 

 the cells with the chlorophyll aids in photosynthesis in deep 

 water. A few genera occur in fresh water. More than 3000 

 species are known. 



The red algae are usually filamentous and highly branched; 

 sometimes they are irregular blades, or have slender stalks with 

 leaf-like branches. Among the red algae are a number of families 

 that deposit calcium carbonate about them. These are the 



