138 ORIGIN OF THE YEASTS 



The investigations of Guilliermond l have indicated that by the 

 morphological and cytological characteristics, the sporangium of the 

 yeasts presents a remarkable similarity to the ascs of the Ascomycetes. 

 The ascospores develop by the same process. 



The ascospores in certain yeasts present, on the other hand, 

 characteristic forms absolutely analogous to the ascospores of cer- 

 tain Ascomycetes. Thus it is that the ascospores of Willia anomala 

 are identical with those of Endomyces decipiens, Endomyces fibul'ger 

 and Ascoidea rubescens. Those of Willia saturnus, Schwanniomyces 

 occi'dentalis, Debaromyces globosus, Monospora cuspidata, Nematospora 

 coryli have forms which suggest very strongly those of certain ascomy- 

 cetes. Without doubt, the number of ascospores in the sporangium 

 of a yeast is variable although it is constant for an asc. How- 

 ever, one notices that the number of ascospores tends to become 

 fixed in an asc in most of the yeasts while with some, it remains 

 variable. Thus it is that in Schizosaccharomyces the number 4 or 8 

 is usually seen. In Saccharomyces Ludwigii the ascospores are con- 

 stantly present to the number of 4. Even in those cases in which 

 this varies, there is a slight tendency for it to become fixed. 



Finally, the discovery of a copulation in the origin of the asc in 

 Schizosaccharomyces, the Lygosaccharomyces and Debaromyces globo- 

 sus which absolutely resembles that of certain Ascomycetes (Bremas- 

 cus and End. Magnusii) furnishes a strong argument in favor of 

 their homologation. The existence of this copulation, together with 

 morphological and cytological characteristics of ascs of yeasts, suffices 

 to demonstrate their place with Ascomycetes. The question of the 

 origin and systematic relationship of the yeasts is definitely settled 

 today. The Saccharomycetes constitute an autonomous group of lower 

 Ascomycetes. It has been stated that among the true yeasts which 

 form ascs, there are some which do not sporulate; such are the My- 

 coderma and Torula. But, as will be pointed out further on, many 

 of the yeasts are able on account of special conditions, to definitely 

 lose their property of sporulating. It is possible that these are true 

 Saccharomycetes having become asporogenous but it is also possible 

 that they are derived forms from molds fixed in the state of yeasts. 

 The question of their origin and their position in classificatory sys- 

 tems is then not settled. Ought we to separate the family of Sac- 

 charomyces in which are the true yeasts? 



higher Ascomycetes, less is known. According to Harper, it consists of a true 

 copulation to give the perethecia; according to Dangeard, it is simply a nuclear 

 fusion. The question is still very obscure. Among the Endomyces, copulation 

 is very clear. 



1 Guilliermond, A. L'origine des levures. Annales mycologici, 5, 1907. 



