EXP 



EXT 



exhibiting, on a transverse section, a 

 series of concentric circles or zones. 



•2. Exo-phyllous {(pvWov, a leaf), A 

 term applied by Dumortier to the exo- 

 rrhizous embryo, in consequence of the 

 cotyledons being always naked, i. e. not 

 evolved from a coleophyllum or leaf- 

 sheath. 



3. Exo-pUle {miKov, a feather). A 

 term applied by Lestiboudois to the dico- 

 tyledonous embryo, in consequence of its 

 plumule being naked, i. e. not enclosed 

 within the substance of the cotyledons. 



4. Exo-rrhizous {pi^a, a root). A term 

 expressive of the mode of germination 

 in exogenous plants, in which the radicle 

 appears at once on the surface of the 

 radicular extremity of the cotyledons, 

 and consequently has no coleophyllum or 

 sheath at its base, as occurs in the en- 

 dorrhizous germination. 



5. Ex-osmose {uxt/xov, impulsion). The 

 property by which a rarer fluid passes 

 through membranous substances out of a 

 cavity into a vessel containing a denser 

 fluid. 1 



6. Exo-stome (o-ro^ia, a mouth). The 

 foramen or orifice of the outer integu- 

 ment, or primine, of the ovule in plants. 



7. Exo-thecium {Oi]K.r\, a case). A term 

 applied by Purkinje to the coat of the 

 anther, in plants. 



EXOCHNATA (efoxoc, prominent). A 

 designation of the long-tailed Crustacea, 

 as the lobster and slirimp. 



EXOTE'RIC (e^wTeptKof, external). 

 A term applied to those disciples of Py- 

 thagoras and others, who were not yet 

 initiated into their highest philosophy; 

 as distinguished from the esoteric, who 

 were scientifically taught. The terra 

 "exoteric" was also applied to those 

 writings which were in a more popular 

 form, while the " esoteric " writings were 

 of a more scientific and exact character. 



EXFANSIBPLITY [expando, to spread 

 out). That property of a body by which 

 it is capable, under certain circumstances, 

 of occupying more space than it usually 

 requires. The principal agent in the ex- 

 pansion of bodies is caloric. 



EXPERIMENTUM CRUCIS. A cru- 

 cial or decisive experiment in attempting 

 to interpret the laws of nature ; so called, 

 after Bacon's manner, from the crosses, or 

 way-posts, used to point out roads, be- 

 cause they determine at once between 

 two or more possible conclusions. 



EXPLOSION. The sudden and vio- 

 lent expansion of the constituent parts of 

 a body. 

 132 



EXPO'NENT {expono, to explain). A 

 small figure, or other symbol, placed at 

 the right hand of an algebraical quantity, 

 to express its power. It is equivalent to 

 the number of factors, and is also called 

 the index of the power. Thus, in the 

 expression a^, the figure 2 is the index 

 or exponent, and denotes that the quan- 

 tity is the square of a. 



1. Exponent of a rank. The number 

 or place of any term in a series : thus, in 

 the series 1, 3, 5, 7, 9, 11, 13, 15, &c., 7 is 

 the exponent of the rank of 13, this term 

 being the 7th in the order of the series. 



2. Exponent of a geometrical ratio. 

 The quotient which arises from dividing 

 the consequent by the antecedent of the 

 ratio. Thus, in the ratio of 2 to 8, the 

 exponent is | = 4 ; and, in the ratio of 

 8 to 2, the exponent is | = ^. Some ma- 

 thematicians, however, consider loga- 

 rithms as the exponents of ratios. 



EXPONE'NTIAL. This term is va- 

 riously applied. The exponential calculus 

 is that part of Algebra which relates to 

 exponential quantities, or quantities raised 

 to powers of which the exponents are in- 

 determinate or variable. An exponential 

 curve is a curve defined by an exponential 

 equation, or an equation which contains 

 an exponential quantity. Exponential 

 equations are commonly resolved by 

 means of logarithms. 



EXSERTED {exsertus, thrust out). A 

 term applied to the stamens of plants, 

 when they are longer than the corolla. 



EXSICCA'TION {exsicco, to dry up). 

 A variety of evaporation, producing the 

 expulsion of moisture from solid bodies 

 by heat, and generally employed for de- 

 priving salts of their water of crystalliza- 

 tion. 



EXTENSION {extendo, to stretch out). 

 That property of matter by which it occu- 

 pies space : it relates to the qualities of 

 length, breadth, and thickness, without 

 which no substance can exist ; but has 

 no respect to the size or shape of a body. 

 This property is termed, in common lan- 

 guage, size or volume. 



EXTINE (extimus, outermost). The 

 outermost membrane of the pollen-grain 

 in plants. 



EXTRACTION OF ROOTS. The 

 arithmetical or algebraical operation of 

 finding the root of a number or quantity ; 

 in other words, the finding that number 

 or quantity which, multiplied into itself 

 a certain number of times, will produce 

 the given number or quantity. See Evo- 

 lution. 



