27 
In this case the field was disked on the i8th, 21st, and 25th of May, 
harrowed on the latter date, and examined June 9, fifteen days after 
the last treatment. 
More remarkable, on the whole, was the effect of once harrowing 
with an Acme harrow May 22 and 23, after numerous heavy rains 
from the 15th to the 20th of May, 1905. Here a single treatment 
(Experiment 3, Table V.) with the disk harrow, used as soon as 
the ground was dry enough to work properly, reduced the number 
of hills infested by ants and aphids by fifty-eight per cent, and sixty- 
four per cent, respectively, and the number of insects in the field by 
ninety per cent, for the ants and eighty-nine per cent, for the aphids. 
The least effective treatment, according to Mr. Kelly's notes, was 
a single disking, May 5, of plat Ai on the Hinman farm (Table III.), 
which, as shown by a comparison with C i of the same table, seems 
to have reduced the number of hills infested by only sixteen per 
cent, for the ants and seventeen per cent, for the aphids^ and the 
number of insects by four per cent, for the former and fourteen per 
cent, for the latter. As these plats were not examined until May 
31, that is to say twenty-six days after the treatment, these figures 
probably ought not to be taken into account. It was hardly to be 
expected that the original difference between check and experi- 
mental plats should continue unchanged during this interval of 
nearly four weeks. 
Five of the pairs of plats brought into comparison differed in re- 
spect to treatment only by the fact that the experimental plat was in 
each case treated with a disk harrow once more than its correspond- 
ing check. If the ratios for these five plats be averaged, it appears 
that the result of a single disking in 1905 on the Hinman and Fin- 
negan places may be described in general terms as reducing the 
number of hills infested by forty-four per cent, for the ants and fifty- 
one per cent, for the aphids, and the number of insects by fifty-seven 
per cent, for the ants and sixty-three per cent, for the aphids. Or, 
still more generally speaking, it may be said that the average effect 
of a single treatment with the disk harrow was to reduce the number 
of infested hills by a little less than half, and the number of insects 
in the field by about two thirds. If, in view of the doubtful charac- 
ter of one of these comparisons above mentioned, in which nearly 
four weeks intervened between the experimental operation and the 
inspection of the plats, we omit this" case from our calculation, this 
statement may be revised to the effect that a single disking may be 
expected to reduce the number of infested hills by something more 
than half, and the number of insects in the field by nearly three 
fourths. 
