THE GREAT GROUPS OF ALG.E 47 



specialized forms, and are so much more highly organized 

 than all other Algae, that they will be passed over here with 

 a bare mention. They grow in fresh or brackish waters, 

 fixed to the bottom, and forming great masses. The cylin- 

 drical stems are jointed, the joints sending out circles of 

 branches, which repeat the jointed and branching habit 

 (Fig. 31). 



The walls become incrusted with a deposit of lime, 

 which makes the plants harsh and brittle, and has sug- 

 gested the name " stone worts." In addition to the highly 

 organized nutritive body, the antheridia and oogonia are 

 peculiarly complex, being entirely unlike the simple sex 

 organs of the other Algae. 



