SPORE GERMINATION 



359 



formation of the germ tube was calculated to add approximately 2 or 3 

 per cent to the volume of the ungerminated conidium. It is believed 

 possible that this slight increase in volume might be accounted for by 

 one or both of the above factors. Yarwood (1936) offers no explanation 

 of the process of germination at such a low humidity but reports a decrease 



o 



3 

 •*- 

 O 



a. 

 £ 



70 



95 



100 



75 80 85 90 



Relative humidity in percent 



Fig. 74. Germination curves for Aspergillus niger under variable temperature and 

 humidity. Note that the optimum temperature for germination varied with the 

 relative humidity, being near 30°C. at relative humidity of 100 per cent and near 40°C. 

 at 93 per cent. As the temperature or humidity digressed from the optimum, ^the 

 time required for germination increased. (Courtesy of Bonner, Mycologia 40 : 733, 

 1948.) 



of about 24 per cent in volume of the Erijsiphe conidia during germina- 

 tion. Spores of all other fungi (except other powdery mildews) which he 

 tested showed increases in volume during germination. 



Dormancy of some spores may be broken by alternate wetting and 

 drying. This treatment apparently makes the thick resistant wall more 

 permeable to water. 



Oxygen supply. Since respiration is greatly accelerated during spore 

 germination, it follows thg^t an adequate supply of oxygen is a prerequisite 



