OPI 



ORA 



" The potato onion {Allium tubero- 

 sum) does not produce seed as other 

 onions, hut it increases by the root. 

 One single onion, slightly covered, 

 will produce six or seven in a clump, 

 partly under ground. 



" The bulhs are generally planted 

 in the spring, from twelve to eighteen 

 inches apart ; but they will yield bet- 

 ter when planted in autumn, as they 

 will survive the winter if slightly cov- 

 ered with dung, litter, or leaves of 

 trees, &.c." 



O.MOX, WILD. A troublesome 

 weed in meadows and open grounds. 

 It is to be removed by a few hoed 

 crops and heavv liming. 



O .\ I S C I B'jE. Insects like the 

 wood louse (Oniscus). 



OOLITE. Roe stone. A lime- 

 stone of the secondary epoch, the 

 parts of which are rounded so as to 

 resemble a fish roe. It is unknown 

 as a formation in the United States, 

 at least on the seaboard. Oolitic is 

 a derivative. 



OPAL. An iridescent, silicious 

 mineral. 



OPEN CUTS. Ditches not cov- 

 ered. 



OPERCULUM. A lid or covering. 

 The coverings of the theca of moss- 

 es. In zoology this term is applied 

 to the apparatus supported by four 

 bones, which protects the gills of 

 fishes ; also to the horny or calcare- 

 ous plate which closes the aperture 

 of univalve shells ; and to the four 

 calcareous pieces which defend the 

 entrance to the tube of Balanites, or 

 bell barnacles. 



OPHIDIANS, OPHIDIA (from 

 odif, a snake). The order of reptiles 

 resembling snakes. 



OPHTHAL.MIA (from cHkBalfio^, 

 an eyrA. Inilammation of the mucous j 

 membrane of the eye. I 



OPIU.M. The concrete juice of 

 the poppy, obtained by wounding the | 

 unripe seed capsules of the Papaver 

 somniferum, collecting the milky juice | 

 which e.xudes and dries in the sun, I 

 and kneading it into cakes. The ' 

 cakes of the best opium are covered 

 externally with pieces of dried leaves 

 and the seed causules of some spe- . 



cics of Rumex. It should be of a rich 

 brown colour, tough consistency, and 

 smooth, uniform texture ; its pecu- 

 liar narcotic smell should be strong 

 and fresh ; its taste bitter, warm, and 

 somewhat acrid. The chemical anal- 

 ysis of opium has rendered it proba- 

 ble that its activity as a medicine de- 

 pends upon the presence of a peculiar 

 alkaline base, called morphia, in com- 

 bination with an acid which has been 

 termed meconic acid. Opium also con- 

 tains narcotine. narccine, codcin, gum 

 resin, extractive matter, and small 

 portions of other proximate princi- 

 ples. 



The chief countries in which opi- 

 um is prepared are India. Egypt, Tur- 

 key, and other parts of Asia ; it is 

 even cultivated in Italy, France, and 

 England ; but the climate of Europe 

 seems to be too uncertain to allow 

 of its regular production. 



There is no substitute for this in- 

 valuable drug in allaying pain. See 

 Poppy. 



OPOBALS.\M. Balm of Gilead. 

 A fragrant gum resin, from a species 

 o( Amyris. 



OPODELDOC. A liniment of 

 soap with camphor. 



OPOPONAX. A gum resin of a 

 bad odour, from the Pastimca opo- 

 ponax. 



OPOSSUM. The genus Didelphis 

 of marsupials, peculiar to the Amer- 

 ican continent. 



OPTIC NERVES. The second 

 pair from the brain. They enter the 

 back of the eyes, and form the re- 

 tina. 



OPTICS. The science which in- 

 vestigates the property of light, and 

 all that relates to vision. 



ORACHE. The genus Atriplex, of 

 the family Chenopodiacece, which con- 

 tains the beet and spinach ; most of 

 the species are weeds in rich soils, 

 but A. hortensis is cultivated and 

 used like spinach in some parts of 

 Europe. 



O R A N G E. Citrus aurantium. 

 This tree and the genus are cultiva- 

 ted only in situations free from frost, 

 and suffer even in Florida ; with suf- 

 ficient shelter to protect them from 



