_The Frozen-Sap Blight_ is a much more serious difficulty. Its nature and origin are now pretty well settled. In every tree there are two currents of sap: one passes up through the outer wood, to be digested by the leaves; the other passing down in the inner bark, deposites new wood, to increase the size of the tree. Now, in a late growth of this kind of wood, the process is rapidly going on, at the approach of cold weather, and the descending sap is suddenly frozen, in this tender bark and growing wood. This sudden freezing poisons the sap, and renders the tree diseased. The blight will show itself, in its worst form, in the most rapid growing season of early summer, though the disease commenced with the severe frosts of the previous autumn. Its presence may be known by a thick, clammy sap, that will exude in winter or spring pruning, and in the discoloration of the inner bark and peth of the branches. On limbs badly affected on one side, the bark will turn black and shrivel up. But its effects in the death of the branches only occur when the growth of the tree demands the rapid descent of the sap: then the poisoned sap which was arrested the previous fall, in its downward passage, is diluted and sent through the tree; and when it is abundant, the whole tree is poisoned and destroyed in a few days; in others more slightly affected, it only destroys a limb or a small portion of the top. Another effect of this fall-freezing of sap and growing wood, is to rupture the sap-vessels, and thus prevent the inner bark from performing its functions. This theory is so well established, that an intelligent observer can predict, in the fall, a blight-season the following summer. If the summer be cool, and the fall warm and damp, closed by sudden cold, the blight will be troublesome the next season, because the plentiful downward flow of sap, and rapid growth of wood, were arrested by sudden freezing. If the summer is favorable, and the wood matures well before cold weather, the blight will not appear. This is of the utmost practical moment to the pear-culturist. Anything in soil, situation, or pruning, that favors early maturity of wood, will serve as a preventive of blight; hence, cool, moist situations are not favorable in climates subject to sudden and severe cold weather in autumn. Root-pruning and heading-in, which always induce early maturity of wood, are of vast importance; they will, almost always, prevent frozen-sap blight. If, in spite of you, your pear-trees will make a late luxuriant growth, cut off one half of the most vigorous shoots before hard freezing, and you will check the flow of sap, by removing the leaves and shoots that control it, and save your trees. If blight makes its appearance, cut off at once all the parts affected. The effects will be visible in the wood and inner bark, far below the external apparent injury. Remove the whole injured part, or it will poison the rest of the tree.