STATE AGRICULTURAL SOCIETY. 
605 
still abroad as numerous as before, the presumption becomes very strong, 
that they must have other places for cradling their young, in addi¬ 
tion to the fruit. And the enquiry thus arises, whether the curculio 
is known to breed elsewhere than in young fruit. To this comes the reply, 
that there is one other situation in which it is well ascertained they do 
breed, with avidity, to wit, in those singular excrescences on plum and 
cherry trees, called the black knot. And as the curculio has so often been 
said to cause these excrescences, and the opinion is still entertained by 
many persons that they are produced by some other insect, if not by this, 
I may here turn aside to give some account of this remarkable disease— 
since, to ascertain whether it really was caused by an insect or not, I have ex¬ 
amined it more closely, perhaps, than has ever been done by any other person. 
This black-knot excrescence is a disease peculiar to the plum and cherry 
trees in this country. It is a large, irregular, black, wart-like excres¬ 
cence, which grows upon the limbs, causing the death of all the limb above 
it, and extending down the limb farther and farther every year till the 
whole branch is destroyed, other limbs at the same time becoming affected 
in the same manner, and also the limbs of other trees in the vicinity. If 
it is neglected, it in a few years kills the tree. 
This disease commences upon the small limbs, the wood of which is but 
a year or two old. It is recognized at first by a slight swelling of the bark 
at a particular point, on the upper side of the limb, which begins in autumn 
and remains stationary through the winter. When the sap begins to cir¬ 
culate in the spring this swelling increases, rupturing the cuticle or thin 
outer skin of the bark, and continuing to grow and puff out till in June 
some inches in length of the limb at the place affected is three or four 
times its diameter elsewhere. The bark and a portion of the wood under 
the bark arc the tissues involved in this disease, both the bark and woody 
fibres being changed into a spongy substance, but not at all juicy like the 
fruit of a tree. This spongy substance is of a pale yellow color when 
growing, changing to coal black when it is mature; and then a minute 
black fungous plant, resembling the head of a pin grows upon its surface. 
You will see, on looking at these black knots, that their whole surface is 
covered and crowded with little smooth black granules, which are the fun¬ 
gus plant alluded to. They are a species of the genus Sphceria, and are 
described by that profound botanist, the late Rev. L. de Schweinitz, under 
the name Sp/ian-ia morbosa. It is a curious fact that the surface of these 
exerescenses, when mature, are always covered with this plant, which never 
grows, or at least has never been found, in any other situation. 
There has been much speculation as to the cause and the true nature of 
these excrescences, they are so unlike anything else with which we are 
acquainted. Most persons suppose them to be of insect origin. The larvae 
of the curculio are almost always found in them, and these larvae consume 
nearly all of the spongy matter of the warts, but do not touch the little fungus 
growing on their surface, which remains, forming a kind of shell, after the 
whole inside is devoured. But as these excrescences are sometimes found 
