As every thing relating to this destructive affection of our plum trees is important, I have taken the liberty to enclose you a letter from Prof. Harris on the subject of the insect named, and also a twig punctured by the insect, furnished me by George Clarke, Esq., of Springfield, Otsego county. Mr. Clarke and his gardener have observed the attacks of the insect, as he informs me, for several seasons; and whenever he has left the twigs with the puncture upon them, the black warts have appeared the second season after the attack; but when he has removed the puncture carefully which contains the eggs, he says the limbs have not been affected. I give this, that examinations may be made, as suggested by Prof Harris, in the hope that something may be elicited on the subject that may be useful. .

Perhaps I should further state that Mr. Clarke is of opinion that the black color of the surface of the warts is occasioned, as noted by Prof. Harris, by the black fungi alluded to, but that the first cause of this excrescence arises from the deposit made by the insect. By examining the twig sent you, you will find the eggs deposited, as described by Prof. H. B. P. Johnson, Albany, N. Y.