134 K. V. KossiKOV 



cells arise which are capable of fermenting an adequate 

 sugar. In control experiments we found no changes of a kind 

 which could be explained as the appearance of spontaneous 

 mutations. 



(2) The study of inheritance by yeast cells of the properties 

 which arose as a result of adaptation to fermentation of sucrose 

 and maltose has shown that these properties are transmitted 

 to offspring not only in vegetative but also in sexual repro- 

 duction (spore formation). In the latter case segregation was 

 observed. One-half of the spores formed by altered cells 

 usually give cultures which ferment sugar, the remainder form 

 cultures which do not ferment an adequate sugar. In S. 

 jyaradoxus forms were also obtained, adapted to fermentation 

 of maltose, which on sexual reproduction did not show 

 segregation. 



(3) The control of the stability of fermentative properties 

 acquired by yeast when resown in agar media containing other 

 sugars has shown that the capacity to ferment both sucrose 

 and maltose remains stable. 



(4) Stability of fermentative properties which arose in the 

 cells is clearly evident, also, in crossing altered strains with 

 original (unaltered) strains. We obtained a dominant capacity 

 to ferment an adequate sugar in the first generation and a 

 segregation by the same characteristics in the second sexual 

 generation. 



All these experimental data testify to the fact that directed 

 hereditary changes were obtained under the influence of the 

 substrate. 



(5) As a result of our experiments we obtained new forms. 

 From S. globosus we obtained: (i) forms additionally ferment- 

 ing sucrose and one-third of rafiinose; (ii) forms additionally 

 fermenting maltose, and (iii) forms additionally fermenting 

 sucrose, maltose and one-third of raffinose. These forms may be 

 classified, according to their fermentative capacities, as species 

 of S. paradoxus, S. chodati and S, ellipsoideus respectively. 



From S. paradoxus we obtained: (i) forms additionally 

 fermenting maltose and (ii) forms additionally fermenting 



