ORB 



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O R N 



flat. In botany, leaves are so called when 

 their length and breadth are equal, and 

 their form nearly circular. 



O'RBIT. (orbita, Lat. orbite, Fr. orbita, It.) 

 The line described by the revolution of a 

 planet ; the path of a planet, or of a 

 comet. The mean distance of a planet 

 from the sun is equal to half the major 

 axis of its orbit. A planet moves in its 

 elliptical orbit with a velocity varying 

 every instant, in consequence of two 

 forces, one tending to the centre of the 

 sun, and the other in the direction of a 

 tangent to its orbit, arising from the 

 primitive impulse, given at the time when 

 it was launched. into space. 



ORCHI'DE^E. (from bp\tQ, Gr. orchis, Lat.) 

 An order of monocotyledonous plants. 

 Perianth superior, sepals three, usually 

 coloured, the odd one uppermost, from 

 the twisting of the ovarium ; petals three, 

 usually coloured, of which two are the 

 uppermost, while the third, called the 

 labellum, is usually lobed, and differs in 

 figure, colour, or size, from the other 

 two, and is often spurred ; stamens three, 

 united in a central column, the two lateral 

 generally abortive, the central one per- 

 fect ; anther either persistent or decidu- 

 ous ; pollen either powdery or cohering 

 in granular or waxy masses ; ovarium 

 one-celled, with three parietal placentae ; 

 style forming part of the column of the 

 stamens ; stigma a viscid space in front 

 of the column ; fruit usually a capsule, 

 dehiscing by three valves, sometimes bac- 

 cate ; seeds numerous, testa loose and 

 reticulated, no albumen, embryo a solid 

 undivided fleshy mass ; herbaceous plants, 

 either stemless, or forming a kind of 

 tuber above ground ; or sometimes with 

 a true stem ; leaves simple and entire, 

 sometimes articulated with the stem ; in- 

 florescence terminal or radical^ spikes, 

 racemes or panicles, occasionally solitary. 

 Natives of all countries, except very 

 cold or very dry. There are thirty-seven 

 British species ; and, probably, altogether 

 not fewer than fifteen hundred species. 



The flower of the orchidise is very pe- 

 culiar ; the calyx and corolla consist of 

 three pieces each, and one of those form- 

 ing the latter, differs very greatly in size 

 and form from the other two ; it is called 

 the labellum, or little lip, and is often 

 spurred. In many species, this resembles 

 an insect, and hence they have received 

 the name of bee, fly, spider, c. &c. 



ORCHI'DEOUS. Belonging to the order 

 Orchidese ; parasitical plants. 



O'RDER OF SUPERPOSI'TION. That ar- 

 rangement of strata in which they are 

 invariably found. The order of superpo- 

 sition is never inverted. Strata are fre- 

 quently absent, but the order of superpo- 



sition of such as are present is invariably 

 the same. 



ORE. (erz, Germ.) A metallic compound. 

 Metals are found usually combined with 

 other substances : the compounds they 

 thus form are called Ores, when the metal 

 exists in them in sufficient quantities to 

 form a considerable portion of the mass. 



ORGA'NIC. (bpyaviKOQ, Gr. organicus, Lat. 

 organique, Fr. organico, It.) Consisting 

 of various parts co-operating with each 

 other ; consisting of natural instruments 

 of action or operation. 



ORGA'NIC BO'DIES. Such as possess na- 

 tural instruments of action ; on the action 

 of each, arid their co-operation together, 

 depend the growth and perfection of the 

 body. 



ORGA'NIC REMAI'NS. The relics of what 

 were once living bodies : generally applied 

 to the fossil remains of animals or plants. 



ORISMO'LOGY. (from opto-juof, definition, 

 and Xoyo, discourse, Gr.) Called also 

 terminology. In entomology, orismology 

 contains the various technical terms used 

 in explaining the perceptible differences 

 in the body of an insect, and at the same 

 time acquaints us with its exterior visible 

 parts in the several periods of its exist- 

 ence, until its full and perfect develop- 

 ment. Mr. Kirby introduced the term 

 orismology. Shuckard. 



ORISMOLO'GICAL. Relating to orismology. 



ORNITHI'CKNITES. (from oyvig, a bird, 

 and 0iyw, to touch, Gr.) The footmarks 

 of birds found in different formations. 

 Some recent discoveries of ornithicknites 

 are very remarkable ; the footsteps appear 

 in regular succession, on the continuous 

 track of an animal in the act of running 

 or walking, with the right and left foot 

 always in their relative places. An ac- 

 count of these has been published by 

 Prof. Hitchcock, in the American Journal 

 of Arts and Sciences : they were disco- 

 vered in the new red sandstone of the 

 valley of Connecticut. The most remark- 

 able were those of a gigantic bird, twice 

 the size of an ostrich, whose foot measured 

 fifteen inches in length, exclusive of the 

 largest claw, which measured two inches. 

 The discovery of these ornithicknites is 

 exceedingly interesting to the palaeonto- 

 logist, as proving the existence of birds at 

 the early epoch of the new red sandstone 

 formation. 



ORNI'THOLITE. (from opiate, a bird, and 

 XiOoe, a stone, Gr.) A fossil bird. Stones 

 of various colours and forms, bearing the 

 figures of birds. Specimens of this kind 

 may be obtained at Matlock, in Derby- 

 shire, arid at other places where the water 

 is surcharged with lime. 



ORNITHO'J-OGY. (from opvig, a bird, and 

 , discourse, Gr.) That department 



