EFFECTS OF RADIATION ON FUNGI 903 



light emitted is usually of shorter wave-length and consequently has 

 greater lethal properties. This might possibly be an explanation of the 

 different results obtained by Houghton and Davis, and Fairhall and 

 Bates. Pichler and Wober (146) working with Tilletia as well as Petri 

 (144) working with Microsphaera reported that a slightly acid medium 

 augments lethal action while a slightly alkaline medium diminishes it. 



Few workers have taken into account the possible effects of tempera- 

 ture changes during irradiation of spores. Becquerel (4) showed what 

 large effects extremes of temperature may have when he exposed Aspergil- 

 lus, Sterigtnatocystis, and various Mucor spores to ultra-violet radiation 

 both at room temperature and at the temperature of liquid air. It 

 took 15 times as long to kill at the temperature of liquid air. Smith (168) 

 irradiated Fusarium spores with ultra-violet at temperatures ranging from 

 0° to 50°C. At zero degrees the survival curves are sigmoid, but they 

 rapidly approach the logarithmic type as the temperature is increased. 

 The spores are somewhat more sensitive at the higher temperatures. 

 The average temperature coefficient between 0° and 40°C. is 1.13, and 

 between 40° and 50°C. it is 1.37. These coefficients are characteristic of 

 a physical or photochemical reaction. The higher temperature coef- 

 ficient between 40° and 50°C. may indicate that temperature has not 

 merely a sensitizing effect but also a lethal effect in conjunction with 

 ultra-violet radiation. These experiments show that while temperature 

 has little effect within rather narrow limits on the inhibitive effects of 

 radiation, extremes of temperature do play an important role. They 

 also show that temperature and radiation cannot be considered as 

 separate factors. 



It has already been mentioned that radiation may affect the time 

 required for germination and also the ultimate growth of the culture. 

 Buller (19) and Hutchinson and Ashton (79) showed that radiation may 

 markedly retard germination, the amount increasing with the exposure. 

 Hutchinson and Ashton (79) also showed that the cultures from ger- 

 minated spores may have a subnormal growth rate which gradually 

 approaches the normal. Luyet (111) reported that when the lengths of 

 mycelium developed by spores of Rhizopus nigricans irradiated with 

 monochromatic light are plotted against the exposure, the curve is 

 approximately logarithmic. 



MUTATIONS AND SALTATIONS 



The changes in fungi which have been described thus far as due to 

 the influence of light have not been heritable. They have been in no 

 sense mutations. Stevens (177), however, reported that under the 

 influence of ultra-violet radiation from a quartz mercury arc Glomerella 

 cingulata produces mutations by sectoring. Dickson (29) exposed cul- 

 tures of Chaetomium cochliodes on malt agar at a distance of 26 cm. 



