Vaucheriacese 



247 



dioecious species, the oogonia and antheridia usually arise side by side on the 

 same filament (fig. 159 A and 7>) or on short lateral branches (figs. 157 H ; 

 159 C and D). The oogonia, which are developed either as lateral outgrowths 

 of the filaments or terminating short branches, swell out and assume a more 

 or less rounded or ovoid form and are then cut off by a basal septum. The 

 apex of the oogonium generally develops a rostrum or beak, which is in most 



o 



Fig. 160. 1 3, 5 10, Vaucheria sessilis (Vauch.) DC. 1, .young sexual organs; 2, partially 

 ripe antheridium ; 3, transverse section of same ; 5, almost ripe sexual organs ; 6, the same 

 at the moment of fertilization ; 7, longitudinal section through a young oogonium, in which 

 there are many nuclei ; 8, older oogonium cut off from the filament by a wall, with only one 

 nucleus (ek) ; 9, fertilized egg ; 10, ripe zygote (oospore) and decayed antheridium. 

 4, antherozoids of V. synandra Woron. a, antheridium ; ek, nucleus of oosphere (egg-cell) ; 

 k, nuclei ; o, oogonium ; oe, oil drops ; pi, plasma-secretion from the oogonium ; sk, nuclei 

 of spermatozoids (antherozoids) ; sp, spermatozoids (antherozoids). (After Oltmanns.) 



cases turned to one side, either towards the antheridium or away from it. 

 The protoplasm of the oogonium contains much oil, numerous chloroplasts, 

 and, after the appearance of its basal wall, only one nucleus. There is only 

 a single oosphere or egg-cell which in most species of Vaucheria completely 

 fills the oogonium 1 ; its nucleus remains near the apex of the oogonium until 

 just before fertilization when it takes up a central position. 



1 V. ornithocepJiala (fig. 159 E), V. aversa and V. piloboloides are notable exceptions. 



