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 zodspores of the 
kelps. 
The lowest forms where sexual cells occur, 7.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, 7.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 Rep Aca (Rhodophycee) 
Among the most beautiful of all plants are the Red 
Algz or Rhodophycez, 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 Algz, 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 alge 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 Phzophy- 
cee, still the great majority of the Rhodophycee 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. 
