BLACK KNOT. 



THE BLACK KNOT ON THE PLUM.* 



liY WM. MKRVINE, UTIC.V. 



^fANV causes b-ave been assigned for tbe disease in question, none oi" wbieb, so far as 

 my intbrmatioD extends, are satisfactory. Some bave supposed it to be occasioned by 

 di¥;easod sap, or vegetable ulcer; some, tbat it is tbe work of tbe curcubo; otbers, 

 witb more plausibiHty, assert tbat it is tbe result of porsou infused by tbe minute sting 

 of an insect. But none of tbose entertaining tbe latter opinion bave desa-ibed tbo 

 kind of insect, or its cbaracteristics ; nnd it is tbcrefore fair to nssume tbat tlieir 

 belief rests upon conjecture alone. Tbo latter opinion, bowever, witb tbe exception 

 of tbe minuteness of tbe sting, is correct. It will be permitted me to say, tbat I 

 believe myself to be first in determining tbe fact, and in ascertaining, certainly, tbe 

 babits and cbaracter of tbe insect. I will, tberefore, proceed as briefly as may be, and 

 witbout regard to possible cbarges of egotism, for asserting in opposition to many 

 scientific men on tbe subject, wbat I know beyond a doubt to be the origin of tbe 

 excrescence, or tumor, and to describe the insect which causes it, its babits, and the 

 best method of guarding against its attacks and increase. 



Tbe insect here referred to belongs, I believe, to tbe Ilymonoptera class, and is 

 about an inch in length ; color, pale yellow ; has four wings, and bind legs resembling 

 tbose of the grasshopper, which seem designed for similar use ; and, although furnished 

 with wings, it uses them only, so far as I have discovered, for calling its mates. This 

 it efteets by shrill notes through the medium of vibrations, created by a rapid motion 

 of them, and which affbrds tbe means of tracing it. The abdomen of the female is 

 much larger than tbat of tbe male, in the extremity of which is concealed a sting of 

 about a quarter of an inch in length, with which it pierces any shrub or limb selected 

 as a receptacle for its eggs — often numbering a dozen or more, which are deposited 

 with some acid poison in seperate cells, longitudinally. From these eggs the larvae 

 are batched — change to the pupa?, or chr3-salis state, and emerge during the ensuing 

 June. 



Tbe excrescence does not appear until after the escape of tbe insects, tbe swelling 

 of which is caused by the circulation of tbe sap being arre^^led in its natural course 

 by tbe poison infused, which flows round tbe punctured parts, extravasates, and 

 gi'adually forms tbe tumor. On dissecting ojie of these tumors, a grub may be some- 

 times found, but it does not cause the excrescence. Any one may satisfy himself of 

 the truth of the foregoing remarks by observing tbe ajjpearance of the insect during 

 tbe months of August and September, especially tbe latter, tbat being tbe season of 

 coition, when it may be found making its deposits ; these, on being completed, are 

 varnished over witb a water-proof substance, presenting a dark, glazed appearance, 

 by which it may be known, and on carefully splitting a stung limb in tbe direction 

 of the perforations early in June, the insect may be found in the larvaj state. 



bave carried on for two years past a war against this insect, and never sufier one (^ 



* This paper was read before the the Utica Scientific Association the past winter. 



