THE PLUM. 
357 
a most troublesome disease, and it lias, in neighbourhoods where 
it has been suffered to take its course, even destroyed the whole 
race of plum trees. 
The knots is a disease attacking the bark and wood. The 
former at first becomes swollen, afterwards bursts, and, finally, 
assumes the appearance of large, irregular, black lumps, with a 
hard, cracked, uneven surface, quite dry within. The passage 
of the sap upwards, becomes stopped by the compression of the 
branch by the tumour, and, finally, the poison seems to dissemi- 
nate itself by the downward flow of the sap through the whole 
trunk, breaking out in various parts of it. 
The sorts of plum most attacked by this disease, are those 
with purple fruit, and we have never known the green or yellow 
fruited varieties infected, until the other sorts had first become 
filled with the knots. The common horse plum, and damson, 
appear to be the first to fall a prey to it, and it is more difficult 
to eradicate it from them, than from most other sorts. The 
common Morelia cherry is, also, very often injured by the same 
disease in Pennsylvania. 
There is yet some doubt respecting the precise cause of these 
knotty excrescences, though there is every reason to think it is 
the work of an insect. Professor Peck and Dr. Harris believe 
that they are caused by the same curculio or plum-weevil that 
stings the fruit ; the second brood of which, finding no fruit 
ready, choose the branches of this tree and the cherry. This 
observation would seem to be confirmed by the fact that the 
grubs or larvae of the plum-weevil are frequently found in these 
warts, and that the beetles have been seen stinging the 
branches. 
On the other hand, the following facts are worthy of atten- 
tion. First, in some pails of the country, where the curculio 
has been troublesome for many years, the knots have never been 
known. Secondly, in many cases, the knots have been abun- 
dant on plum trees, when the fruit was entirely fair and unin- 
jured by the curculio, even upon the same branches. 
These facts seem so irreconcilable with the opinion that the 
curculio produces both these effects, that we rather incline at 
present to the belief, that though the curculio deposits its eggs 
in the tumours on the branches while they are yet soft and tender, 
yet it is not to the curculio, but to some other insect or cause, 
that we owe this unsightly disease. 
Practically, however, this is of little account. The experi- 
ence of many persons, besides ourselves, has proved, most satis* 
factorily, that it is easy to extirpate this malady, if it is taken 
in season, and unremittingly pursued. As early as possible in 
the spring, the whole of the infected trees should be examined, 
and every branch and twig that shows a tumour, should be cut 
off, and ini mediately burned. Whatever may be the insect, we 
