Notes on the comparative Resistance to high Temperatures of the 
Spores and Mycelium of certain Fungi 
By ABIGAIL A. O’ BRIEN 
It is a well-known fact that the spores of bacteria are more 
resistant to heat than are the vegetative cells. It has been gener- 
ally believed that the same is true of fungi, that is, that the spore 
is better able to resist a high temperature than is the mycelium. 
The method of fractional sterilization has in fact been based upon 
that belief. Professor B. M. Duggar suggested to me that in the 
case of some fungi, especially those with thin-walled spores, the 
mycelium might be at least as resistant to moist heat as are the 
spores. His work on Sporotrichum globuliferum * indicated that 
with this fungus such is the case. The following series of experi- 
ments on five representative fungi, carried on under his directions, 
confirms his results in general. 
Methods—The fungi experimented upon were Aspergillus 
flavus, Botrytis vulgaris, Rhizopus nigricans, Sterigmatocystis nigra 
and Penicillium glaucum. They were grown upon beet cylinders 
in test-tubes. The mycelium used in these experiments was taken 
from the culture tubes within two and one half days after the 
fungus had begun to grow and before any spores had formed. 
The spores used in the experiments were from one to two weeks 
old. The spores were placed in sterilized test-tubes filled to the 
height of about one inch with beet decoction. The tubes were 
then put in a boiler heated to the desired temperature and left for 
five, ten, fifteen, thirty or sixty minutes. After the exposures, 
drop cultures of the decoction in the tubes were made in Van 
Tieghem cells. The spores of Aspergillus and Sterigmatocysts 
showed a tendency to float on the surface of the liquid and to col- 
lect in small masses. It was therefore found necessary to immerse 
them in distilled water before putting them in the decoction. In 
the experiments with the mycelium, a bit of the hyphal mass was 
removed from the plug with a sterilized needle, and was then 
treated exactly as the spores were. The cultures were in ao 
* Bot. Gazette, 31: 38-66. Ja. 1901. 
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