58 



MANUAL OF BOTANY 



The reproduetiA^e processes of the group may be sexual or 

 asexual. The sexual cells are usually all alike and are free- 

 swmiming ciliated gametes, which conjugate in pairs. Vau- 



cheria is exceptional 

 Fig. 806. in producing anthe- 



ridia and oogonia 

 (fig. 805), which are de- 

 veloped in close prox- 

 imity to each other 

 from the surface of a 

 filament. Each be- 

 comes shut off from 

 the rest of the coeno- 

 cyte by a cell- wall. 

 The antheridium gives 

 rise to a number of 

 antherozoids which 

 are liberated by the 

 rupture of the apex. The oogonium contains a single oosphere, 

 and when it is mature it opens at the apex, and a drop of muci- 

 lage is extruded. An antherozoid enters the oogonium and 



Fig. 806. Part of a filament of Ulothrix from which 

 the gametes, g, are escaping. ^'. Free gamete. 

 g", g"". Gametes conjugating. 



Fig. 807. 



Fig. 807. Conjugation in Spirogyra. Two filaments are lying side by side, 

 and from cells opposite to each other protuberances are growing out to 

 meet, a, «'. Each produces a gamete, h. When the protuberances have 

 met and fused, one gamete passes over and imites with the other, c, 

 d. Adult zygospore. 



effects fertilisation. There is no sporophytic form, the zygote 

 germinating to produce a new gametophyte. 



In S2)hcsro2}lea, which is composed of several coenocj^tes, any 

 segment of the body may become an antheridium or an 



