Ch. X] THE RED ALG.E 443 



where they are fertilized, usually on the rising tide, by the 

 small laterally biciliate sperm cells set free from the antheri- 

 dia. So great is the contrast in size between egg cell and 

 sperm cell in Fucus that this plant is commonly cited as 

 representative of one of the theoreti- 

 cal stages in the evolution of sex 

 (page 304). 



In this order belongs also the Sar- 

 gassum, the floating brown seaweed of 

 the Sargasso Sea, which, originally 

 attached, now floats freely and in- 

 creases by vegetative multiplication. 

 This plant is further noteworthy for 

 the remarkable specialization of its 

 thallus into seeming leaf and stem 

 (Fig. 309), with axillary stalks carry- 

 ing floats and reproductive bodies; 

 but the arrangement bears no morpho- 

 logical relation to that familiar in the 

 higher plants. 



Ecologically the Phaeophyceae are 

 hydrophytes which for a time can en- Fig. 309. — Sargassum vui- 

 dure exposure to air, perhaps to their gare; x *' ( FromSachs -) 

 profit. Phylogenetically they are a specialized group inde- 

 pendent of all other kinds in their higher forms, but in their 

 lower showing marked affinities with the Flagellates and lower 

 Chlorophycese (Fig. 275). Though they have attained a 

 higher specialization than the Green Algae, they have not, 

 unlike the latter, given rise to any higher forms. 



Class 8. RHODOPHYCEiB : the Red Alg^e 



These comprise the majority of the Algae of the sea, espe- 

 cially in tropical waters. Most typical are the kinds called 

 Sea Mosses, noted for their great beauty of color, from rose 

 red to violet or purple, and for the extreme grace of their 

 elaborately fringed or divided fronds. They are mostly 



