144 EFFECTS OF RADIATION ON FUNGI 



(1930), who obtained most stimulation in slow-growing cultures 

 of yeast. They also conclude that some wavelengths result in 

 stimulation, others in retardation, of growth. Since they did not 

 take into consideration differences in total energy in the different 

 wavelengths that they used, however, their conclusions cannot be 

 accepted with finality. 



EFFECT ON SPORULATION 



Among other effects of ultraviolet irradiation is modification in 

 spore production. Ramsey and Bailey (1930), using a quartz- 

 mercury-vapor arc with filters to screen out radiations below a 

 certain wavelength, and exposing for 15 to 30 minutes at a dis- 

 tance of 60 cm, found the greatest production of conidia by 

 Macrosporhmi tomato and Fusarium cepae within the range 2535 

 to 2800 A. Radiations within this range could also be used to 

 inhibit the growth of these organisms or to kill them. Their evi- 

 dence indicates that increased sporulation was not the result of 

 increased temperature nor modification of the medium, as was 

 suggested by Smith ( 1935) from her studies of F. eumart'u. When 

 the filters employed by Ramsey and Bailey permitted the trans- 

 mission only of radiations of wavelengths greater than 3120 A, 

 there was slight stimulation in spore production. Radiations of 

 wavelengths greater than 3334 A, however, were without appre- 

 ciable effect in this respect. They also noted that the minimum 

 duration of exposure for stimulation was 30 seconds and that sev- 

 eral exposures at short intervals were more effective than a single 

 exposure equal in duration to the sum of the several short ex- 

 posures. When irradiated, their cultures of F. coeruleum formed 

 conidia, whereas this strain was never observed to do so in non- 

 irradiated cultures. On the other hand, their cultures of F. argil- 

 laceum, when irradiated, failed to form conidia, producing only 

 chlamydospores. 



Stevens (1928, 1930, 1931) exposed Glomerella crngulata and a 

 species of Coniothvrium to a Cooper-Hewctt quartz-mercury- 

 vapor arc operated at 4.5 amp and 66 volts. The agar plates were 

 uncovered during exposure at a distance of 21 cm from the source 

 of light. With exposures at less than 1 min, perithecia were 

 formed in abundance by G. cingulata and pvcnidia by Coniothv- 

 rium. In both species these structures normally appeared on the 



