BLADDER WRACK 



27 



and gases and which function as floats to keep the plant 

 vertical at high tide and horizontal during the rise and fall 

 of the tide. 



FIG. 4. Brown alga. Above 1, ribbon like thallus; 2, paired air vesicles; 

 3, antheridia bearing conceptades; below 1, thallus; 4, mature oogonia bear- 

 ing conceptaclesj"5, immature female conceptades. 



The ends of the thallus are forked or dichotomously 

 branched owing to the fact that sooner or later the end of 

 each branch develops two growing points. During repro- 



