Induced Mutational Changes in Yeast 117 



fermentation of maltose. The adapted culture was designated 

 as 37,6 m-1. At the end of 490 days, secondary fermentation 

 was observed in a second flask. Seeding of cells from this 

 flask into fresh medium, containing maltose, showed that cells 

 had become adapted to fermentation of maltose. The adapted 

 culture was designated as 37,7 m-1. The remaining 6 flasks 

 were weighed over a period of a further 270 days, and not one 

 of the 6 showed secondary fermentation. 



Experiment 2. This experiment, in parallel with the previous 

 one, was carried out on adaptation of S. paradoxus 37 to 

 fermentation of maltose, on solid medium (wort-agar). The 

 methods used and the experimental conditions were much the 

 same as those used in adaptation of S. globosus to maltose- 

 fermentation on wort-agar. 



After approximately 350 days of cultivation, secondary 

 colonies began to appear. Five secondary colonies were 

 observed, 3 of which were found to be adapted to fermentation 

 of maltose. Out of the maltose-fermenting and asci-forming 

 colonies, we selected (by means of a micromanipulator) 29 

 cultures obtained from single spores, and these were tested 

 for ability to ferment maltose. These cultures, which were 

 designated as A37-9/2m-l-N, all fermented maltose ; however, 

 in 7 of them growth ceased and the cultures died on reseed- 

 ing into wort-agar. This cell-death of adapted S. paradoxus 

 on wort-agar was quite unexpected, because all cultures of 

 S. globosus, which had become adapted to fermentation of 

 maltose and sucrose, and which had also been obtained from 

 single spores, propagated very well when reseeded into wort- 

 agar, and retained their fermenting ability quite strongly. 

 Besides the 7 cultures of S. paradoxus which died, in 3 other 

 test-tubes almost all cells died, and in only one place — i.e. on 

 slanting agar — did there develop one colony the cells of which 

 propagated normally. This phenomenon observed during 

 reseeding of maltose-fermenting cultures of S. paradoxus was 

 most interesting. Cell-death did not occur immediately on 

 seeding; the seeded cells multiplied slightly, then ceased to 

 grow and acquired first a light brown and then a dark brown 



