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Rhododendron (Old Greek name from rhodos)

(an old Greek name, from rhodos, a rose, and dendron, a tree; in allusion to the rose-red flowers of many of the species). Rose Bay. Azalea and Rhodora are merged, by the authors of the "Genera Plantarum," into this genus, but for garden purposes they have been kept distinct in this work. ORD. Ericaceae. A large and popular genus of highly ornamental, glabrous, pubescent, tomentose, or lepidoted, stove, greenhouse, or hardy shrubs, rarely trees. The species, which number upwards of 100, are natives of the mountains of Europe, Asia, the Malayan Archipelago, and North America, often gregarious, being copiously found on the Himalayan mountains. Flowers usually large, often disposed in terminal, many or few-flowered, sometimes subracemose corymbs, rarely axillary or solitary; calyx variable, five-sepaled, five-toothed, patelliform, cup-shaped, or obsolete, coriaceous or leaf-like, persistent; corolla variable, often funnel-shaped or bell-shaped, rarely tubular, salver-shaped, or sub-rotate; limb more or less oblique, five (rarely six to ten) lobed or rarely parted, very rarely sub-bilabiate, the lobes imbricated; stamens eight to ten, rarely five or twelve to eighteen, more or less unequal sometimes spreading; filaments subulate-filiform or short and thick, usually pilose or bearded at the base. Capsules short or elongated, woody, five to twenty-celled. Leaves alternate, often clustered at the tips of the branchlets, entire, coriaceous, rarely membranous, annual or biennial. Rhododendrons may justly be classed amongst the most beautiful and attractive of evergreen, flowering shrubs. Their foliage is at all times attractive, and the flower-trusses, which vary much in size with the species or variety, are usually borne in the greatest profusion whenever the plants succeed. Amongst outdoor shrubs, none are more showy when in flower than the gorgeous varieties and hybrids raised from R. ponticum. This species itself has now been so generally superseded by varieties or hybrids, that it need no longer be grown extensively, except for covert planting, and for the supply of stocks whereon to graft the superior forms. Some of the grandest indoor plants, where space can be allowed them to develop, are specimens of the Himalayan species, many of which have flowers highly perfumed, in addition to their other good qualities. Of late years, numerous hybrids have been raised, by using, for crossing and inter-crossing, several of the species and hybrids which have been from time to time obtained. These are all beautiful, and well adapted for culture in small pots, for greenhouse decoration. They have always been much valued, and seem deservedly to be fast increasing in popularity. Propagation. There are several methods by one or more of which the species, hybrids, and varieties of Rhododendron may be increased-namely, seeds, cuttings, and layers, and by grafting. Budding and inarching are also practicable. The seeds, which are very minute, require to be sown in thoroughly-drained pots, or shallow pans, of sandy peat. The top layer should have a little more sand intermixed than is necessary for the other portion, and should be passed through a fine sieve. After the surface has been rendered smooth and pressed firm, the pots, or pans, should be watered previous to sowing, and then allowed to drain. Scatter the seeds thinly over the top, press in, and cover very lightly with a little silver sand. To prevent the soil from drying too readily, the plan of placing a little moss over the soil is often practised; this must not be allowed to remain after the seeds begin to germinate. The pans may be placed in gentle heat, or in a cold frame; and shading from sunshine is necessary. February and March are the best seasons for sowing. When the plants come up, and are large enough to handle, they should be pricked off in pans of soil similar to that in which they have previously been growing, and be kept shaded and close until re-established. Afterwards, they may gradually have air and light admitted to harden them. Cuttings intended for propagating should be made of partially-ripened wood, inserted in sandy peat, and kept close and shaded. After they have callused, a slightly higher temperature may be allowed than at first, such as a gentle hotbed affords. Layering may be practised in autumn or spring, when the parent plant is sufficiently dwarf to allow of its being done. Roots proceed from almost any part of the firm wood near the base, but only very slowly indeed. Grafting is one of the principal methods adopted for increasing established varieties of Rhododendron, the stocks used being procured from seedlings or cuttings obtained from medium or strong-growing common varieties or species of good constitution. Grafting is most extensively practised towards the latter part of summer, when the scions have become ripened; with the tender indoor species, it is best done in winter. Grafted plants require to be kept for a time in close frames until a union has been effected. Culture of Indoor Greenhouse Rhododendrons. Many of these develop into very large bushes, where space can be afforded, and provision made for planting them out. Amongst the species may be specially mentioned the magnificent R. Nuttallii, also R. arboreum, R. Aucklandii, R. Edgeworthii, &c. An open, peaty soil suits best, and good drainage is essential, as large quantities of water are requisite in summer. Unless seeds are required, the whole of the seed-vessels should be carefully removed when flowering is over, and the plants should then, if possible, be kept rather close while making their annual growth. Specimens of the species above-named may also be grown successfully in large tubs or pots, as the root space required is not really so much as the size of head would suggest. All the beautiful hybrid greenhouse Rhododendrons are most desirable subjects for decorative purposes in cool houses. They are mostly free-growing, and exceptionally free-flowering, as, by affording what is known as a warm greenhouse temperature, some of the plants in a collection are nearly always to be seen in flower. Especially are these remarks applicable to the section raised from R. jasminiflorum, R. javanicum, &c., which require more heat in winter than R. ciliatum, R. Edgeworthii, and others mentioned above. The hybrids succeed in rather small pots; good turfy peat and some silver sand is the most suitable compost to use. The plants should be kept under glass, but subjected to plenty of air in summer after their annual growth has been made. Water must be very carefully administered, particularly after potting, or if signs of ill-health are apparent. Rain-water for these, as for all other hard-wooded plants, is much to be preferred to any other.

Culture of Hardy Outdoor Rhododendrons. Hardy Rhododendrons succeed under various conditions regarding situation and soil, but one thing is always fatal to the well-doing of most of them, namely, the presence of lime or chalk in the compost within reach of their roots. Naturally, they prefer a rather moist situation and partial shade, but these conditions are not absolutely necessary, as the plants are hardy enough to grow and flower splendidly where fully exposed to the sun. Peat and leaf soil are unquestionably best suited for Rhododendrons; but R. ponticum and its numerous beautiful varieties grow well where there is a good proportion of loam, provided the destructive ingredients already referred to are absent. It is generally necessary to have beds specially prepared for these plants, by taking out the ordinary soil and refilling with a prepared compost, If peat is procurable, it should form the bulk; leaf soil and sandy loam may be added more freely when they can be obtained more easily. Dried cow-manure is also a good addition. Prepared beds for Rhododendrons should, if possible, be from 2ft. to 2 1/2ft. deep; it is far better to make them properly at first, and large plants require that depth, although they always root near the surface. Transplanting may best be performed in spring; but there are few shrubs that withstand it so well at any season, provided the balls are not kept long out of the ground, and watering is well attended to afterwards. Large standard specimens of the numerous beautiful hybrids are exceedingly telling in pleasure-grounds, either isolated or planted amongst other smaller plants of Rhododendrons, or such subjects as are usually grown with them, hardy Ericas, Kalmias, Pieris, &c. The ponticum hybrids form valuable forcing subjects; they may be lifted from the open ground after the flower buds are set, and potted up. If introduced to heat in early spring, the flowers soon expand, and showy specimens are thereby obtained early for greenhouse decoration.

R. ferrugineum and R. hirsutum are dwarf, free-flowering species, well adapted for planting in small beds by themselves, or in prepared borders in different parts of rock-gardens, &c. They are always dwarf and some-what slow-growing, so that, if associated with the vigorous ponticum varieties, they are liable to become overgrown and smothered. All Rhododendrons have extremely small, fibre-like roots, which are disposed very close to, and even on, the surface of the soil. It is important that these be kept protected from the sun; if the foliage does not insure sufficient shade, a top-dressing of leaf soil, cocoanut-fibre refuse, or similar material, proves of great advantage through the summer time, when the roots require to be kept cool and moist. The best-known species and varieties are described below. Except where otherwise indicated, all are shrubs, and require greenhouse treatment. R. aeruginosum (verdigris-coloured). A synonym of R. campanulatum. R. albiflorum (white-flowered). fl. drooping, on fascicled, rarely solitary peduncles; calyx large, deeply cut into five brownish-green segments; corolla pure cream-white, twice as long as the calyx, rotate-campanulate, five-lobed; stamens ten, included. July. l. deciduous, elliptic-lanceolate, shortly petiolate, entire, glabrous, penninerved, 1in. to 1 1/2in. long; stipules brown, early deciduous. Branches erect. h. 2ft. to 3ft. Rocky Mountains. Hardy. (B.M. 3670.) R. album (white). fl. small, on pedicels 1in. to 1 1/2in. long; calyx minute; corolla pale yellowish-white or cream-colour, broad-campanulate, its five lobes nearly equal, rounded, retuse; stamens ten; corymbs umbellate, terminal, shorter than the leaves. November. l. rather copious, spreading, 3in. to 4in. long, oblong-lanceolate, acute, on short, lepidoted petioles, glabrous and dark green above, thickly clothed with minute, ferruginous scales beneath. Branches clothed with reddish-brown bark. h. 1ft. Java. (B.M. 4972.) R. Anthopogon (bearded-flowered).* fl. sulphur-coloured, glomerate: calyx with a short, five-lobed limb; corolla salver-shaped. with a woolly throat and a spreading limb of roundish, undulately-curled segments; stamens eight, inclosed. April and May. l. oval, rusty beneath from lepidoted tomentum, biennial, coriaceous, terminating in a reflexed mucrone. Branchlets downy. h. 1ft. to 1 1/2ft. Central and Northern Asia, 1820. Hardy. (B. M. 3947.) R. arboreum (tree-like).* fl. white, rose, or blood-colour, disposed in dense heads; calyx absent; corolla campanulate; stamens ten. March to May. l. large, coriaceous, lanceolate, acute, cordate at base or attenuated into a thick petiole, of a beautiful green above, below impressed with netted veins, glabrous, silvery or ferruginous-pubescent. h. 20ft to 25ft. Himalayas, 1820. A magnificent, half-hardy tree, sometimes attaining a circumference of 150ft.