THE PRACTICAL ENTOMOLOGIST. 



49 



or a little earlier or later according to the latitude, 

 talcing care to cut a few inches below the affected 

 part, the Black-knot can be checked and probably 

 entirely eradicated ; but if this operation is delayed 

 till August, it will he of no benefit whatever. Hence 

 we can easily account for a circumstance which has 

 puzzled many men wonderfully, viz : that cutting 

 off and burning the diseased twigs is pronounced 

 by some to be a sovereign remedy and by others to 

 be a delusive humbug. Those that do this early 

 enough, find it effectual; those that delay it till too 

 late, find it of no use. 



This perhaps will be sufficient for some few im- 

 patient souls, who take everything upon trust that 

 they see in print, and care nothing about the ra- 

 tionale of a mode of treatment, so long as it be prac- 

 tically available. But for the benefit of that large 

 class of intelligent Agriculturists, who have been 

 deluded by too many quack prescriptions to place 

 much faith in any man's ipse dixit, ^\iA who in any 

 case like to understand the principle of a remedy 

 before they apply it, I subjoin a full account of all 

 that is at present known on this subject, and of the 

 different theories respecting it entertained by differ- 

 ent writers. There exists an American edition of 

 Euclid's " Elements of Geometry," with all the de- 

 monstrations omitted bodily. Those whose taste 

 lies that way, and who prefer assertion unaccompa- 

 nied by proof, can skip the rest of this article. 



Three radically different theories have been 

 broached as to the nature and origin of Black-knot : 

 \st, that it is a mere disease of the tree like the 

 cancer or the gout in the human race, which is the 

 view maintained by Dr. Fitch, the State Entomolo- 

 gist of New York; ind, that it is what naturalists 

 term a " gall," produced by some unknown insect 

 depositing its egg in the twig — ^just as the well- 

 known "oak-apples" are produced by a Gall-fly 

 ( Cynipix) depositing its egg in the bud of the oak — 

 which is the opinion that I myself formerly held 

 and maintained, before I had fully examined into 

 the subject; {Proc. Ent. Soc. Phil. III. pp. 613— 

 618;) and Zrd, that it is what Botanists term an 

 Epiphytous Fungus, growing on the tree as a mush- 

 room or toad-stool grows on the ground, which is the 

 opinion of the botanist Schweinitz, and which has 

 recently been re-asserted by Mr. Glover, the Ento- 

 mologist of the Bureau of Agriculture at Washing- 

 ton, though without adducing any proof of the fact. 

 {Agric. Rep. 1863, p. 572.) This last is the opinion 

 which, upon full enquiry, I have now adopted. 



Before discussing these theories, the facts arrived 

 at by myself in the summer of 1865 must first be 



briefly noticed. It should be premised that the old, 

 dry Black-knot remains on the tree for many years, 

 and that the place to look for new Black-knot is on 

 such trees as have been already attacked and are 

 loaded with old Black-knot, without being as yet 

 completely killed by it. 



\st. By the middle of June the new Black-knot 

 is pretty well developed, and may then be readily 

 distinguished from the old by its dull, opaque, 

 brown-black color, while the old is coal-black and 

 more or less glossy. When cut into, it is found to 

 be fleshy inside, like an apple, but not juicy, and of 

 a pale greenish-yellow color, with fibres radiating 

 from the axis of the twig, while the old Black-knot 

 is internally hard and woody, and of a reddish-brown 

 or rust-red color. The brown-black color of the 

 external surface is retained till the last week in 

 July, when the surface of the new Black-knot be- 

 comes gradually covered all over with little, coal- 

 black, hemispherical plates, about the size of the 

 head of a pin, each of which is a distinct fungus, 

 named long ago by Schweinitz " Sphoeria morbosa.'* 

 Even on the old Black-knot tTiis fungus may be rea- 

 dily seen, at any time of the year, covering its en- 

 tire surface. So far I have added little to the in- 

 formation already published on this subject, except 

 by the specification of dates. But in additiou to 

 these facts, I discovered that about the last of July 

 or the first week in August, there grows from each 

 fungus on the surface of the Black-knot a little cy- 

 lindrical filament about one-eighth of an inch long, 

 which no doubt bears the seed or " spores" as they are 

 technically termed of the fungus, and that these fila- 

 ments very shortly afterwards fall off and disappear, 

 leaving behind them the hemispherical plates, which 

 alone had been hitherto noticed by the Botanists. 

 In another Epiphytous fungus, which grows com- 

 monly and abundantly in Illinois on the Red Cedar, 

 but which differs from the Black-knot in being at- 

 tached to the twig by a very short stalk or pedun- 

 cle, and in being roundish and externally of a red- 

 dish-brown color instead of elongate and black, there 

 is a precisely similar phenomenon ; except that the 

 plates and filaments are very much larger, and that 

 each filament when it falls off leaves a ragged scat 

 behind it. In a single specimen of Black-knot no- 

 ticed August 6th, 1 discovered that the filaments 

 not only covered the entire surface of the Black- 

 knot itself, except where a few of them had already 

 fallen off, but that they were thinly studded over 

 the twig for an inch or two above and below the 

 swollen black part; thus proving that the fungus 

 sometimes extends rather further thau on a cursory 



