146 CLASSIFICATION OF THE MICRO-OKGANISMS. 



III. THE YEAST on BUDDING FUNGI. 



A common characteristic of all forms of budding fungi 

 is that they consist of microscopical cells which multiply 

 by budding, the cell membrane bulging out like a bladder 

 at one or both ends of the cell, this projection becoming 

 filled with a part of the contents of the mother cell, 

 gradually assuming the same size and form, and 

 finally becoming separated from the mother cell by 

 a transverse division at the point of attachment of 

 the bud. 



Toruiagrowth A similar yeast-like mode of growth is seen in a 

 fum?? uld number of fungi which under other conditions assume 

 quite different developmental forms. This is the case 

 in Exoascus taphrina, where as a rule asci, arranged side 

 by side in a palisade-like manner, are formed from a 

 thread-like mycelium ; the ascospores expelled when 

 ripe germinate in water or in nutritive solutions, and 

 grow by typical and often repeated budding. This is 

 also the case with Mucor racemosus when it is culti- 

 vated below the surface of saccharine fluids (see p. 133) ; 

 also with Exobasidium, a family belonging to the hymeno- 

 mycetes, in which the spores developed from basidia 

 send out yeast-like buds when they germinate. Accord- 

 ing to Zopf fumago behaves similarly ; and so, according 

 to de Bary, does Dematium pullulans, which probably 

 belongs to fumago or pleospora; and this also occurs, 

 according to Brefeld's most recent investigations, in the 

 tremellini and ustilagineas (see p. 109). 



Budding- fungi This mode of growth by budding is specially developed 

 proper. j n a c j agg o f f un gj j which are termed, therefore, budding 



or yeast fungi. To this class belong the ordinary yeasts, 

 the vinegar plant, and the fungus of thrush. It is 

 probable that they must all be classed among the lower 

 ascomycetes, and are most nearly allied to the species 

 exoascus, mentioned above; at least in some typical 

 yeast fungi a form of fructification has been found in 

 which spores are formed within the cells corresponding 

 exactly to the process known in connection with asci. 

 In the cas3 of other yeast fungi this higher form of 



