G18 [December 



of Dr. Fitcli's positive asseveration I cannot help believing-, and whieli 

 Peck and Harris and others have believed before me, — it must in all 

 probability, if we assume the truth of the above law, be the work of a 

 Gall-gnat. 



That the Black-knot is not, as has been supposed by many, the work 

 of the Curculio, has been sufficiently demonstrated by Dr. Fitch from 

 the fact, that specimens occur without any larvae at all in them. It 

 might be thought at first sight, that the same fact would bear equally 

 hard against the hypothesis of its being the work of a Gall-gnat. But 

 the singular phenomena with regard to several imdoubtedly Ceeido- 

 myidous galls, which I have ah'eady referred to — no matter to what 

 cause we choose to attribute them — take the case of the (lall-gnats out 

 of the general rule. I will endeavor in this coming spring to examine 

 the recent Black-knots and see whether, as I suspect, they are really 

 inhabited by the larvae of Gall-gnats, and if so to rear the perfect Gall- 

 gnat from them. 



If, then, as I have little doubt, the Black-knot be really a mere Ce- 

 cidomyidous gall, we can at once solve a problem which has perplexed 

 Economic Entomologists for the last half century, viz : how to get rid 

 of it. All that is required in order to save onr diseased Plum-trees 

 from a premature death, is simply to cut off and burn the galls before 

 the Cecidomyia makes its appearance in the imago state. Cutting off 

 and burning the galls (tfter the Cecidomyia has made its appearance 

 in the imago state, will be just labor lost; for the eggs are then already 

 laicT, that will produce the next year's crop of Black-knot. 



It will be noticed, that contrary to the hitherto generally accepted 

 belief, I have not, in the reasonings ju.st now adduced, enumerated 

 Snout-beetles ( Curculio nidse) as amongst the true Gall-making in- 

 sects. I doubt very much whether any true Galls are produced by 

 CurcuHonidse. The holes that these last insects bore are bored, 

 not by any ovipositor, but by their snouts ; and to suppose that they 

 can originate true galls, presupposes that they have the faculty of 

 voiding from their snouts poisonous matter, similar to the poisonous 

 matter that I have shown to be deposited along with the egg by the 

 ovipositor of Cynijjs, {Froc. EiU. Soc. Fhil. II. pp. 472 — 6), which is 

 contrary to analogy. In all probability the various Curculionidae, that 

 are stated by authors to produce galls, are in reality nothing but inqui- 



