Among the more showy stove plants may be mention ed, the different species of Strelitzia, Limodorum Tanker villi, rosea, Canarina campanula, and Lantana odorata. Along the rafters may be trained Passifiora quad rangularis, which in the West Indies affords the fruit call ed Granadilla, but which in this country requires the utmost heat of our stoves to induce it to Om its brilliant and fragrant flowers. P. alata is also highly deserving of a place.
Diseases of Plants.
540. In treating of the different kinds of fruit-trees and esculent plants, several of the maladies to which they are subject have already been noticed, as well as the usual means adopted either for prevention or cure. The diseases of plants shall therefore be only very slightly touched in this place. Any extensive discussion of the subject, in deed, could not be attempted : our knowledge of it is yet in its infancy. Some authors have no doubt given us lists of diseases of the vegetable race, drawn up in the formal style of nosological nomenclature ; but they are in general destitute of the requisite permanence and precision of type and character. We shall therefore continue to use the popular terms, such as Canker, confessing at the same time that they are sometimes much too indefinite.
541. Canker is by far the most prevalent and the most fatal disease incident to fruit-t•ees in this country. It may be described as a sort of gangrene, which usually be gins at the extremities of the branches, and proceeds towards the trunk, killing the tree in two or three years. It seems, in different situations, to arise from different causes ; very often from had subsoil, trees planted over a ferruginous and retentive soil being observed to be very liable to it. Sometimes it appears to take its origin merely from some external injury, or from injudicious pruning, and leaving ragged wounds and snags. In other cases, it makes its first appearance after exudations of gum ; and Mr Spence of Hull has remarked, that the foundation of canker in full grown trees is often laid by the attacks of insects, particularly the larvae of Tortrix Wceberana. It fre quently happens that cions for grafting have been taken from infected trees; and the young trees produced in this way are, as might be expected, peculiarly obnoxious to the disease. Among apple trees, those which come soonest into a bearing state, such as the Nonsuch and Hawthorn dean, are observed to be most subject to canker. Trees trained as standards or against espalier rails are more liable to it than wall-trees; the more tender and finer sorts of fruits than those that are hardy,—the reasons of which seem to be, that the young wood, not being thoroughly ripened, is killed in the course of the winter, or the buds and early shoots are incurably injured from the same cause.
In order to guard against canker, if the subsoil be in different, the trees should be planted as much on the sur face as possible. (See§ 78.-and 110.) If certain varieties of fruit seem peculiarly liable to the disease in any par ticular garden, other varieties should be introduced by means of grafting. The greatest care should be taken, in pruning, to make the cuts quite clean, and to cover with a plaster any accidental wound. Where the extremities of unripe shoots are nipped by the frost, they should be carefully removed with a sharp knife. Mr Forsyth, as is well known, was remarkably successful in overcoming the ravages of canker, in the Royal Gardens at Kensington, by means of heading down the trees, and thus procuring new branches ; an example which may in similar cases he followed. Mr Knight seems to consider canker as princi pally affecting those varieties of fruit-trees which are in an advanced stage of existence, or which have long been propagated by means of grafts or buds ; and the observa tion is probably well founded. Mr Sang of Kirkcaldy (Scottish Hort. 1ire111. i. 339.) very justly icisists on the im portance of grafting only on healthy stocks, and mentions a case which occurred in his own experience. where many stocks became diseased with canker, apparently from hav ing been raised in an unpropitious soil. For further in formation regarding canker, the reader may be referred to a paper on that subject by Mr James Smith, gardener at Hopeton House, published in tke first volume of Scottish Horticultural Memoirs, p. 221, et seq.
542. Blight commonly means the effects of cold winds, or of hoar-frosts, on the foliage and blossoms of trees. In this country, easterly winds, accompanied with fogs, often produce blight ; the buds are nipped, and the tender ves sels burst ; innumerable minute insects soon appear, feed ing on the extravasated juices, and these are often crro supposed to have been wafted hither by the wind, or engendered by the hazy'' east. ‘Vhen some line weather has induced the blossom to expand itself prema turely, and frost supervenes, blight very often ensues. It is not therefore desirable, especially in the northern parts of Britain, that fruit trees should come early into flower : on the contrary, it would he advantageous if the flowering were retarded. Various devices are resorted to for pro tecting early blossoms, some of which have already been described, § 84.