SOIL DISINFECTION WITH HOT WATER. 11 
tomato plants. Again, the check plants in infested soil showed 
severe nematode and fungous infection and were much dwarfed and 
yellowed. (See PL IV, fig. 2.) Some of the plants grown in untreated 
greenhouse soil, supposedly umnfested, showed mild nematode 
infestation, while more than half were attacked by Rhizoctonia. 
Because of the partial infestation of the greenhouse soil, it was 
not possible to determine how much of the increased plant growth 
in the soil treated with boiling water was due to the killing of the 
pathogenes and how much resulted from the stimulating effect of 
the heating. 
A scrutiny of the results of the 8-inch pot treatments given in 
Table IV shows a verification of those secured in Experiment Series I ; 
viz, a marked reduction of the diseases in the 2,000 c. c. treatments 
and their elimination in the pots which received 3,000 c. c. of boiling 
water (PL V, fig. 1), and a considerable increase in the number, size, 
and vigor of plants in treated pots above that shown in the check 
pots (PL V, fig. 2). As might be expected, the added 4,000 c. c. 
treatment gave similar results. 
Again, on account of the nematodes and Rhizoctonia in the fresh 
greenhouse soil, no conclusive results were obtained regarding the 
degree of growth stimulation which might be caused by the heating 
alone. It may be noted that in general the percentage of germina- 
tion and the plant growth were larger in the fresh greenhouse soil 
than in the old infested soil (PL V, fig. 2). 
The results from the repeated bench experiment, as given in Table 
V, show only data from tomatoes, since the lettuce was destroyed 
by mice shortly after the experiment was started. Here, again, sub- 
stantial confirmation of the results of Experiment Series I was 
secured. As in Experiment Series I, the treatment approximately 
equivalent to 1,000 c. c. per 8-inch pot reduced the amount of disease. 
In the 2,000 c. c. treatment of Experiment Series II only 11 per cent 
of the plants showed mild root-knot infection, as compared with 96 
per cent of more severe root-knot in the check, while the 3,000 c. c. 
application practically eliminated the trouble. 
A study of Table VI, which gives the soil temperature records, 
shows that in 8-inch pots treated with 3,000 and 4,000 c. c. of boiling 
water and in the bench section treated at the rate of 7 gallons per 
cubic foot of soil, all of which treatments killed the pathogenes, a 
relatively short time was required to raise the soil temperature to 
the maximum in each treatment and that the soil retained the 
heat for a strikingly long period. In all cases the temperature was 
maintained above 60° C. for more than 30 minutes and above 55° 
C. for 48 to 65 minutes, both temperatures being well above the 
thermal death point of the root-knot nematode, as determined by 
the first writer, and presumably above that of the fungi in question. 
