PISTON 



267 



PLANTAGO 



Piston, (pis'ton). [The French -word.] A disc 

 of wood or iron working air- 

 tight in a cylinder ; in a steam- 

 engine the piston is moved to 

 and fro by the force of the 

 steam, which it communicates 

 to the machinery. 



Pisum, (pi' sum). [The Latin 

 name.] A plant belonging to 

 Leguminaceae. 



Pitch, (pich). [1 and 2. Pi*. 

 the Latin word; 3 and 4. F. 

 pic, peak.] 1. A hydrocarbon obtained from 

 coal-tar ; a resin-like variety of bitumen. 2. 

 A resin obtained from Pinus sylvestris and 

 other trees. 3. The pitch of a musical note, 

 depending upon the number of vibrations. 4. 

 P. of a screw: the distance through which it 

 moves in one turn. P. stone: a mineral; 

 (1) a variety of obsidian ; (2) a silicate of 

 aluminum. Mineral P. = Asphalt. Concert 

 P. varies from 512 to 538 vibrations per 

 second for C on the treble clef. 



Pitchblende, (pich'blend). [Pech-blende, the 

 German name.] An amorphous mineral, 

 chiefly uranium oxide, with copper, lead, 

 iron, &c. 



Pitcher. P. plant; 1. A slender climbing 

 plant, which has pitcher-shaped leaves=Ne- 

 pentb.es, v. Nepenthacese. 2.=Darlingtonia 

 California: a plant of California. P. leaves: 

 also called ascidia. 



Pith, (pith). [Pidha, the A.-S. word.] The 

 soft, spongy, cellular substance found in the 

 centre of exogenous stems and branches. 



Pithecia, (pi-the'si-a). An American monkey 

 with a bushy tail. 



Pithecus, (pi-the'kus). [Gk. pithekos, monkey.] 

 Apes^Simia: tailless monkeys, having teeth 

 in the same number as man. P. leuciscus= 

 Gibbon, of Java. P. acUyrtusOiang-ovtang. 



Pitta, (pit'ta). A large thrush-like bird, hav- 

 ing long legs and a very short tail ; found 

 only in Sumatra and adjacent islands. 



Pittosporaceae, (pit-to-spo-ra'se-e). [Gk. pitta, 

 gum; sporos, seed.]=Pittosporads: trees and 

 shrubs, with symmetrical flowers and small 

 embryos, with much albumen, belonging to 

 Berberales; found chiefly in New Holland; 

 named from the resinous seeds. 



Pituitary, (pi- tu'i-ta-ri). [L. pituita, 

 phlegm.] Relating to phlegm. P. body: irithe 

 brain, at the front of the notochord; named 

 from being thought to secrete phlegm. 



Placenta, (pla-sen'ta). [L. placenta, cake.] 

 A developed condition of the chorion, by 

 which the young is nourished previous to 

 birth, and which in man is discoid in shape; 

 also called " after-birth." 



Placentalia, (pla-sen-ta'li-a). [Placenta, q.v.] 

 Term used by Owen for all Mammalia except 

 Marsupialia and Monotremata. 

 Placentiferous, (pla-sen-tif'er-us). [Placenta, 

 q.v. ; ferro, I carry.] Bearing a placenta. 

 Placodus, (plak'o-dus). [Gk. plax, plate; 

 odous, tooth.] A reptile, known only by 

 fossil remains, found in Muschelkalk rocks ; 

 named from having short, flat teeth. 

 Placoid, (plak'oid). [Gk. plax, plate; eidos, 



form.] P. fishes: having irregular bony 

 plates and spines on the skin ; rare as fossils. 



Placoidei, ( pla-koi'de-I ). [Gk. plax, plate; 

 eidos, form.] = Selachii ; sharks and rays: 

 a sub-division of Elasmobranchii, q.v. 



Plagiaulax, (pla'ji-aw-laks). [Gk. plagios, 

 oblique; aidax, groove.] A mammal, fossil 

 remains of which are found in Purbeck 

 beds; named from the oblique grooves in the 

 teeth. 



Plagioclastic, (pla-ji-6-klas'tik). [Gk. plagios, 

 oblique ; klasis, fracture.] P. minerals : 

 have cleavages that are oblique to each other. 



Plagiostoma, (pla-ji-os'to-ma). [Gk. plagios, 

 oblique ; stoma, mouth.] An oyster-like 

 animal, known by fossil remains found in 

 Lias rocks. 



Plagiostomi, (pla-ji-os'to-mi). [Gk. plagios, 

 oblique; stoma, mouth.] Used by Siebold 

 for a sub-division of fishes, including the 

 shark and ray, forming a sub-division of 

 Elasmobranchii. 



Plaice, (plas). [Platessa, the Latin name.]= 

 Platessa vulgaris: a flat fish, belonging to 

 Pleuronectidse. 



Plan, (plan). [L. planus, flat.]=Map onalarge 

 scale; view looking vertically downward. 



Plane, (plan). [L. planus, level.] A level 

 surface. P. geometry: the geometry of plane 

 surfaces. P. sailing, v. Sailing. P. trigono- 

 metry, v. Trigonometry. P. of the Ecliptic: 

 the plane in which the earth moves in its 

 revolution round the sun, and to which the 

 orbits of the other planets closely approxi- 

 mate. Scotch P.=Acer pseudoplatanus ; a 

 tree, named from its broad leaves. 



Planes, Shrubs and trees belonging to Urti- 

 cales=Platanacese, q.v. 



Planetoids, (plan'et-oidz). [Planet, q.v.; Gk. 

 eidos, form.]=Miuor Planets, q.v. 



Planets, (plan'ets). [Planeta, the Latin 

 name.] Wandering stars: bodies resembling 

 our globe, belonging to the solar system (i.e. , 

 revolving round the sun), which shine only 

 by the reflection of the sun's light. Superior 

 P.: those farther from the sun than the 

 earth is; Mars, Jupiter, Saturn, Uranus, 

 and Neptune. Inferior P.: those between 

 the sun and the earth : Mercury, Venus, and 

 possibly Vulcan. Minor P.=Asteroids: be- 

 tween Mars and Jupiter; see Minor Planets. 

 Major P.; Jupiter and the planets beyond 

 it; Saturn, Uranus, and Neptune. Terrestrial 

 P.: a term used to comprise the earth and 

 the planets approximating to it; Mercury, 

 Venus, and Mars; the planets between the 

 sun and the Minor Planets. 



Planimeter, (plan-im'e-ter). [L. planus, flat; 

 Gk. metron, measure.] Any instrument for 

 the measurement of plane surfaces. 



Planorbis, (plan-or'bis). [L. planus, flat; 

 orbis, circle.] A fresh-water snail-like, 

 molluscous animal, belongingto Gasteropoda. 



Plantaginacese, (plan-ta-jin-a'se-e). [Plantago, 

 <?.v.]=Rib-worts; herbs belonging to Cortu- 



Plantago, (plan-ta'go). [L. planta, sole of the 

 foot.]=Plaintain; rib-grass; an herb the 

 type of Plantaginacese. 



