"It is a black, puffy, irregular swelling on the twigs and smaller limbs of plum and cherry trees, and, in one instance that came under my personal observation of peach trees, making its first appearance in the latitude of New York early in June, and attaining its full growth by the end of July. Usually a tree, that is attacked in this manner, is affected worse and worse every year, until it is finally killed; and wherever one tree of a group is affected, the malady usually spreads to them all in process of time. In 1865 whole cherry orchards were destroyed in Western New York by this disease, and I have myself seen many groups of wild plum trees in Illinois that were gradually perishing by it; but in Southern Ohio, as I am told, the Black-knot is never met with. In the Eastern States it has been observed from time immemorial, and various contradictory opinions have been broached as to its real nature and origin. "In 1865 I watched the Black-knot carefully through all its stages, from its earliest commencement to its complete maturity, experimenting at the same time on numerous specimens collected week after week, so as to ascertain what insects bred in it. The practical conclusion I have arrived at, is simply this:--_If the diseased twigs are all cut off and destroyed early in July in the latitude of New York, or a little earlier or later according to the latitude, taking 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 be 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 impatient souls, who take everything upon trust that they see in print, and care nothing about the _rationale_ of a mode of treatment, so long as it be practically 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_, and 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 different writers.