Environment and Adaptation 191 



differentiated into eggs and spermatozoids. It may 

 be that life in salt water may tend to check the 

 evolution of the sexual system. It is true that in 

 one group of brown algae, the Fucacese, sexuality 



FIG. 20 



The Sea-palm (Postelsia), an alga adapted to life in the 

 surf; the long flexible stem is firmly anchored to the rocks 

 by a powerful holdfast, a root-like grappling organ. 



is well developed, but in a very much larger num- 

 ber the sexual elements are very simple, being 

 motile gametes, or the plant may be entirely sexless. 

 In the largest of all of the brown algae, the giant 



