SExM 



SEP 



clothed with its own integuments, and 

 containing the rudiment of a future 

 plant. It is the point of development at 

 which vegetation stops, and beyond which 

 no increase, in the same direction with 

 itself, can take place. 



SEGMENT {seco, to cut). That part 

 of a circle which is contained by a 

 straight line and the circumference it 

 cuts oflf. 1. The angle of a segment is 

 that which is contained by the straight 

 line and the circumference. 2. An angle 

 in a segment is the angle contained by 

 two straight lines drawn from any point 

 in the circumference of the segment to 

 the extremities of the straight line which 

 is the base of the segment. 3. Similar 

 segments of a circle are those in which 

 the angles are equal, or which contain 

 equal angles. 



SELA'CHII. The Shark and Ray 

 tribe; an order of Chondropterygious or 

 cartilaginous fishes, distinguished by the 

 peculiar conformation of the mouth, the 

 jaws not being united into a ring, and 

 the true jaw-bones not being developed. 

 Several of the species are viviparous. 



SE'LENITE {ae\i)vt], the moon). 

 Sparry gypsum. A simple mineral, con- 

 sisting of pure gypsum, or sulphate of 

 lime. 



SELENIUM {<r€\l]vn, the moon). A 

 metal discovered in the sulphur of Fah- 

 lun, and named from its strong analogy 

 to another metal, tellurium, which is 

 named from tellus, the earth. It com- 

 bines with oxygen, forming the selenious 

 and selenic acids. 



SEMI-. A Latin prefix, derived from 

 semis, half, and corresponding with the 

 term hemi in Greek compounds. 



1. Semi-amplexicaul. Half stem-em- 

 bracing ; as applied to the leaves of plants 

 which partially sheath the stem. 



2. Semi-anatropous. A term denoting 

 the same as amphitropous, except that in 

 the former the ovule is parallel with the 

 funiculus, while in the latter it is at 

 right angles with it. 



3. Semi-circle. Half a circle ; a figure 

 contained by a diameter of a circle, and 

 the portion of the circumference cut off 

 by the diameter. 



4. Semi-diameter. Half a diameter, or 

 a right line drawn from the centre of a 

 circle, or sphere, to its circumference ; it 

 is otherwise called a radius. 



5. Semi-flosculous. A term applied to 

 the ligulate, or strap-shaped, florets of 

 some of the compositae, as of dandelion ; 

 in this and similar plants, the limbs of 



300 



the cohering petals are united on one 

 side of the floret, giving it the appear- 

 ance of half a floret. 



6. Semi-metals. A term formerly ap- 

 plied to those bodies which possess the 

 qualities of metals, with the exception 

 of malleability. 



7. Semi- opal. A variety of opal, of 

 white, grey, and brown colours ; some- 

 times in spotted, striped, or clouded deli- 

 neations ; occurring in porphyry and 

 amygdaloid. 



8. Semi-quadrate or semi-quartile. An 

 astrological term denoting an aspect of 

 the planets when distant from one an- 

 other half a right angle, or 45°. The 

 terms semi-quartile and semi-sextile have 

 similar meanings, the former denoting 

 the half of a fifth of the complete circle, 

 or 36°, the latter the half of a sixth, or 

 30°. 



9. Semi-tone. An interval in music 

 whose ratio is 16 : 15, as CC % It can- 

 not correctly be called half a tone, as 

 there are different kinds of semitones, 

 greater, lesser, and natural. 



SENECTI'NiE. Sea-snails ; a sub- 

 family of the TrochidcB, named from the 

 genus senectus, resembling the garden 

 snail in form, but perlaceous, and fur- 

 nished with a thick, round, fleshy oper- 

 culum. 



SEN'SIBLE {sentio, to perceive). A 

 vague term applied indifferently to a 

 body capable of receiving, of producing, 

 or of conducting sensation. It has been 

 suggested that the term sentient should 

 be applied to the first of these cases, and 

 sensitive to the third. In the fourth and 

 most ordinary acceptation of the word 

 sensible, it is used to express the state 

 of the intellectual powers. 



SE'PAL. The botanical designation 

 of each of the leaves composing the 

 calyx, or external envelope of the floral 

 apparatus. When the leaves are distinct 

 from one another, the calyx is termed 

 poly-sepalous ; whe i they cohere, it 

 is called gamosepalous, or, incorrectly 

 though popularly, mono-sepalous. A se- 

 pal may be hollowed out into a conical 

 tube, as in larkspur, and is then said to 

 be spurred. 



SETIAD^ {sepia, the cuttle-fish). A 

 family of cephalopods, vulgarly known 

 as cuttle-fish , and divisible into two 

 groups, the octopods and the decapods. 



SEPTA'RIA {septum, a division). Lu- 

 di Helmontii. Flattened balls of stone, 

 generally a kind of iron-stone, which, on 

 being split, are found to be separate i in 



