330 Report oF THE DEPARTMENT OF ENTOMOLOGY OF THD 
larve. In the previous experiment, No. V, it seemed evident 
that the treatment of the scales was inefficient because of the 
lack of these same insecticidal compounds. As the precipitate 
in this experiment, No. VI, was the residue from No. V, it is 
safe to assume that the destruction of the scales in the present 
experiment is to be credited to the mechanical effects of the 
precipitate and not to any soluble compounds present with it. 
The low percentage killed, shown by the table (apples 27 and 
30), is due to the smaller number of young. 
CHECKS. 
A series of experiments shown in the following table was 
carried out as checks to the foregoing experiments. Apple No. 
1 was treated with a thin coating of whitewash, thus supplying 
the conditions, so far as the mechanical effect of a practically 
neutral heavy wash is concerned, prevailing in those experiments 
in which the precipitate was abundant, especially Nos. I, II, 
IV and VI. The only important difference was that in the case 
of the checks the whitewash acts as a purely mechanical mixture 
while it is possible, in most of the above experiments, that some 
poisonous qualities of the insoluble ingredients of the wash 
may have an influence in destroying the scales. Apples Nos. 2 
and 3 were sprayed every day with water for fourteen days to 
determine the effect of the water alone upon the scale, and 
thus to act as a check upon experiments in which the soluble 
ingredients alone of the wash were used. Apples Nos. 4, 5 and 
6 were not treated and were thus a check upon all of the 
experiments. 
