122 K. V. KossiKOV 



haploid cell. Since the culture of S. paradoxals readily pro- 

 duced spores, and adaptation occurred on a solid medium 

 (wort-agar), the presence of a sufficient number of spores has 

 thus been provided for. However, a different explanation is 

 also possible: cells adapted to fermentation of maltose were 

 heterozygous as regards this capacity ; in the process of spore- 

 formation they formed spores which yielded not only viable 

 maltose-fermenting cultures but also maltose-fermenting 

 cultures of low viability. It was these cells that died during 

 reseeding on wort-agar. 



(b) Stability of fermentative properties developed during cultiva- 

 tion on agar medium containing other sugars : Cultures obtained 

 from single spores were inoculated into wort-agar after it had 

 been found that they fermented their corresponding sugar. 

 When yeasts adapted to fermentation of maltose were re- 

 seeded into wort-agar, the conditions of existence were 

 changed (aerobic instead of anaerobic), but the mass of the 

 nutrient substrate contained the same sugar, i.e. maltose. 

 In the case of yeasts adapted to fermentation of sucrose not 

 only were the conditions of existence changed, but also the 

 substrate, since the wort-agar contained a very slight per- 

 centage of sucrose. 



So as to exclude completely from the medium the sugar to 

 which the cells had become adapted, the experimental 

 cultures (after having been trained on wort-agar) were 

 reseeded into agar with galactose (3 per cent galactose; 0-4 

 per cent autolysed yeast extract). Here, the altered cells did 

 not need to use their newly acquired ability to form an active 

 enzyme, since galactose can be fermented by the original 

 unaltered yeast. 



Sixty-six of the cultures, adapted to fermentation of sucrose, 

 were tested. They were cultivated on wort-agar for 261-628 

 days. None of the cultures tested lost their ability to ferment 

 sucrose; in fact, this ability was retained undiminished. 

 When the same cultures were cultivated on the medium 

 containing galactose for 53-54 days, they retained their 

 ability to ferment sucrose and only in 8 of them was this 



