90 VEGETABLE FORCING 
Instead of the soil in the pots all being heated to 212 degrees they 
received the following various degrees of heat before planting: 
ele hcaee 14 118 127 140 147150 19 161 163 163 170 176 
“Result: Nos. 1, 2 and 3 all damped off. The remainder were 
perfectly free from the damping-off fungus and nematodes. 
“Exp. d. Sixteen pots of cucumbers were treated the same as ‘c.’ 
No. of pot 12 8 4 5 6 7 0:11 12 18 14 15 16 
Temperature 147 149 154 159 163 167 168 172 176 183 185 186 192 194 196 199 
“Result: No nematodes. 
“From these experiments, which only represent about one-half 
of what was done, it appears that a very high temperature is not 
necessary in order to free infested soil of nematodes. The number 
of degrees of heat necessary is about 140 degrees, but as a matter of 
safety the temperature should go above this, inasmuch as in large 
areas of soil the distribution of heat is always unequal, and while 
one portion may be heated as high as 190 degrees another portion 
may not exceed 110 degrees. The conclusion, then, that the soil 
must be heated under pressure to a temperature of 225 or 235 de- 
grees in order to kill nematode life is therefore not valid in all 
cases. These experiments were made with sufficient care and were 
repeated often enough with the same results to consider them trust- 
worthy.” 
Stone has since stated, and his statement is based upon 
further research, that the soil should be heated to a 
temperature of 180 degrees and that 212 degrees is better. 
This corroborates the views of growers who have been 
successful in steaming soils. While 140 degrees will 
kill insects and nematode eggs, there are disease germs 
which require higher temperatures. A high temperature 
is also necessary to secure the thorough permeation of 
the soil particles which harbor and protect insects and 
disease germs. 
Time required—Steam sterilization is really the cook- 
ing of every particle of soil, and considerable time is 
required to accomplish this. Steam under pressure 
passes through open, coarse, sandy soils more rapidly 
