270 THE PLUM. 



The knots is a disease attacking the bark and wood. The 

 former at first becomes swollen, afterwards bursts, and, finally, 

 assumes the appearance of large, irregular, black lumps, with a 

 hard, cracked, uneven surface, quite dry within. The passage 

 of the sap upwards, becomes stopped by the compression of the 

 branch by the tumor, and, finally, the poison seems to dissemi- 

 nate itself by the downward flow of the sap through the whole 

 trunk, breaking out in various parts of it. 



The sorts of plum most attacked by this disease, are those 

 with purple fruit, and we have never known the green or yellow 

 fruited varieties infected, until the other sorts had first become 

 filled with the knots. The common horse plum, and damson, 

 appear to be the first to fall a prey to it, and it is more difficult 

 to eradicate it from them, than from most other sorts. The 

 common Morella cherry is, also, very often injured by the same 

 disease in Pennsylvania. 



There is yet some doubt respecting the precise cause of these 

 knotty excrescences, though there is every reason to think it is 

 the work of an insect. Professor Peck and Dr. Harris believe 

 that they are caused by the same curculio or plum-weevil that 

 stings the fruit ; the second brood of which, finding no fruit 

 ready, choose the branches of this tree and the cherry. This 

 observation would seem to be confirmed by the fact that the 

 grubs or larvae of the plum-weevil are frequently found in these 

 warts, and that the beetles have been seen stinging the branches. 



On the other hand, the following facts are worthy of attention. 

 First, in some parts of the country, where the curculio has 

 been troublesome for many years, the knots have never been 

 known. Secondly, in many cases, the knots have been abun- 

 dant on plum trees, when the fruit was entirely fair and unin- 

 jured by the curculio, even upon the same branches. 



These facts seem so irreconcilable with the opinion that the 

 curculio produces both these effects, that we rather incline at 

 present to the belief, that though the curculio deposits its eggs 

 in the tumors on the branches while they are yet soft and tender, 

 yet it is not to the curculio, but to some other insect or cause, 

 that we owe this unsightly disease. 



Practically, however, this is of little account. The experi- 

 ence of many persons, besides ourselves, has proved, most satis- 

 factorily, that it is easy to extirpate this malady, if it is taken 

 in season, and unremittingly pursued. As early as possible in 

 the spring, the whole of the infected trees should be examined, 

 and every branch and twig that shows a tumor, should be cut off, 

 and immediately burned. Whatever may be the insect, we thus 

 destroy it, and, as experience has taught us that the malady 

 spreads rapidly, we will thus effectually prevent its increase. 

 If the trees are considerably attacked by it, it will probably be 

 necessary to go over them again, about the middle of May, 



