io8 MORPHOLOGY AND LIFE-HLSTORY OF YEASTS. 



to be called yeast, sufficient indefiniteness attached even to 

 the limitation of this term to the ferments belonging to the 

 Eumycetes. For some years after Schwann's discovery, the sole 

 botanical definition of yeast was : a unicellular organism, repro- 

 ducing by means of a peculiar method (termed budding), and 

 exhibiting the power of forming alcohol and carbon dioxide from 

 sugar. In 1857, Th. Bail (I.) discovered the occurrence of 

 budding mycelia (§ 219) in the family Mucoracece, and ten years 

 later assumed the descent of beer yeast from Mucov racemosus. 

 Doubt on this point seemed to him to be the more inadmissible, 

 as he had noticed a weak alcoholic fermentation on submerging 

 these budding Mucov mycelia in nutrient solutions containing 

 sugar. Under the prevailing limitation of the term yeast, the 

 name Mucor yeast was justifiable, though the same cannot be 

 claimed for the generalised assumption, deduced from this ob- 

 servation, that a connection exists between the life history of 

 yeasts and that of the higher fungi. 



Soon afterwards a successful endeavour was made by M. 

 Reess (I.) to become better acquainted with the yeasts, before 

 disputing over their relationship to other fungi. Following up 

 the previous discovery of the formation of ascospores (§ 247) in 

 the cells of wine yeast and beer yeast, he recognised the import- 

 ance of this phenomenon for the systematology of the yeasts, and 

 did it justice by announcing this peculiarity as a principal char- 

 acteristic of the now remodelled genus Saccliaromyres, which he 

 relegated to the Eumycetes group. Subsequently, the establish- 

 ment of this characteristic led to a separation, which was ob- 

 jectionable from the standpoint of fermentation physiology : of 

 the group of alcohol-producing budding fungi hitherto united 

 under the common denomination " yeast," all those recognised 

 as incapable of developing ascospores were rejected, and mostly, 

 under the title " noii-Saccharoinyces of unknown systematic posi- 

 tion," relegated to the group of Fungi imperfect i. The terms 

 yeast and SaccJiaromyces ceased to be coincident. Many budding 

 fungi capable of exciting alcoholic fermentation, e.g. several of 

 the genus Torulci, which still have some claim to be considered 

 as yeasts, are therefore excluded fi'om the Sarcharomyces family 

 because of their inability to put forth ascospores. On the other 

 hand there are certain true iiaccliaromycetes, which are unable to 

 excite alcoholic fermentation and therefore have no title to the 

 name yeast (in the above sense of the term), Saccharoniyres 

 membrancefaciens being an example. 



After the publication of Schwann's discovery, that of Reess 

 was the first advance in the systematology of the yeast fungi ; 

 and it was left to E. Chr. Hansen to make the next move, viz. 

 to separate the units (species, races, varieties) of the genus 

 t'Sacchawinyces, introduce experimental investigation into syste- 

 matic description, and, for the fii-st time, base this research on 



