340 



COMPARATIVE MORPHOLOGY OF FUNGI 



ment. Furthermore, without copulation the ascogonia seem to be able 

 to continue their development parthenogenetically. The ascogenous 

 hyphae of Ascobolus carbonarius show a marked separation into a pri- 

 mary and a secondary phase, as in Pyronema confluens (p. 130) and in the 

 Plectascales. The ascogenous hyphae which bud directly from the 

 ascogonia are vertical and at first unbranched. Later their ends branch 

 to secondary hyphae which subsequently proceed to the formation of 

 hooks and asci in the usual manner. 



Ascobolus carbonarius is the only known example in the Pezizales 

 where a sexually active ascogonium, in the absence of antheridia, copu- 

 lates with vegetative structures in order to draw from them the necessary 

 foreign nuclear material. Thus it is characteristic for its double position 



Fig. 226.- — Ascobolus carbonarius. 



Development of ascogonia. 

 Dodge, 1912.) 



( X 265 ; after B. O. 



that, on the one hand, the ascogonia are still adjusted for cross fertiliza- 

 tion, while on the other hand, the antheridia have disappeared, so that 

 this cross fertilization may only occur by a substitute. It is also charac- 

 teristic that this cross fertilization, as in the Pyronemaceae, is not obliga- 

 tory but that when it is absent the ascogonia may develop independently. 

 It is also noteworthy that this species is heterothallic (Betts, 1926). 

 Single spore cultures fail to produce apothecia. This sexual differentia- 

 tion takes place in the ascus, since cultures from the spores of a single 

 ascus gave equal numbers of -f- and — mycelia. 



This cross fertilization, since of the numerous forms studied only A. 

 carbonarius shows the transitional type, appears to have been rapidly 

 lost or is only realized in a few cases as conidial copulation. In the large 

 majority of the previously investigated forms, it is replaced by true 

 deuterogamous compensation. 



