605 



RHODONITE. 



RHUS. 



Within the last few years a number of species of these beautiful plants 

 has been found hi the Himalayan Mountains by Dr. Joseph Hooker, 

 who has described them in his 'Monograph of the Rhododendrons of 

 the Sikkim Himalaya.' The most beautiful of these forms are the 

 following : 



R. Falcmeri, a white flowered species, never occurring below 10,000 

 feet above the level of the sea, is one of the most striking and distinct 

 of the genus. 



R. Dalhousice is parasitical on the trunks of large trees, especially 

 oaks and magnolias. It has large flowers, three to seven, in a terminal 

 umbellate head, the spread of which is greater than than of the 

 leaves. The calyx large, deeply-divided almost to the base into five 

 ovate-elliptical very obtuse spreading foliaeeous lobes ; corolla very 

 large, 3J inches to 4^ inches long, and as broad at the mouth, cam- 

 panulate, white, with an occasional tint of rose ; in size and colour 

 and general shape almost resembling that of the white Bourbon Lily, 

 very frequently having the odour of the lemon. 



R. barbattim, a tree from 40 to 60 feet high, branched from the 

 base. Flowers of a moderate size, of a deep puce or blood-colour, 

 collected into a compact globose head, from 4 to 5 inches in diameter. 

 It is one of the most beautiful of the Himalayan species, and is 

 readily distinguished by its having bristly petioles and numerous 

 branches floriferous at their apices. 



R. Inncifolium is a shrub 6 or 8 feet high ; the bark reddish, 

 papery, easily separating and falling off. Branches spreading, tortuous, 

 wrinkled, and knotted ; flowers of a moderate size, collected into a 

 rather dense head at the ends of the branches ; corolla of a rich 

 purple colour. 



S. Wallichi is a very distinct and handsome species, with lilac- 

 coloured flowers. Its leaves are quite unlike any Indian species, and 

 the flowers in colour and size resemble those of the much-cultivated 

 R. Ponticwn. 



R argentum is a tree 30 feet high, having leaves very beautiful in 

 the leaf-buds, erect and silky, at first enveloped in large scales, so 

 closely imbricated and BO large as to resemble the cones of some 

 species of pine, the outer or lower scales broad and coriaceous, 

 glabrous, coloured (reddish-brown), the innermost ones oblong spathu- 

 late, pubescent. The flowers are 2 to 3 inches long, 2 to 2J inches in 

 diameter, always white. 



Thirty-two species of the genus Rhododendron have been dis- 

 tinguished by De Candolle in the seventh volume of his ' Prodromus,' 

 in 1639 ; the maximum of known species at the present time exists 

 in Asia; for, commencing with Borneo and other Malayan islands 

 in the tropics of the southern hemisphere, and proceeding north, 

 we find them recorded in the mountain regions of all intervening 

 countries that have been botanically investigated, even to northern 

 and extreme arctic Siberia. As we proceed westward into Europe 

 they gradually disappear, one only inhabiting Sweden and Norway, 

 R. lapponicum, and that seems not to extend to the western coasts. 

 No species grows in Mexico or near the coasts of Oregon or California, 

 and none in the isthmus of Panama. Throughout the whole of 

 Africa and Australia the genus is unknown, and it will be observed 

 that it only enters the southern hemisphere through the medium of 

 the Indian Archipelago. 



Mr. Griffith in an excursion to one mountain in Bootan detected 

 eight species, and Dr. Hooker, during a very limited sojourn in 

 Sikkim, and notwithstanding great difficulties, was able to collect and 

 describe a far larger number. These facts would lead to the conclu- 

 sion that if the maximum of Rhododendrons be in Asia, their head- 

 quarters are on the lofty ranges of the Eastern Himalayas, where the 

 inild and moist atmosphere is eminently suited to their habits. 



(Lindley, Vegetable Kingdom; Dr. Hooker, Rhododendrons of the 

 Sikkim. Himalaya.) 

 RHODONITE. [MANGANESE.] 

 RHODOPHY'SA. [ACALEFHA] 

 RHODOSPERME/E. [ALO.E.] 



RHODYMENIACE^E, an order of Alga, consisting of purplish or 

 blood-red Sea- Weeds, with an expanded or filiform inarticulate frond, 

 composed of polygonal cells, occasionally traversed by a fibrous axis ; 

 superficial cells minute, irregularly parted, or rarely disposed in fila- 

 mentous series ; fructification double ; conceptacles external or half- 

 immened, globose or hemispherical, imperforate, containing beneath 

 a thick pericarp a mass of spores affixed to a central placenta. The 

 root is disc-like or branched, sometimes much matted ; frond very 

 variable in habit and colour, either leafy or filiform, and much 

 branched, never articulate ; in some an intense scarlet, iu some crim- 

 son, in others brown-red or purple, usually growing somewhat darker 

 in dyeing. The species are widely dispersed ; all our genera having 

 representatives in very distant countries, with very various climates. 



Rhodymcnia is an ill-defined genus, and will probably be divided 

 into several distinct genera; many of the species, especially of the 

 section Calophyllit, are among the most splendidly coloured of crimson 

 and carmine A Igce. Other*, as R, Hombroniana, are clothed in royal 

 purple ; while others, like the sober dulse of our coasts, R, palmata, 

 have often as much of brown as of purple in their attire. 



Many of the Rhodymeniacea are valuable in an economic sense. 



R. palmata, the Dulse of our coasts, is collected largely in Scotland 



and Ireland, and forma an important article of diet. Many of the 



9racilan(e are largely used in the East as ingredients iu soups and 

 jellies, and also as substitutes for gluo. One of them G. spinosa, is the 

 Agar Agar of the Chinese, and is largely collected both for culinary 

 purposes, and as a component part of some of the strongest Chinese 

 'lues. It has recently been imported into England, and is occasionally 

 used instead of carrageap moss in making jellies and blancmanges. 



(Harvey, British Algce.) 



RHOMB SPAR, a Mineral, a variety of Magnesian Carbonate of 

 Lime containing from 5 to 10 per cent, of oxide of iron or manganese. 



RHOMBOI'DES, a genus of Molluscs, [PYLORIDIA.] 



RHOMBUS. [Cosus; PLEUBONECTID^E.] 



RHUBARB. [RHEUM.] 



RHUS, the name of a genus of Plants belonging to the natural 

 order Anacardiacece, and to the tribe Sumachinece. One of the species, 

 R. cptinus, appears to have been known to Pliny, who refers to its 

 dyeing properties, and its place of growth, the Apennines, under the 

 name of Cotinus. This genus has an extensive geographical range, 

 from the south of Europe to the Cape of Good Hope. It ia also 

 found in Asia and North and South America. Most of the species 

 are poisonous, but they are much cultivated as ornamental shrubs, 

 especially on account of the beautiful red colour of their leaves hi 

 autumn. Many of them are used also for the purposes of dyeing and 

 tanning ; as an astringent principle, to which is frequently added an 

 acid, is common to the whole genus. 



The genus Jthus lias the following characters : Flowers bisexual, 

 or polygamous ; calyx small, persistent, 5-partite ; petals 5, inserted 

 under the margin of the disc, imbricate in aestivation; stamens 5, 

 hypogynous ; ovary 1-celled, sessile ; fruit, a dry drupe ; seeds solitary, 

 exalbummous; radicle opposite the hiluin, and bent downwards along 

 the edge of the cotyledons. Leaves alternate, simple, or compound ; 

 panicles axillary or terminal. 



De Candolle enumerates about 90 species, to which other writers 

 have made additions, but there is reason to believe that many of the 

 new species are merely varieties. We shall here enumerate only a 

 few of those which have interest on account of being cultivated, or 

 their uses in medicine and the arts. 



R. cotinus, Venus-Sumach, or Wild Olive. Flowers hermaphrodite, 

 arranged in loose panicles of a greenish-yellow colour; leaves simple, 

 entire. This is a very ornamental shrub, and is one of the European 

 species, growing wild in various districts of the south of Europe. It 

 is made use of, like many other of the species, for tanning, in Italy, 

 and is called Scotino. The wood is used by the modern Greeks for 

 dyeing wool, which is said to be of a beautiful rich yellow. It is 

 frequently cultivated on account of its beauty. 



R. typhina, Fever-Rhus, or Stag's-Horn Sumach. Leaves with 8-10 

 pair of leaflets and an odd one, lanceolate-acuminate, serrated, pilose 

 beneath. There are two forms of this plaut : the one R. t. arbor- 

 escens, in the form of a tree, from 10 to 25 feet in height; the other 

 R. t. frutescem, shrubby, and only from 2 to 10 feet high. The young 

 shoots are covered with down, which, with their somewhat crooked 

 and stunted branches, give them the appearance of young stags'-horns ; 

 hence their name. The flowers are in dense spikes, at the ends of 

 the branches, the pistilliferous ones developing themselves into woolly 

 drupes, which are very couspicuous when ripe. It is found in every 

 part of North America, and its dark-red leaves add much to the 

 beauties of an American autumn. The fruit of this plant is exceed- 

 ingly sour, and on this account it is frequently called vinegar plant, and 

 is even used in some parts as a substitute for vinegar. 



R. glabra, Smooth-Leaved Sumach. Leaf like the last, but broader 

 and glabrous. Branches also glabrous. Fruit red, covered with silky 

 hairs. This species, as well as another named R. viridifolia is con- 

 sidered by some botanists as only a variety of R. typhina. Like the 

 last, tjis species is abundant in North America, over-running some- 

 times a whole district, and forming a troublesome weed. Its fruit is 

 very sour, but may be eaten with impunity. Bees arc very foud of 

 the blossoms. 



R. vcrnicifera, Varnish-Bearing Sumach, or Japan Varnish-Tree. 

 Leaf with 5-6 pairs of leaflets, all ovate, long, acuminate, entire, 

 glabrous above, velvety beneath. It is a native of Japan and Nepaul. 

 Its leaves are very large and beautiful, rendering it one of the hand- 

 somest of shrubs. According to Thunberg, this is the plant which 

 yields the celebrated Japan Varnish. 



R. venenata, Poison Sumach, or Swamp-Sumach. Leaf 6-7 pair of 

 leaflets, almost glabrous, entire, lanceolate-acuminate, reticulated 

 beneath. Fruit white. It is a native of North America from Canada 

 to Carolina, and also in swampy districts in Japan. This plant is 

 exceedingly poisonous, so virulent that it is said to affect some persons 

 by merely smelling it. A touch will sometimes produce violent 

 inflammation. It is a beautiful shrub, and well worthy of cultivation, 

 but great care should be taken to prevent its being carelessly handled. 

 R. coriaria, Hide, or Elm-Leaved Sumach. Leaf 5-7 pairs of villous 

 leaflets, elliptical, bluntly aud coarsely toothed, petioles naked. 

 Flowers in largo loose panicles of a whitish-green. Drupes villous. 

 This plant is a native of the south of Europe. It is extensively used 

 for the purpose of tanning, and it is said that all the leather made in 

 Turkey is tanned with the bark of this species of Rhus. The fruit 

 is acid and astringent, and the seeds are often used as tonics for 

 exciting the appetite. 



