E X 



[165] 



A C 



to separate and emit through the 

 pores. 



E'XOGEN. Exogens are plants which 

 have a pith in the centre of their 

 stems, not descending into the roots; 

 or having their woody system sepa- 

 rated from the cellular, and ar- 

 ranged in concentric zones. They 

 increase by additions to the outside 

 of their wood, as the name implies. 



EXOGENOUS, (from ew and fyeiWu?, 

 Gr.) Plants in which the growth 

 takes place by additions from with- 

 out, or by external increase. Exo- 

 genous trees augment, both in height 

 and diameter, by the successive 

 application, externally, of cone 

 upon cone of new ligneous matter, 

 so that if we make a transverse 

 section near the base of the trunk, 

 we intersect a much greater number 

 of layers than nearer to the summit. 

 "We can ascertain the age of an oak 

 or a pine, by counting the number 

 of concen trie rings of annual gro w th, 

 seen in a transverse section near 

 the base, so that we may know the 

 date at which the seedling began 

 to vegetate. The Baobab- tree of 

 Senegal is supposed to exceed al- 

 most every other in longevity. 

 Adanson was of opinion that one 

 which he measured, the diameter 

 of which was thirty feet, had at- 

 tained an age of 5150 years. 



EXO'SSATED. (exossaius, Lat.) De- 

 prived of bones. 



EXO'SSEOTTS. (from ex and ossa, Lat.) 

 Destitute of bones; animals not 



EXOSTO'SIS. (from e and oa-reov, Gr.) 

 A diseased growth of bone. 



EXO'TIC. (exoticus, Lat, ll-ionico*, Gr. 

 exotique, Fr. esotico, It.) In botany, 

 plants not natives of the countries 

 in which they are cultivated. 



EXPLANA'BJA. A genus of stony 

 polypifers, fixed, expanded in a 

 free, foliaceous, undulated, or con- 

 voluted and sublobated membrane, 

 with one stelliferous surface. 



EXTE'NSOR. (from extendo, Lat. exten- 

 seur, Fr.) The name of such 

 muscles as extend or straighten 

 the parts, and serve as antagonist 

 muscles to the flexors. 



EXU'VI^J. (Lat.) Cast shells; cast 

 skins; organic remains. 



EXTT' VIABLE. That may be cast or 

 thrown off, as the skeletons of 

 articulated animals. 



EYED AGATE. The name given to 

 such specimens of agate as have 

 their coloured zones arranged in 

 concentric circles. The lapidary, 

 by cutting and rounding these 

 agates in a particular manner, is 

 able to produce a striking resem- 

 blance to the eyes of certain animals. 



FAB'ACEOUS. (fabaceus, Lat.) Of the 

 nature of a bean; resembling a bean. 



FABOIBEA. The name given to a 

 genus of fossil seeds found in the 

 London clay, and resembling our 

 garden beans, whence the name. 

 Twenty-five species are described 

 by Mr. Bowerbank. 



FACE. (face, Fr. faccia, It. fades, 

 Lat.) One of the figures which 

 compose the superficies of a body ; 

 the surface which presents itself to 

 the sight. Polyhedrons have se- 

 veral faces ; a cube has six faces. 



FA'CET. (facetta, It. facette, Fr. I'un 

 des cotes d'un corps qiri a plusieurs 



