278 



A TEXTBOOK OF THEORETICAL BOTANY 



i'SP 



Vegetative cell 



Ascospores 



Fig. 269. — Saccharomyces cerevisiae. Formation of 

 ascospores. 



When an ascus breaks down the four spores germinate, and normally 

 they fuse together in pairs with fusion of nuclei to produce two zygotes 



^, 



Fig. 270. — Saccharomyces eUipsoideiis. A and B, 

 Two germinating spores. C and D, Fusion 

 of buds. E, A second zygote has been formed 

 by the conjugating spores and both are 

 germinating. {After Winge.) 



(Fig. 270), which start budding immediately and produce vegetative cells, 

 which will in time give rise to asci again. It sometimes happens, however, 

 that an ascospore germinates without conjugation, and in this case it gives 



