96 



CHLOROPHYCEAE 



masses which grow into new filaments. Sexual reproduction is 

 distinctly oogamous, the different species being either monoecious 

 or dioecious. The oogonia, which are sessile or stalked, are cut off 

 by a septum at a stage when there is only one nucleus left in the 

 oogonium. Some authors maintain that the extra nuclei, which are 



Fig. 66. Vaucheria sessilis. Stages in development and fertilization of oogonium. 

 April 1-6, 1930. ( X 195.) A, young antheridium and " wanderplasm " in place 

 from which oogonium will arise. B, young oogonium. C, oogonial beak formed; 

 "wanderplasm" retreating into thread; oil globules passing into oogonium; 

 antheridial wall forming. D, "wanderplasm" out of oogonium. E, basal wall of 

 oogonium forming. F, antherozoids emerging. G, oogonial membrane forming 

 at tip, some antherozoids in egg. H, cytoplasm extruded and rounded off; 

 fertilization occurring. I, ripe egg. zc^ = wanderplasm. (After Couch.) 



potential gametes, degenerate, whilst others consider that the 

 surplus nuclei, enclosed in a mass of cytoplasm or ''wanderplasm", 

 travel back into the main thread before the septum is laid down. It 

 is probable that in some species all the surplus nuclei pass out with 

 the "wanderplasm", whilst in other species some nuclei may be 

 left behind and degenerate later after the septum has been laid 



