120 [Assembly 



that the liquid be so applied as to reach the under surface of the 

 leaves where the mites occur. It is worthy of note that in the above 

 quince attack most of the mites were observable upon the upper 

 sides of the leaves. 



The attack of this little mite is undoubtedly far more frequent than 

 is supposed, for the reason that the ci'eature can hardly be seen with 

 the naked eye, and an ordinary pocket magnifier only shows it as an 

 animated speck. A nasturtium in my garden, which had been for 

 some time showing yellow leaves or yellow blotches upon the leaves 

 without any apparent cause, was found, upon examination for this 

 mite, to show its presence in considerable numbers, in the larval and 

 in the adult stages. As an experiment, one of the infested leaves 

 was dipped in water in which some soap had been stirred, with the 

 result of speedily killing all of the mites upon it. 



The Black-Knot of the Plum-Tree and its Guests. 



A piece of a limb of a plum-tree having the well-known " black 

 knot" upon it was sent to me in July, with the inquiry of the kind 

 of insect that caused its gi'owth, and if there was any remedy for the 

 attack. The tree from which the piece was taken was wholly free 

 from it in the spring. 



It is a very common belief that the black-knot, so common on plum 

 and cherry trees, and which causes annually the death of thousands 

 of these trees throughout the United States, is produced by an insect 

 attack. There is some foundation for this popular belief in the fact 

 that insect larvas are frequently found within it. These, however, 

 are not the cause of the obnoxious growth, but merely enter it for 

 food or shelter during its early formation. 



The common curculio, Conotrachelus nenuj)Jia7\ which is so 

 destructive to the fruit of the plum-tree, has been bred by Dr. Fitch, 

 Mr. Walsh, and others from larvee inhabiting the black-knot. Mr. 

 Walsh has also bred from it five other species of insects — two of 

 flies, viz. : Ceratopogon sp., and Dijplosis sej)temmaGulata Walsh, 

 and three species of Ismail moths, probably of the genus Hedya 

 {Practical Entomologist, i, p. 50). Larvae have on different occa- 

 sions been taken by me from their cocoons made upon the margin 

 of the black-knot, where it was overgrowing an excision of the pre- 

 ceding year, and the empty pupa-cases of evidently the same moth 

 have been seen protruding from the knot. The moth, unfortunately, 

 was not obtained, but it was probably that of ^Egeria pictipes Grote- 

 Rob., which is known to infest plum-trees sometimes in great num- 

 bers {North American Entomologist, i, 1879, pp. 17-21, with plate). 



Although it is not many years since the origin of the black-knot 

 was in doubt, for even in 1859, Dr. Fitch pronounced it not a fungus 

 {Trans. AT. Y. State Agricultural Society for 1859, xix, p. 606), it is 

 now known to be a fungus growth of a species long ago described and 

 named as Sj)h(JBria morbosa Schw, Quite recently it has been trans- 



