BROWN ALGAE 381 



by the forward cilium. Such fixed females become centres of attrac- 

 tion for the still motile males, which collect round them in number, 

 and come into contact with the female by their forward cilium 

 (Fig. 321, i). Presently one of them draws up to the female and 

 begins to fuse with it (2) ; all the rest at once move away. Gradually 

 the fusion is completed (3-5), the resulting zygote rounds off and 



FIG. 319- 



A, Mature male conceptacle of Fucus serratus, filled with branched antheridial 

 hairs (After Thuret.) B, Mature female conceptacle of Fucus serratus, 

 containing unbranched hairs, and oogonia. (After Thuret.) Incidentally these 

 drawings show the structure of the mature thallus (p. 379)- 



forms a cell-wall, and may presently germinate into a new plant. 

 In E. siliculosus both types of sporangia and of gametes are alike in 

 form. But in E. secundus the sporangia (gametangia) are not alike ; 

 and they produce gametes of different sizes (Fig. 322, i.). The smaller- 

 celled gametangia (antheridia) produce smaller gametes that are male 

 (spermatozoids, ii.) ; the larger-celted (oogonia) produce larger gametes 

 that are female (ova, iii.)- But still they are of the same form as the 

 zoospores of the whole group. After their escape the ova soon lose 

 their motility, and their fertilisation by the smaller spermatozoids 



