A SERIOUS LETTUCE DISEASE. 
135 
Records were taken of the temperature at eacli thermometer every 
15 minutes from the time steam was turned on until the end of the 
steaming, also of the steam pressure on the boiler (see table). 
In this bed were planted 1,260 lettuce plants, care being taken to 
prevent the carrying of the disease into the bed from other infected 
beds; of these plants 88 or 6.98 per cent, had the characteristic dis¬ 
ease. In the control bed, B, of 1,260 plants there were only 38 that 
showed the disease. This discrepancy may he accounted for by the 
fact that infection was worse in Bed A, before it was treated; but 
it is evident that such steaming did not give promise as a method of 
control. t 
Beds G and II were steamed with the Sargent Sterilizer, Fig. 29. 
The sterilizer was covered with heavy canvas during use. Beds G 
and H were each 30 feet long, and together they contained 696 plants. 
The soil was heated to 90 to 95 C., in less than 10 minutes, and that 
temperature maintained for thirty minutes. Of the 696 plants, 33 or 
4.8 per cent, showed the disease, and again considerably more than in 
the control. 
Experiment 4. To test the efficacy of top dressing with disinfected 
soil. The ends of three separate beds, C, B, and E, were used because 
these were more convenient to the steam connection with the boiler 
house. 
A box was made 2 x x 4 feet, thus capable of holding 48 cubic 
feet of soil. Soil was skimmed from the surface of the three beds; 
to a depth of one inch from E, of two inches from D, and of 3 inches 
from C, making in all a total of 150 cubic feet or approximately three 
times the box full. Soil was placed in the box to half fill it, then a 
system of drain tile was laid upon this soil and enough more soil was 
placed upon the tile to fill the box. Steam was turned on through the 
inlet, the ends of the drain tile being stopped with cement. The soil 
was heated to 90 degrees C. and kept at that temperature for one hour. 
This soil, after heating, was then scattered over the beds from which it 
had been taken and the disinfecting box filled again. Care was taken to 
sterilize the shovels each time after unsterilized soil had been handled 
with them. 
The results of this top dressing of the beds is shown in the following 
table. 
TABLE XVI.—SHOWING EFFECT OF TOP DRESSING WITH STEAMED SOIL 
Bed 
No. of Plants 
in Bed. 
Healthy 
Plants 
Diseased 
Plants 
Percentage 
of Disease 
Depth of Top 
Dressing 
E 
320 
399 
21 
7.02 
1 inch 
D 
320 
304 
16 
5.26 
2 inches 
C 
320 
308 
12 
3.89 
3 inches 
It is seen that the disease decreased with the increase in depth of 
the disinfected top dressing. 
Experiment 5. To determine the effect of carbon bisulphide, one 
litre per square metre. One-half of Bed F was treated with carbon 
