DISCOMYCETES 



[CH. 



104 



that in both oogonium and antheridium some nuclei degenerate 



Hvphae from the ascogonial and antheridial branches and also from the 



surrounding cells, begin to grow up even before ferfhzahon, and later 



envelop the sexual organs. . 



When fertilization is about to take place an area of cytoplasm in the 

 region of the antheridium, against the wall of which the tip of the trichogyne 

 is pressed is differentiated as a very finely granular disc from which the 

 nuclei are withdrawn. Although located in the antheridium this area 

 resembles the receptive spot seen in the oosphere of many algae. The tip 

 of the trichogyne has by this time developed as a beak-like projection, and 

 this also is empty of nuclei and contains dense and finely granular cytoplasm. 



The walls of the antheridium and trichogyne now break down at the 

 point of contact and a pore is formed. The process is gradual, consisting 

 probably of a softening and solution of the wall material, which seems to 



Fig. 62. Pyronema conjluens ; a. antheridium, trichogyne and oogonium, 

 male and female nuclei collected in the middle of the latter ; b. c. fusion 

 of male and female nuclei ; after Harper. 



spread out into the cytoplasm of the beak, suggesting that the solvent 

 action is mainly exerted from the interior of the trichogyne. The open 

 pore now becomes thickened around its margin so that an exceedingly 

 strong ring unites the antheridium and trichogyne, and they can be bent 

 or turned upon each other without being pulled apart. This arrangement 

 is no doubt necessary to withstand the strain set up by the flow of nuclei 

 from the relatively wide cavity of the antheridium through the narrow pore 

 and beak. 



