PHYLOGENY OF 'THE YEASTS 139 



Phylogeny of the Yeasts. Their Affinities in the 

 Group of Ascomycetes 



What place, in the classification of the Ascomycetes, shall the 

 yeasts occupy, what are their relationships to the other Ascomycetes? 

 We shall now take up that question. 1 Up to recent times, it seemed 

 incapable of being answered. 



The species of Exoascus are filamentous fungi, in which certain 

 terminal cells form octosporous ascs after a fashion comparable to 

 those formed by the yeasts. The ascospores germinate, producing 

 generations of yeasts. It is evident that, by the characters of their 

 ascs and the shape of the yeast-like structures to which they give 

 birth, they are like the Saccharomyces. They differ in the presence 

 of a typical mycelium. But we have seen that the yeasts themselves, 

 under certain conditions are able to manifest a tendency, more or 

 less marked, to vegetate with a mycelium. The investigations of 

 Dangeard and Ikeno have shown that the asc in Exoascus possesses 

 two nuclei at the time of its formation, and these fuse into one hav- 

 ing the nuclear divisions necessitated by 8 ascospores. Dangeard 

 regards this fusion as karyogamy and the equivalent of fecundation 

 but the interpretation of this process remains very much discussed. 

 The yeasts are closely distinguished from Exoascus in that they show 

 no nuclear fusion in the asc. It is true that in a few varieties, the 

 asc results from a true copulation but in all of the varieties in which 

 this phenomenon is lacking one is unable to detect nuclear fusion. 

 Then, from this point of view, the yeasts resemble Exoascus. 



On the other hand it has been noticed for a long time that the 

 family of Endomyces includes varieties related to the yeasts. But 

 our information with regard to this group has remained very vague. 



Recent investigations by Guilliermond l have allowed us to fill 

 this gap in our knowledge and -at the same time determine the sys- 

 tematic relationships of the yeasts. The results of these investiga- 

 tions are sufficiently important to receive more extended treatment 

 at this time. The family of Endomycetes presents only a small num- 

 ber of representatives in which the genera Eremascus and Endomyces 

 are best known. We shall take up some of the shapes of these genera. 



Only two genera of Eremascus, the E. albus and E. fertilis, re- 

 cently discovered by Stoppel, have been known up until recently. 

 The former is not well known; the latter has been subjected to a 

 conscientious investigation by Stoppel whose results were confirmed 

 by Guilliermond. The mycelium of E. fertilis presents cells which 



1 Guilliermond, A. Recherches cytologiques et taxonomiques sur les En- 

 domycet<es. Rev. g. de Botan. 26, 1909. 



