188 TRANSACTIONS OF THE ILLINOIS 



As it is certain that our Illinois insect infests both root and trunk, 

 we may assume, so far as practical purposes are concerned, that the two 

 supposed species (rejecting Fitch's winged specimens) are identical, and 

 treat them as such. 



These minute pests, having reached the roots in a way not yet fully 

 and satisfactorily explained, by their numerous punctures and the extrac- 

 tion of the sap cause irregular distortions, swellings and knots to be 

 formed thereon. The effect of this, when the roots are badly infested, 

 especially of young trees and nursery stock, is to cause them to become 

 sickly and finally die. Where they are sufficiently numerous to cover 

 and deform the root of a tree, that root almost invariably rots, then the 

 lice leave it. As a matter of course, the effect produced by these insects 

 on a young tree is much sooner perceived than on those that are older 

 and larger. Prof. Riley found, from some observations made by him on 

 an orchnrd at St. Louis, that young nursery trees whose roots were badly 

 infested died the following season, the roots always rotting previous to 

 the death of the tree. He appears . also to think this rot can be dis- 

 tinguished from that produced by any other cause, by its being more 

 porous and soft and approximating the brown mould of a rotting log. 

 Although there is a tendency in the deformities to disappear when the 

 exciting cause is removed, yet where the lice only leave because it is 

 dying it appears scarcely possible that tlie deformities should entirely 

 disappear, as the only means of removing them is gone when vitality is 

 wanting; and these, if remaining, would indicate at once the cause of 

 the rot. Most orchardists are aware that the work of these insects can 

 generally be detected where they have been working about the collar of 

 the trunk, even after they have disappeared ; there is a peculiarity in the 

 appearance of the bark which is readily detected by the experienced eye. 

 In such places they usually cause a mass of minute granulations, giving 

 the bark a roughened or shagreened appearance, and looking as though 

 the thin, delicate outer layer of bark or epidermis had been removed. 

 If present, they may easily be recognized by the peculiar bluish-wliite, 

 cottony matter they secrete from their bodies, which is never met with in 

 the case of the common Apple-tree Plant-louse {Aphis mali). The same 

 thing is also true in reference to the spots on the trunk and branches 

 which they attack.' When they locate on these portions of the tree, they 

 usually, and so far as my observations go, always select as a starting point, 

 some fissure, cut, break or otherwise injured portion of the bark ; or, if 

 these cannot be found, the wrinkles about the axils or forks of the larger 

 limbs and elsewhere. I noticed some the past summer, in little scattered 

 colonies, on the smaller limbs and even twigs of an apple tree standing 

 in my yard. If a tree is neglected and allowed to send up sprouts from 

 the base of the trunk, the point where these join the trunk at or below 

 the surface will be found a favorite resort for these insects. 



Do they pass from the trunk and branches to the roots? Or, in other 

 words, what relation do the two races bear to each other? 



Dr. Fitch thinks the parent insect insinuates herself downward, 

 along the side of the root, at the close of autumn, and there deposits her 



