238 



STRUCTURAL BOTANY 



As regards the subsequent development of the asco- 

 gonium, 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 becomes the 

 ascus. It contains two nuclei, which fuse into one and 

 then divide repeatedly, giving rise to eight daughter-nuclei, 



p 



FIG. 97. A-C, Sphcerotheca Castagnei. A, early stage iu forma- 

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

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

 hyphae. 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 () 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.) 



around each of which a cell is formed. These eight cells 

 are the ascospores. In the meantime the cell next below 

 has sent out several branches, which grow up around the 

 ascogonium, completely enveloping it in a double layer of 

 densely crowded hyphse (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 



