190 CLASSIFICATION OF THE YEASTS 



We shall eliminate from the Saccharomycetes all of the yeasts which 

 do not form ascospores. Such are the Torula, Mycoderma, and the 

 pathogenic yeasts. These yeasts do not offer any characteristic which 

 permits giving them an accurate place in classifications of fungi. 

 The one may represent forms derived from mycelial fungi and fixed 

 in the state of yeasts, the others may be true yeasts which have 

 become asporogenic. They may be placed apart in a separate group 

 from the Saccharomyces. 



In the family of Saccharomyces, we shall include all yeasts which 

 sporulate whatever their mode of division. Contrary to Hansen, 

 we shall not separate the Schizosaccharomyces. These yeasts, if they 

 are differentiate from the other yeasts by the mode of division 

 (transverse partition), belong incontestably to the Saccharomycetes 

 by the copulation which preceded the formation of the asc with the 

 greater part of them. They are related to the Saccharomycodes in 

 which the cells divide by an intermediate method between typical 

 partition and budding and which offer a form of transition between 

 the Schizosaccharomyces and other yeasts. We shall subdivide the 

 Saccharomyces into five groups. 



The first group will include the Schizosaccharomyces characterized 

 by their method of division, transverse partition. By the formation 

 of the asc which results from an isogamic copulation, this group 

 may be regarded as strictly related to the Endomycetes. 



In the second group are placed those yeasts which offer in the origin 

 of the ascs, a copulation iso- or heterogamic and which, having lost their 

 sexuality, have, however, preserved traces of it. It is a very primitive 

 group from which seem to be derived all other budding yeasts. 



In the third group, we find all yeasts in which the* formation of 

 the asc is not preceded by any sexual phenomenon and which in liquid 

 media, vegetate, at first, as a sediment and produce later a scum 

 very slowly more or less mucous. In certain species, a parthenogamy 

 between ascospores may intervene. Almost all of the species in this 

 group are able to induce fermentations. This group corresponds to 

 Hansen's first group less the yeasts of our second group. 



In the fourth group are yeasts which, without any trace of sex- 

 uality in the formation of the asc, form in liquid carbohydrate media 

 a mycodermic scum. After the air has penetrated into its interstices, 

 it takes on a dry opaque appearance. Most of these yeasts do not 

 cause fermentations but produce ethers. Some of them have parthe- 

 nogamy between the ascospores. This group corresponds to Hansen's 

 second group. 1 



1 The classification of Hansen differs from ours only in the following points: 

 First, the Schizosaccharomyces are excluded and considered as a special group of 



