434 
Journal of Agricultural Research voi. xxvn, no. 7 
Another series of experiments on the overwintering of spores was 
conducted cooperatively with the Missouri Botanical Garden during the 
winter of 1922-23. Diseased leaves had been collected in 1922 from 
plants grown in the field at Granite City, Ill., and in the greenhouse at 
Arlington Experiment Farm, Rosslyn, Ya. These leaves were ground 
in a food chopper, mixed with two parts of soil in a Mason jar, and placed 
in small, 2-inch flowerpots on November 24, 1922. These pots were 
divided into two lots and buried in the soil so that the tops of one lot 
were 1 inch below the surface of the ground and those of the other 5 
inches below. The height of the pots being 2.5 inches, the spore mixtures 
in each pot of the first lot were from 1 to 3.5 inches and those in the other 
from 5 to 7.5 inches beneath the soil surface. The two depths at which 
the pots were buried are recorded in Table IV as 2 and 6 inches, respec¬ 
tively. In addition, six pots, similarly filled, were watered and kept in the 
greenhouse for 4, 8, and 12 days. At the end of each of these three 
periods, two pots were buried, one at each depth recorded above. As the 
viability of the spores is considered to be decreased during long intervals 
of wetness, the late sowings of spores which had been watered for 4, 8, 
and 12 days before burial were intended to simulate to a slight extent 
the periods of fall rains. Thus, if the spores had been in the soil through 
late summer and early fall, their viability might have been lessened by 
the time these experiments were begun. As a check on the viability of 
the spores a part of the soil and spore mixture was kept in the Mason 
jar until the first pots were dug on January 4, 1923. 
At various intervals of about two weeks, some of the pots in each 
series were taken into the greenhouse. Seed of Little Club was sown 
in the pots and allowed to grow. The soil temperatures for the different 
sowings were not the same, the temperatures for March and April being 
considerably higher than those for January and February. After the 
resulting seedlings had produced one or two strong leaves, they were 
transplanted in clean soil in the benches. The pot buried on November 
24, with the spores 2 inches below the surface, had its contents destroyed 
by mice after it was dug up on January 4 and wheat seed sown. Also 
the seed sown on January 4 in the pot buried 6 inches below the soil 
surface on December 6 and brought in on January 4 was destroyed by 
mice. Additional seed was resown in this pot on January 12, 1923. 
The infection results are given in Table IV. 
From Table IV it seems that watering the spores and keeping them in 
the greenhouse for 4, 8, and 12 days before they were buried in the soil 
did not diminish their viability. Indeed, four of the rows showed 100 
per cent infection, which was slightly higher than that of the control. 
The spores showed a marked decrease in viability about February 3. 
The coldest weather of the year was during the two weeks following 
this time, the minimum temperature recorded being about i° F. By 
February 18, the ground had begun to thaw and the pot at the 
2-inch depth was brought in, though the one at the 6-inch depth could 
not be dug from the ground until February 22. There was an infection 
of 11.1 per cent in the plants grown in the pot buried at the 6-inch 
depth and brought in on March 16. There was no infection in the plants 
sown in pots removed from the soil on April 14, but the plants did not 
grow well because of the high air and soil temperatures in the green¬ 
house. However, as previously stated, there was infection in the plants 
sown in April, 1922, in the infested soil which had been removed from the 
field at Granite City, Ill., on April 10, 1922. 
