bears a very high proportion to the central 

 thread, as in Dasyglcea. 



In some of the species, especially of the 

 typical genus Oscillaria, a regular motion 

 has been observed backwards and forwards 

 like that of a pendulum, from whence the 

 name. Such motion has in some cases un- 

 doubtedly not been independent, but in 

 some species cilia have been observed in 

 the terminal joints, by which it is in all 

 probability effected. 



In most of the genera multiplication 

 takes place by the division of the central 

 thread, which often protrudes and breaks 

 up, each fragment forming a new plant. 

 When the central thread protrudes at the 

 sides, we have a peculiar mode of branch- 

 ing, the two branches growing in different 

 directions, one directed downwards and 

 the other upwards, as in Scytonema. Occa- 

 sionally the outer coat is so tough, and at 

 the same time so yielding, that a fascicle 

 of parallel thread is formed within it, there 

 being no room for the branches to expand. 

 In this case we have such genera as Cceno- 

 coleus, one of whose specie.sis amongst the 

 commonest Alga? on the tops of mud walls 

 and on the naked ground. Under the mi- 

 croscope it looks like little sausages stuffed 

 with threads. The curious genus Tricho- 

 desmium, to which we shall advert here- 

 ; after, owes its origin to a similar structure. 

 In one genus, Rhizonema, the outer coat 

 itself is cellular. 



Oscillatorice grow in various situations — 

 in salt and fresh water, on damp ground, 

 amongst grass on close-shaved lawns, like 

 lichens on the trunks of trees, floating on 

 the surface of lakes and seas, or suspen- 

 ded like a cloud, giving rise to variously 

 coloured waters. One or two fine purple 

 species form thick woolly fleeces in the 

 hotter parts of India, while many inhabit 

 hot springs. [31. J. B.] 



OSEILLE COMMUNE. (Fr.) Bumex 

 Acetosa. — DE BREBTS. Rumex Acetosel- 

 Ig. — DE GUINEE. Hibiscus Sabdariffa. — 

 EPINARD. Rumex Patientia. — , GRANDE. 

 Rumex Acetosa. —.PETITE. Rumex Aceto- 

 sella. — SAUVAGE. Rumex Acetosa. 



OSHAC, or OOSHAK. The Persian name 

 for Dorema aramoniacum. 



OSIER. Salix viminalis. —, BASKET. 

 Salix Forbyana. — , GOLDEN. Salix vi- 

 tellina. — , GREEN. Salix rubra. — , 

 RED. Salix rubra. — , VELVET. Salix 

 viminalis. 



OSIER DES ILES, 0. DE RIVIERE, or 

 O. BLANC. (Fr.) Salix viminalis. — 

 BRUN. Salix triandra. — FLEURI. Epi- 

 lobiurn august; folium. — JAUNE. Salix 

 vitellhia. — ROUGE. Salix purpurea. — 

 VERT. Salix viminalis. 



OSMANTHUS. A genu3 of Oleaeece, 

 closely allied to Olea and Phillyrea. The 

 corolla is four-parted, the anthers adnate, 

 and the style two-cleft, its lobes thick 

 and conical. Fruit unknown. The flowers 

 of 0. fragrans, better known as Oleafra- 

 grans, are used by the Chinese to perfume 



tea. The plant is in cultivation in this 

 country. O. ilicifolius is a very elegant 

 evergreen hardy Japanese shrub, with 

 holly-like leaves. [M. T. M.J 



OSMONDE. (Fr.) Osmunda regalis. 



OSMUNDACE^, OSMUNDINECE. One 

 of the principal subdivisions of the Poly- 

 podiacece, well distinguished by bearing 

 spore-cases which are two-valved and 

 burst vertically at the apex. In the other 

 subdivisions of the order the spore-cases 

 are not valvate. The Osmundinece differ 

 further in having on the spore-cases only 

 a rudimentary ring. The group comprises 

 Osmunda with paniculate, and Todea with 

 dorsal fructification. ["T. M.] 



OSMUNDA. The principal genus of the 

 Osmundinece, and that of which our native 

 Flowering Fern or Royal Fern, O. regalis, 

 is the type. It comprises a few species of 

 somewhat various aspect : some, like our 

 own 0. regalis, having the upper pinnae of 

 the fronds transformed into a sporangi- 

 ferous panicle ; others, like 0. Claytoniana, 

 having a few of the lateral pinnae trans- 

 formed and sporangiferous, the base and 

 apex being leafy and sterile; and others 

 again, like O. cinnamonea, having distinct 

 sterile and fertile fronds. In all cases, 

 however, the fertile parts are contracted, 

 and generally rachiform. They have cau- I 

 diciform or tufted stems, and pinnate or 

 bipinnate fronds, the segments of which 

 are often articulated, and are always tra- | 

 versed by free forking veins. The spore- l 

 cases are crowded on the margins or over i 

 the surface of the segments, and have an ' 

 incomplete ring represented by a few pa- i 

 ! rallel striae near their apex. Our native | 

 : species or forms, closely allied, are found j 

 widely distributed over the temperate re- 

 ! gions of both hemispheres. One species, 

 ! 0.javanica,v/ith pinnate coriaceous fronds, 

 rather distinct in character, is found in the 

 tropical Eastern Islands. [T. M.] 



! OSMUND ROYAL. Osmunda regalis. 



OSSEOUS. Bony, hard, brittle, and very 

 | close in texture, not to be cut without 

 difficulty ; as.the stone of a peach. 



OSTE"OSPERME PORTE-COLLIER. 



(Fr.) Osteospermum moniliferum. 



OSTEOSPERMUM. A genus of Compo- 

 site, of the subtribe Calenclulew, con- 

 sisting of South African shrubs and un- 

 dershrubs or sometimes herbs, with entire 

 or pinnatifld leaves, and yellow radiating 

 flower-heads, remarkable for the achenes 

 of the ray becoming hard nuts or drupes 

 without any pappus, whilst those of the 

 disk are constantly abortive. There are 

 nearly fifty species known, among which 

 O. spinosum and O. moniliferum used to 

 be occasionally cultivated in continental 

 flower-gardens. 



OSTERICK. Polygonum Bistorta. 



OSTIOLUM. The orifice through which 



spores are discharged, as in the perithe- 



I cium of such f ungals as Sphceria ; also an 



