646 THE PEAR. 



The remedy for the insect bligJU is very distinct. It is that 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 emerging from 

 his burrow, and will speedily escape us, to multiply his mischief else- 

 where. If there is much appearance of the insect blight, the tree 

 should be examined every noon, so long as there are any indications of 

 disease, and the amputated branches carried at once to the fire. 



2. THE FROZEX-SAP BLIGHT. We give this term to the most for- 

 midable phase of this disease that affects the pear-tree. Though it is by 

 ordinary observers often confounded in its affects 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 pruning, 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 extremities, of black, 

 shrivelled, dead patches of bark. 



Third. In early summer months the disease fully manifests itself 

 by the extremities shrivelling, turning black, and decaying, as if sud- 

 denly killed. If these diseased parts are cut off, the inner bark and 

 heart-wood will be found dark and discolored some distance below 

 where it is fresh and green outside. 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 summer having 

 been dry, the growth of trees was completed early, but this excess of 

 dampness in autumn forces the trees into a vigorous second growth, 

 which continues late. While the sap-vessels are still filled with their 

 fluids, a sharp and sudden freezing takes place, or is, perhaps, repeated 

 several times, followed, in the daytime, by bright sun. The descend- 

 ing current of sap becomes thick and clammy, so as to descend with 



* 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 very 

 prevalent, and will be remembered by all as having been especially the 

 case in the autumn of 1843, which preceded the extensive blight of the next 

 season. 



