as those whose history I have thought it worth while to follow in detail. 
In order to determine more precisely the value of the services per-— 
formed by their guardians, I arranged in several years a series of exper- 
iments designed to show to what extent the plant lice could help them- 
selves if left unattended. Owing to the waywardness of the ants, which 
in most cases refused to content themselves in confinement, but one of — 
these experiments came to a successful issue. April 13, 1889, corn root 
aphis eggs were placed in the earth among smartweed roots to test the 
ability of the young lice hatching to find the roots for themselves. A 
check experiment was started at the same time with eggs placed in ar- 
tificial cavities beside smartweed roots. April 25 no insects could be 
found on the plants of the first experiment, while the cavities made in 
the second experiment contained young lice upon the roots in fine con- 
dition. 
RELATION TO THE CORN LEAF APHIS. 
Ever since Walsh, in 1862, doubtfully connected a leaf louse of 
corn, first reported by him,* with the root aphis described by Fitch from 
the roots of corn under the name of Aphis maidis,+ the relations of these 
insects has been a moot point. There has never been any evidence, how- 
ever, of their connection as simply different forms of the same species 
other than the facts that they belong to the same genus, that they re- 
semble each other more or less closely in specific characters, and that they 
infest different parts of the same plant in the same territory, and often. 
at the same time. On the other hand, the differences of specific charac- 
ter are such that they may very well belong to different species, and 
should, indeed, have been held to be distinct until their identity had 
been demonstrated. They do not by any means vary together in abun- 
dance either in time or in place; neither do they by preference infest 
the same species of plant. The corn leaf aphis occurs much more abun- 
dantly on sorghum and broom corn, especially the former, than it does 
on Indian corn itself; while the root louse occurs but rarely on those 
plants. Many other species whose roots are infested by the root aphis 
have not been known to support the corn leaf aphis at any time. The 
bare possibility, however, that these two forms may nevertheless alter- 
nate in such a manner that the one may be derived from the other throws 
some doubt on all propositions for an economic procedure, since if this is 
the case, both leaf and root louse must be taken into account in any 
measures intended to arrest the multiplication of either. 
On account of the economic importance of this point, elaborate ex- 
periments have been made necessary with both root and aérial lice. The 
distinctness of the two can only be shown by tracing the life history of 
each throughout the entire year under conditions such as to insure the 
production of the one from the other if such production be possible. 
Even then the demonstration would be incomplete unless both root and. 
leaf lice had been followed generation by generation throughout the en- 
tire season from the egg of one year back to the sexual generation and the 
ego of another year. These experimental conditions have now been sub- 
~~ * Proc, Ent. Soe Phila., Vol. I. (1863), p. 300. 
T TENOD. Lise sING. Noes De oe. 
