If the soil by its ungenial character induces the disease, the obvious and only remedy is its amelioration; and if the subsoil is the cause of the mischief, the roots must be prevented striking into it. In all cases it is the best practice to remove the tap root. Many orchardists pave beneath each tree with tiles and broken bricks. If the trees are planted shallow, as they ought to be, and the surface kept duly fertile, there is not much danger of the roots striking into the worse pasturage of the subsoil. On this point the experience of Mr. W. Nichol, the gardener at Newick-place in Sussex, agrees with my own. He says, that the canker may be avoided in most instances, by paying proper attention to the soil in which the tree is planted. Canker, he thinks, will seldom occur if the surface soil is good, for in that case the roots will never descend into the prejudicial subsoil, but spread out their radicles near the surface, where they find food most abundant. If this is not kept up, the roots descend into the obnoxious substratum, and the disease assuredly follows.

It remains for me to detail the course of treatment that I have always found successful in effecting a cure in any variety, not decrepid from age, if the canker has not spread to the roots.

Having completely headed down, if the canker is generally prevalent, or duly thinned the branches, entirely removed every small One that is in the least degree diseased, and cut away the decayed parts of the larger, so as not to leave a single speck of the decayed wood, I cover over the surface of each wound with a mixture while in a melted state, of equal parts tar and rosin, applying it with a brush immediately after the amputation has been performed, taking care to select a dry day. I prefer this to any composition with a basis of cow-dung and clay, because the latter is always more or less absorbent of moisture, and is liable to injury by rain and frost, causing alternations of moisture and dryness to the wounds, that promote decay rather than their healing, by the formation of new wood and bark. The resinous plaster seldom or never requires renewal. Mr. Forsyth, the arch-advocate of earthy and alkaline plasters, finding that they promoted decay, if applied to the wounds of autumn-pruned trees, recommends this important act of cultivation to be postponed to the spring. Such a procrastination is always liable to defer the pruning until bleeding is the consequence. If a resinous plaster be employed, it excludes the wet, and obviates the objection to autumnal pruning.

Mr. Forsyth's treatment of the trunks and branches of trees, namely, scraping from them all the scaly dry exuvia of the bark, is to be adopted in every instance. He recommends them to be brushed over with a thin liquid compound of fresh cow-dung, soap-suds, and urine, but I very much prefer a brine of common salt; each acts as a gentle stimulus, which is their chief cause of benefit, and the latter is more efficacious, destroying insects, and does not, like the other, obstruct the perspiratory vessels of the tree. The brine is advantageously rubbed in with a scrubbing or large painter's brush. Some persons recommend a liquid wash, containing, as prominent ingredients, quick-lime and wood-ashes, which, as the disease arises from an over-alkalescent state of the sap, cannot but prove injurious, and aggravate the disease. Mr. Forsyth, formerly gardener at Kensington Palace, made a considerable sensation at the close of the last and at the commencement of the present century, by the wonderful effects produced upon trees, as he asserted, by the following composition, used as a plaster over the wounds from which the decayed or cankered parts had been cut out: - One bushel of fresh cow-dung; half a bushel of lime rubbish, that from ceilings of rooms is preferable, or powdered chalk; half a bushel of wood-ashes; one-sixteenth of a bushel of sand; the three last to be sifted fine.

The whole to be mixed and beaten together until they form a fine plaster.

Mr. Forsyth received a parlimentary grant of money for his discovery; but this, as Mr. Knight observes, "affords a much better proof that he was paid for an important discovery, than that he made one".

It has been very ingeniously suggested, that if a destruction of the bark by external violence, and consequently likely to terminate in canker, has occurred, it would be a good plan to insert, as in budding, a piece of living bark, exactly corresponding to the excision, from a less valuable tree.

In conclusion, I would enforce upon the orchardist's attention the importance of obtaining his grafts or buds from trees not affected by the disease, because apparently it is hereditary; and, although after-culture may eradicate the malady, it is always far better to avoid the infection, than to have to employ a specific. Having noticed the gangrene as it appears in various forms upon our trees, we may now turn to a few of the many instances where it occurs to our fruits and flowers, for it is not too much to say that scarcely a cultivated plant is within our enclosures that is not liable to its inroads. It assumes different aspects, and varies as to the organs it assails; yet still in some mode, and in some of their parts, all occasionally suffer, for it is the most common form of vegetable disease.

The canker in the auricula is of this nature, being a rapidly-spreading ulcer, which, destroying the whole texture of the plant where it occurs, prevents the rise of the sap. Some gardeners believe it to be infectious, and therefore destroy the specimen in which it occurs, unless it be very valuable; but this I believe to be an erroneous opinion, the reason of its appearing to be infectious or epidemic being, that it occurs to many when they are subjected to the same injurious treatment which gives birth to the disease.

It appears to be caused by the application of too much water, especially if combined with superabundant nourishment. Therefore, although cutting out the decaying part, when it first appears, and applying to the wound some finely-powdered charcoal, will effect a cure if the disease has not penetrated too deeply, yet it will be liable to return immediately if a less forcing mode of culture be not adopted. No auricula will suffer from this disease if it be shifted annually, and the tap root at the time of moving be shortened; a thorough system of draining being adopted, either by using one of the pots suggested in another part of this work, or by having the pot used one-fourth filled with pebbles, and excessive damp during the winter being prevented by proper shelter.

Parsley grown in a poor soil is also liable to canker in the winter. Mr. Barnes says, he never found any application which eradicated this disease so effectually as a mixture in equal parts of soot and slaked lime, sown over the plants. The cure is complete in a few days, the vigour of the plants restored indicating, that this species of ulceration, like that which is found in the dwellings of the poor, arises from deficient nourishment.

The tubers of the potato also are liable to the speck, black spot, or dry gangrene, a disease which I once thought was occasioned by the calcareous earth, lime, or chalk contained by the soil, but more lengthened observation has convinced me of my error; and having observed it in all soils, and in seasons characterized by opposite extremes of wetness and dryness, I am induced to consider that the disease arises from some defect in the sets employed, or to potatoes being grown too often on the same site. It is quite certain, from my own experience, that in ground tired of potatoes, the disease invariably, and most extensively, appears. This suggests that it is occasioned by a deficiency of some constituent in the soil, a suggestion confirmed by the fact, that in the fields of the market gardeners near London, which are supplied without stint with the most fertilizing manure, this disease of the potato is comparatively unknown.

The stems of succulent plants, such as the cacti mesembryanthemums, and the balsam, as well as the fruit of the cucumber and melon, and the stalk of the grape, are all liable to moist gangrene, all requiring for the development of the disease excessive moisture in the air, though the immediate cause of its outbreak is usually a sudden reduction of temperature. - Principles of Gardening.