134 MORPHOLOGY AND LIFE-HISTORY OF YEASTS. 



but also in those present in one and the same asciis. The 

 number {2 to 9) of the spores in the different asci will also be 

 found to vary. What has already been said of the cells of 

 sedimental yeast, also applies to the ascospores : neither form 

 nor dimensions is a reliable indication of species, and therefore 

 these characteristics cannot serve unaided for their specific 

 differentiation. It is only in special instances that this is 



possible, namely whena species 

 of the group Sacrli. anomalus 

 is present. The first represen- 

 tative of this group was dis- 

 covered by Hansen (XYII.) in 

 a Bavarian stock yeast, and 





C if_ 



i^^cMhO. 



Fig. 142. — Sacch. cerevisise I. Hansen. 



Ascosporulation. Magn. 1000. 

 {After Haiuen.) 



it was he who gave it the fore- 

 going specific appellation. This 

 new species differs from those 

 we have known hitherto, inas- 

 much as the ascospores, instead 

 of being perfectly globular, are minus a more or less consider- 

 able portion of the sphere ; and as the margin of this flat or 

 slightly arched terminal surface is surrounded by a projecting 

 bordei', the whole ascospore has the form of a hat (see Fig. 143). 

 In the course of time other species producing similar ascospores, 

 but differing in other respects, have been discovered, so that 

 at present we have to deal with a whole group of such Saccharo- 



mycetes, which will be I'eported on 

 more fully in a later section. More 

 will also be said later on aljout the 

 special method of spoiulation ob- 

 served by H. ScHicEXXixG (I.) in 

 ScJi izosacf'haromi/ees ocfOf^poru.< and 

 possibly to be regarded as a sexual 

 act. 



When it becomes necessary to 

 express in figures the time limit 

 for sporulation, the moment selected 

 is that at which the first appear- 

 ance of spores becomes visible. To wait until the period of 

 ripening, is, on the other hand, impracticable, there being no 

 reliable means of determining when that state is attained. 

 Taking the first-named as the critical moment, Hansen (XII.) 

 was the first to determine the relation between temperature and 

 the time limit of sporulation of six species of Sarcharomycetef. 

 Afterwards a series of Avorkers made similar determinations with 

 a large number of species: H. Will (VIIL, IX., XVII.), 

 J. Chr. Holm and S. V. Poulsen (II.), with European beer 

 yeasts; A. Lasche (IV.), with American beer yeast; L. Marx 

 (I.), Ed. Kayser (VII.), and the latter along with G. Barba (I.), 



Fig. 143.— Saccharoniyces anomalus 

 Hansen. 



Asoospores. In three instances 

 these have already been set free. In 

 one the membrane of the parent cell 

 is just breaking'; in the remainder 

 this has not yet happened, ilagn. 

 1000. (After Hansen.) 



