894 THE PLUM. 



practical success three things are necessary : 1st. That the land should 

 be decently clean, and not overgrown with rank weeds four or five feet 

 high. 2d. That the orchard be a sufficiently large one to pay the inter- 

 est on the prime cost of the machine. 3d. That the trees have a clean 

 trunk of some three or four feet." 



For those wishing a full description of the machine, we refer them 

 to the Doctor's own statement in the American ^Entomologist for July 

 1869. 



2. Gathering the fruit and destroying the larvae. As the insect, in 

 its larva or grub form, is yet within the plums when they fall prema- 

 turely from the tree, it is a very obvious mode of exterminating the next 

 year's brood to gather these fallen fruits daily, and feed them to swine, 

 boil, or otherwise destroy them. 



A simple and easy way of covering the difficulty, where there is a 

 plum orchard or enclosure, is that of turning in swine and fowls dur- 

 ing the whole season, when the stung plums are dropping to the 

 ground. The fruit, and the insects contained in it, will thus be de- 

 voured together. This is an excellent expedient for the farmer, who 

 bestows his time grudgingly on the cares of the garden. 



The knots or black gum. In some parts of the country this is a 

 most troublesome disease, and it has, in neighborhoods where it has been 

 suffered to take its course, even destroyed the whole race of Plum-trees. 



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 stop- 

 ped by the compression of the branch by the tumor, and, finally, the 

 poison seems to disseminate 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 pur- 

 ple 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 Morello cherry is also very often in- 

 jured by the same disease, and, in some districts, the sweet cherry also. 



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 larvse 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 trouble- 

 some for many years, the knots have never been known. Secondly, 

 in many cases, the knots have been abundant on Plum-trees, when the 

 fruit was entirely fair and uninjured 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 be- 

 lief, that though the curculio deposits its eggs in the tumors on the 



