THALLOPHYTES 



73 



ing filaments (ascogenous hyphae), whose ultimate branches form asci. 

 This fertilized oogonium giving rise to ascogenous hyphae is usually 

 called an ascogonium. From hyphae beneath the ascogonium branching 

 filaments arise that produce the colored paraph yses, and still other 

 sterile hyphae give rise to the ascocarp (fig. 178). Usually several 

 ascogonia are involved in a single ascocarp. 



FIG. 177. Pyronema: oogo- 

 nium with its conjugating tube (or 

 trichogyne) ; antheridium curved 

 around the trichogyne (hence in 

 section the latter appears as if 

 piercing the former); trichogyne 

 tip fused with antheridium and 

 receiving nuclei; nuclei collecting 

 in oogonium. After HARPER. 



FIG. 178. Pyronema: somewhat diagram- 

 matic section of an ascocarp (involving two 

 ascogonia), showing ascogenous hyphae aris- 

 ing from the fertilized oogonium (ascogonium) 

 and producing asci. After HARPER. 



Ascobolus. In this form structures resembling sex organs have 

 been found, and may be interpreted with the help of the life history of 

 Pyronema. From the mycelium there arises a large, bow-form, septate 

 hypha (the "swollen hypha "), to which other slender branches become 

 attached. No fusion has been observed, but the position of the slender 

 branches suggests that their function may be that of antheridia. In 

 any event, the septate swollen hypha becomes a single chamber by the 

 disappearance of the cross walls, and then gives rise to ascogenous 

 hyphae that bear the asci. The paraph yses and the ascocarp also 

 arise in the way described for Pyronema. It seems safe to infer that the 



