PIS 



PLA 



similar terms, as pirinatifid, pinnatipar- 

 tite, pinnatisected, and pinnatilobate. 

 A pinnate leaf which has no terminal 

 leaflet or tendril, is said to be equally or 

 abruptly pinnate. 



PFNNATIPEDS {j>inna, a fin,pes, the 

 foot). An order of birds which have the 

 digits bordered by membrane. 



PINNOTHE'RIANS. A tribe of the 

 third family of the brachyurous crusta- 

 ceans in the arrangement of Miliie 

 Edwards, named from the genus pin- 

 notheres, and characterized by their pecu- 

 liar habit of being housed between the 

 mantle-lobes of certain conchifers, as of 

 mytilus, pinna, &c. 



PIPE-CLAY. A plastic and tenacious 

 variety of clay, of a greyish- white colour, 

 with an earthy fracture, and a smooth 

 greasy feel ; found near Poole in Dorset- 

 shire. 



PIPERA'CE^. The Pepper tribe of 

 dicotyledonous plants. Shrubs or herba- 

 ceous plants, with /mre^ opposite i flowers 

 achlamydeous ; stamens adhering to the 

 base of the ovarium, which is superior 

 and one-celled. 



PI'PRID^. The name given by Mr. 

 Vigors to a family of the Dentirostres, 

 from the genus Pipra. Mr. Swainson, 

 rejecting this family, gives the name 

 Piprinae to the manakins, which he 

 makes a sub-family of the Ampelidae, 

 Fruit-eaters, or Chatterers. 



PISCES {piscisy a fish). The first 

 class of the Vertebrata or Encephalata, 

 consisting of fishes, or oviparous ani- 

 mals, inhabi'ing the water, breathing by 

 means of permanent branchiae, and hav- 

 ing fins for progressive motion. See 

 Ichthyology. 



PISCES (in Astronomy). The twelfth 

 and last of the zodiacal constellations, 

 consisting of 113 stars. It denoted the 

 third month, extending from the 20th of 

 August to the 20th of September. During 

 this period, the inundation of the Nile 

 spreads over the whole of Egypt, and the 

 fishes move about, 



PISCIS AUSTRALIS. The Southern 

 Fish ; a constellation, consisting of 

 twenty-four stars, the principal of which 

 is Fomalhaut. 



PISCIS VOLANS. The Flying-fish ; 

 a modern southern constellation, con- 

 sisting of eight stars. 



PFSOLITE (TTtVoy, apea, MBoi, stone). 

 A variety of carbonate of lime, possess- 

 ing a structure like that of an aggluti- 

 nation of pease. It occurs in the middle 

 Oolite Formation. 

 261 



PI'STACITE. The name given by 

 Werner to some mineral substances, now 

 more generally designated by the name 

 of epidote, a sub-species of prismatoidal 

 augite. 



PISTIL {pistillum, a pestle). The 

 name given by botanists to the female 

 apparatus in plants. It occupies the 

 centre of the flower, and is distinguished 

 into three parts ; viz. the ovary, the 

 style, and the stigma. 



PISTON. A short plug of metal, or 

 other solid substance, fitted exactly to 

 the cavity of the barrel or body of a pump. 

 It serves the purpose of exhausting the 

 air from the barrel, and is hence com- 

 monly called the sucker. There are two 

 kinds of pistons used in pumps, the one 

 with a valve, and the other without a 

 valve, called a, forcer or plunger. 



PIT COAL. Common coal ; so called 

 from its being obtained by sinking pits 

 in the ground. 



PITCH-ORE. The hydrous protoxide 

 of uranium, also called indivisible ura- 

 nium; found in primitive rocks. 



PITCHSTONE. A quartzose rock, of 

 a uniform texture, belonging to the un- 

 stratified and volcanic classes, which has 

 an unctuous appearance like that of in- 

 durated pitch. 



PITTACAL (TTi'TTa, pitch, Ka\6?, 

 beautiful). A beautiful blue colouring 

 matter, discovered in the oil of tar. 



PITTED TISSUE. Bothrenchyma. A 

 variety of the celluhir tissue of plants, hav- 

 ing its sides marked by pits, sunk in the 

 substance of the composing membrane. 

 It was formerly designated by the term 

 dotted ducts, vasiform tissue, &c. 



Pl'TTIZlTE. Pitcliy iron ore; a 

 variety of bog iron ore found near Li- 

 moges in France. 



PLACE'NTA. Tn Botany, that part 

 of the ovary from which the ovules arise. 

 It generally occupies the whole or a 

 portion of one angle of each cell. It is 

 sometimes elongated in the form of a 

 little cord, called the umbilical cord, as 

 in the hazel. 



PLAGIO'STOMI (TTAaviop, transverse, 

 <Tr6fxa. a mouth). An order of cartilagi- 

 nous Fishes, which have tneir mouth 

 placed transversely beneath the snout. 



PLANE, or PLANE SURFACE. In 

 geometry, this is a surface such that the 

 right line, which joins every two points 

 which can be assumed upon it, lies en- 

 tirely in the surla-e. Hence, a plane 

 rectilineal figure is any p(»rtion of a plane 

 surface which is included by right lines, 



