THE ALGiE 



233 



of the conceptacles when the plants which bear them 

 become partially dry between tides. When the plants 

 are again covered with sea-water, each egg becomes sur- 

 rounded by actively swimming sperms which set the egg 

 itself in motion 

 (Fig. 163, 5). The 

 egg is soon fertil- 

 ized, becomes an 

 oospore surrounded 

 bj' a special cell- 

 wall, germinates, 

 and forms a new 

 plant. The unlike- 

 ness of the male 

 and female gametes 

 of Fucus in form, 

 size, and motile 

 power is very great; 

 tens of thousands 

 of sperms would 

 be needed to make 

 up a bulk equal to 

 that of a single egg. 

 299. Summary 

 of the Brown Algae. 

 — The brown algee 

 are practically all 

 of them marine, 

 abounding most in the northern seas, and are usually 

 known as seaweeds. They vary greatly in size, some being 

 almost microscopic, while others, like the giant kelps of 

 the Pacific, reach a length of from six hundred to nearly 



Fig. 164. Transverse Section, of Conceptacle of a 

 Rook weed (Fucus platy carpus) . ( x about 35. ) 



h, hairs; u, antheridia; o, oogonia. 



