Pistil 



Plane of Symmetry 



Pis'til, Pistil' lum (Lat., a pestle), (1) 

 the female organ of a flower, con- 

 sisting of ovary, style and stigma, 

 when complete; (2) the archegonium 

 of the genus Andreaea (Hooker 

 and Taylor) ; pistilla'ceous ( + 

 aceous), growing on the pistil ; 

 pis'tillary, relating to the pistil ; ~ 

 Cord, "a channel which passes 

 from the stigma through the style 

 into the ovary " (Lindley) ; pis'til- 

 late, pistilla'tus,(\) having a pistil ; 

 (2) applied to a flower having pistils 

 only, a female flower ; pistillif'er- 

 ous, -rus (fero, I bear), bearing 

 pistils ; Pistmid'ium, pi. Pistillid'ia, 

 archegonia, organs analogous to 

 pistils ; pistillig'erous (gero, I bear), 

 pistillif erous (fero, I bear), bearing 

 one or more pistils ; Pistillo'dy, the 

 change of floral organs into carpels. 



Pit, (1) a small hollow or depression, 

 as in a cell- wall ; (2) the endocarp 

 of a drupe containing the kernel or 

 seed-stone (Crozier) ; ~ Cham'ber, 

 the cavity of a bordered pit on 

 each side of a closing membrane. 



Pitch, a resinous exudation from the 

 spruce, Picea alba, Link, etc. 



Pitch'er, a tubular or cup-shaped 

 vessel, the terminal portion of a 

 leaf-blade, usually containing a 

 secreted digestive fluid ; an as- 

 cidium ; ~ shaped, campanulate, but 

 contracted at the orifice. 



Pith, the spongy centre of an exo- 

 genous stem, chiefly consisting of 

 parenchyma; the medulla ; ~ Flecks, 

 dark marks in timber due to the 

 cavities made by the larvae of in- 

 sects in the cambium, but at once 

 filled up by cellular tissue (Hartig). 



pit'ted, marked with small depres- 

 sions, punctate ; used in a re- 

 stricted sense for pits in cell-walls ; 

 <~ Ves'sels, dotted ducts, vessels 

 with secondary thickenings leaving 

 thinner spots. 



pitu'itous (pituita, phlegm), relating 

 to mucus (Crozier). 



Pityri'asis (irlrvpov, scurf) versic'olor, 

 a skin disease caused byMicrosporon 

 Furfur, Rob, 



Placen'ta (Lat., a cake), (1) the organ 

 which bears the ovules in an ovary, 

 often the margin of the carpellary 

 leaves ; (2) in Cryptogams, the 

 tissue from which sporangia arise ; 

 ~ shaped, placentiform ; Pla'- 

 centary, t a placenta which is long 

 and narrow and bears many ovules ; 

 Placenta'rium, placenta ; Placen- 

 ta'tion, Placenta'tio, the disposition 

 of the placentae ; placentif erus 

 (fero, I bear), bearing placentae; 

 placen'tiform, placentiform' is (for- 

 ma, shape), quoit-shaped or like a 

 flat cake. 



placochromat'ic (ir\d, ir\dicos, a flat 

 body, xpuwriKo s, relating to colour), 

 used of Diatoms with endochrome 

 in plates or disks ; cf. COCCOCHRO- 



MATTC. 



placo'des (TrXa/ct&Sijs, flat), used by 

 Koerber for Lichens resembling a 

 rounded plate in figure. 



Plac'ophytes (ir\d%, a flat body, <f>vrov, 

 a plant), a term applied by Schuett 

 to the Peridineae, Diatomaceae and 

 Desmideae ; cf. SAC'COPHYTES. 



plagiod'romous (irXdyios, oblique, 

 Sp6fjt,os, a course), applied to tertiary 

 leaf-veins when at right-angles to 

 the secondary veins ; Plagiophoto- 

 tax'y (0<Ss, <t>w6s, light, rdij, 

 order), the oblique arrangement of 

 chlorophyll granules with regard 

 to incident light(Oltmanns) ; plagio- 

 phototroplc (rpoTT-fj, a turning), 

 assuming an oblique position to 

 the rays of light, as the leaflets 

 of Hobinia, Tropaeolum, etc., 

 (Oltmanns); plagiotrop'ic, having 

 the direction of growth oblique 

 or horizontal ; Plagiot'ropism, the 

 condition described. 



plain, applied to a margin which is 

 not undulate, though it may be 

 sinuate (Crozier). 



plait'ed, plicate. 



plane, pla'nus (Lat.), level, even, flat : 

 Plane of Insertion, a plane which 

 passes through the point of inser- 

 tion of a lateral organ and coincides 

 with the main axis and that of the 

 organ ; ~ of Sym'metry, that which 



198 



