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P L A
meafure ceafes : the plant by degrees grows black, as the fmoak arifes, and as Toon as perfectly black all over, it takes. fire. When the flame ceafes, the leaves appear white ; but if any black fpots remain, there are always feen fparks of fire fcatter- ing thcmfelves about on them, till the blacknefs is perfectly confumed. The afhes being now become perfectly white, yield no fmell nor the leaft appearance of fire; and they yet retain, after all this violence of fire, the perfect form of the plant, even to a microfcopic obfervation : for, if examined by glaffes, there will be found every feature and lineament of the plant, even the hairinefs of the ftalks, or down upon the leaves ; every rifing and cavity natural to the plant, appear alio diftinct, and every the fmalleft fibre. But this only remains while they are unmoved, the moment they are difturbed, tho but by breathing upon them, the whole falls to duff, and the form is irrecoverably loft.
The afhes thus carefully prepared, are perfectly infipid and fcentlefs, and when lixiviated in the common way for making the fixed fait, afford no fait at all ; but only on the evaporation leave a fmall quantity of a matter refembling lime : the re- maining afhes are wholly terreftrial, and ferve excellently for the making copels, for the ufe of allaying. Boerbaave's Chem.
P. 2. p. ig.
From this we learn, that the plant, by having been previoufly boiled in water in the diftillation, was divefted of all its falts; and that in general, water, with a great degree of heat, is ca- pable of extracting from any vegetable all its faline particles, whether volatile or fixed. We find, however, that water can never feparate the fixed oil, which here fhews itfelf to have wholly remained in the plant, by the fmoak, fmell, and flame it yields ; and by the fparks of fire in the remaining black parts of the plant, which were wholly owing to the remains of this oil, no fire being able to make the fmalleft fpark af- terwards appear in the afhes.
Air, as well as fire, is neceffary to this oil's taking flame; for in a covered veflel it will not blaze till the cover is taken off. This thick oil is extremely different from what we call the ef- fential oil of a plant, and feems to be the fame in all vege- tables ; and to this they owe their cohefion : while the eflential oil and fait are extracted from the plant by boiling, it yet holds together in its native figure and ftrength ; but as foon as the black oil is difiipated by burning, the whole firmnefs of the plant is loft, and a breath of air blafts it to duff.
Face of a Plant. Seethe articleFACE.
Senjittve Plant. See Mimosa and Sensitive.
Sea Plants. See the article SEA-plants.
Food tf Plants. See Food of plants.
Nowijhment of Plants. See Nourishment.
Propagation of Plants. See Propagation.
Refufcitatlm of Plants. See Resuscitation.
Pajlnre ^/"Plants. See the article Pasture.
Jukes o/~Plants. See Juices of plants.
OH of Plants. See the article Oil.
Salts rf Plants. It has been obferved by all who have exa- mined the different eflential falts of plants, that fome of them, when thrown on the fire, have the effects of falt-petre, and others of common fea-falt ; and it has been concluded from hence, that they really contained particles of thofe falts which their roots had taken in with their nourifhment, and conveyed up into the ftalk and leaves with the juices ; and that thefe falts ftill retained their original nature, and were no otherwife altered than by the mixture with other fubftances in the plant.
. But as two plants of different qualities, when fet in the fame earth clofely by one another, fhall out of the fame juices make a medicine, a fallad, or a poifon ; it cannot be, but that the fubftances abforbed by the root, be they what they will, muff, be greatly altered in the plant; infomuch, that a fait purely nitrous, when received into the root, might become of the nature of fea fait, or of the volatile urinous kind, ac- cording to the different organs of the plants, and the different natural fermentations it might meet with there. To be per- fectly informed of this, Mr. Romberg made the following experiment :
He took a large quantity of rich black garden mould, and wafticd it in feveral waters, to carry off all the falts it might contain : this done, he divided the earth into four boxes or cafes of wood, into each of which there was put about two hundred weight. Two of thefe cafes of earth he watered with a folution of falt-petre, fo as to make each imbibe about two ' ounces of that fait; the other two cafes were left with the earth infipid as the waffling had made it, and care taken to water them with none but perfectly pure water, fo that they might remain as fimple as poftible. In one of the cafes of ni- trous earth, and in one of thofe of fimple earth, he fowed ■ fennel ; and in the other two, garden creffes.
The herbs in all the cafes grew very well, and when they . were grown to about eight inches high, they were all gathered ; arid when the roots were cleanfed, and the whole product J weighed, thofe plants which had grown on the fimple earth weighed twenty-five ounces, and thofe in the nitrous earth twenty-fix^ their fmell and taffe manifefted no fort of differ- ence in either. In order to examine thefe plants, while yet quite frefh, by means of fire, he put a pound and an half of I each, with their roots, into a retort of glafs : he placed thefe
retorts firft in a bajneum maris, and then in a fand-heat, in order to drive over all the aqueous humidity. The quantity of water from each retort was within a few grains of the fame- weight ; and from the beginning to the end of the diftillation there was not the leaft appearance of any acid. After this, the crefles which had grown in the infipid earth yielded a drachm of volatile fait ; and that which had grown in the earth which had imbibed falt-petre, yielded feventy-five grains.
The oil of each was very nearly the fame in quantity ; that from the plants in the falt-petre earth weighing fix grains more than that of the plants of the infipid earth. The lixivial fait was two drachms from the plants in the ni- trous earth, and one drachm and fixty-feven grains from thofe in the infipid.
The differences between thofe two parcels of plants upon the analyfis, appeared on the whole fo little, that it could not be counted any thing; fince the more or lefs clofe luting of the veffels, or many other accidents in the diftillation, might have eafily occafioned as much in plants perfectly the fame in all refpects. If there be any thing, however, to be collected from the experiment, it is, that the earth moiftened with a folution of nitre, yielded more of the principles than the other; probably from its actually affording a quantity of fait to the juices of the plant in the growth : but as the nitrous earth afforded a plant which yielded more oil than that from an infipid foil, it muff, be from this that the lotions of the earth not being able to carry off any of the fatty parts, they remained in the fame quantity in both ; but that the nitre, where it was, had contributed fomewhat to the breaking of them, and the rendering them more fit to be abforbed by the plants. From the differtnt weights of the plants when gathered, after the fame time of growth, from the fame feed, and with all the fame advantages in common, proves, that the nitrous falts in the earth are noteflentially neceflary to vegetation, fince the plants in the infipid earth grew very well without them ; yet that they are very ufeful, fince the plants produced there were of a greater bulk, and according to the whole analyfis, if the differences are to be depended on as refulting wholly from the nature of the fubjects, they yielded more of all the active principles ; and therefore, that they were to all purpofes better plants.
The fennel in thefe boxes was not gathered with the creffes, but left till it began to bud for flowering : at this time there was found a very great difference, both in the fize and appear- ance of the pla?iis of the two forts of earth. That in the in- fipid earth was lank, weak, and of a yellowifh green ; and being gathered, weighed only nineteen ounces : whereas the fennel growing on the nitrous earth feemed in a very vigorous ftate, its leaves were of a dark green, and it weighed full two pounds. Mr. Homberg weighed nineteen ounces of each of the plants frefh, and with their roots, to make the analyfis of them in the fame manner as he had before done that of the creffes. In the firft diftillation the water began to tafte acid in the firft drops, and continued to increafe in acidity as Ion? as it ran ; and the infipid earth left by the fennel which grew in the nitrous earth, was an ounce more in weight than there- fiduum of the plant which had grown in the infipid foil. That of the nitrous earth yielded one drachm and twelve grains of oil ; that in the infipid, only fixty-three grains : neither one nor the other yielded any volatile fair, only the laft ounce of the aqueous liquor made fomelittle effervefcence. The firft fait was in the quantity of three drachms from he fennel of the nitrous earth, and two drachms and ten grains from the infipid earth. The plants had appeared above ground in the fame time from their feeds in the nitrous and in the infipid earth, and orew equally vigorous and well for a month; but after that time, tho' both were watered in the fame manner, and the fame care in all refpects was taken of them, the plant on the infipid earth became languid, and that on the nitrous earth continued to grow vigoroufly and well.
It feems that in the firft ftages of the growth of the plants, the two lobes of the feed furnifhed a proper nourifhment to the ftalk and leaves, and required no more than mere water, a pure fimple fluid to divide its parts and carry it up from the root; but that when thefe lobes were wholly confumed, and the plant was to find its whole nourifhment in the earth, there an earth rendered infipid by the carefully wafhing away all its falts, could not fupply a proper and fufficient nourifh- ment, but that an earth, after it had been made to im- bibe a certain portion of nitre could : whence the fen- nel in the infipid earth could not continue to grow vigoroufly, after the lobes of the feed were deftroyed, tho' that in the earth impregnated with an adventitious fait could. It is true, indeed, that the plant in the infipid earth did not entirely perifh, and it is reafonable to conclude thence, that all the warning we can give with hot water cannot diveft earth of all its falts, but only of thofe which are moft eafily foluble ; whence it takes away not all. but only the principal fund of nutrition. All the wafhings in the world muft alfo leave earth impregnated with all the fatty particles it ever had, and thefe are very inftrumental to the growth of plants ; but thefe, without fome falts, ceafe to be of their proper ufe, fince they cannot be broken or divided into parts fmal'i enough to enter
the
