Pycnospores are easily killed under certain conditions, but can survive
in considerable numbers under certain other circumstances. Their
length of life in water depends to some extent upon the temperature.
Thirty-three per cent. survived in water at 55°C, after 42 days. A
large percentage can survive freezing for a considerable period. They
are washed down to the ground from blight cankers, during every rain,
and have never been found to disappear entirely from the soil during
the longest periods between rains. As many as 12 per cent. of those
originally present in a soil sample have survived drying for 63 days.
The longevity of the pycnospores is greater in the “spore horn” stage
than when they are separated by rains and then dried. They have been
killed in twenty-four hours by drying in certain tests, while the act
of drying alone is generally responsible for the death of 50-60 per
cent.