324 THE PEAR. 



elsewhere. 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. 



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 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 decay- 

 ing, as if suddenly killed. If these diseased parts are cut 

 off, the inner bark and heart- wood will be found dark and 

 discoloured 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 gra- 

 dually decline, 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 ; 2nd, the downward 

 current, which descends through the inner bark, (or liber,) 

 forming a deposite 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 .ate. While 

 the sap vessels are still filled with their fluids, a sharp and sud- 

 den freezing takes place, or is, perhaps, repeated several times, 

 followed, in the day time, by bright sun. The descending cur- 

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

 difficulty ; it chokes up the sap-vessels, freezes and thaws 



* Being distributed towards the centre of the stem by the medullary rays 

 which communicate from the inner bark to the pith. 



t Which always happens previously to a summer when the blight, is very pre- 

 valent, and will be remembered, by all, as having been especially the case in the 

 utumri of 1843, which preceded the extensive blight of the past season. 



