70 EVOLUTION OF PLANTS 



the rock-weeds (Fucus) (Fig. 18, B), and the gulf-weed 

 (Sargassum) (Fig. 18, A), have clearly marked, sexual 

 cells, large, non-motile eggs, and small, ciliated sperma- 

 tozoids, closely resembling the biciliate zoospores of the 

 kelps. 



The lowest forms where sexual cells occur, i.e. Ecto- 

 carpus, have similar motile gametes, while in others, 

 like Cutleria, there is a marked difference in size, 

 although both gametes are motile. The most highly 

 specialized forms, i.e. Fucus and Sargassum, produce 

 large non-motile eggs and minute spermatozoids, both 

 of which are discharged into the water when the egg is 

 fertilized, in a manner which recalls that of many low 

 animals, such as the starfish or sea-urchin. 



The Red ALGiE (^EliodophyceoB) 



Among the most beautiful of all plants are the Red 

 Alg8B or Rhodophycese, whose brilliant colors and grace- 

 ful forms are familiar to the most superficial student of 

 the marine flora. They differ in structure so much from 

 the other Algae, that they are sometimes considered to 

 form a group entirely apart from these. However, the 

 lower members of the class show sufficient resemblance 

 to the green algte to make it seem likely that there 

 is a relationship between the two classes, although it is 

 probably a remote one. 



While not so strictly marine as the typical Phseophy- 

 cese, still the great majority of the Rhodophycete occur 

 only in salt water. The few members of the class which 

 grow in fresh or brackish water are insignificant in size 

 and dull in color, and belong to the lower orders of the 

 class. 



