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M. Westergaard 



Table I 



Nuclear mutations 

 Back mutations 



Cytoplasmic 



Phenocopies 



breakage 



(1) Giles (1951), Westergaard (1957) 



(2) Levan(1951) 



(3) Wilson (1950) 



(4) Ephrussi (1953) 



(5) Provasoli, Hutner and Pintner (1951) 



(6) Goldschmidt (1935), Uapoport (1947), 



Bertschmann (1955) 



(7) Landauer (1954) 



(8) Nachtsheim (1956) 



higher organisms can be induced by many enzyme poisons, 

 for instance salts of heavy metals, which may not induce 

 mutations in the cytoplasm or in the nucleus. It is also 

 characteristic of the induction of phenocopies that it is re- 

 markably specific, since almost 100 per cent of a treated 

 population may show the same phenocopy if the treatment 

 is properly applied. 



The evidence for the induction of cytoplasmic mutations 

 rests mainly on the work of Ephrussi and his colleagues on the 

 induction of "petite" in yeast by treatment with acridines 

 and related compounds (I am aware of the fact that due to 

 the partial sterility of the vegetative "petite" type, the proof 

 for true cytoplasmic inheritance is still inconclusive). Again it 

 is characteristic that the induction of "petite" is surprisingly 

 specific, and we should keep in mind that the effect of the 

 chemical is probably a destruction or inactivation of the 



