372 



THE NON-VASCULAR PLANTS 



to the rocks, and their tough leathery bodies are not injured 

 by the beating of the waves. The rockweeds, which are 

 members of this group, have air bladders, and swollen tips 

 in which the oogonia and antheridia occur. (See Figure 

 170.) The largest of this group are the kelps, some of 



which attain a length 

 of several hundred feet. 

 (See Figure 171) Io- 

 dine is obtained from 

 seaweeds which belong 

 to this group. 



(4) RhodophycecB. — 

 The word means red 

 algce. These forms are 

 smaller and more deli- 

 cate than the brown 

 algae. They get their 

 name, like the brown 

 ones, from the pigment 

 which obscures their 

 chlorophyll. These are 

 the seaweeds which are 

 often dried on card- 

 board and taken away ' 

 as souvenirs of the sea- 

 side. There are violet, 

 purple, and pink ones, 

 as well as red. They 

 often have very graceful branching forms. They do not 

 grow so far north as the brown algae, and are most abun- 

 dant in the tropics. (See Figure 172.) Some of the red 

 algae have rather complex methods of sex reproduction. 



Fig. 170. — Rockweed {Fucus). A common 

 kind of seaweed. One of the brown algse. 

 Note the swollen tips in which oogonia and 

 antheridia occur ; also the air bladders which 

 add much to the buoyancy of this plant. 



