THALLOPHYTA: FUNGI 159 



organs. Where these are well developed, the oogonium (ascogonium) 

 often resembles that of the red algae. The zygote may develop directly 

 into an ascus or, more commonly, may give rise to many ascogenous 

 hyphae that, in turn, produce the asci. The Basidiomycetes have no 

 sex organs (unless the spermogonia of the rusts are so regarded), but 

 fusions between vegetative cells are common. In the Ascomycetes and 

 Basidiomycetes the sexual nuclei come together without immediately 

 fusing. The nuclear fusion, which takes place in the ascus or basidium, 

 is followed at once by the production of ascospores or basidiospores, 

 respectively. 



