12 
the difference of the two plats with reference to ants and root-Hce 
can fairly be attributed. 
For a comparison of these plats seventy-five hills of corn were 
dug up in the check plat and one hundred in the experimental plat. 
Reducing the numbers given, for convenience of comparison, to a 
unit of one hundred hills, it appears (Table II.) that sixty-two per 
cent, of the hills were infested with ants on the check plat, and 
twenty-five per cent, on the experimental plat; that forty-four per 
cent, of the check hills were infested by root-lice, and eleven per cent, 
of the' experimental hills ; that one hundred of the check hills con- 
tained 1 96 1 ants, and one hundred of the experimental hills, 630 
ants; that one hundred of the check hills contained 1464 root-lice, 
and one hundred of the experimental hills, 198 root-lice. Or, more 
briefly and generally stated, and comparing equal areas of the two 
plats, we see that the check plat contained approximately three 
times as many ants infesting two and a half times as many hills, and 
seven times as many root-lice infesting four times as many hills as 
did the experimental plat. 
The difference in apparent effect of treatment between the Gales- 
burg field and the Harvel field may have been due to the fact that the 
Harvel field was much worse infested than the other. Twenty-eight 
per cent, of the hills were infested with ants at Galesburg and sixty- 
two per cent, at Harvel ; and seventeen per cent, of the hills were 
infested with root-lice at Galesburg and forty-four per cent, at Har- 
vel, with a difference of only four days in the dates of inspection. 
Where both ants and root-lice are numerous, the chances that 
some of the former will find some of the latter after both have been 
thoroughly scattered through the soil, is doubtless greater than where 
both ants and root-lice are relatively few. Of course, as fast as root- 
lice or their eggs are recovered by the ants, whether originally the 
property of the ants or not, they will be appropriated and established 
on the plants in the field. Furthermore, later observations reported 
in this paper, have made it probable that ants actively convey their 
charges from one part to another of the field as conditions become 
less favorable where they were established. It is likely, consequently, 
that in a crowded field the root-lice would be carried over to plants 
lightly infested on the experimental plat, and that the normal re- 
sults of the treatment would be thus to some extent masked or lost. 
It is at any rate made certain by our later observations that as 
the food plant becomes crowded, much larger percentages of winged 
lice appear, and these, by emerging from the ground and scattering 
abroad, tend to diminish the ratio of increase in the over-infested 
field and to increase it elsewhere. Such a migration of winged lice 
