Mar. 15, 1925 
Spore Dissemination of Venturia Inaequalis 
535 
a. m., and the first discharge of the 
season was recorded by the apparatus. 
Ascospores were caught at the average 
rate of 1 ascospore to 30 liters for the 
3-hour period covered. From 8.30 to 
10.30 a. m., while the leaves were still 
wet, the average rate of catch was 
1 ascospore to 89 liters. From 10.30 
a. m. to 6 p. m. it was 1 to 204 liters; 
and from 6 p. m., May 19, to 8 a. m., 
May 20, 1 to 840 liters. No spores 
were caught from 8 a. m. to 6 p. m., 
May 20, by which time the leaves had 
thoroughly dried. 
During the night of May 20-21 rain 
or sleet fell almost continuously and 
rather high winds prevailed. Unfor¬ 
tunately, in spite of the shelter which 
had been erected to protect the mem¬ 
brane from weather, it was so washed 
by rain and sleet that no trustworthy 
record could be taken. In the morn¬ 
ing, however, the winds became less 
violent. The rain continued from 9 
a. m., when a new membrane was put 
on, until about 4 p. m. From 9 a. m. 
to 5.30 p. m. ascospores were caught at 
the average rate of 1 ascospore to 0.4 
liters. This proved to be the heaviest 
discharge recorded during the experi¬ 
ments. The wind velocity for the 
period of this run varied from 14 to 23 
miles an hour. 
Rain began to fall about 11 p. m. 
May 21 and continued until about 1 
p. m. May 22. From 7 p. m., May 21, 
to 7 a. m., May 22, ascospores were 
caught at the average rate of 1 asco¬ 
spore to 23 liters. The wind velocity 
for the period during which this rain 
fell varied from 21 to 34 miles an hour 
(NE. to NW.). No record is available 
for the daylight hours of May 22. The 
machine ran from 6 p. m., May 22, to 8 
a. m., May 23, and recorded an average 
catch of 1 ascospore to 109 liters. 
Apparently the leaves were sufficiently 
moist from the morning’s rain to con¬ 
tinue this light discharge. Following 
thorough drying the next morning, 
discharge ceased and no spores were 
caught until the next rain. 
Light showers fell between 1 and 7 
a. m., May 26, but no record for this 
period is available. From 10 to 11 
a. m., however, during traces of rain¬ 
fall, the machine was run, and asco¬ 
spores were caught at the rate of 1 
ascospore to 40 liters. From 11 a. m. 
to 5.30 p. m., with no additional rain¬ 
fall, the catch was only 1 to 7,800 liters. 
Showers fell during the night of May 
26-27, and spores were caught at the 
rate of 1 ascospore to 24 liters. The 
wind velocity during this rain period 
varied from 10 to 22 miles. 
No more ascospores were registered 
by the machine until the night of May 
29-30, when, following traces of rain, 
they were caught at the rate of 1 asco¬ 
spore to 2,133 liters. On May 30, 
however, an excellent opportunity for a 
fractional study of a discharge period 
presented itself. From 9 to 10 a. m. a 
trace of rain fell, followed by a fairly 
heavy rain from 10 to 12, a trace from 
12 to 1, and almost continuous rain 
throughout the remainder of the after¬ 
noon. The wind velocity from 10 
а. m. to 6 p. m. varied from 13 to 23 
miles an hour. From 10 to 11 a. m. 
ascopores were caught at the average 
rate of 1 ascospore to 0.5 liters; from 
11 to 12, 1 to 1.14; from 12 to 3, lto 
б. 3; from 3 to 4, 1 to 12.1; from 4 to 6, 
1 to 13. From midnight until 8 a. m., 
May 31, it rained almost continuously. 
However, from 6 p. m., May 30, to 8 
a. m., May 31, the average rate of catch 
was only 1 ascospore to 188 liters. The 
old leaves on the ground remained wet 
in the tall grass of the orchard until 
about 3:30 p. m., May 31. By this 
time the wind, which had freshened 
about 3 p. m., had begun to dry them 
perceptibly. This is very well reflected 
in the ascospore content of the air. 
From 9 to 10 a. m., May 31, spores 
were caught at the rate of 1 ascospore to 
5 liters of air; from 10 to 11.30, 1 to 
8.9; from 11.30 to 2.30, 1 to 8.1; from 
2.30 to 3.40, 1 to 9; from 3.40 to 6, 1 to 
109. It appears that, at the beginning 
of this rain period, there was an 
abundance of mature ascospores ready 
for discharge. During the first 2 hours 
(10 to 12 a. m., May 30) the rate of 
discharge was very high. Subse¬ 
quently, however, it dwindled rapidly, 
and relatively few mature spores appear 
to have been available for discharge 
during the rain of the following night. 
The rate of discharge increased very 
markedly on the morning of May 31, 
probably due to the maturing of asci 
during the current moist period. 
No further discharge was recorded 
until the rain of the night of June 1-2, 
when ascospores were caught at the 
rate of 1 ascospore to 5.1 liters (8 p. m. 
to 8 a. m.). From 9.30 a. m. to 2.30 
p. m., June 2, it rained continuously, 
and ascospores were caught at the 
rate of 1 ascospore to 2.4 liters. From 
2.30 to 6 p. m., although showers con¬ 
tinued, the rate of catch fell to 1 to 
32 liters. During the following night, 
no spores were caught. In this in¬ 
stance, the period of rapid discharge 
was considerably more prolonged than 
was the case in the preceding rain. 
No further discharge was recorded 
until the rain of the night, June 5-6, 
when the average rate of catch from 
8 p. m. to 8 a. m. was 1 ascospore to 
2.4 liters. The rain continued through- 
