WINTER-KILLING.--A most serious evil, both to the nurseryman and orchardist, is the severe injury sometimes done to the trees by frost. This is commonly known by the term "winter-killing," which has, at times, destroyed millions of trees, and thus blighted the hopes of long-continued labor and large investments of capital. Some orchardists have been disheartened, and have given up in despair. The investigation of the causes of this disaster, and the conditions under which it occurs, will be of great value to future planters; and though, perhaps, we have not yet at command sufficient data for the full explanation of the phenomenon, it may be well to look into the attendant circumstances that have been observed; and as some of the most important considerations depend upon the soil and exposure, they may be well introduced in this place. I have already alluded to the theory, that the north hillsides maintain a later growth than other situations, and have stated that the facts do not sustain the position. The warm exposures on southern slopes and sheltered nooks, are apt to favor the premature starting of the sap in the mild weather that often occurs during the winter, in our changeable climate. On the prairies, and on flat lands elsewhere, an excess of humidity in the soil will contribute to this disaster; and in such situations we may often observe the most terrible destruction following a great and sudden change of temperature. Exposure to long-continued cold, with severe winds, seems to dry up the juices of the plants, in some instances, and thus effect their destruction. This, in the far North, is believed to be a frequent cause of the evil. The condition of the tree upon the access of severe cold is too important a subject to be lost sight of, and has already been alluded to. Of any given variety, the more perfectly dormant the plant, and the more complete its condition of hybernation, the greater will be its immunity from this evil. The atmospheric changes and conditions we can not control, and we can modify them only in a very limited degree, by hedges, by timber-belts, and by evergreen screens, the value of which begins to be appreciated. The state of the soil, as to its moisture, is under our control, and by thorough and surface-drainage, we may obviate one very important condition that conduces largely to the injury under consideration--the excess of moisture in and upon the soil. The more perfect ripening of the wood, is likewise a matter of great moment, and this is also subject to our control, particularly in young trees in the nursery and orchard.