MANNER OF PRODUCTION OF MUTATIONS 593 



Work on fungi also has yielded evidence of differences in mutational 

 spectra. The first apparent case was that described in a series of papers 

 by McAulay and Ford and co-workers (McAulay, Plomley, and Ford, 

 1945; Ford, 1946; McAulay and Ford, 1947; Ford and Kirwan, 1949) 

 in experiments (see Sect. 11) on spores of the ascomycete Chaetomium 

 globosum. These investigators found that ultraviolet and visible light 

 over the range studied, 2654-4047 A, showed a markedly different dis- 

 tribution of mutagenic efficiencies among the different wave lengths for 

 "saltations" of the peculiar morphological type designated as "K" than 

 for the other morphological "saltants" as a group or for lethal effects 

 (which agreed with the latter in their production spectrum). Over the 

 range 2654-2967 A, the K saltants were some 2J^^-4 times as frequent as 

 all other morphological saltants taken together and, in fact, attained the 

 surprising frequency of over 25 per cent (a figure so high as to raise the 

 question whether they were really gene mutations). However, at 3342 A 

 the K type tapered down to one-third as frequent as all the other form 

 changes taken together, and at still longer wave lengths, K gave no 

 evidence whatever of being produced. On the other hand, the other 

 morphological saltants, as mentioned in Sect. 11, were produced to some 

 extent even by wave lengths as long as 4047 A. With X rays also it 

 was found (Ford and Kirwan, 1949) that, despite the production of 

 morphological saltants of other types, none of type K were produced. 

 With X rays, there was, in addition, a significantly higher frequency of 

 pigment mutations, in proportion to other morphological types, than 

 there was with ultraviolet treatment. 



McAulay is inclined to interpret the wave-length specificity of the 

 change to K as indicating that a mutation to K is induced when a given 

 protein, with an absorption band at 2600 3000 A, has this band excited. 

 However, the significance of these studies for problems of mutation is 

 made very doubtful by the findings of these investigators that K is often 

 unstable in the early stages of development of the clone and that it usually 

 fails to be transmitted through another cycle of spore formation. It 

 thereby becomes likely that it represents not a mutation in the chromo- 

 somal material but the appearance, due to a change in the cytoplasm, of 

 an alternate state with regard to the production of a particular substance, 

 as in the case of antigen production in Paramecium worked out by 

 Sonneborn (for review, see Sonneborn, 1951). Such a state, once estab- 

 lished, tends to continue through some process of an autocatalytic nature, 

 such as a flux equilibrium, but it can be disturbed by varied means. In 

 Paramecia, one of these means consists in the application of ultraviolet. 

 The chromosomal genes, however, determine the alternate cytoplasmic 

 states that are possible. All this emphasizes the desirability of genetic 

 analyses in such cases. 



Tatum (1950) in a review article has summarized the results of differ- 

 ent investigators on the relative freciuencies of origination of different 



