Induced Mutational Changes in Yeast 115 



in a 10-12 mm. -thick layer. A 48-hour culture of S. globosus 

 was seeded onto the surface of the agar ; and in 3-4 days this 

 surface was covered with a thin layer of yeast cells multi- 

 plying in the presence of the wort-monosaccharides. It was 

 expected that if cells became adapted to fermentation of 

 maltose, they would propagate and form secondary colonies; 

 such secondary colonies did develop after 200-300 days of 

 cultivation at 25° C. Cells from these colonies were seeded 

 into a medium containing maltose, in test-tubes with gas- 

 traps. In 3 of the 14 secondary colonies tested, cells were 

 detected which were adapted to fermentation of maltose. 

 Numerous reseedings of these cells into liquid wort and wort- 

 agar showed that the maltose-fermenting ability is retained in 

 all 3 cases, and is inherited by the progeny. 



Experiment 3. In this experiment on adaptation to fermenta- 

 tion of maltose, we used cultures of S. globosus which had pre- 

 viously become adapted to fermentation of sucrose. We used 

 20 such cultures, each of which was obtained from a single 

 spore. These cultures did not differ in fermenting ability from 

 cultures of S. paradoxus; both these species fermenting 

 monosaccharides and sucrose to the same degree. 



The experiment was carried out in Maysle flasks, with 

 gas-seals, each flask containing 100 ml. beer-wort (sacchari- 

 meter: 14°) at 25-26° C. As in Expt. 1, adaptation to fer- 

 mentation of maltose was determined by secondary fermenta- 

 tion. The flasks were weighed daily for the first ten days and 

 then every tenth day. During the first 3-4 days there was a 

 slight decrease in the weight of all the flasks, due to fermenta- 

 tion of the wort-monosaccharides. At the end of this period 

 fermentation ceased, and only 200 days later did secondary 

 fermentation begin in one of the flasks. Reseeding of cells 

 from these flasks into fresh medium, containing maltose, 

 showed that in this case cells had become adapted to fermenta- 

 tion of maltose. Numerous reseedings of these cells into 

 liquid wort and wort-agar showed that this fermenting 

 ability is strongly retained and is inherited by the progeny. 

 The remaining 19 flasks were weighed over a period of a further 



