118 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



" Is the 'black wart' on plum trees caused by the curculio? These ex- 

 crescences are very common in this h)cality on certain varieties of plum 

 trees e:rafted on the Canadian plum stock; more especially are the Lombard 

 and Duane pnrple thus diseased. I have veatched them very closely in 

 , their germination and growth, and when in the gum and soft state, have seen 

 the curculio in the act of perforating and depositing its eggs on the sur- 

 face. I have also followed the subsequent growth of the larvse to maturity, 

 and am quite certain with the doctor, that this insect is in no way con- 

 nected with the prodnctinn or growth of this fungus. It simply uses it, in 

 common with the fruit of the tree, as a repository for its eggs. Now a 

 word or two in regard to the treatment of the plum wart — with me it has 

 been excision, in its true surgical sense, either by cutting off the entire 

 limb, or cutting out the entire fungus growth in its incipient stages. This 

 latter operation may be made successful for a time at least, if care be taken 

 to extend the incision sufficiently wide and deep enough to include the 

 wh^-le of the disease. I think it absolutely necessary to cut to the heart or 

 pith of the branch. I do not pretend to decide the question whether the 

 disease starts from the centre or surface of the limbs; but one thing is 

 certain, no superficial cutting in any stage of its growth will assist it only 

 for a short time. And as cancer in the human system, notwithstanding 

 the temporary check it may receive from the surgeon's knife, is likely, in 

 the end, to cause the death of the subject, so this disease is pretty sure to 

 impede the growth and thrift of the tree, and ultimately destroy it. Please 

 excuse the liberty I have taken in addressing you, but being a constant 

 reader of the discussions in the Farmers' Institute Club — are excuses 

 which I trust you will consider." 



Mr. Hite remarked that he had frequently practiced this surgical opera- 

 tion for the black-knot, and had always found the limb marked with a 

 dark colored line under the excrescence; and the incision must be deep 

 enough to remove all this line, or there will be no cure. Sometimes this 

 line extends below the pith, and then the limb is almost certain to die if the 

 line is all cut out. In such cases the whole limb may as well be cut away. 



Dr. Trimble. — I will not affirm that the curculio does not cause this 

 excrescence, because there is a mystery about the matter in this respect. 

 There is not a particle of doubt that an insect so exactly like the curculio 

 that the difference cannot be distinguished deposits its eggs in these ex- 

 crescences, for I have seen them at work, and have cut off the limbs and 

 hatched out the eggs, and produced something exactly like curculios; yet 

 I have never been able to get these insects from the knots to work upon 

 the fruit when offered to them. Again, when I had a plum orchard that I 

 used to protect from curculio by the only means that I ever found effec- 

 tual — that is, jarring them down upon sheets — I had no black-knot, 

 although there was an orchard near by that was so destroyed by the 

 disease that it was finally all cut down; and then my trees were attacked, 

 and as fast as the excrescences made their appearance in June, I cut them 

 all off and reduced them to ashes, and thus got rid of the disease. 



