440 BULLETIN OF THE BUSSEY INSTITUTION. 
No. 24.— The Black Knot. By W. G. Fartow, Assistant 
Professor of Botany in Harvard University. 
Wirunout doubt, the most striking disease of vegetable origin occur- 
ring on fruit-trees in this couritry is that commonly known as the black ~ 
knot. The disease takes its name from the unsightly, black, wart-like 
excrescences with which every one is familiar on plum-trees and differ- 
ent kinds of wild and cultivated cherries. It is found in all parts of our 
country east of the Rocky Mountains, and is so common and destruc- 
tive, that, in some districts, one seldom sees a plum-tree free from the 
knot. An idea may be formed of the small crop of plums now: 
raised in New England from the fact, that two dollars and a half were 
given in Boston last autumn for a peck of damsons for preserving. 
In some parts of New England, particularly in Maine and along the 
sea-coast, the raising of cherries has also been almost abandoned in 
consequence of the ravages of the black knot. The disease is pe- 
culiar to America, and has been the bane of fruit-growers from early 
times; but, although much has been written in agricultural papers 
about its injury to the fruit crop, the subject has been almost entirely 
neglected by botanists. In the present paper, we shall consider the 
cause and prevention of the knot, and the question whether the 
disease is the same on plums and cherries. As a preliminary step, it 
will be well to trace the development of the knot as it occurs on a 
single species, and, for this purpose, the choke cherry, Prunus Vir- 
giniana, L., may be selected. 
The choke cherry abounds in all the hedges and thickets of New 
England, and is recognized by its thin ovate or obovate, abruptly acu- 
minate leaves, and reddish, harsh-tasting fruit, in racemes. In winter, 
its branches are generally plentifully covered with the knots, which 
are partly concealed by the foliage in summer. ‘They are black, 
and vary in size from half an inch to eight or ten inches, or even a 
foot, in length, and are about two inches in circumference. In some 
cases, they completely surround the branch on which they are growing, 
but more frequently they extend only part way round; their course, 
when very long, being usually somewhat spiral round the stem. If they 
