RED SEAWEEDS 85 



the case in Algse in which sex is not so highly 

 specialized. 



In Bladder- Wrack (Fucus vesiculosus) the male and 

 female elements are formed in separate conceptacles ; 

 they are expelled into the water, where they meet and 

 fertilization takes place. The egg-cell of Pelvetia produces 

 two ova, but that of F. vesiculosus divides into eight. 



The Red Seaweeds, or Rhodophyce^e, are not only 

 marked off from other Algae by their distinctive colour 

 and their consequent adaptation to deeper water, but 

 they have methods of reproduction peculiarly their own. 

 They form a quite isolated group, displaying no definite 

 affinities; they do not appear to indicate any stage of 

 transition to plants higher than themselves, and we 

 must regard them as a side-issue of evolution, filling 

 their own particular place in the economy of nature. 

 They propagate by asexual spores, and sexually by 

 means of unciliated cells which have no motile power. 

 Some kinds are thickly encrusted with carbonate of 

 lime. Such are the Corallines so frequently found in 

 rock-pools, and which, in some localities, form reefs in 

 the sea. About 1,800 species of Red Seaweeds have 

 been distinguished. There is great diversity of form 

 among them ; very few exist unattached to a substratum. 

 In all but the lowest types the protoplasmic bodies of 

 the cells of the thallus are connected by delicate strands 

 of protoplasm. 



The asexual spores of the Red Algse are known as 

 " tetraspores," because they occur four together in a 

 mother-cell; they could not be called "zoospores," as 

 they are not motile. The spores escape from the 

 mother-cell and immediately grow into new plants. 



