536 
Journal of Agricultural Research 
Vol. XXX, No. 6 
out the day of June 6, the catch from 
9 a. m. to 6 p. m. being at the rate of 
1 to 3 liters. During the following 
night, although there were slight- 
showers, the rate fell to 1 ascospore to 
145 liters. In this, as in the preceding 
instance, the period of rapid discharge 
was fairly prolonged, probably extend¬ 
ing over about 15 hours. It appears 
likely that the more extended periods 
of these later heavy discharges, as 
compared with that of May 31, are to 
be attributed to a more generally 
advanced stage of maturity of asci and 
possibly to more rapid ripening. 
Minor discharges occurred during 
1>he showers of June 7, 12, 13, 14, and 
15. Although fairly heavy rains fell on 
June 12 and 13, the discharges were 
very light. It appears that the heavy 
discharges on and prior to June 7 went 
far toward exhausting the supply of 
ascospores. The failure to catch any 
spores whatever during the rainfall 
of 0.03 inch of June 9 is not understood. 
It is possible that there was less pre¬ 
cipitation in the orchard than at the 
weather station. It is conceivable, 
on the other hand, that the supply of 
ripening asci was so nearly exhausted 
that no significant, numbers were in 
condition to discharge at this time. 
No spores were caught during the 
dry period from June 16 to 20. 
Due to the absence of the senior 
author, no record was taken for the 
period of June 21 to 29. 
Rain fell in the latter part of the night 
of June 30-July 1. From 6 p. m. to 
8 a. m., the average rate of catch was 
1 ascospore to 30 liters. When it is 
considered that most of the discharge 
of this period evidently occurred from 
about midnight to 5 or 6 a. m., it 
is apparent that this represents a fairly 
heavy discharge for so late a date. 
During the dry period, July 2 to 4, 
no ascospores were caught. 
The next run was made on the night 
July 11-12, when light showers fell 
from about 6 to 8 p. m. The catch 
was at the rate of 1 ascospore to 33 
liters. From 8.30 a. m. to 6 p. m. 
July 12, there was no rain, and no 
spores were caught. 
The next run was made on the night 
of July 17-18. Light showers fell be¬ 
tween 7 and 9 p. m. From 6 p. m. to 
8 a. m. the rate of catch was 1 asco¬ 
spore to 56 liters. 
Showers fell from 6 to 8 p. m., July 
18. No ascospores were caught in a 
run from 6 p. m., July 18, to 8 a. m., 
July 19. During the following 24 
hours, no rain fell and no spores were 
caught. 
From 2 to 4 a. m., July 22, 1.36 
inches of rain fell. From 6 p. m., July 
21, to 8 a. m., July 22, no ascospores 
were caught. It appears that the 
season’s supply was exhausted at this 
time. 
From the results of these experiments 
it is readily apparent that the presence 
of an adequate amount of water is a 
primary requisite for the ejection of as¬ 
cospores of Venturiainaequalis. Under 
the conditions of the tests, dew alone 
was not sufficient to occasion dis¬ 
charges of any considerable conse¬ 
quence. It is apparent, further, that 
rain water is very important, not only 
in relation to the discharge of asco¬ 
spores, but for their maturation as well. 
This latter point has been more clearly 
established in later studies by the 
junior author and his coworkers and 
will be discussed in a later paper. 
The records of May 31, June 3, and 
June 6-7 show that when ascospores 
in abundance are in condition to be 
ejected, heavy discharges occur at the 
beginning of a rain period and con¬ 
tinue during continuous rain as long 
as the supply of ripe asci lasts. The 
periods of heavy discharge varied from 
several hours on May 31 to about 15 
hours on June 3 and June 6-7. 
The maximal average concentration 
of spores for a single run of the ma¬ 
chine, 1 ascospore to 0.4 liters, was 
obtained between 9 a. m. and 5.30 
p. m., May 21. When one considers 
that only traces of rain fell after 2 
p. m., it appears likely that, at the 
period of maximal discharge, the con¬ 
centration of spores may have been 
considerably greater than the average 
for the entire run. In order to gain a 
still more concrete conception of such 
concentrations of spores it seems to be 
of value to compute on the basis of 
the records just mentioned the number 
of ascospores which would have passed 
in the 8J^-hour period studied through 
an imaginary orifice 10 cm. square in¬ 
terposed 3 feet above ground perpen¬ 
dicular to the wind direction. With 
the average wind velocity for this 
period of 18.5 miles an hour and the 
average ascospore content of the air 
3 feet above ground of 1 ascospore to 
0.4 liters, as shown by the records, it 
appears that over 6,300,000 ascospores 
would have passed through the orifice 
postulated. 
In considering these records of 
ascospore discharge in relation to the 
seasonal development of the host plant 
and to control measures it would 
appear that they are in accord with 
the widely prevalent idea that the 
first ascospore discharges of Venturia 
