THE FUNGI : ARCHIMYCETES AND PHYCOMYCETES 239 



from the antheridium a fertilization tube, which penetrates the receptive 

 spot and enters the oosphere. All the nuclei in the antheridium and the 

 oosphere now undergo a second nuclear division, while the nuclei in the 

 periplasm disorganize. A single female nucleus passes to the centre of the 



OOSPHERE 



ANTHERIDIUM 



FERTILIZATION 

 ' TUBE 



PERIPLASM 



FEMALE 

 NUCLEUS 



OOSPORE 

 Q WALL 



Fig. 230. — Cystopus candidus. Sexual reproduction. A, Mature 

 oogonium^ B, Formation of receptive spot in connection with 

 antheridium. C, Development of fertilization tube. D, Post- 

 fertilization stage, with oospore wall appearing and single fusion 

 nucleus. E, Later stage in oospore formation with multiple nuclei. 

 F, Mature thick-walled oospore, including remains of fertilization 

 tube. {After Wager.) 



oosphere and remains there, while the others pass to the periphery and 

 finally abort. A single nucleus from the antheridium, together with a small 

 amount of cytoplasm, passes in through the fertilization tube and the male 

 and female nuclei come into contact and fuse. The fertilization tube collapses 

 and is withdrawn from the oosphere, leaving a large vacuole. The wall of the 

 oospore, thus formed, is now laid down. It is a thick, two-layered structure 

 consisting of a thin endospore and a thick, often almost spiny, exospore 



(t^ig- 231)- 



