THE GEEAT GROUPS OF ALG^E 63 
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. 231). 
The walls become incrusted with a deposit of lime, 
which makes the plants harsh and brittle, and has sug- 
gested the name " stoneworts." 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. 
18 
