THE YEAST FUNGI. 147 



fructification has not yet been observed; nevertheless 

 the position above indicated may be assigned to the 

 whole class of the yeast fungi.* 



Many of the yeast fungi excite fermentation, and are 

 able to set up alcoholic fermentation in saccharine 

 solutions. Nevertheless there are typical budding fungi, 

 such as the pink torula, &c., which are not able to set 

 up fermentation ; and on the other hand the yeast-like 

 developmental forms of mucor, and of other of the above 

 mentioned higher fungi, have a certain though restricted 

 power of exciting fermentation. 



The peculiar mode of multiplication of the yeast fungi Muitipiica- 

 goes on to an almost unlimited extent so long as all budding. 

 the conditions of existence are favourable; the new 

 formed cells which arise by budding develop fresh 

 daughter cells which either soon become separated and 

 continue to grow as independent individuals, or remain 

 united to the mother cell for a time, and thus give rise 

 to chains and masses. The cells have a spherical or 

 oval form, are surrounded by a thin colourless membrane, 

 and contain a granular protoplasm, in which are vacuoles 

 filled with cell juice. 



By a special mode of cultivation it is possible to By spore for- 

 obtain multiplication by ascospores in various forms of m 

 yeast (beer and wine yeast, mycoderma of wine) . If the 

 yeast is cultivated, after being washed and freed from 

 adhering wort, on solid moist soil which provides little 

 nourishment, e.g., on slices of potato or carrot, two or 

 more round cells appear within the mother cell by free cell 

 formation just as in spore tubes, these young cells being 

 surrounded by a thick membrane and becoming free 

 after some time by solution of the wall of the mother 

 cell ; in other cases the cell contents contract so as to 

 form a single spherical body. The spores thus formed 

 germinate in sugar solution, and develop in the form 

 of ordinary yeast. 



At times a tendency to form mycelial threads is Formation of 

 observed. If the yeast is cultivated on the surface of 



* De Bary 1. c., p. 292. Compare the contrary views of Brefeld in 

 Botan. Unferstichungen uber Rt f epilze. Leipzig, 188?. 



