Induced Mutational Changes in Yeast 113 



by us, when cultivated on a sucrose medium, the frequency of 

 formation of the enzyme p-D-fructosidase was eighteen times 

 that of the formation of the enzyme a-glucosidase. 



Experiment 3. In this experiment, unhke the previous ones, 

 adaptation to fermentation of sucrose was carried out on a 

 soKd medium with agar. The medium consisted of 4 per cent 

 sucrose, 3 per cent glucose and 0*3 per cent autolysed yeast 

 extract. It was poured into shallow glass plates of a capacity 

 of 1000 ml., as much as 200 ml. being poured into one plate. 

 The inoculum used was the 48-hour culture of S. globosus 349. 

 After 3-4 days the surface of the agar was entirely covered 

 with a layer of yeast cells multiplying in the presence of 

 glucose. It was assumed that secondary colonies would be 

 formed during the development of cells adapted to fermenta- 

 tion of sucrose. Such secondary colonies did start to appear 

 after approximately 30-40 days of cultivation in a thermostat 

 at 25-26° C. After 58 days, cells from 4 secondary colonies 

 were tested for ability to ferment sucrose, and in 3 of those 

 colonies adaptation of cells was found to have occurred. 

 Numerous reseedings of these cells, on fresh medium contain- 

 ing sucrose, showed that their adaptation to fermentation of 

 sucrose was strongly retained in all 3 cases, and is inherited by 

 the progeny. 



Adaptation of Saccharomyces globosus to 

 Fermentation of Maltose 



Fewer experiments were carried out to elucidate the 

 adaptation ofS. globosus to fermentation of maltose than were 

 carried out in the case of adaptation to fermentation of 

 sucrose; our data show that it is much more difficult to 

 develop the former type of adaptation than the latter. 



Experiment 1. In this experiment we used 12 cultures ob- 

 tained from single spores of S. globosus 349, and 20 cultures 

 obtained from single spores of second-generation hybrids 

 (S. globosus X S. ellipsoideus). Preliminary tests showed that 

 neither the hybrid cultures nor the S. globosus cultures 



