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Wfyz CmsJurg of 28otani?. 



978 



RHODOMYRTUS. This genus of Myrla- 

 cece differs but little from Myrtus, except 

 in the flowers, which are rose-coloured 

 (whencethe name) ; and in the seeds, which 

 are compressed, flat, and arranged in two 

 rows in each of the compartments of the 

 fruit. R. tomentosa, a native of China, is 

 in cultivation as a greenhouse plant. It 

 much resembles the common myrtle, save 

 in the colour of the flowers, and in the 

 fact of the leaves being downy on their 

 under-surface. [M. T. MJ 



RHODORA. Rhododendron. 



RHODORRHTZA. A small genus of 

 Gonvolvulacece. confined to the Canary 

 Islands, and by most authors regarded as 

 identical with Convolvulus. It derives its 

 name from the rose-like smell peculiar to 

 the rootstocks and lower part of the 

 stems, which yield a kind of Rosewood 

 (lignum rhodii). Prom them is extracted 

 by distillation the powerfully-scented oil 

 known as Oleum ligni Rhodii cethereum, 

 used in some countries for ointment, but 

 more frequently for the adulteration of 

 attar of roses. This Rosewood is called by 

 the French Bois des Rhodes des Parfum- 

 eurs, and must not be confounded with the 

 so-called rosewood of commerce used for 

 furniture. Rhodorrhiza is composed df 

 two species : R. scoparia (Convolvulus 

 scoparius) and R. florida {Convolvulus 

 floridus), both having woody erect stems, 

 linear leaves, terminal panicles of flowers, 

 five sepals, a bell-shaped corolla, a single 

 style bearing two stigmas, and a two- 

 celled capsule, each cell of which has two 

 or by abortion one seed. [B. SJ 



RHODOSPATHA. A genus of Orontiacece, 

 comprising certain Peruvian herbaceous 

 plants, throwing down roots from their 

 trailing stems, having large leaves and 

 very large rose-coloured spathes, whence 

 the name of the genus. It differs from 

 Calla and Monstera in the definite stamens, 

 and in the structure of the fruit. [M. T. MJ 



RHODOSPERME.E. The Rhodosperms 

 form one of the three great divisions of 

 Algce, distinguished by their rose-coloured 

 spores, which are of two kinds— the one 

 contained in capsular bodies of various 

 structure and denomination, external or 

 immersed ; the others of spores, always 

 four together uetraspores), formed by the 

 cell-division of the endochrome of a sin- 

 gle cell, which is generally globular, but 

 sometimes cylindrical. Antheridia are 

 also found in many genera, and probably 

 are universal. One or two genera which 

 are not of this group, as Bangia and Por- 

 phyra, have spores of a similar colour, but 

 they have not the double fructification. 

 It has been questioned which is the true 

 fruit. At present the tetraspores are re- 

 garded as gemma? not requiring impreg- 

 nation. 



The Rhodosperms divide naturally into 

 two great tribes, JDesmiospermece and Gon- 

 (lylnspcrmew, in the former of which the 

 spores are formed in a joint or joints of 

 the spore- threads; in the other they are 



congregated without order in a hyaline 

 mucous or membranaceous mother-cell. 

 The genera depend partly on the structure 

 of the frond, and partly on the nature of 

 the fruit, whether capsular or tetraspored. 

 It is to the younger Agardh especially that 

 we are indebted for the present improved 

 arrangement, which has been diligently 

 followed out by Montagne, Harvey, and 

 others. Kiitzing also has done a good deal, 

 but unfortunately has not clear notions 

 as to the extent of genera and species. 

 Rhodosperms are found in all parts of the 

 world ; but, like other bright-coloured pro- 

 ductions, their maximum is attained in 

 warmer climes, however abundant they 

 may be elsewhere. [M. J. B.] 



RHODOSTOMA. A genus of Cinchonar 

 cece, of which one species is in cultivation 

 in hothouses, but whence obtained is 

 doubtful. It is a small shrub, with smooth 

 somewhat glossy leaves, white or pinkish 

 flowers in terminal cymes, the small 

 branches of which are of a rich flesh- 

 colour. The five lobes of the calyx are re- 

 flected ; the corolla is funnel-shaped, with 

 a long tube concealing the stamens ; the 

 ovary is two-celled, adherent to the calyx, 

 and surrounded by a fleshy disk. The plant 

 is a pretty stove-shrub, and known under 

 the name of R. gardenioides. [M. T. MJ 



RHODOTHAMNUS. A genus of Erica- 

 cew, distinguished by its wheel-shaped and 

 flve-lobed corolla, and by the ovary being 

 two-celled, and when ripe opening through 

 the backs of the cells into five valves. 

 The only species has been long known as 

 Rhododendron Chamwcisius, a small hand- 

 some shrub with solitary rose-coloured 

 flowers, and alternate oval leaves. The 

 generic name expresses the general red- 

 dish tint of the plant. [G. DJ 



RHODYMENTA. The typical genus of the 

 natural order of rose-spored Algfe, Rhody- 

 meniacece,vfh\ch are characterised by an in- 

 articulate membranaceous frond composed 

 chiefly of many-sided cells, the surface- 

 cells forming a continual coating, and the 

 nucleus lodged in an external conceptacle, 

 and either single or compound; spores 

 at first moniliform. Rhodymenia itself has 

 a flat forked or irregularly cleft frond with 

 a simple nucleus. R. palmata, which is 

 common everywhere on our coasts, and is 

 parasitical on Fuci and Laminarice, &c. in 

 the United States, is the Dulse or Dillisk 

 of the Scotch ; and though tough and of a 

 parchment-like texture, is not an unaccept- 

 able food to hungry men, as we have our- 

 selves experienced in former days amongst 

 the Western Islands, when travelling was 

 not so easy as it is now. It varies much in 

 width, and is sometimes wider than it is 

 long. [M. J. BJ 



RHOMBEUS, RHOMBOID, RHOM- 

 BOIDAL. Oval, a little angular in the 

 middle, as the leaf of Hibiscus rhombi- 

 folius. 



RHOPALA. A proteaceous genus of 

 trees or large shrubs, natives of South 



