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fecond, and the fourth the fame meafure to the right hand of the third : and this two inches and an half muft be carefully meafured from the center of one hole to the center of the other. Each of thefe holes is a mortaife of an inch and quar- ter wide, and is three inches and an half" long at the top, and three inches at the bottom. The two oppofite fides of this hole are parallel to the top and bottom, but the back is ob- lique, and determines the obliquity of the flanding of the coul- ter, which is wedged tight up to the poll. The coulter is two foot eight inches long, before it is worn ; the handle takes up fixteen inches of this length, and is allowed thus long, that the coulter may be driven down as the point wears away. Tull's Horfe-hoeing Hufbandry, p. 132, feq. See Coulter.

Tre/ubing-pLOUGH. See the article Trenching.

Plough-*^, in our old writers, a right of tenants to take wood to repair ploughs, carts, and narrows, and for making rakes, forks, &£.

Plough-/j<W, a name given by the farmers to the foremofl half of the plough, or that part containing the two wheels and their fpindle, the box, the crow-ftaves, the pillow, the wilds, the tow-chain and bridle chain, and the flake: all which, fee under their feveral heads, and under the article Plough. Tull's Hufbandry.

Plough-^// a name given by the farmers to that part of a plough which contains the beam, the coulter, or coulters, the fhare, the meat and under-fheet, the earth-board and handles, as atfo the drock, the ground-wrifls, and the retches : all which fee under their feveral heads, and under the article Plolch. Tull's Hufbandry.

PLUKNETIA, in botany, the name of a genus of plants de- fcribed by Plumier, and called by this name in honour of Pluknet, the great Englifh botanift.

The characters are thefe : It produces male and female flowers on the fame plants. The male flowers have no cup, but are compofed of four expanded petals of an oval figure, and in the place of ftamina, there is placed in the center of the flower a fliort pyramidal hairy body. The female flowers have no cup, and the petals in thefe are difpofed as in the male. The ger- men of the pifHIlum is fquare. The ftyle is (lender, very long, and crooked. The fligma is peltated and divided into four parts. The fegments are obtufe and flat, and each has a remarkable fpot in the center. The fruit is a deprefled fquare capfule, hollowed at all the angles : it contains four bivalve cells : the feeds are fingle, roundifh, and comprefled, and bluntly pointed at one end.

Linnaeus obferves, that this fructification is verv Angular, and is very defirous that fome perfon fhould examine carefully the growing plant, fince Plumier, who was not over curious about the nicer parts of the fructification of plants, may have in fome fort mifreprefented this. Plumier 1 3. Linncei Gen. PI. p. 5.7.

PLUM-f/w, prunus, in botany. SeePRUNUs.

All the fpecies of plums have within their fruit a hard {tone, within which there is contained a foft and tender kernel : this kernel contains the fcminal plant, from which would be pro- duced another tree of the fame kind, if it were fet in the ground ; and it is very natural to fuppofe, that the only ufe of the thick ftone or bulk of this, was only to preferve its tender fubftance from rotting too foon in the earth, and to give it a proper time for developing its parts, to preferve its natur. 1 oilynefs during that time, and to furnifh from its own fub- fiance a proper nourifhment to the growing plant 5 for obfer- vation fhews, that it finally breaks into a very fine powder. There has not been found any fpecies of plum which had not its kernel contained in a ftony coat of this kind, from what- ever grafts they h ,ve been propagated; nor is there any art known by which the kernel of this fort of fruit can, while growing, be deprived of its coat.

Mr. Marchand, however, in the year 1735, fhewed before the academy of feiences at Paris, cem'm plums, whofe kernels had no ftone or fheil round them ; and found that they grew upon a tree which never had produced any others, and which had been known to produce fuch for twenty years The kernel in thefe was covered with a reddifh (kin, which was rough to the touch; and within that, with another which was thinner and white The kernel had nothing particular in it, except that it carried on one fide of its outer furface, and that always in the fame place, a little flony prominence, more or lefs dented on its convex part : this is ufually a twelfth of an inch broa I and two thirds of an inch long, and has no other appearance but that of a diflempered part of the kernel, only that all the kernels have it.

The thick wrinkled fkin which furrounds the kernel, feemsin this cafe to fupply the place of the flone or hard fhell ; and in this alio it refembles it, that the pulp of the fruit parts eafily and readily from it; and the hard oblong body, which is placed on one fide of the kernel, i, by no means proper for this pur- pofe. Mem. Acad. Scienc. Par. 1735.

All the forts of plums are propagated by budding, or grafting them upon (locks of the mu(de-plum, the white pear-/>/zw;, the St. Julian, or the bonum magnum. See the article Inoculating. Budding is much properer than grafting for thefe trees, as they

are apt to throw out a great deal of gum from the wound : and the trees fhould be no more than one year's growth from the bud, when they are tranfplanted ; for if they are more they feldom fucceed well, being very fubject to canker; and if they efcape that, they ufually produce only two or three luxu- riant branches. The whole management of planting and pruning them is the fame with that of peaches. See the ar- ticle Peach.

If the walls againft which they are planted are low, they fhould be fet eighteen feet afunder; if they are higher, then fourteen or fixteen.

Plums fhould have a middling foil, for they feldom fucceed well either in too moiit or two dry a one ; and when planted againft walls, fhould have an eafl or a fouth-eafl profpecr. If they have one at full fouth, they are apt to fhrivel up, and mealy.

Plums in general fucceed very well with proper care on efpa- liers ; they will alfo bear very well as flandards, but the fruit will not be fo well tafted, Plums do not only produce their fruit on the lafl year's wood, but alfo on fpurs that come out of the woo^ of two or three years old. It is a common error to be too free with the knife in the winter-pruning, cutting off" the extremities of all the branches; the confequence of which is, that there are an over quantity of young fhoots produced, and the fruit is fmall and poor. Millers Gard. Diet.

PLUMBAGO, leadwort, in botany, the name of a genus of plants, the characters of which are thefe : the flower confifis of one leaf, and is of a funnel-fhape, and divided into feg- ments at the edge. The cup is tubular, and from it arifes a piflil, which is fixed like a nail to the lower part of the flower, and afterwards ripens into an oblong pointed feed, which remains in the cup to ripen.

The fpecies of plumbago, enumerated by Mr. Tournefort, are thefe: 1. 'I he ordinary plumbago, called by fome lepidium and dentilkria. 2. The white flowered plumbago. 3. The American plwnbago, with a large beet-like leaf. 4. The prickly climbing American plumbago, with a fmaller beet-like leaf. Tourn. Infl. p. 140.

Plumbago, in the hiftory of the gems, a word ufed by the Ro- man authors to exprefs a blemifh common to their worfe kinds, and greatly debafing their value. It was a fort of bluifh or blackifh deadnefs in the flone, which mixed itfelf with the other colour, be that what it would, and rendered it dull and dead. The emerald was of all the other gems the moft fubject to this fault ; and in this cafe, its fine green co- lour was always rendered cloudy and bluifh; and in fome lights the flone appeared of a dufky greyifh blue, with no green at all in it The Bactrian emeralds, which were in great efleem with the antients, were often fubject to this im- perfection ; and thofe of Cyprus, taken out of the copper- mines, tho' fubject to many other imperfections, were ufually quite free from this.

Plumbago, in mineralogy, a name given by many authors to a fort of foflil, having very much the appearance of a lead-ore, bur not fuch in reality.

It is called alfo galena, blende, and mock-lead. It is ufually of a plated texture, and dark blackifh blue colour, like the lead-ores ; but on trial yields no metal. See BtACK-lead.

PLUMBATA, among the antients, a kind of fcourge, the thongs of which were armed with leads. Pit'ifc. in voc.

Plumbat;e likewife fignified leaden balls, ufed by foldiers to annoy the enemy with ; whence the foldiers were called mar- tiobatbuli. Pit'ifc, in voc.

PLUMBUM (CvJJ— Plumbum nativum, native had. It is pretended by fome, that the famous W-mineral, found near Freyung, in the Upper Palatinate, is native lead : but this is an error ; we have an account of it in the philofophical tranf- adtions, which does not give any ground for this thought. All that is there faid of it is, that it was at that time much efteem- ed among the aflayers of metals, as containing no mixture of any other metal with the lead: this might well recommend it to them, as faving much confufion, or much trouble in fepa- rating its heterogene contents ; but it is faid exprefly there, that it is an ore, not a native metal : there being two kinds of it, one a chryflaliine ftone, almofl all pure lead; the other not fo rich, but of a more rough and coarfe texture. Neither of thefe could be native lead; and it is remarkable, that they had lefs appearance of being fo than many of our common ores. Phil. Tranf N Q. 3. See ihe article Lead.

Plumbum ujiam. See Lead, Cycl, and Suppl.

PLUMERIA, in botany, the name of a genus of plants, the characters of which are thefe : the flower confifls of one leaf, and is of the funnel-fhaped kind, and divided into feveral feg- ments at the edges. The piflil aaifes from the cup, and is fixed in the manner of a nail to the hinder part of the flower. This finally becomes a podded fruit, ufually double ; and when ripe, opening in the middle, and difcharging a number of ob- long foliated feeds, which were placed like fcales over one another in the feed-veflel, and affixed to a placenta. The fpecies of plumerie, enumerated by Mr. Tournefort, are thefe: 1. The plumeria with a rofe-coloured and very fweet flower. 2. The fnow- white-flowered plumeria, with long, narrow, and pointed leaves. 3. The plumeria with fnow-whitc flowers, and fhort obtufe leaves. Tourn. lnft p. 659.

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