156 HICKORY. LIMBS HICKORY-GALL APHIS. 



frequent occurrence that it has probably been observed by many 

 of my readers. About fifteen years ago I first noticed a tree upon 

 my farm which was severely affected by this disease, and which 

 has continued to suffer from it annually down to the present time. 

 Within two rods of this tree are two others which have remained 

 wholly unaffected, and have regularly produced a fair yield of 

 fruit, whilst not a single nut has been matured upon the diseased 

 tree. The excrescences upon the limbs at the time of gathering 

 the fruit in autumn, which was the only time I had heretofore 

 noticed them, are black, ragged, leathery and cup- shaped, having 

 a marked resemblance to some of the species of fungi of the genera 

 Peziza, Cenangium, and their kindred. But whether they really 

 were of a vegetable nature or were the work of insects I was un- 

 able to determine from their appearance at that period of the year. 

 Mr. T. B Ashton having recently informed me. that he had al-. 

 ways met with the Elegant weevil {Conotrachelus elegans Say), 

 a species most nearly related to the Plum weevil (C. JVenuphar 

 Herbst), exclusively upon these diseased hickory trees, although 

 I had myself captured it upon butternut, hazlenut and other foli- 

 age, I resolved the present year to investigate these excrescences 

 at the commencement of their growth, and ascertain their cause, 

 not knowing but it might throw some light upon the mooted 

 origin of the black knots upon the plum and cherry. I have been 

 successful in this examination, and have ascertained that although 

 these excrescences are of insect origin, the weevil alluded to has 

 no direct conection with them, and if it really is more common 

 upon these diseased walnut trees than elsewhere, as Mr. Ashton's 

 observations indicate, it is only because, like many other insects, it 

 prefers diseased and weakened vegetation to that which is healthy 

 and of rank vigorous growth. 



The insect which forms these excrescences is a female plant- 

 louse, and her proceedings and the effect which they produce is 

 truly wonderful. Hatching probably from eggs that were laid 

 the preceding autumn, each individual, early in the season sta- 

 tions herself at a particular spot, either upon the mid-vein of one 

 of the leafets, upon the leafstalk, or still farther down, upon the 

 green succulent twig which is the growth of the present year. 



