36 MORPHOLOGY AND DEVELOPMENT OF YEASTS 



Guilliermond 1 accidentally observed the same phenomenon in the 

 same yeast and in others (S. Ludwigii, Willia Saturnus) by a pro- 

 cedure much more simple, by making the yeast ascospore germinate 

 on slices of carrot. In this nutrient medium, the ascospores ger- 

 minate very rapidly and produce numerous generations of vegeta- 

 tive cells. But at the end of a few days, 

 the multiplication is arrested, probably by 

 an accumulation of toxic substances which 

 may play a role similar to the chalk. 

 The cells are then caused to sporulate. 

 But as the majority of ascospores ger- 

 minate immediately in this medium, 

 others, less vigorous, do not begin to ger- 

 minate until the vegetative cells produced 

 by the germination of the first begin to 

 Abnormal Germina- sporulate. Under these conditions, ger- 

 mination of these tardy ascospores is 

 without doubt restrained by the presence 

 of toxic substances, secreted by the vege- 

 tative cells. Thus they are not able to 

 bud nor be transformed into ascs. With 

 S. Ludwigii, for example, one may see fused ascospores which, with 

 an enlarged copulation canal, produce new ascospores inside. We have 

 formed, in this way, two swellings connected by an isthmus and 

 resembling very closely an asc of Zygosaccharomyces or Schizosac- 

 charomyces. (Fig. 44.) Sometimes the ascospore attempts to ger- 

 minate and produces a tube for germination which, not being able 

 to complete its development, enters the asc stage. 



Guilliermond has found the same thing in Sch. octosporus. Here, 

 the ascospores are able to fuse two by two and form an egg which 

 soon is transformed into an asc. Often, they undergo one or two 

 divisions, the daughter cells fusing to produce new ascs. (Fig. 45.) 



This direct germination of ascospores in the ascs is explained 

 easily by the fact that the ascospores have the import of a vegetative 

 cell. It may be able to sporulate when conditions are favorable 

 and may not have need to undergo a preliminary multiplication. 



1 Guilliermond, A. Observations sur la germination des spores du S. Lud- 

 wigii. Bull. Soc. de mycol. de France, 2, 1903. 



Fig. 45. 



tion of Ascospores of Schi- 

 zosaccharomyces octosporus on 

 slices of carrot. 



The ascospores fuse two by two, pro- 

 ducing ascs immediately, or soon 

 form cross walls producing cells to 

 make ascs. 



