DAMPING-OFF IN FOREST NURSERIES. 
75 
Table XI. — Results of inoculation, at the time of solving, with Pythiwm 
deoaryanwn on Pinus banksiana in different sowing densities in pots of 
autoclaved soil.. 
[The percentages of " Damping-otT," columns4 and 
given in columns 3, 5, 6, and 8 
7 , are based on the number of seedlings 
are based on the number of seeds.] 
the percentages 
Num- 
ber 
of 
pots 
in 
ex- 
peri- 
ment . 
Results (per cent). 
Density of seed sowing. 
Experiment 58. 
Experiment 59. 
Emerged. 
Damp- 
ing-ofl. 
Sur- 
vival. 
Emerged. 
Damp- 
ing-off. 
Sur- 
vival. 
1 
2 
3 , 
4 
5 
6 
7 
8 
10 
5 
5 
5 
15 
8 
1 
6 
43 
65 
100 
33 
10 
3 

4 
26 
8 
11 
17 
13 
91 
34 
37 
23 
Triple 
7 
Regular, but 10 additional seeds near 
11 
MOISTURE AND TEMPERATURE FACTORS. 
The relation of damping-off to moisture and temperature are sub- 
jects less easily studied. In 1907 and 1908 Mr. W. H. Mast, then 
supervisor of the Nebraska National Forest, conducted daily counts 
of the number of seedlings damped-off and compared these records 
with temperature and rainfall records. The writer in 1909 repeated 
his work, maintaining parallel records of damping-off, air and soil 
temperatures, soil moisture, atmospheric humidity, wind movements, 
and evaporation. The 1909 records of damping-off, temperature, 
soil moisture, and evaporation appear in figure 20. The damped-off 
seedlings were counted and removed in the morning and evening, the 
day period thus being in most cases 10 to 11 hours and the night 
period 13 to 14 hours. Because the period was not always the same 
length, the data are reduced to a per hour basis. Air temperature 
was recorded by a sheltered thermograph 3 feet above the soil sur- 
face. The evaporation graph represents the mean loss per hour 
from two porous cup atometers of the writer's own design, in which 
the rather long and slender Chamberlain filter bougie was used and 
supported in a horizontal position just above the soil surface so as 
to be under as nearly as possible the same atmospheric conditions as 
the seedlings. The two bougies were placed at right angles to each 
other in order to eliminate as far as possible the effect of change of 
wind direction on their mean loss. While the rain-correction mount- 
ing had not at that time come into use, the error due to rain absorp- 
tion appeared negligible; atometers filled shortly before rainfall 
were read immediately after without any gain being found in the 
water in the reservoir. The psychrograph and wind-movement rec- 
ords are not presented, as the evaporation values are more easily inter- 
preted. Soil moisture was periodically determined in the soil of the 
