RADIATION STUDIES ON FUNGI 



435 



wave lengths around 2800 A but not at longer wave lengths (around 8300 

 A), while "saltations involving modifications of growth rate and form, 

 mycelium and perithecia are produced" in constant proportion to lethal 

 effect at all wave lengths tested (2300-4047 A) (McAulay et al., 1945; 

 Ford, 1947). However, experiments of 7-10 days duration (as were the 

 irradiation exposures at wave length 4047 A) are open to question on the 

 grounds of contamination by shorter wave lengths, as well as of changes 

 in the organism. The percentage of colonies showing the K-type sector 

 has reached as high in some experiments as 30-50 per cent (Ford, 1946), 

 with the peak activity at 2804 A (McAulay and Ford, 1947). 



Table 11-3. Organisms Showing Wave-length Dependence for Killing 

 AND Mutation with Ultraviolet Radiation 



The wave-length dependence of the production of K type and other 

 saltants led to two conclusions: (1) a protein excitation near 2800 A gives 

 rise to K type, and is responsible for most efficient production of other 

 mutants, and (2) a second, less efficient process, can occur at all wave 

 lengths tested to produce mutants other than K type (McAulay and Ford, 

 1947). Figures ll-2a,6 graphically summarize these points. The major 

 emphasis was that protein absorption, not nucleic acid absorption, gave 



