Studies on the Downy Mildew op Onions 



31 



Figure 11. various types of germination of the conidia of peronospora destructor 



germ tubes were found to grow very rapidly and the growth rate 

 increased with the increase in temperature up to about 21° C. In 

 studying the rate of germination, Katterfeld found that, where he ob- 

 tained a germination of 100 per cent, from 64 to 100 per cent of the 

 .spores germinated between two and two and one-half hours after being 

 sown, and that the rate was lower when the total germination was lower. 

 He found that all viable conidia germinated in five hours. These 

 results differ from those presented in figure 7, in that at the optimum 

 temperature only 50 to 60 per cent of the conidia had germinated by 

 the end of the first two and one-half hours and complete germi- 

 nation was not accomplished for about twenty-four hours. 



Katterfeld found that conidia capable of germination could be readily 

 recognized by their appearance. The viable conidia refracted light, had 

 tense walls, and were completely filled with protoplasm. Loss of vital- 



