58 



MANUAL OF BOTANY 



Fig. 806. 



The reproductive processes of the group may be sexual or 

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

 swimming ciUated gametes, which conjugate in pairs. Vau- 



cheria is exceptional 

 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 



Fi(j. 806. Fart of a filament of Ulo/hrix Irom which 

 tlie gametes, g, are escaping. g\ Free gametel 

 (/\ &'. Gametes conjugating. 



Fig. 807. 



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

 and f I om cells opposite to each other protuberances are growing out to 

 meet, a^a\' Each produces a gamete, b. When the protuberances hare 

 met and fused, one gamete passes over and unites witll the other, c, 

 d. Adult zygospore. 



effects fertilisation. There is no sporophytio form, the zygote 

 germinating to produce a new gametophyte. 



In Sphceroplea, which is composed of several coenoeytes, any 

 segment of the body may become an antheridium or an 



