210 



THE ALG^E 



The kelps reproduce by zoospores developed in one-celled 

 sporangia that are formed in large patches upon the blades. 

 A conjugation of these zoospores in pairs has been reported, 



indicating a method 

 of sexual reproduction. 

 237. The rock- 

 weeds. The rock- 

 weeds (order Fucales) 

 are the highest forms 

 of the brown algae, 

 both in vegetative 

 structure and because 

 of the complex sexual 

 conditions (heterog- 

 amy), with character- 

 istic eggs and sperms. 

 The commonest 

 genus is Fucus (Fig. 

 198), which is very 

 widely distributed in 

 the colder seas and 

 forms the bulk of the 

 algal vegetation be- 

 tween tide marks 

 (Plate IV). The plant 

 body of Fucus forks 

 very regularly (dichot- 

 omous branching), 

 and the growth is from 

 a region of cells situ- 

 ated in a pit at the end 



FIG. 198. A rockweed (Fucus vesiculosus) 



of each branch (Fig. 



A, habit sketch, showing the forking of the branches; -i QQ \ 



6, air bladders; r, swollen fruiting tips (recepta- *"| Cy- 

 cles), with the sunken cavities (conceptacles) which The sexual organs 

 contain the sexual organs; p, pit at a growing , ., 



point. S, base of a plant; fc, holdfast arise fr m tne Sldes 



