Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/547

R H R H 527 then, are trees or shrubs, never herbs, with simple, ever- green or deciduous leaves, and flowers in terminal clusters surrounded in the bud by bud-scales but not as a rule by true leaves. The flowers are remarkable for the frequent absence or reduced condition of the calyx. The funnel- or bell-shaped corolla, on the other hand, with its five or more lobes, is usually conspicuous, and in some species so much so as to render these plants greatly prized in gardens. The free stamens are usually ten, with slender filaments and anthers opening by pores at the top. The ovary is five- or many-celled, ripening into a long woody pod which splits from top to bottom by a number of valves, which break away from the central placenta and liberate a large number of small bran-like seeds provided with a mem- branous wing-like appendage at each end. The species are for the most part natives of the mountainous regions of the northern hemisphere, extending as far south as the Malay Archipelago and New Guinea, but not hitherto found in South America or Australia. None are natives of Britain. They vary greatly in stature, some of the alpine species being mere pigmies with minute leaves and tiny blossoms, while some of the Himalayan species are moderate sized trees with superb flowers. Some are epi- phytal, growing on the branches of other trees, but not deriving their sustenance from them. The varieties grown in gardens are mostly derived from the Pontic species (R. ponticum) and the Virginian _/?. catawbiense. These are mostly hardy in England. The common Pontic variety is excellent for game-covert from its hardiness, the shelter it affords, and the fact that hares and rabbits rarely eat it. Variety of colour has been infused by crossing or hybridiz- ing the species first-named, or their derivatives, with some of the more gorgeously-coloured Indian varieties. In many instances this has been done without sacrifice of hardihood, but even where the infusion of Indian blood has brought about a tenderness of constitution the magnificence of the bloom amply repays the very slight shelter which is re- quisite in winter. What are termed greenhouse rhododendrons are derivatives from certain Malayan and Javanese species, and are consequently much more tender. They are characterized by the possession of a cylindrical (not funnel-shaped) flower-tube and other marks of dis- tinction. Azaleas now referred to Rhododendron are derived from Chinese and Japanese species chiefly. The " Indian " azaleas, so- called, have nearly evergreen foliage like a rhododendron, but with stiff hairs on the under surface of the leaf, and the flower-buds comprise leaves and not bud-scales only as in true rhododendrons. Rhododendron (Azalea) indicum is truly a native of China and Japan, but not of India. What are called in gardens Ghent azaleas are hardy varieties with deciduous gummy foliage and tufts of fragrant, brilliantly-coloured flowers. These are derivatives from A. calendulacea, A. viscosa, and other north-east American species. Another group of garden azaleas are derivatives from Rhododendron (Azalea) sincnse (of which R. mollis is a form). These are scarcely less hardy than the preceding. Azalea amcena of gardens is a dwarf form of R. indicum, remarkable for having " hose in hose " flowers, a state of things brought about by the fact that the calyx in this variety becomes petaloid like the corolla. The foliage of rhododendrons contains much tannin, and has been used medicin- ally. Whether the honey mentioned by Xenophon as poisonous was really derived from plants of this genus as alleged is still an open question. RHONE (Fr. Rhone), the largest European river flow- ing directly into the Mediterranean, rises in the Swiss canton of Valais, passes through the Lake of Geneva, strikes across the line of the Jura, and turning southward through France falls into the Gulf of Lyons. It has a length of 447 miles according to Strelbitzky (505 according to other authorities), and its principal affluent the Saone has a length of 268 miles above the confluence, which is 200 miles inland. The drainage area of the whole river- system is 38,000 square miles, and the mean discharge at the river mouth is 60,000 cubic feet per second, the maxi- mum being 428,840 cubic feet and the minimum 19,426. The natives give the name of source of the Rhone (locally Rotten or Rodden) to three warm springs that rise in a circular stone basin near the Hotel du Glacier du Rhone ; but the real beginning of the river is the well-known glacier. According to M. Gosset, 1 a Swiss engineer, the Rhone glacier, which at present measures about 9 miles in length by about 3200 feet in width, is proved to have retreated 3028 feet between 1856 and 1881 and sunk upwards of 300 feet. In geological time the Rhone glacier filled the whole valley to a depth of 4800 feet and spread out over the Swiss plain now partly occupied by the Lake of Geneva. Obstructed by the Jura, it divided into two branches, one of which found its way (as the river does still) by the " ecluse " between the Jura and the western Alps to deposit its erratic blocks on the heights in the neighbourhood of Lyons, while the other branch, bending northward, widened out so as to distribute its burden at Freiburg, Bern, Soleure, and even Aarburg. 2 In the first 30 miles from the foot of the glacier (5751 feet) to Brieg (2214 feet) the stream has a fall of 1 in 46 ; in the next 70 miles to Villeneuve it descends at the rate of 1 in 378. 3 It passes between the Bernese and the Pennine Alps, receiving the tribute of 260 glaciers, of which the Aletsch is one of the most important. At Martigny, where it is joined by the Drance (a glacier-fed stream memorable for the terrible inundation of 1818 caused by the sudden bursting of the ice barrier by which its waters had been dammed back), the Rhone turns suddenly north- west, and below the defile of St Maurice (about 90 miles from its source) it enters the wide alluvial plain formerly occupied by the south-eastern arm of the Lake of GENEVA (q.v.), which has now retreated about 12 miles northward. The limpid character of the Rhone water as it issues from the south-western end of this great settling vat has become a commonplace of geographical illustration, and equally well-known is the contrast afforded at the confluence about a mile below Geneva between the current of the main river and that of its turbulent affluent the Arve, which has found no resting place in its 2000 feet descent by a course of 60 miles from the valley of Charnouni and the glaciers of Mont Blanc. It is the Arve that is mainly responsible for the dangerous inundations of the Rhone valley farther down ; while its volume is sometimes not more than 1235 per second, 4 at other times it pours into the Rhone (whose maximum at this point is 2000 cubic feet) no less than 24,700 cubic feet, sometimes causing the river to flow backwards towards the Lake of Geneva. 5 To obviate the evils of their irregularity it has been proposed to divert the lower course of the Arve into the Lake of Geneva. The annual maximum of the Rhone at Geneva, according to observations between 1806 and 1880, occurs on the 7th of August. Since 1862 there has been an increase of high levels owing to the dyking of the river and the destruction of forests (see Plantamour, "Obs. limniinetriques," in Mem. de la Soc. de Geneve, 1880). The defile or " ecluse " by which the Rhone passes between Grand Credo, the terminal bastion of the Jura, and Mont Vouache, one of the Alps of Savoy, is com- manded by one of the great frontier fortresses of France, 1 A sketch of M. Gosset's remarkable labours is given in the Alpine Journal, 1878-80. 2 See Falsan and Chantre, Monographic geologique des anciens glaciers et du terrain erratique de la partie moyenne du bassin du RMne, 1880. See also the map illustrating Auguste Jaccard's paper in Bull, de la Soc. Vaudoise, Feb. 1885. 3 A large-scale profile of the upper Rhone accompanies Gerlach's paper " Die Penniuischen Alpen" in Mem. de la Soc. Helv., 1869. 4 Professors Paul Chaix and Plantamour, on one occasion in March, found the volume of the Arve as low as 812 cubic feet per second, and that of the Rhone 1612. B See the annual Observations hydrometriques suisses sur le bassin du Rh6ne issued by the Bureau federal des travaux publics.