INSECT ENEMIES AND THEIR CONTROL 107 
wire on which we could build the smudge and pass it up 
into the box through the second piece of pipe. The 
dimensions of the pipe were 4 feet long and 7 inches in 
diameter. The smoke was thus cooled somewhat before 
it came in contact with the lettuce. The exposure as 
before was 15 minutes. When the box was raised the 
temperature was 90 degrees, being 15 degrees lower than 
in the previous trial. The leaves were not injured nearly 
as much, but in the same manner, indicating that the 
injury was proportional to the amount of heat accom- 
panying the smudge. This injury occurs rarely in 
practice.” 
A practical grower has observed that lettuce is easily 
injured by tobacco fumigation at a temperature of 60 
degrees, that light treat- 
ments may be made at 55 de- 
grees without injury, that 
strong fumigations may oc- 
cur at 50 degrees without 
injury, and that it is almost 
impossible to damage the 
crop at a temperature of 45 
degrees. 
The danger of injury will 
be very much less if the 
plants are dry during the 
smudging. It is necessary, 
of course, to have the house 
well filled with the smudge 
in order to make the treat- 
ment fully efficacious. 
The stems are sometimes 
placed on the walks, but it 
is better to put them in 
kettles, cans, wire cages or Fig. 34.—Garbage can suspended to 
Obhermuetal utensils: Some! “fey tect, Mm femleating “with to- 
