210 



THE ALG.E 



There is no method of sexual reproduction known, and this 

 is remarkable, for groups as highly developed and eminently 

 successful as the kelps almost always have well-established 



and complex methods 

 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 

 of each branch (Fig. 



>P)- 



The sexual organs 



from the sides 



FIG. 108. A rockweed (Fucus vesiculosus) 



A, habit sketch, showing the forking of the branches ; 

 b, air bladders; r, swollen fruiting tips (recepta- 

 cles), with the sunken cavities (conceptacles) which 

 contain the sexual organs; />, pit at a growing 

 point. -B, base of a plant ; 7? , holdfast 



