STATE AGRICULTURAL SOCIETY. 361 



PLUM. LIMBS. 



and of a triangular shape, resembling that of a beech nut, and of 

 a uniform pale green color without any spots or stripes. Like 

 other tree hoppers (which name I apply to insects of the family 

 Membracidai) and leaf hoppers {Tettigoniidce) these insects when 

 approached by the finger give a sudden strong leap and become 

 lost to the view. 



I am indebted to George Clark, Esq., of East Springfield, Otsego 

 county, for the above information respecting the work of an insect, 

 which, from his description of it, will be the species which I have 

 named; but specimens which were sent to Dr. Harris a few years 

 since, were said to be the Ceresa hubalus (See No. 22) in a letter 

 from him, published at that time in the Journal N. Y. State Ag. 

 Society. Mr. C. informs me the insect he alludes to has no pro- 

 jecting points resembling horns, anteriorly, and is of a uniform pale 

 or pea green color, destitute of any spots or marks, whereas the 

 hubalus when alive is deeper green, freckled with whitish dots, 

 and has a pale yellow streak from the horn backwards along each 

 side. The bubalus, however, is closely related to this insect and 

 is common upon the fruit and other trees in our yards, and both 

 these species it is probable cut the bark of the plum and other 

 trees in the manner stated above, and w^e presume the plum 

 weevil also makes a curved incision in the limbs of the plum 

 similar to those we have noticed in the pear. 



Mr. Clark has for several years given particular attention to the 

 slits which this tree hopper makes in the bark of the plum and is 

 confident these wounds are the foundation of that most fatal maladv 

 the " Black knot." The examinations of this disease wliich I ha\'e 

 made have convinced me that the different insects whicli writers 

 in our agricultural periodicals have pointed out as producing these 

 excrescences are species which are wholly innocent of the crime 

 laid to their cliarge. I have w^atched the growth of the excres- 

 cences from tlieir first commencement to their full develo])ment, 

 without being able to detect the least indication of an insect in 

 some of them, and in otlier instances where insects have been 

 present it was plain they were there as a consequence and not as 

 a cause of the disease. The fact, however, that tree hoppers and 

 the phim weevil make incisions in the bark at tlie same place 

 where this disease shows itself, calls fur future investigations, to 



