THE FUNGI : ARCHIMYCETES AND PHYCOMYCETES 225 



septum. The tip now becomes swollen, and the protoplasm separates into a 

 central granular portion, the oosphere, and a peripheral layer, the periplasm. 



ANTHERIDIUM 



STALK OF 

 OOGONIUM 



OOGONIUM 

 OOSPORE 



YOUNG 

 OOGONIUM 



OOSPHERE 



DEAD 



ANTHERIDIUM 



YOUNG 

 ANTHERIDIUM 



FERTILIZATION TUBE 



FUNCTIONAL 

 Q ANTHERIDIUM 



Fig. 215. — Pythiitm deharyamiw. Sexual reproduction. A, Young oogonium 

 with antheridium attached before the formation of the fertiUzation tube ; 

 mature oospore on left. B, Mature oogonium with oospore and dis- 

 organizing antheridium. C, Oogonium with oosphere inside and several 

 antheridia attached, one with fertilization tube passing from the antheridium 

 through the oogonium into the oosphere. 



All except one of the included nuclei migrate to the periphery and abort, 

 so that only one functional female nucleus remains in the centre (Fig. 216). 



Antheridium 



Fig. 216. — Pythium debaryamun. Smooth 

 oogonium with single oospore and 

 attached antheridium. 



Meanwhile the antheridium is developed as a club-shaped branch, either 

 on the same or on an adjacent hypha, and is also cut off by a transverse wall 

 (Fig. 215). The antheridium now elongates, its tip comes into contact with 

 the wall of the oogonium, which it dissolves at this point, and a fertilization 

 tube is formed which penetrates the oogonium and passes into the oosphere. 

 It is probable that only a single male nucleus enters the oogonium, and this 



