BULLETIN OF THE BUSSEY INSTITUTION, 451 
the month of March, 1875, we went to a hedge of wild cherries, in 
search of specimens of the knot, but found them only on one tree, 
although very abundant on that. When the trees had leaved out, a 
few weeks later, we passed by the hedge and observed that all the 
trees but one were Prunus serotina; and that one (the same from 
which we had gathered specimens of the knot) was P. Virginiana. 
Prunus Pennsylvanica, L., the bird cherry, is subject to the disease ; 
and, also, Prunus Americana, Marsh, the wild plum, on the authority 
of Prof. C. E. Bessey, Walsh, and others. Harris makes the statement 
that the last-named species is not subject to the knot; but he was proba- 
bly mistaken, as so many others affirm the contrary. Prunus maritima, 
Wang, the beach plum, as far as our experience in southern Massa- 
chusetts goes, is free from the knot. Of Prunus Ohickasa, Michx., we 
have no definite information. The single case reported by Walsh of 
a black knot occurring on a peach-tree is extremely doubtful. 
If we turn now to the cultivated varieties of plums and cherries, we 
also find that some are susceptible to the disease and others are not. 
Without doubt, the morello cherry is more susceptible than any other 
variety, and next in order comes the mazzard. Whether any other varie- 
ties of cultivated cherries are liable to the knot, we cannot say, speaking 
from our own experience, and the accounts published in the journals are 
so indefinite and contradictory that one does not know what to believe. 
That some varieties are free from the disease, we know to bea fact; for 
we have very frequently seen orchards of other varieties than the mo- 
rello and black mazzard entirely free from the knot, although, in some 
cases, infected choke cherries were actually growing under the cultivated 
trees, and plum-trees in the neighborhood were badly diseased. 
We have little hesitation in asserting, judging from our observations 
and the more reliable reports in the agricultural journals, that there is 
no variety of cultivated plum which is not subject to the black knot. 
To suppose that the disease came from the wild plum, rather than the 
wild cherry, is quite superfluous; for, in the region of Boston, where 
the black knot has almost completely destroyed the cultivated plums, the 
wild plum is very rare, if it occurs at all, and the disease must have 
come from the choke cherry or the bird cherry. We have made 
direct experiments to show that the spores of the knot on the choke 
cherry will germinate and produce the knot in healthy plum-trees, and 
the results will be given in a future number of the Bulletin. 
