238 



STRUCTURAL BOTANY 



As regards the subsequent development of the 

 ascogonium, the main facts are clear. After two or three 

 transverse divisions one of the cells of the row (either 

 the last or the last but one) increases in size, and be- 

 comes the ascus. Its nucleus divides repeatedly, and 

 gives rise to eight daughter-nuclei, around each of which 



A p 



FIG. 97. A-C, Sphceroiheca Castagnei. A, early stage in forma- 

 tion of fruit ; p, antheridium ; c, ascogonium. B, more ad- 

 vanced ; p, antheridium ; c, ascogonium ; e, enveloping 

 hyphse. C, ripening fruit in section ; c, ascogonium, from 

 which the young ascus (a) is now developed ; e, e, envelop- 

 ing hyphae, forming perithecium. D and E, S. pannosa ; 

 D, ripe perithecium (e) bursting to set free the ascus (a), in 

 which only six out of the eight ascospores are shown. E, 

 chain of conidia, borne on a vertical branch of the mycelium. 

 Magnified 600. (After De Bary.) 



a cell is formed. These eight cells are the ascospores. 

 In the mean time the cell next below has sent out several 

 branches, which grow up around the ascogonium, com- 

 pletely enveloping it in a double layer of densely crowded 

 hyphae (Fig. 97, B and C). From the inner cells of the 

 envelope thus formed short branches filled with very dense 

 protoplasm grow inwards and apply themselves closely to> 



