AXIS

(Lat.), n. m. ’i2s, Gen., ax'is. Pl., axes. Gr., ätev. Fr., axe, e ieu (8th def.), axoïde [Chau ier] (8th def.). Ger., Achse, Axe. It., a e. Sp., eje. 1. A fixed line, actual or imaginary, about which anything revolves. The a. of a balance is the fixed line about which the beam of the balance turns. [B; C.] 2. The central part of anything; hence a line occupying the centre of anything or about which other parts are symmetrically disposed (a. of symmetry)..] 38. In botany, a term applied generically to any portion of a plant that increases by apical growth and sends out lateral offshoots. It is, hence, often used as synonymous with the entire stem of a plant, including both the portion above and that below the surface of the ground (see Ascending a. and Descending a.). It is further Spelled to those lateral outgrowths from the stem which are themselves the source of secondary lateral growths. and is especially applied to the rhachis of a raceme or spike of flowers (see Primary a., Secondary axes, and Tertiary axes). Ina special sense, it is the same as ped i cell us axiformis (q. v.). [B, 1, 84, 167, 198.] See also A. of a flower and A. of a fruit. 4. Any particular diameter of an object, especially its long diameter. 5. In optics, the general direction or course followed by a ray. The a. of a microscope or a telescope is the straight line connecting the centres of the objective and the eye-piece, coinciding with the principal axes of both. [B.] 6. The bony or horny piece by means of which the anterior wing of an insect is connected with the prothorax. [Kirby (L, 180).] 7. In the trilobites, see TERGUM. e second cervical vertebra, so called because the atlas and the cranium turn upon its odontoid proce as on a pivot. [A, 385; C.] 9. An East Indian animal of the deer tribe (the Cervus a. of Linnæus), the horn of which has been used in medicine. [A, a iy See Ger., Nebenachse. A secondary a. of a t. (B.19.] See Secondary axes.—Antero-posterior a. of the eye. See Optical a—Ascending a. Lat., a. ascendens, Fr., are ascendant. Ger., aufsteigende Achse. It., a e ascendente. The stem of a plant; that portion of the a. which is usually above ground and is distinguished by regularly producing buds., 34.] Axes of the eye. See Optical a., Vertical a. of the eye, Horizontal a. of the eye, and Visual a..-band. See A.-cylinder.—A. cerebro-spinal is. See Cerebro-spinal a.—A.-cord. Ger., Ach sen strang. See A.-corp and Primitive srreaK.—A.-corpuscle, See Axile CORPUSCLE.—A.- cylinder. Lat..fibraprimitiva. Fr.,cylindre-axe. Ger., Ach sen cylinder, Achsenband, Achsenfaser, Achsenschlauch. It., a e cilindrico, cilindra e, cilindro centrale (o dell’ a e), Syn.: axial fibre, a.-band (or -fibre, or -tube), band-(or central, or cylinder-) a., flattened (or primitive, or Remak’s) band. The central and e ential part of every nerve fibre, its size varying directly with that of the whole fibre. It may he inclosed in one or more sheaths, or it may he naked (see Primitive SHEATH, MYELIN, Mauthner’s SHEATH, and Naked a.-cylinder). As shown by Schultze, the a.-c. is composed of delicate longitudinal fibrils (see Primitive FIBRILS), and it is su ed to be a continuation of the a.-c. proce of a nerve cell. [J, Be 3l, 82.]—A.-eylinder proce . See under Proce .—A. de- See Decwnbent a—A See Descending > cumbens. » descend ens. a.—A. encephalo-spinal is. See Erect a.—AÀ. exeurrens. See Cerebro-spinal a.—A. erect us. See Excurrent a.—A.-fibre. See A.-cylinder —A.fibrilke. See Primitive FIBRILS—A. fun i form is. See FUNICULUS central is.—A. gemmzæ. Syn.: column a gemmæ. The rudimentary offshoot constituting the bud-stalk and bearing the other parts (leaves or flowers) inclosed in the bud; the base of a bud. [B, 198.]—A. of a crystal. Fr., axe d’un cristal. See A. 4 crystallization and Optical a. (ist def.).— » of a lens. See Optical a., Principal a., and Secondary axes.—A. of a magnet. See Magnetic a.—A. of a mirror. See Optical a., Principal a., and Secondary axes.—A. of erystallization. Fr., axe de cris tallis at i on. A line about which the particles of a crystal are more or le symmetrically disposed; a line following the intersection of two of the planes with reference to which the co-ordinates of the crystalline particles are drawn. By reason of variations in the length and direction of these axes, six different systems of crystallization are formed. In the first (regular or cubic) system, there are three axes of equal length and at right angles to each other. In the second (hexagonal) system, there are four axes, three of which, lying in the same lane, make angles of 60° with each other (secondary axes), and the fourth ( principal a.) differs from the others in length and is at right angles to their plane. In the third (quadratic, square prismatic) system, there are three axes, two of which (secondary axes) are equal in length and at right angles, while the third (principal a.) is longer or shorter than they and at right angles to both. In the fourth (rhombic) system, there are three axes at right angles to each other and all of unequal len; S that one along which the crystal is most full developed, or along the direction of which modifications most frequently occur, is called the principal a., and the others are termed secondary axes, the longer one being the macrodiagonal, and the shorter one the brachydiagonal a.’ In the fifth (monoclinic, monosymmetric) system, there are three unequal axes, The secondary ares are at right angles to each other, and one of them (the orthodiagonal a.) is at right angles to the sie ek a., while the other (the clinodiagonal a.) is inclined at an oblique angle to the latter. In the sixth (triclinic asymmetric) system, there are three unequal axes, no one of which forms a right angle with another, the principal a., as in the fourth system, being abl sean N