190 AMERICAN POMOLOGY. 



they apply it, I subjoin a full account of all that is at 

 present known on this subject, and of the different theo- 

 ries respecting it entertained by different writers. 



" Three radically different theories have been broached 

 as to the nature and origin of Black-knot : 1st, that it is 

 a mere disease of the tree, like the cancer or tlie gout in 

 the human race, which is the view maintained by Dr. 

 Fitch, the State Entomologist of New York ; 2d, that it 

 is what naturalists term a " gall," produced by some un- 

 known insect depositing its eggs in the twig just as the 

 well-known " oak-apples " are produced by a GaJl-fly, 

 (Cynips)) depositing its egg in the bud of the oak 

 which is the opinion that I myself formerly held and main- 

 tained, before I had fully examined into the subject ; (Pro- 

 ceedings JEJnt. Soc., Phil., Ill, p.p. 613-618 ;) and 3d, that 

 it is what botanists term an epiphytous fungus, growing 

 on the tree as" a mushroom or toad-stool grows on the 

 ground, which is th^ opinion of the botanist Schweinitz, 

 and which lias recently been re-asserted by Mr. Glover, 

 the Entomologist of the Bureau of Agriculture at Wash- 

 ington, (Ag'lRep., 1863, p. 572.) This last is the opinion 

 which, upon full inquiry, 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 the new Black-knot is on such trees as 

 have been already attacke.d and are loaded with old Black- 

 knot, without being as yet completely killed by it. 



" 1st. By the middle of June the new Black-knot is 

 pretty well developed,* and may then be readily distin- 



