vu 



ox Y 



difference of a given line and the other 

 side." 



OVARIUM OF PLANTS. The hol- 

 low case at the base of the pistil, enclosing 

 the ovules. It is said to be inferior, 

 •when the tube of the calyx contracts ad- 

 hesion with its sides ; superior, when no 

 such adhesion exists. Hence, an infe- 

 rior ovary involves a superior calyx; a 

 superior ovary, an inferior calyx. When 

 an ovary adheres to the calyx merely by 

 its back, it is termed parietal. 



OVERLYING ROCKS. Interjected 

 Rocks. A geological term applied to 

 those rocks which appear lying over, or 

 interspersed among, the stratified rocks. 

 They are probably connected with de- 

 posits situated beneath the fundamental, 

 having apparently been ejected in a 

 melted state, through fissures in the 

 strata. 



OVERSHOT WHEEL. A water-wheel, 

 to which the water is conveyed over the 

 top of the wheel, and applied above the 

 axle ; in this case the water acts merely 

 by its weight, and not by the impulse of 

 the stream. 



OVI'GEROUS {ovum, an eg^, gero, to 

 bear). A term applied to parts which 

 contain or support the egg. 



OVI'PAROUS {ovum, an egg, parte, 

 to bring forth). A designation of those 

 animals, which produce their young in 

 an egg, the egg being hatched after its 

 exclusion from the parent, as in the 

 cases of birds and most reptiles. 



OVIPO'SITOR [ovum, an egg, pono, 

 to lay down). An instrument with which 

 some Hymenopterous insects are fur- 

 nished for depositing their eggs. It is 

 formed by a prolongation of the last seg- 

 ment of the body in the females, and 

 possesses the power of boring a hole in 

 certain substances. In other insects of 

 this order, the ovipositor is replaced by a 

 sting. 



OVO-VIVI'PAROUS {ovum, an egg, 

 vivus, alive, pario, to bring forth). A 

 designation of those animals which bring 

 forth their young in the living state, the 

 egg having been previously hatched 

 within the body of the parent. 



OVULE OF PLANTS. A small pulpy 

 body, borne by the placenta, and gra- 

 dually changing into a seed. It consists 

 of two tunics and a nucleus. 



OVU'LIN^. The egg-shells ; the sub- 

 typical group of the Cyprceidce, or Cow- 

 ries, named from the genus ovula, and 

 resembling the cowries in general form ; 

 but the extremities of the aierture are 

 245 



generally produced, and there are no 

 teeth to the inner lip. 



OXA'LIC ACID. An acid existing, in 

 the form of an acid salt of potash, in 

 many plants, particularly in the species 

 of Oxalis and Rumex ; combined with 

 lime, it forms a part of several lichens. 



OXALIDA'CEiE. The wood-sorrel 

 tribe of Dicotyledonous plants. Herba- 

 ceous plants, undershrubs, or trees, with 

 leaves alternate ; flowers symmetrical ; 

 stamens hypogynous ; fruit capsular. 



O'XAMIDE. A white insoluble sub- 

 limate, obtained by decomposing oxalate 

 of ammonia by heat. The term is de- 

 rived from the first syllable of oxalic acid 

 and ammonia. 



OXFORD CLAY. Clunch clay; a 

 great argillaceous bed interposed between 

 the lower and the middle oolite. It is of 

 a dark blue colour, some \>i the beds are 

 bituminous, and abound in septaria, or 

 masses having internal dissepiments. In 

 its lower part are beds of limestone called 

 Kelloway Rock. 



OXIDATION. The process of con- 

 verting metals or other substances into 

 oxides, by combining with them a certain 

 portion of oxygen. It differs from acidi- 

 fication, in the addition of oxygen not 

 being sufiicient to form an acid with the 

 substance oxidated. 



O'XIDE. A generic term, consisting 

 of the first syllable of oxygen with a termi- 

 nation indicative of combination, applied 

 to compound neutral bodies and bases. To 

 this the name of the other element is 

 joined, to express the specific compound. 

 Thus, a compound of oxygen and hydro- 

 gen is oxide of hydrogen ; if oxygen and 

 potassium, oxide of potassium ; of which 

 compounds the first, or water, is an in- 

 stance of a neutral oxide ; the second, or 

 potash, of a base or alkaline oxide. But 

 the same elementary body often com- 

 bines with oxygen in more than one 

 proportion, forming two or more oxides ; 

 to distinguish them, the following pre- 

 fixes are employed : — 



1. Proto (TTpwTov, first), denoting the 

 minimum of oxygen, as /?ro/oxide. 



2. Deuto (deurepof, second), denoting 

 a second proportion, as deutoxi^e. This 

 is also called 6in- oxide. 



3. Trito (rptVop, third), denoting a 

 third proportion, as ^ri^oxide. This is 

 also called ter-oxi^e. 



4. Per {very much), denoting the max- 

 imum of oxidation, as peroxide. 



OXY {h^v9, acid). A prefix, denoting 

 in some terms, the presence of acidity; 

 M3 



