894 THE PLTTM. 



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

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

 high. 2d. That tlie 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 descrijition of the machine, Ave refer them 

 to the Doctor's own statement in the American J^ntotJioIof/ist for July, 

 1869. 



2. Gntherhig the fruit and destroy trig tlte larvcp. As the insect, in 

 its larva or grvib 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 Avhole season, when the stung plums are drop])ing to the 

 ground. The fruit, and the insects contained in it, will th\is 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 hlach gum. In some paints of the country this is a 

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

 sufl'ered 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, finall}', 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 trimk, breaking out in various parts of it. 



The soits of plum most attacked by this disease are those Avith pur- 

 ple fruit, and we liaA^e never know^n 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 thefu 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 cheriy 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-wecAdl that stings the fruit ; the second brood 

 of which, finding no fruit I'eady, choose the branches of this tree and 

 the cherry. This observation Avould seem to be confirmed by the 

 fact that the grubs or larva? of the plum-AvecAal are frequently found in 

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



On the other hand, the folloAviug facts are Avoi-th}' of attention. 

 First, in some parts of the country, Avhere 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, Avhen the 

 fruit was entirely fair and uninjiired by the curculio, CA'en upon the 

 same branches. 



These facts seem so irreconcilable Avith the opinion that the curculio 

 pi-oduces 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 



