Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/707

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V E G

fides of their ftalks • thefe in three years time produce perfect plants with their flowers ; and what are thefe but fo many fe- minal points ready upon occafion to be developed. Nothing is fo obvious, as that the flips, or cuttings of trees, when planted in the ground, produce roots in one part, and buds for branches from another, and fo finally become trees, like thofe from which they were cut ; and this, though the piece that is planted, has no vifible appearance of any bud in any part of it.

We alfo know, from daily experience, that many plants fhoot out roots from their ftalks as they grow, and that though this ufually happens in places where there is fome folid fubftance for thefe new roots to fatten themfelves to, yet it happens alfo in fome plants where there is no fuch ufe for them ; and what are thefe roots in a new part of a plant, but the effect of fo many feminal points, ready to grow both into roots and into branches, in all thofe places.

Among the thick and flefhy leaved plants, as the opuntia, and other of the fucculent plants of the Indies, there needs no more to produce a new plant, but to cut off a part of a leaf, and flick it into the earth, where it will at once take root, and produce a new plant in a very fhort time. A thoufand other inftances of this kind might be given ; but thefe may be fufficient to prove, that there are, in almoft all parts of plants, certain feminal points, which, like the plrmtula feminalis, in- clofed in the perfect feed of each, need only humidity, and a proper degree of warmth, to develop and unfold themfelves into perfect plants.

We are not therefore to wonder at the imitation of perfection in any irregular productions of vegetables, fince it appears that there are numbers of perfect plants contained in every part of a growing plant, of the fame kind. Mem. Acad. Par.

The perpendicular afcent of the branches and trunks of trees, while their roots are at the fame time running perpendicularly downwards, has been a fubject of admiration to all who have confidered the laws of Vegetation ; and none feem to have well underftood or explained it, till Mr. de la Hire, in the . memoirs of the Paris Academy in 1708. He fuppofes that, in all vegetables, the root is furnifhed with juices of a much thicker and coarfer kind than thofe of the trunk and branches, and that the juices of this part are heavy and denfe ; while thofe of the upper parts of the fame vegetable are much more light and fine.

In effect, the root of the plant pafles with all naturalifts as a part analogous to the ftomach in animals, where the nourish- ment is digefted, and refined to fuch a degree as is neceflary for its being received into the finer and tenderer veflels of the trunk and branches.

This difference of the juices for the fervlce of the different parts of the plant, neceflarily fuppofes a different fhapc and fize of veflels for its reception, and, in a word, a different contexture in the parts ; and there is no doubt but that this contexture is preferved in its different manner, even in the firft: rudiments of the plant or tree, in the feed. We are therefore to conceive, even in this embryo plant, a fort of divifion between the root and the ftalk} fo that all that is to be on the one fide of that divifion, is to receive a finer juice for its nourifhment, and all that is on the other fide, a coarfer. Now fuppofmg that the plantula feminalis, or em- bryo plant in the feed, be turned the wrong end upwards, in the fowing or placing that feed, fo as to have its root turned upward, and its ftalk downward ; yet the veflels of the root being larger than thofe of the ftalk, and confequently capable of receiving coarfer and heavier fluids j thefe weighty fluids muft always bend its tender fibres downwards, though their natural pofition in the feed would point them upward ; they will always be bent downward alfo by the greater force, the longer they grow. For, fuppofmg the fixed point, already mentioned, to be at firft at any given diftance from the extre- mities of the roots, and they bending downward, it is plain that, as they increafe in length, they will be of more force, as the arms of a lever are always more powerful the longer they are.

While all this is doing in the root, the communication being open between that and the ftalk, the finer juices are received there, and thefe as naturally throw the ftalk into an erect po- fture, as the others bend down the root ; fo that, in a few days the whole plant becomes turned right, the fixed point between the root and ftalk having remained unmoved, and all on the one fide of it having conftantly had a tendency up- wards, while all on the other had the fame tendency down- ward.

From this time forward the root pufhes with more regularity downward, and the ftalk upward, than before. There is, however, this great difference in their growth, that the ftalk and branches find no refiftance to their mooting up, while the roots find a great deal to their fliooting downward, by means of the folidity of the earth, whence the branches advance much fatter and farther in their growth than the roots ; and thefe lafl, often finding the refiftance of a tough earth unfurmount- able, turn their courfe, and fhoot almoft entirely horizon- tally. Mem. Acad. Par. 1708. Artificial Vegetation. Many of the procefles and opera-

tions in chemiftry afford productions, whether of falts or me- tals, or of whatever other fubftance, which very much refera- ble plants of one kind or other, whence they have been called metallic Vegetations. But though many have been hence in- duced to believe, that thefe productions were formed in the manner of vegetables, there is not the leaft ground for fuch an opinion from reafon or experiment.

Mr. Homberg, who has treated very accurately of the feveral kinds of thefe chemical Vegetations, divides them into three different clafles.

Thofe of the firft clafs are fuch as confift of a pure mafly me- tal, without the mixture of any foreign matter whatever. Thofe of the fecond clafs are compofed of a difTolved metal, which, though it has concreted afterwards, yet retains a part of the menftruum in it : And the third clafs contains thofe which have no metal in them, but are .merely compofed of falts, oils, or earths, or of combinations of thefe. All the productions of the firft kind are made without the ad- mixture of any liquor, and are merely owing to the force of fire. Thefe are of a firm and folid texture, and may be ta- ken out of the veflels in which they were made, without dan- ger of breaking them. On the other hand, the Vegetations of the fecond kind are all formed in a fluid, and are all fo brit- tle, that they are not to be touched without breaking. Of the third kind, fome are formed, or will fubfift at leaft, in the dry air j others are very tender, and are formed only in fluids, the very ftirring about of which deftroys them. Examples of the firft kind may be feen in the following pro- cefles : Make an amalgama, with an ounce or two of fine gold or filver, with fix times the weight of pure mercury revived from cinnabar ; break the amalgam to pieces, and wafh it fe- veral times with river water, till it leaves no longer any co- lour or foulnefs in the water ; after this, let it be dried, and, putting it into a glafs retort, diftil it in a gentle fand heat, which fhould be continued two days. The longer the heat is preferved, before all the quickfilver is raifed and carried over, the more beautiful and perfect will the Vegetation be. At the conclufion of the operation, the fire muft be raifed to fuch a degree, as to carry over all the mercury, after which, let the fire go out. All the mercury will be found in the receiver, and all the gold or filver will be left in the retort. It will be foft and pliable, and of the moft beautiful colour the metal is capable of receiving ; and from the main mafs, at the bottom, there will be thrown out a number of beautiful branches, of different heights, and differently ramified, fo as to reprefent flirubs or plants. Thefe may be feparated from the mafs at the bottom, and preferved. They really referable, with great exactnefs, fome forts of vegetables ; but when we con- fider the fortuitous rife of thefe, and the regular organized bodies of the true vegetables, with their manner of explication from the feed, there is but a very faint rcfembkince to be per- ceived between the one and the other.

Another of thefe Vegetations of the firft clafs, is this : Melt an ounce or two of pure filver in a crucible, and when it is in fu- fion, caft upon it, at different times, an equal weight of com- mon fulphur in powder. Stir the whole about with an iron rod, and, taking it from the fire, let it cool. Beat the mafs to powder, and put it into another crucible. Set it in a fmall fire, or in a fand heat, to drive oft" the fulphur in fumes, with- out running the metal into fufion. As the fulphur rifes into vapour, it will carry up along with it a part of the filver, above th5 furface of the reft, in form of fine flender filaments, or flat and thin plates, which will remain fixed at their lower end to the mafs out of which they are raifed, and will be very foft and pliable, and extremely bright and glofly. The fila- ments will often rife to two inches high in this procefs, and the flakes or plates will be of the length and bieadth of a card ufed in play.

A third Vegetation of this clafs Is the following : Melt toge- ther two ounces of filver, and fix ounces of lead. Put the mixture into a copel under a muffle in a furnace, and give fuch a fire as is neceflary to purify filver by the copel. When the filver appears fine, take the copel out of the fire, and leave it to cool. Soon after it is taken from the fire, there wiil arife out of the furface fome filaments of melted filver, of the thicknefs of a hog's brittle, and of three quarters of an inch high. They are often larger and thicker than this, and not unfrequcntly emulate the figure of branches of coral. They are ufually hollow within, and are fixed at the bottom of the mafs of the filver.

Of the fecond clafs, of metallic Vegetations, is the famous arbor Dianas, and the feveral other ramifications of metals after fo- Jution. See the article Dian.s; Arbor, Cych hinfra. The third clafs, that is, of fuch chemical Vegetations as con- tain no metallic matter, the following procefs gives an inftance : Take eight ounces of fait petre, fixed by coals ; fet it in a cel- lar, and let it run into an oil per deliquium : Filtre this liquor, and pour on it, by a little at a time, as much oil of vitriol as will perfectly fa titrate it. After this, evaporate all the humidity, and there will remain a compact (aline mafs, which will be hard, very white, and of an acrid tafte ; powder it grofsly, and pour upon it a fufficient quantity of water, in an earthen veffel ; the water will begin to evaporate, after it has ftood uncovered

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