70 
Journal of Agricultural Research 
Vol. II, No. i 
Table I. —Longevity tests of pycnospores in soil in the field in 1913 —Continued. 
Rainfall. 
h 
T3 
Number of 
viable 
spores per 
gram of 
soil. 
Trap No. and 
soil sample No. 
Date. 
Inches. 
Date of 
collection. 
Date of 
cultures. 
*3 ti 
r 
CD 
Condition of soil 
when tested. 
Trap VI: 
Sample 16. 
Sample 20. 
Sample 24. 
[Apr. 27- 
28. 
lApr. 29 
2-43 
[Apr. 30 
jMay s 
[May 12 
May 1 
May 6 
May 13 
Days 
I 
6 
Wet from rain.. 
Air-dry. 
490, OOO 
I, 100, OOO 
368, OOO 
. II 
13 
Loose, air-dry 
surface soil 
exposed to 
sun. 
TESTS OF LONGEVITY UNDER LABORATORY CONDITIONS 
For use in determining the longevity of pycnospores dried in soil and 
stored in the culture room in the laboratory to secure longer periods of 
desiccation, samples were collected in much the same manner as has been 
described for the field tests. A much larger quantity of soil was taken 
from the bases of diseased trees after a rain and transported to the lab¬ 
oratory in sterile tin containers. During storage in the culture room the 
tin covers were replaced by layers of absorbent cotton held in place by 
rubber bands. Thus, ample opportunity was afforded for thorough dry¬ 
ing of the soil. 
These samples were tested as soon as possible after collection while the 
soil was still wet and at convenient intervals thereafter during the period 
of storage to ascertain the number of viable pycnospores to the gram. 
With some exceptions the method used in the tests was identical with that 
already described for the field tests. Previous to each test, however, the 
soil in each container was thoroughly shaken to secure as uniform a 
mixture as possible. As in the previous work, no allowance was made 
for loss of weight due to evaporation of the soil moisture. Most of this 
loss occurred during the first period of drying, the soil being practically 
air-dry and readily reducible to dust at the end of one week. By numer¬ 
ous trials the loss in weight due to air-drying was found to represent an 
average decrease of 35 to 40 per cent of the weight at the time the first 
test was made. A factor of 1.66^ might be applied to the figures given 
in the first or control analysis of each sample to compensate for this 
error. 
In all of the cultures made previous to July 30, 3 per cent dextrose 
agar +10 was used as the medium. In the cultures made on July 30, 
August 8, and August 26 chestnut-bark agar made from diseased bark 
was employed; in the final tests chestnut-bark agar made from healthy 
bark was employed. Furthermore, relatively larger portions of inocu¬ 
lum were used in the final tests (September 25), 1 c. c. being transferred 
from the first suspension to a flask containing only 9 c. c. of sterile water 
from which 1 c. c. and fractions thereof were plated out. The results 
obtained are presented in Table II. 
