PEZIZALES 



341 



Ascobolus citrinus will serve as an example of the parthenogamous 

 group (Schweizer, 1923). At germination the ascospores swell, rupture 

 the exospore and form one, rarely several germ tubes. After four to 

 five days, especially in cultures rich in protein, there appear on branches 

 of the hyphae, large clavate protrusions which are abjointed from the 

 main hypha and subsequently develop to bow-shaped, slightly helical 

 ascogonia (Fig. 227, 1 and 2). Besides the stipe cells, these contain 

 usually six multinucleate cells of which the highest is distinguished by 

 size and density of protoplasm. From the stipe cells, several thick 

 hyphae which surround the ascogonium intertwine to a plectenchymatic 



Fig. 227. — Ascobolus citrinus. 



Development of sexual organs. 

 1923.) 



( X 725 ; after Schweizer, 



sheath and supporting tissue. In this condition, the fructification is 

 about a quarter of a millimeter in size. 



Through pores, the cells of the ascogonium come into open communi- 

 cation so that the nuclei of the other ascogonial cells migrate toward the 

 large central cell. There they pair and pass out into the ascogenous 

 hyphae, which radiate from this central cell only (Fig. 227, 5). The 

 nuclei remaining behind degenerate. In contrast to Pyronema confluens, 

 therefore, the sexuality of Ascobolus citrinus has been shifted toward the 

 simpler Hypocreales, like that of Poly stigma rubrum. Instead of amphi- 

 mictic fertilization, there occurs parthenogamy, a cell fusion with the 

 female organ. 



A. stercorarius (Welsford, 1907), A. glaber (Dangeard, 1907), A. 

 immersus (Ramlow, 1915), A. Winteri (B. O. Dodge, 1912), Ascophanus 

 carneus (Cutting, 1909; Ramlow, 1915) correspond essentially with this 



