MORPHOLOGY AND CLASSIFICATION 141 



yeasts) and (2) those which fail to produce such spores (torula 

 or wild yeasts). They are further distinguished by differences 

 in the form of the cells, but especially by differences in physi- 

 ological characters, such as the fermentation of sugars and the 

 production of pigments. 



In the yeasts there is no definite differentiation of cells. 

 Various cell structures such as cell-wall, nucleus and cystoplasm 

 with vacuoles and granules, can be demonstrated. The cell 

 membrane is, as a rule, more delicate than in the molds. It 

 sometimes secretes a gelatinous material which forms a thick 

 capsule about the cell. The nucleus is shown by appropriate 

 methods of staining as a single more or less sharply defined 

 mass of chromatin. Under suitable conditions the true yeasts 

 produce endospores, usually multiple, and as many as eight in 

 one cell. These are spherical or ovoid masses surrounded by a 

 definite wall, and usually about half the diameter of the yeast 

 cell. When supplied with nutriment these spores swell and burst 

 the mother cell, and then begin at once to multiply by budding. 

 Dry commercial yeast cakes contain spores of yeast along with 

 bacteriaand molds; moist, "compressed," yeast contains vegetat- 

 ing yeast cells, also mixed with other organisms. 



Bacteria. Bacteria (schizomycetes) are minute unicellular 

 organisms 0.2 to 4//. in width which multiply solely by simple 

 transverse division (fission), ordinarily resulting in the produc- 

 tion of two cells of equal size. In many instances the cells re- 

 main attached to each other so as to* form long filaments. 



Trichobacteria. Certain of them grow into long filaments 

 without dividing at once into shorter segments. These forms 

 which are classed as higher bacteria or trichobacteria, suggest 

 a very close relationship to the molds and may, perhaps, be re- 

 garded as intermediate between the molds and the lower bacteria. 

 Many of them exhibit a differentiation of the filament into base 

 and apex, some of them branch in an irregular fashion, and in 

 some there is a suggestion of the formation of special fruit 

 organs. These higher bacteria require further study to deter- 



