Dear Sir: I have examined the punctured twigs and the insects which you sent to me with much interest The insects are tree-hoppers, and the scientific name of them is Membracis bubalus, so called by Fabricius, the first desecriber of this species. You will find an account of the tree-hoppers, and an allusion to this species, in the second edition of my Treatise, p. 192. It is one of the kinds whose history has not hitherto been particularly investigated, and of which it is stated in my work, that "the habits of some of the tree-hoppers are presumed to be much the same as those of the musical harvest flies; for they are found on the limbs of trees where they deposit their eggs, only during the adult state, and probably pass the early period of their existence under ground".

This little tree-hopper, it appears by the specimens sent, punctures the twig of the cherry and of the plum tree. This operation is performed by a piercer, which is lodged in a grove beneath the tail of the insect The puncture begins with a small longitudinal incision through the outer bark of the twig, and is carried obliquely through the inner bark to the wood. In this wound the insect deposits its eggs, pushing them beneath the bark on each side of the incision. The eggs are very minute, of a white color, and long oval shape, and strikingly resemble those of the Cicada, except in being much smaller. The eggs appear to remain unhatched through the winter. On being hatched in the spring, or in the early part of the summer, the young probably, like the young of the Cicada, drop or descend to the ground, burrow beneath the surface, and live there upon the sap of the roots of plants, which they imbibe by suction through their sucking tubes. Like the Cicada, too, when they have come to their growth and are ready for their transformation to the winged form, they probably come forth from the ground, ascend the stem of tome plant, east their skins, and appear in the adult or perfect condition, in which they are prepared to continue their kind.

Whether these insects hare any connexion or concern with the production of the warts on the cherry and on the plum tree, is a question of considerable importance. Your friend George Clarke, Esq., who furnished you with the specimens sent to me, has satisfied himself, you say, that the warts originate from the punctures of these insects. Having watched the operations of the latter for three years past, he has found the warts to appear on the wounded twigs; and has found, al?o, that, when the wounded part was cut out, the production of warts was prevented. Since (he receipt of your specimens, I have examined (not very thoroughly indeed) my plum trees, which have always had some warts on them every summer; but I do not discover any incision of the Membracis upon the twigs. This examination, however, is not to be considered as a sufficient or satisfactory test My trees have been very severely pruned and shortened on the first appearance of the warts, and in this way have been kept free from the unsightly excrescences with which other trees are disfigured. I can detect the wart in its incipient stage, before even the delicate outer skin of the twig is broken by the tumid condition of the bark, and then apply the knife freely, and put fine salt or strong brine upon the wound.

I propose this spring to wash over all the limbs and twigs of my plum trees with strong soft soap, in order to ascertain whether alkali will prevent the production of the wart-be their cause what it may. Before this is done, however, I will examine the trees again more carefully, and if any incisions of the Membracis are found, will mark the spot by tying around it loosely a piece of yarn-will then leave it untouched by the soap, and watch the result I hope other persons may be induced to make the same experiment I should observe that Membracis bubalus is not an uncommon insect here, and that it may be found by a careful collector almost every summer. Yours, etc, Thaddeus Wm. Harris.

Cambridge, Mass., March 28, 1858.

P. S. - You will find by my Treatise, page 70, that the black color of the surface of the warts on the plum tree is occasioned by numerous little black spherical fungi, which give to the wart a granulated appearance. The constant occurrence of these fungi on the surface of the warts, and upon nothing else, and the invariable death of the warts when the fungi have come to maturity and have shed their spores (cr seeds), are of much significance in connection with the origin and history of this peculiar affection. T. W. H.

We are greatly obliged to CoL Johnson for the information he has communicated. Whether or no the "Membracis" produces the plum tree warts, it is well that attention should be called to it, that the precise nature of its depredations be understood.

The three great draw backs in fruit culture in America are the pear blight, the curculio and the Plum tree warts. These subjects merit thorough and ceaseless experiment and investigation.