Induced Mutational Changes in Yeast 103 



theoretical assumptions, is becoming more and more urgent. 

 It is reasonable to base these assumptions on the direct 

 influence of environmental factors on the variability of micro- 

 organisms; and by so doing we can easily explain the above- 

 mentioned regularities in adaptive changes, and the reversion 

 in certain cases of the adapted forms to the original type, 

 when the adapting factors cease to exert an influence. 



However, the question arises as to whether the adaptive 

 changes can, in nature and stability, equal mutational changes, 

 which are usually considered to be spontaneous. In other 

 words, the question (which applies both to vegetative and 

 sexual reproduction) is whether there appear in the process 

 of adaptation changes, other than these already mentioned, 

 which will be inherited even if the adapting substrate is 

 removed from the medium. 



This paper is concerned with the elucidation of these 

 questions, and in particular with the directed changes of the 

 fermentative properties of yeasts of some species of the genus 

 Saccharomyces, and with the inheritance of new properties 

 developed in them. 



Adaptation of Saccharomyces globosus to 

 Fermentation of Sucrose 



The present author first observed adaptation of S. globosus 

 to fermentation of sucrose in 1948, when the phenomenon 

 occurred in a control test-tube on the sixty-seventh day after 

 seeding. At the time, this aroused the interest of the present 

 author because it could not be readily accounted for by the 

 appearance of the adaptive enzyme (cf. fermentation of 

 galactose by certain yeasts), and it led to the systematic 

 investigation of the variability of fermentative properties of 

 S. globosus and other yeasts (Kossikov, 1948, 1951, 1952, 

 1954). 



We investigated cultures obtained from single spores of S. 

 globosus 349. During the germination of spores, diploidization 

 occurred resulting in the development of homozygous diploid 



