14-14 THE YEAST CELL 



ent diploid, but is also dependent on the mutational potentialities of 

 the haploid strains studied. Despite the additional flexibility at- 

 tained through haploid variation, it is perhaps a little surprising 

 that such a wide variety of physiological types are found within a 

 given family. 



Meyerhof (1925) compared the physiology of various yeasts and 

 found that they differed markedly in their metabolic characteristics. 

 However in the case of his investigation, the comparison was not 

 between members of the same family. Highly selected brewing and 

 wine yeasts were compared with standard Torulopsideae (Cryp- 

 tococci). In the present study, the twelve original strains were 

 commercial bakers' yeasts. They were thus the result of inten- 

 sive selection toward a particular physiological property, namely, 

 aerobic CO2 production on sucrose. Despite intense selection they 

 still possess the potentiality for giving rise to strains possessing 

 almost diametrically opposed behavior with respect to the very 

 physiological character for which they were selected. 



These findings have implications for studies of the biochemis- 

 try of yeast strains. Any experimental procedure which permits 

 sporulation to occur with the consequent introduction of the hap- 

 lophase may give rise to widely divergent results on what may 

 have been considered the same strain. In this connection, it may 

 be of interest to note that abundant sporulation may occur on the 

 surface of package yeasts sold commercially. Reproducibility of 

 physiological measurements on a sporulating strain can be attained 

 only if it is transferred sufficiently frequently to avoid sporulation. 

 Although the variability observed, if not controlled, prevents an 

 adequate description of strain physiology, it can serve as a useful 

 tool for the isolation of biochemically interesting types. 



