ACTING STATE ENTOMOLOGIST. 
59 
that have been lost by his neighbors, through what, from his description, must be the 
same “rotten-root” that prevails, so extensively in South Illinois. Mr. L. Woodard, 
nurseryman, of McHenry county, North Illinois, also told me, that he had occasionally 
noticed a few woolly lice on the roots of his young apple-trees, accompanied by the 
usual deformation of the root. Mr. Ira L. Bailey, President of the Carroll County 
Horticultural Society, North Illinois, likewise informed me that he had himself lost 
three large apple-trees by the same universal “ rotten-root.” And finally I heard that 
Dr. Pennington, the extensive fruit-grower of Whiteside Co., North Illinois, had some¬ 
times noticed “ woolly plant-lice” on the limbs of his apple-trees, but not in any 
considerable numbers. Hence there is pretty satisfactory evidence that this insect 
exists, though apparently in greatly reduced numbers, up to the most northerly parts 
of the State. 
I found it to be a very general notion at Cobden, that the soil there was full of this 
Root-louse —that it existed inearth that contained no roots at all and in old rotten 
stumps — and that it was abundant on the roots of almost all forest-trees, especially 
on those of the Persimmon (Diospyros virginiana.) No plant-louse, however, can 
possibly live, except on the sap of some living and growing plant; and therefore, if any 
of these Root-lice are found in old dead stumps &c., they must, for purposes which 
will be afterwards explained, have been carried there by the ants ; as I have ascertained 
to be actually the case with certain other species of the very same genus. That there 
is a Plant-louse inlesting the roots of the Persimmon in that neighborhood, I fully 
believe ; because, on digging down among the roots of that tree, Mr. Riley and myself 
discovered the peculiar bluisli-white mould, which is characteristic of Root-lice, though 
wrn failed to find the insect itself. But it is impossible that this can be the same species 
as infests the Apple-tree, because the Persimmon and the Apple-tree belong to widely 
distinct botanical families ; and it is a rule to which there is not one solitary exception, 
that, when a particular species of Plant-lice infests more than one species of plants, 
those species of plants always belong to the same botanical family, and usually to the 
same botanical genus. Por the same reason, if any Root Plant-lice are found on Oak, 
Beech, Ash, Mulberry, Sassafras, Tulip-tree (Poplar), Cucumber-tree, Elm, Hickory, 
Walnut, Birch, Poplar (Cottonwood &c.,) Hackberry, Sumac, Dogwood, Grape-vine, 
Sycamore (Plane-tree,) Hazle, Basswood, Maple, &c., they cannot possibly belong to 
the same species as infests the Apple-tree, and, if transferred to the roots of the Apple- 
tree, they would soon starve to death and perish. On the other hand, it is highly 
probable, that the very same species, that infests the roots of the Apple-tree, infests 
also the roots of the Crab and the Thorn ; and it may possibly occur on those of the 
Plum, the Cherry and the Peach, and even on those of the Blackberry and the Rasp¬ 
berry 'i for all these last named plants belong to the same botanical family as the Apple- 
tree. It is observable, however, that, although Apple-trees and Peach-trees are 
commonly grown in the same orchard near Cobden, yet I did not hear of a single case, 
where the roots or bark of the Peach-tree had been found to be infested by this insect, 
or any other at all resembling it. 
Persons, who are not familiar with the habits and classification of Insects, aie apt to 
think that all Plant-lice — different as some of them are in shape, color, size and habits 
— are mere varieties of one and the same species ; just as all dogs, however much the} 
may differ from one another in such respects, yet belong to one and the same species. 
But it is by no means so. Whatever food one variety of Dog will live on, another 
variety of Dog will live on equally well. But shift the Apple-tree Plant-louse on to a 
