326 DorAN: ON THE GERMINATION OF FUNGOUS SPORES 
Rhizopus nigricans. Cardinal temperatures for the germination 
of the other spores used had been previously determined (Doran, 
The results obtained with the conidia of Venturia inaequalis are 
shown in TABLE II and by the curve in Fic. 2. For the germina- 
tion of the conidia of Venturia inaequalis, the minimum tem- 
. perature is 3° C., the optimum temperature is 14°-15° C., and 
the maximum temperature is 31° C. The conidia can germinate 
through a range of twenty-eight degrees. 
This is an unusually long range. Since the causal fungus of 
apple scab is not especially exacting as regards temperature for 
the germination of the conidia the indications are that the 
distribution or severity of this disease, following the primary 
infection by the ascospores is dependent more upon rainfall 
than upon temperature. The conidia of Venturia inaequalis are 
disseminated most freely during June, July and August. As 
shown in Fic. 2, warm nights do not prevent their germination. 
A study of the temperature-germination curve in F1G. 2 shows 
that the falling off in germination of the conidia is more rapid 
from the optimum to the minimum temperature than from the 
optimum to the maximum temperature. Over 40 per cent of the 
number of spores germinating at the optimum (14°-15° C.) 
germinate at 9° C. and 24° C., respectively. 
TABLE II 
Effect of temperature on the germination of the conidia of 
Ventur ria inaequalis 
Relative germination at different temperatures measured in degrees Centi- 
grade 
2°1.3°.16 |S. {to°. (12°, [4°jz5°1z8° [20° [24° [28° 130° -i31° 132° 
2 42 
© | 4 | 18 | 60 | 80 |r100}100/ 68 | 58 | 46 | 24 | 10 
ae 
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8 
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on 
on 
w 
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So oN & 
oo °o 9 
Mean} o 0.75} 3 |21.5)/56 2|76.5/100'100|77 2 
56.5/41.5|22.2| 11 21.0 
2 
In these studies of the relation of spore germination to tem- 
perature, as to all other external conditions, the relative number 
of spores germinating was taken as an indicator of the reaction 
