138 THE ASCOMYCETES 



mvcetous stasre, but orenetic connection with a conidial stagre has 

 not been established. 



A structural parallelism between conidia and ascospores has 

 been observed [Orton (1915)] in several of the more common 

 genera, such as Endothia, Pleospora, Coccomyces, Diplocarpon, 

 Gibberella, Venturia, Glomerella, Cucurbitaria, Erysiphe, and 

 Mycosphaerella. It does not occur universally, however, among 

 Ascomycetes. 



Sexual reproduction. The sac or ascus, normally containing 

 eis^ht ascospores, is the resultant of sexual processes among Asco- 

 mvcetes. As will be apparent in the accounts that follow, the 

 young asci in all species are binucleate. These two nuclei then 

 fuse to form the nucleus of the primary ascus. There follow 

 three nuclear divisions, after which the ascospores are delimited 

 by a process of free-cell formation, leaving portions of the 

 cytoplasm outside the spores. Great differences, however, exist 

 in observations of the origin of the pair of nuclei and the kinds 

 of structures in which they are produced. The two sex organs, 

 as in Eremascus, may be quite alike, or there may be well-differ- 

 entiated antheridia and ascogonia, as in Pyronema confliiens. 

 Lateral hyphal branches may either be coiled archicarps or bear 

 clusters of spermatia, as in Fleiirage anser'ma. Separate locular 

 stromata may become differentiated into spermogonia, bearing 

 spermatia, and carpogonia, bearing archicarps, as in Mycosphae- 

 rella bolleana. One or the other of the sex ors^ans may be abortive, 

 and in consequence parthenogenesis may occur. In any event 

 one or more ascogenous cells occur within each developing asco- 

 carp. In these ascogenous cells (ascogonia) one or more func- 

 tional pairs of nuclei occur. Hyphal protrusions that become 

 the ascogenous hyphae arise from the ascogonium. The asco- 

 q^enous hyphae recurve (crosier formation), and the penultimate 

 cell of each hyphal tip becomes the ascus. 



Some workers maintain that apogamy is of wide occurrence 

 among Ascomycetes. In our opinion it seems more probable that 

 it is rare. It must be admitted, though, that spermatization, sup- 

 plemented by cytologic evidence of fertilization, has been re- 

 corded in only a few species. Spermatia and ascogonia are too 

 commonly present, it would appear, to be regarded as vestigial 

 and nonfunctional. Strangely, however, many well-trained my- 

 cologists have never seen these structures amon^ Ascomycetes. 



