OTA 



[349] 



X Y 



The membrane which covers the 

 bones ; that, however, which covers 

 the bones of the skull is called 

 the pericranium. 



PEHIPHOKA/NTHITTM. When bracts are 

 collected into a whorl, as in um- 

 belliferous plants, they are said to 

 form an involucre, which, if very 

 small, receives the diminutive 

 name of involucel. This kind of 

 organ is very remarkable in com- 

 pound-flowered plants, appearing 

 as if it constituted a calyx common 

 to many flowers ; and hence it 

 used to be called a common calyx. 

 It, however, does not differ from 

 the involucre in any thing more 

 than its bracts being more nu- 

 merous, more closely packed, and 

 parallel with each other, instead 

 of diverging. Foreign botanists 

 have given the names Periphoran- 

 ihium and Peticlinium to this kind 

 of involucre. 



PER'MEABLE. fpermeo, Lat. from 

 per through, and meo to pass or 

 glide ; permeable, Fr.) That may 

 be passed through without rupture 

 or displacement of its parts. Ap- 

 plied to substances that admit the 

 passage of fluids. All permeable 

 strata receive rain-water at their 

 surface, whence it descends until 

 it is arrested by an impermeable 

 subjacent bed of clay, causing it to 

 accumulate, and to form extensive 

 reservoirs, the overflowing of which 

 on the sides of valleys constitute 

 the ordinary supply of springs and 

 rivers. 



PER'MIAN. The newest of the primary 

 or palaeozoic formations, consisting 

 of the following deposits in ascend- 

 ing order. 1. Red sandstone and 

 marl. 2. Conglomerates and brec- 

 cia. 3. Lower red sandstone and 

 marl. 4. Magnesian limestone. 

 The term Permian is derived from 

 the district of Perm in Russia, 

 where the formation in question 

 is very extensively developed. 

 Lycett. 



PE'RNA. A genus established by 

 Bruguie*res. A flat, irregular, sub- 

 equi valve, compressed, foliaceous, 

 marine, bivalve. Several parallel 

 cavities across the hinge opposed 

 to each other in the two valves, 

 and lodging as many elastic liga- 

 ments : anterior margin with a 

 passage for a byssus. Recent and 

 fossil. 



PE'EOXIDB. When oxygen is com- 

 bined with any substance, in the 

 highest proportion it is capable of, 

 whatever that may be, it is called 

 a peroxide. 



PERSI'STENT. (from persisto, Lat. to 

 abide.) In botany, opposed to 

 deciduous. Not withering and 

 falling; remaining. 2. Unbroken; 

 continuing. In almost every for- 

 mation the individual strata are 

 rarely persistent for a great distance. 



PE'RSONATE. A term applied to a 

 monopetalous flower of an irregular 

 form, the border of the corolla 

 having an oral appearance with 

 the labia closed. 



PE'TAL. (TreVaXoi/, Gr. p&tale, Fr.) 

 The name given to each leaf of the 

 corolla, or flower of a plant. 



PE'TALITE. (from Treraw and .\t0os, 

 Gr.) A mineral, of a reddish, or 

 greyish-white colour, which has 

 only been found in Sweden. It 

 consists of silica 7 7*0, alumina 17 f O, 

 lithia 6*0 ; or according to others, 

 of silica 76-21, alumina 17'22, 

 lithia 5*76. It occurs in a mine of 

 black iron ore, associated with 

 spodumene, felspar, tourmaline, 

 mica, and quartz. Its fracture is 

 foliated; scratches glass; brittle, 

 and translucent at the edges. 

 Specific gravity 2-62. 



PETALO'IDE^E. In botany, the second 

 order of the class Endogens, com- 

 prising the banana, orchis, palms, 

 lilies, &c. 



PE'TIOLE. (from petiolus, Lat. the 

 stalk of fruits.) In botany, a foot 

 stalk; the stalk, or stem, whiclj 

 connects the leaf with the branch. 



