414 
THE PEAR. 
originally suggested by Mr. Lowell, which we and many others 
have pursued with entire success, when the other form of the 
disease was not also present. The remedy consists, at the very 
first indications of the existence of the enemy , in cutting off and 
burning the diseased branch, a foot below the lowest mark of 
discoloration. The insect is usually to be found at the bottom 
of this blackened point, and it is very important that the 
branches be removed early, as the Scolytus is now about emerg- 
ing from his burrow, and will speedily escape us, to multiply his 
mischief elsewhere. If there is much appearance of the insect 
Might, the tree should be examined every noon, so long as there 
are any indications of disease, and the amputated branches car- 
ried at once to the fire. 
II. The frozen-sap blight. We give this term to the most 
formidable phase of this disease that affects the pear tree. 
Though it is, by ordinary observers, often confounded in its 
effects, with the insect blight, yet it has strongly characteristic 
marks, and is far more fatal in its effects. 
The symptoms of the frozen-sap blight are the following: 
First. The appearance, at the season of winter or spring prun- 
ing, of a thick , clammy sap, of a sticky nature, which exudes 
from the wounds made by the knife ; the ordinary cut showing 
a clean and smooth surface. 
Second. The appearance, in the spring, on the bark of the 
trunk or branches, often a considerable distance from the ex- 
tremities, of black, shrivelled, dead, patches of bark. 
Third. In early summer months, the disease fully manifests 
itself by the extremities shrivelling, turning black, and decay- 
ing, as if suddenly killed. If these diseased parts are cut off, 
the inner bark and heart-wood will be found dark and dis- 
coloured some distance below where it is fresh and green out- 
side. If the tree is slightly affected only, it may pass off with 
the loss of a few branches, but if it has been seriously tainted, 
the disease, if not arrested, may, sooner or later, be carried 
through the whole system of the tree, which will gradually de- 
cline, or entirely perish. 
To explain the nature of this disease, we must first premise 
that, in every tree, there are two currents of sap carried on, 1st, 
the upward current of sap, which rises through the outer wood, 
(or alburnum ,) to be digested by the leaves ; 2d, the downward 
current, which descends through the inner bark, (or liber ,) 
forming a deposit of new wood on its passage down.* 
Now let us suppose, anterior to a blight season, a very sudden 
and early winter, succeeding a damp and warm autumn.f The 
* Being distributed towards the centre of the stem, by the medullary 
rays which communicate from the inner bark to the pith. 
f Which always happens previously to a summer when the blight is 
