Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/281

 POP

POP

Pontica vim, a term ufed to exprefs acid, feculent, and

rartarous wines. PONTICUM mel, a name given to a fort of pbifonous honey PONXICUS mw, in zoologv, the name of a creature described by the antiencs, and Cuppofed to be the fame with our fquir- rel. See So virus. _.

PONTLEVIS in the manege, a diforderly refitting action 01 a borfe, in difobedience to his rider ; in which he rears up feve- ral times, and rifes fo upon his hind legs, that he is in danger of coming over. It is cured by clapping fpurs fma'rtly to him, as the fore feet are returning to the ground. POOL (Cyd.)— ?oot -fnipe, in zoology, a name given in many

parts of England to the redfhank. POOR, or Power, in ichthyology, a name given by the people of Cornwall to a fpecies of bearded gad us. Seethe article Gadus. POOSPANhCUM, in natural hiftory, the name of a peculiar fpecies of foffil in the Eaft Indies. It is of the nature of the blende, or mock-lead, with us; but is not formed into fo large flakes, but more refembles the fteel-grained lead ores. It is found in the beds of rivers, and when calcined, it is ufed with the juices of certain herbs, for ulcers and other cutaneous diforders. Before calcination it isalfo ufed by the women to make their hair of a fine glofly black colour, which it per- forms very neatly. PQP/E, among the Romans, were fuch perfons as attended the facrifices, whofc bufmefs it was to provide victims, and to kill them after they had knocked them down. They were half naked, their fhoulders, arms, and upper parts of their bodies being uncovered as far as their navels, and the reft covered to the mid-leg with a linnen apron, or the fkins of the facrifices ; and they wore crowns of laurel upon their heads. Damt in voc. See Pcpe, CycL POPE, in zoology, a name by which the people in many parts

of England call the anas artiica dufii. See the article Duck. POPLAR, poputus, in botany, the name of a genus of irees, the characters of which are thefe : the flower is of the amen- taceous kind, being compofed of a number of fmall leaves, furnifhed with a great quantity of apices ; but thefe are barren. The embryo fruits are produced on thofe trees which produce none of thefe flowers-; thefe are fpiked, and confift of many leaves, under which there lies a fort of bell, which contains the embryo feed vefl'el, which finally becomes a membrana- ceous pod of a comprefled figure. Thefe are difpofed in a fpiked form, and open into two parts, containing feeds winged with down. To this it is to be added, that the poplar has a peculiar and appropriated general appearance, by which it is obvioufly diftinguifhed from the willow. See Tab. i. of Bo- tany, Clafs 19.

The fpecies of poplar enumerated by Mr. Tournefort, are thefe: 1. The common white poplar, with large leaves. 2. The common white poplar, with fmaller leaves. 3. The common black poplar. And, 4. The poplar with trembling leaves, called the afpen-tree. Town. Inft. p. 592. The poplar, whether black or white, may be eafily propagat- ed, either by layers, cutings, or fuckers, of which the white kind always produces a great many from the root. The beft feafon for the tranfplanting thefe fuckers is. in October, when the leaves begin to decay ; and they mould be removed into a nurfery for two or three years, at the end of which time they will have got ftrength enough to be transplanted into the places w>here they are to remain.

When they are to be propagated by cuttings, it is beft to do that in February, cutting off large truncheons of eight or ten foot long ; which being thruft down a foot deep in the ground, •will take root very quickly, and if the foil be moift, will grow to a confiderable fize in a very few years. The black poplar is not fo eafily raifed from thefe large trun- cheons, but mould be planted in cuttings, of about a foot and a half long, planting them a foot deep in the ground. This will grow on almoft any foil ; but does much better on a moift one than on' any other. They are the fitteft of all trees for raifing a made quickly, as they will grow fourteen foot in heighth fometimes in one feafon, and in four or five years will be large trees. Millers Gard. Diet. Poplar-£j//j. The black poplar is famous among naturalifts for producing a fort of galls or protuberances, of various fhapes and fixes, on its leaves and branches, which have been ufually miftaken for the lodgments of worms hatched from the egas of an ichneumon-fly; but they are in reality produced by the operation of a viviparous infect, called the puceron, for the bringing up of its off-fpring. See Puceron. Thefe galls are of the bladder kind, being ufually fkinned over, and more or lefs hollow within, not woody, as thofe of the oak, &c. They proceed from different parts of the plant, fome from the pedicles of the leaves, and many from the young {hoots. They are very various in figure, fome being roundifh, others oblong, others crooked and contorted in va- rious directions, and fome of them are in the figure of horns, like thofe of the turpentine tree, and of the fame origin. "When any of thefe galls are opened at a proper feafon, there is found in them a vaft number of infects of the puceron ' kind, all the family of one female parent, who formed the

bladder or gall for their reception : if they are opened a little earlier than this, there is only one, that is the female parent^ found in them : and finally, if they are examined later, they are found empty, the young brood having made their efcape out of them; and at this time the {talks of the leaves are found twifted about and fwelled ; and in thefe fwellings, which are a new fort of gal's, are found the young pucerons, which had efcaped out of the larger gall or bladder, which had ferv- ed for their common home.

Mr. Malpighi obferved thefe fpiral tubercles on the pedicles of the leaves of this tree, and fas given a figure of them in his twenty-ninth plate ; but he had no knowledge of this ani- mal which occafions them, nor, indeed, any idea of a vivi- parous creature being at all concerned in the formation of galls on vegetables ; his whole fyftem being founded upon their being the effect of the eggs of a fly depofited in thum : he has therefore'defcribed thefe fpiral ones among the reft, as being of the fame origin, and filled with eggs ; but if he had accurately examined the bodies themfelves, he would have found them filled with real living infects, not eggs of any kind. Befides thefe galls on the ftalks and pedicies of this tree, there are alfo others found on the leaves themfelves; and thefe are always joined to and prolonged from the middle rib of the leaf, which is properly only the continuation of the pedicle, and feem only to be the middle rib diftended and fwelled, the rib being wanting in the part where they are, on the upper fide of the leaf, and on the under fide there being only a little flit or crack, hut with its edges nicely joined in the place of it ; and if the leaf be preficd between the fingers, this crack will open wider, and fhew the internal cavity of the gall or bladder that appears on the upper fide, and the little pucerons are feen living in it; but as foon as the leaf is left to itfelf again, the edges of this flit clofe, and the creatures find themfelves as well defended from all injuries as before. There is great reafon for thefe little creatures thus hiding themfelves, for they are, when expofed to the view of other infects, fed upon by many little animals ; and it i a common thing, on taking one of them out of its cell, and fettlng it on the furface of the leaf, to fee a lktle'yeliowifh bug immediate- ly come up, and feize upon it, and fuck it to,, death with its trunk, which is extremely fine, but is eafily introduced into the body of this creature.

The care the pucerons take to hide themfelves, and their young, from thefe enemies, is not, however, always fufn- cient; for it is a very common thing to find a fmall red infect, of an oblong form, and endued with a very long trunk, lodg- ed in the very cells, and eating them up in their .habitations. This is fuppofed by Reaumur to be the bug before mentioned in its nymph ftate, and had doubtlefs been lodged in this place by its parent in the egg, in order to feed upon the young animals.

The pucerons which live upon the poplar have another method of fecUring themfelves from injuries. They have a method of forming a bladder of the very fubftance of the leaf itfelf, and this is very capacious, its cavity being much larger than that of any other kind : this is done by bringing the two edges of the leaf together, fo that the leaf has its whole length, tho' only- half its breadth, and the edges are every- where fattened together, while the whole fpace within remains free, and is a fit receptacle for the animals. 1 he cavity is much largeft near the rib, and the leaves which are thus folded have not the colour or the glofs of the others ; but are covered with a vaft number of little tuberofities of a reddiih colour, and of the.bignefs of 'a pin's head. This is ufually effected while the leaves arc young and green, and at firft there are only found a few fmall pucerons in them ; by thefe may be feen the true caufe of the joining together of the leaf into a fort of fack or cafe. If two or three of thefe are found, as is very frequent on the under fide of the leaf of this tree, they are always found fixed in their fucking pofture, near the middle rib ; and if the upper fide of the leaf be examined, there will be found on it a yellowifh or pale green tubercle, juttoppofite to every one of the infects. Thefe tubercles are fo many fmall bladders or leaf |w//i; and as they continually increafe in fize, and by that increafe force out the middle part of the leaf on which they are placed into a fwellihg up- wards, the confequence is, the drawing together of the edges, fo as to form a cafe or bag, of which the outfide of "the leaf makes the external covering, and the infide the lining. The regularity of the placing of thefe tubercles in the center of the leaf is the reafon of the edges falling evenly together; and fometimes, when the tubercles are lefs. regu- larly fituated, the joinings have feveral empty or open fpaces between them. Thefe two or three firft tubercles are after- wards furrounded by a vaft number of new ones, which are the effects of the progeny of the firft obferved infects; and thus the generality of die larger leaf or bladder-^/// are form- ed, as well on the poplar as on the elm, the apple, and the other trees on which they are fo frequently found. The pucerons which are found inhabiting the leaves of the poplar thus curled up, are of the fame fhape arid figure with thofe of the other parts of the fame tree, and probably are the very fame fpecies ; tho' fome fuppofe them different from the

dif-