WATER RELATIONS AFFECTING GERMINATION 219 



Hemmi and Abe (1933) controlled humidity by exposure over 

 varying concentrations of sulphuric acid with the results shown 

 in Table 1 8 for urediniospores of P. glwnarum. 



TABLE 18 



Germination of Puccinia glumarum as Modified by Various Relative 



Humidities 



Although fungi generally respond to humidity in a manner 

 similar to that shown by P. glumarum in Table 18, certain of them 

 germinate independently of the moisture content of the surround- 

 ing air. The conidia of Erysiphe polygojii, for instance, were 

 found by Brodie and Neufeld (1942) to germinate through a 

 range of relative humidity from approximately zero to 100%. 

 These observations find support in the fact that powdery mildews 

 are known to grow luxuriantly in areas where low relative hu- 

 midities prevail. 



By means of apparatus in which he was able to control relative 

 humidities accurately, Clayton (1942) found that the mean per- 

 centage germination of urediniospores of Puccinia coronata, P. 

 graminis tritici, and P. graminis avenae was lower at a relative 

 humidity of 100% than in water, was considerably less at 99% 

 relative humidity, and was practically nonexistent at 98%. The 

 conidia and ascospores of Venturia inaequalis germinated on dry 

 glass if the relative humidity was 99 to 100%. When chlamydo- 

 spores of Ustilago hordei and 17. nuda were similarly placed on 

 dry glass, they germinated at relative humidities of 95 to 100% 

 but not at 93% or below. Furthermore he was able to germinate 

 the conidia of Erysiphe polygoni on dry glass at relative humidi- 

 ties of zero to 100%, thus verifying the results of Brodie and 

 Neufeld (1942). 



Rippel (1933) presented evidence in connection with his studies 

 on the germination of conidia of Cladosporium fulvum that the 



