Careful experiments show that birds act as carriers of spores of the
blight fungus. Thirty-six birds belonging to nine different species
have been tested. Nineteen were found to carry pycnospores, the maximum
number obtained from a single bird, (Downy woodpecker), being 757,074.
The highest number was always obtained from birds shot a few days after
a rain period.
“SHOOTING” OF ASCOSPORES.
The ascospores are expelled forcibly, but this expulsion depends upon
temperature as well as moisture. No expulsion took place in the field
from November 26th, 1912, to March 21st, 1913, the temperature during
the winter rains being too low. Bark containing ascospore pustules has
continued to expel ascospores for over six months, (in the laboratory).