opening over the disk of the shield of cer- 

 tain lichens. 



OSTODES. A genus of Euphorbiacece, 

 consisting of two Javanese trees very near- 

 ly allied to Aleurites; hut the stamens of 

 the male flowers are free, not monadel- 

 phous, and the ovary of the females has 

 three instead of two cells. 



OSTRYA. The Hop Hornbeam genus, 

 composed of two species, one a native of 

 the south of Europe, and the other of North 

 America. It belongs to the Corylacece, and 

 is closely allied to the Common Hornbeam. 

 Both species form trees thirty or forty feet 

 high, with deciduous feather-veined ser- 

 rated leaves, and unisexual flowers borne 

 in distinct catkins upon the same plant. 

 The male catkins are long, cylindrical, 

 and drooping, composed of a number of 

 simple scale-like bracts, each with twelve 

 or more irregularly united stamens inserted 

 into its base; and the female ones short, 

 with small deciduous bracts, each flower 

 enclosed in a pair of thin involucral scales 

 which become enlarged and grow together 

 so as to form an inflated covering to the 

 fruit, and these being imbricated give the 

 ripe catkin a hop-like appearance. The 

 fruit is a small one-seeded nut bearded at 

 the top. 



O. vulgaris, the Common Hop Hornbeam, 

 is a native of the south of Europe, but is 

 quite hardy in the climate of England. It 

 forms a large spreading tree, and has a very 

 handsome appearance, particularly in the 

 autumn, when the pendent hop-like catkins 

 are in perfection. 0. virginica is extensively 

 spread over North America, and is some- 

 times regarded as a variety of the last spe- 

 cies, the chief difference being that the 

 fruit catkins are upright instead of pen- 

 dulous as in O. vulgaris. The wood of the 

 Virginian kind is excessively hard and 

 heavy, and is called Ironwood ; levers are 

 sometimes made of it, whence it is fre- 

 quently called Lever-wood. [A. S.] 



OSTRYOCARPUS. A weak half-climbing 

 shrub from tropical Africa, constituting a 

 genus of Leguminosce, closely allied to Lon- 

 chocarpus in foliage, in habit, and in most 

 of the floral characters ; but the tenth sta- 

 men is free, the wing-petals do not adhere 

 to the keel, and the fruit is a broad round 

 flat indehiscent pod, something of the 

 shape of an oyster-shell, whence the generic 

 name. 



OSUS. A termination indicating aug- 

 mentation, as radiosus, having a large root. 



OSYRIS. A genus of some half-dozen 

 species of Santalacece, inhabiting widely- 

 separated regions of the eastern hemi- 

 sphere; two being found in the Mediter- 

 ranean region, one in Abyssinia, two in 

 India, and one at the Cape of Good Hope. 

 They are shrubs or small trees, with angu- 

 lar branches, alternate or rarely opposite 

 leaves, and usually unisexual flowers on 

 different trees ; one, however, always has 

 perfect flowers. The flowers are deeply 

 three or four-parted, with {.hree or four 



stamens, and a one-celled ovary containing 

 usually three ovules. The fruit contains a 

 single seed. In Kumaon the leaves of O. 

 arborea, which is sometimes called O.nepa- 

 lensis, are employed as a substitute for tea. 

 This is a small tree, with somewhat ellip- 

 tical leaves an inch and a half to two inches 

 long, and is found all along the foot of the 

 Himalayas. , [A. S.] 



OTACHYRIUM. A genus of grasses be- 

 longing to the tribe Panicece. There are 

 only two species, both Brazilian, and in- 

 cluded by Steudel in Panicum. [D. M.] 



OTHONNA. A genus of Compositce of 

 the subtribe Calendulew, distinguished 

 by the scales of the involucre being united 

 in a single row and valvate at the top, by 

 their female ligulate ray-florets with ache- 

 nes bearing a dense pappus of simple 

 bristles, and by their disk florets being all 

 male with abortive achenes. There are 

 above sixty species known, herbs or shrubs, 

 with entire or divided leaves, often some- 

 what succulent, and solitary pedunculate 

 flower-heads, usually yellow, rarely blue. 

 The O. cheirifolia inhabits the African 

 shores of the Mediterranean, and has been 

 frequently grown in flower-gardens. All 

 the other species are natives of the Cape 

 Colony. 



OTIDIA. Six species of Pelargonium 

 with succulent knobby stems, fleshy pin- 

 nately or bipinnately compound leaves, 

 nearly equal petals the upper ones eared at 

 the base, and five stamens, have been sepa- 

 rated as a genus with the name Otidia ; 

 but they are retained as a section of Pelar- 

 gonium by Dr. Harvey in the Flora Capensis. 

 They are all South African. The flowers 

 are small, usually white, and disposed in 

 few or many-flowered umbels. [A. A. B.] 



OTOCHILUS. A small genus of orchids, 

 natives of the Himalaya mountains, where 

 they are found creeping on trees. They 

 have no rhizomes, but, creep by means of 

 their proliferous pseudobulbs, which are 

 continuously produced one above the other, 

 each successive one coming out just below 

 the apex of the old one and there emitting 

 a few fibrous roots. Each pseudobulb 

 bears a couple of leaves, and from the base 

 of some of the upper ones many-flowered 

 racemes of smallish blossoms are produced. 

 The genus belongs to the tribe Ccelogynida?, 

 and its flowers have equal free sepals and 

 petals, athree-Iobed lip with the side-lobes 

 very small and embracing the column, and 

 the middle one long and petal-like, and a 

 very long club-shaped column, bearing a 

 terminal anther, which contains four pol- 

 len-masses held together in twos by a gra- 

 nular substance. [A. S.] 



OTTELIA. A genus of Hydrocharidacew, 

 consisting of perennial herbs inhabiting 

 the mouth of the Nile, Ganges, and Austra- 

 lasian rivers, and eaten as potherbs in India. 

 They are quite stemless, have cordate 

 leaves, and hermaphrodite flowers placed 

 on a scape, and surrounded by a spathe. 

 The perigone is divided into six parts, the 



