PLA 



PLO 



PLANT LICE. See Aphis. 



PLASHLXG. "A mode of repair- 

 ing or making a hedge bj- bending 

 down a portion of the shoots, cutting 

 them half through near tlie .ground, to 

 •render them more pHable, and twist- 

 ing them among the upright stems, 

 so as to render the whole effective as 

 a fence, and, at the same time, pre- 

 serve all the branches alive. For 

 this purpose, the branches to he plash- 

 ed or bent down must not be cut 

 more than half through, in order that 

 a sufficient portion of sap may rise 

 up from the root to keep alive the 

 upper part of the branches. Where 

 hedges are properly formed and kept, 

 they can very seldom require to be 

 plashed ; but this mode of treating a 

 hedge is most valuable in the cases 

 of hedges abounding with hedge-row 

 trees, when from neglect, or from 

 any other cause, the hedge has be- 

 come of irregular growth. 



PLASTER. A mixture of burned 

 plaster of Paris with water, which 

 sets with great rapidity, and is used 

 in moulding and the finer work of 

 plasterers. 



PLASTER OF PARIS. Gypsum, 

 which S6G 



PLASTIC. Capable of being 

 moulded, adhesive. 



PLATBAND. A square moulding, 

 projecting from the wall less than its 

 width. 



PLATE. In building, a timber ly- 

 ing horizontally on a waif to receive 

 the ends of girders, joists, rafters, &c. 



PLATFOR.M. A level structure 

 of any materials, to receive a super- 

 incumbent building. 



PLATINUM, PLATINA. An ex- 



D D D 



pensive metal, of the appearance of 

 silver, hut very infusible, and of spe- 

 cific gravity 21-5. It resists most 

 chemical reagents, and is used in 

 chemistry for crucibles, and in foil 

 and wire for numerous purposes. 

 The bichloride of platinum, dissolved 

 in alcohol, forms insoluble salts with 

 chloride of potash, or anunonia, but 

 not with soda, and is used to separate 

 the former alkalies from the latter. 



PL.\TYPH YLLU.M. The Katydid, 

 wliich sgg. 



PLATYSOMES, PLATYSOMA. 

 A family of coleoptera with wide and 

 fiat bodies, living under the bark of 

 trees. 



PLEASURE GROUNDS. 

 Grounds laid out in shrubberies, 

 groups of trees, winding walks, and 

 lawns. 



PLESIOMORPHISM (from T:l7]aL- 

 Of, near, and fiop6r], form). A terra 

 used to denote a similarity between 

 different crystals in their angles, but 

 not an identity. 



PLETHORA. A fulness of the 

 circulatory system, almost amount- 

 ing to disease, and calling for bleed- 

 ing. 



PLEURA. The serous membrane 

 surrounding the cavity of the chest, 

 lungs, and heart ; it consists of two 

 parts, which are united along the 

 middle, and forms the mediastinum. 

 Its infiamination is called pleuritis, or 

 plcurisv. 



PLICIPENNATES, PLICIPEN- 

 NES. Neuropterous insects, the in- 

 ferior wings of many of which are 

 larger than the upper pair, and are 

 folded lengthwise, as the caddis flies. 



PLINTH. The lowest form or 

 member of the base of a column, of 

 a square figure and small height. 



PLIOCENE. The uppermost por- 

 tion of the tertiary formation, con- 

 taining recent fossds, for the most 

 part. 



PLOTTING. In surveying, laying 

 down on paper the angles and lines 

 measured to calculate the contents 

 of a given tract ; it is done with a 

 protractcr or plotting scale. 



PLOTTING SCALE. " It con- 

 sists of two graduated ivory scales, 



589 



