THE 



237 



Reproduction. In Fucus, as in Spirogyra, reproduction is 

 accomplished largely by the sexual process, although vegetative 

 reproduction may take place by the growth of parts of the plant 

 body which chance to be broken off by the waves or by other 

 means. The male and female gametangia are borne on separate 

 plants within distinct male and female branches (Fig. 126). 



Receptacle* 



Plant body 

 Floats 



Male conceptacle 



Ostiu 



FIG. 126. Plant body and male reproductive organs of Fucus 



a, plant body, male receptacles, and floats: 6, male conceptacle with antheridial 

 branches ; c, antheridial branch with antheridia 



Like Spirogyra, Fucus is therefore dioecious, and the male 

 gametes seek the females in the open sea during the fertilization 

 period. Both male and female gametangia are borne in flask- 

 shaped cavities, the reproductive cavities, or conceptacles (5). 

 Within the reproductive branches each cavity opens to the sur- 

 face by means of a narrow neck and pore, through which the 

 gametes are finally expelled into the sea water at the time of 

 fertilization. When the male gametes are being shed into the 

 water they give the male reproductive branches a yellowish color, 

 while the eggs impart a greenish tint to the female branches. 



