21 
For the purposes of this discussion the field may be divided into 
two parts : one of twenty acres of corn which had been in that crop 
continuously for at least three years preceding — five acres indeed 
having been in corn since 1899; and the other of forty-five acres 
of oats, thirty-five acres of which had been in corn for three years 
preceding, and ten acres continuously in that crop since 1899 until 
sowed to oats the present spring. 
April 27 several nests of Lasius alienus were explored, each 
containing numerous root-louse eggs and some root-lice. Above 
and immediately about the ants' nests the smartweed was withering 
and the roots were drained of sap, and in many cases blackened and 
decayed. The tunnels of the ants extended sometimes as far as a 
foot and a half from the main entrance, and ranged irregularly from 
a depth of an inch to about six inches. The root-lice were mainly 
on smartweed {Polygonum) roots, from sixteen to twenty on a 
single plant. In that part of the field which had been six years in 
corn and was to be planted to the same crop again this year, eighteen 
nests were found within a distance of two hundred hills; and in 
that part which had been in corn for the three preceding years, thirty 
nests were found between two rows three hundred and fifty hills 
in length. Twelve of the nests were explored in these parts of the 
field, five in the first mentioned and seven in the second. The ants 
in these colonies ranged in number from eighteen to one hundred 
and twenty-six, averaging fifty-seven each. Four of them contained 
from one hundred to three hundred larvae and eggs of ants. All 
were plentifully stocked with the eggs and young of root-lice, 
whether in all cases, or even in the majority, those of Aphis niaidi- 
radicis (the corn root-aphis) it was impossible to say with cer- 
tainty at that early date. Root-louse eggs varied in number from 
seventy-five to two hundred and seventy-five per nest, averaging 
one hundred and sixty-one, and young root-lice were found in num- 
bers varying from two to seventy-eight, with an average of thirty- 
five, a total average of one hundred and ninety-six root-louse eggs 
and young to each ant's nest. 
May I, root-lice nearly full grown, together with many young, 
were taken from roots of smartweed and ragweed {Ambrosia) in 
that part of the field sown to oats this spring but in corn for three 
year preceding. Two hundred oats plants were examined on and 
near the nests of ants containing root-lice, but not a louse was found 
upon them. Here again smartweeds near the nests of ants were 
withered and the roots were dead or actually gone. Cavities and 
gangways had been made by the ants beside the roots of these weeds. 
The first root-louse of the second generation was seen in the field 
