THE TIIALLOPIIYTA 



279 



a heterogamous condition. In genera like Edocarpus we are 

 evidently near the beginning of sexuality in the brown algae. 



The larger forms or kelps may become huge plants, the giant 

 kelp sometimes attaining a length of from two hundred to three 

 hundred meters. They are attached to the rocks by massive 

 holdfasts. The stout "stems" or stipes support broad and 



Fig. 157. — Edocarpus. A, filament with multioellular or plurilocidar 

 sporangia, in which gametes are produced. A young and growing sporangium is 



gamete; at left, the begi 



n gametes are produced. A young ana growing sporangium is 

 filament with a single-celled sporangium, in which zoospores 



shown above, a, tilament witn a singie-cened sporangium, ir 

 are produced. C, various stages in the union of two gametes. 

 „„mete; at left, the beginning of union; at right, the resulting zy; 

 (C after Oltmanns) . 



Above, a single 

 gospore. X 375. 



frequently much-divided blades and often tlisplay a certain 

 degree of structural differentiation. The abundant gametes 

 were long thought to be zoospores, but their true nature as 

 sexual cells is now known and it may be that zoospores are rather 

 rare in this group. 



2. Fucales or Rockweeds. — These plants differ from the kelps 

 in producing no zoospores and in displaying a heterogamous 

 type of sexual reproduction. 



