THE GREEX ALG^ (CHLOROPHYCE^E) 209 



that are the result of the union of similar motile gametes, 

 as in such green algae as Ulothrix and CladopJiora. Others, 

 of which Fucus is a representative, reproduce by means of 

 oospores that are formed by the union of sperms and eggs. 1 



193. Uses by man. At one time the world's supply of iodine 

 was derived from the brown algae ; now it can usually be pre- 

 pared more economically by chemical means. Soda was for- 

 merly 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 se- 

 cured from some species of brown 

 algae. In some coastal portions of 

 this country the farmers collect 

 and carry inland great quantities of 

 brown algae and spread them over 

 the cultivated land as a fertilizer. 



194. The red algse. The red 

 algae (^RhodopJiycece) chiefly inhabit 

 deeper water than do the brown 

 algae. The class is almost wholly 

 confined to salt water, and the few 

 that do live in fresh water do not 



exhibit well the color characteristics of the class. One com- 

 mon fresh-water genus is Batrachospermum (Fig. 172). 



The marine forms of this group present most striking shapes 

 and colors. They are of different shades of red, varying from 

 the most brilliant to those that are dark and somber, while 

 some are a deep purple. Chlorophyll is present, but often is 

 completely obscured by the other colors. Sometimes all the 

 colors are obscured by deposits of calcareous material upon 

 the plants. 



1 If desired to study further the details of reproduction of the brown 

 algse, see Coulter, Barnes, and Cowles, College Botany, Vol. I ; also Bergen 

 and Davis, Principles of Botany. 



FIG. 172. A red alga (Batracho- 

 spermum), which is fairly com- 

 mon in fresh waters 



Slightly magnified 



