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not dream of disease, nor of Aphides on the roots, and did
not look for them.  In the month of May, 1860 four <s>weeks</s> years
after planting, I first saw the Aphis on the leaf: I then
looked for and found them in great numbers on the roots, but
confined entirely to the New Jersey trees.  This induced me
to believe that the insect had been brought in from New Jersey,
and that there was a periodicity in this mutation of the insect;
and that like the Cicada and the apple and peach tree
borers, the Aphis leaves its home in the ground for generations
only.  Subsequent observation has confirmed this belief,
and formed the groundwork for the following conclusion:
That the insect first gets into an uninfected district by flying,
or is carried by the winds; or whilst in the larvae
state by the natural drainage of the soil, or by importationi
in the plants form infected districts: that immediately after
the larvae state the insect goes into the ground, not to
hibernate, my dear Professor, but to find and to establish
its home upon the rootlets of the trees, and there remain
during nearly the whole of their natural lives, bringing forth
their parthenogenetic young in vast numbers, and all alike to
engage in the work of destruction by feeding on the sap of'
the small roots, thus literally taking the life-blood of the
        