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lours in the flowers of plants. We know very well that the flowers of all plants abound' in an eflential oil or fulphur, to which according to this doctrine their colours may be rationally fuppofed to be owing ; and tho' this oil {hould be prov'd to be the very fame fubftance in all, yet their variety of colours may be accounted for from it, fince we find that one and the fame oil, the eflential oil of thyme, according to Mr. Geof- froy's experiments, may be turned to all the colours that we find in the different flowers of plants, from white to deep black, with all the fhades of red, yellow, purple, blue and green, by mixing it with different fubftances ; and by the fame laws, the eflential oils of plants while contained in their flowers may by the different mixtures they meet with give them all their beautiful variety of colours. See the article Effential Oils.
We know that the infufions of flower s, and of other parts of plants become red on being mixed with acids, and green on being mixt with alkalis j and there is no reafon to doubt, but that it is the fulphureous part of the vegetable in thefe infu- fions which thus changes colour on thefe mixtures. This how- ever, ought to be proved poflible, before it is allowed in ar- gument.
This proof is given in the change of colours before mentioned, which are produced in oils merely by the admixture of diffe- rent falts ; and as all the colours in thefe, are the regular re- fult of certain combinations, there is great reafon to believe, that in thofe plants whofe flowers give the fame colours, there may be the fame combinations. The principal colours of plants, and their feveral parts are green, yellow, red, purple, blue, white, black, and tranfparent whttifhnefs ; all the others are produced by different combinations of thefe. The green which is the common colour of the leaves of plants is probably the effect of an oil rarirled in that part of the plant, and there mixed with the fixed and volatile falts of the lap, which re- main intangled by the earthy particles after nioft of the aque- ous humidity is evaporated, and by that means become in a ftate to act upon the oil. A clear proof of this is, that it the leaves are covered up in fuch a manner, that the aqueous humidity of the fap cannot evaporate itfelf, the oil and falts cannot act upon one another as they naturally would, but be- coming diffufed among fo great a quantity of water, lofe the colour they would otherwife have obtained together, and be- come whitifh or tranfparent. This is feen in the obvious in- ffance of fuccory and celeri, the leaves of both which plants, tho J naturally green, become white by being covered up with earth by the gardiner. Mem. Acad. Par. 1707. ■ The leaves both of plants and trees ufually turn red in autumn, or on the attack of the firft frofts ; the reafon of which is, that the feveral canals of the fap being conflringed by the cold, the juices arc detained in the veffels of the leaves, or at leaft its circulation is greatly interrupted, and being detained there, i.t naturally grows four, the acidity of this alter'u juice de- ftroying the green colour produced by the alkaline falts. The fap brings on a red colour, in the very fame manner that an eflential oil made green by a mixture of oil of tartar, is again changed to red, by adding to it a proper quantity ofdiitilled vinegar. Where we find in our common experiments the acids of the mineral kingdom turning the infufions of flowers red ; it feems by the analogy of thefe experiments, to be only owing to their deftroying the blue, brown, or other colour, which the alkaline falts of the plant had made with its eflen- tial oil.
All the fhades and degrees of yellow and faffron colour in the flowers of plants, fecm wholly owing to a mixture of an acid in their juices, with their eflential oil ; as the oil of thyme, which itfelf has very little colour, is made to pafs thro' all thefe fhades of colours, only by digefting it with diftilled vinegar. From the digefting the volatile alkalis, fuch as fpirit of fal armoniac and urine, with the fame oil, it appears that all the fhades of red, from the paleft flefh colour, to purple, and even to the violet blue, are only owing to the different admixtures of an alkaline volatile fait of the urinous kind, mixed in different manners with their eflential oil.
Black, which is a very uncommon colour in flowers, and which in them ought to be regarded only as a very deep violet, feems the effect of an addition of an acid juice to their oil, al- ready turned purple or violet colour by a volatile alkali. All the fhades of blue and purple feem alfo, by the analogy of the fame experiments, to be only the effects of mixtures of alkalis of the fixed and volatile kind, with the oils of plants; fince thefe colours are all produced in thofe experiments, by mixing the fpirit of fal armoniac, and the oil of tartar with oil of thyme.
The bright green of fame flowers feems alfo to be produced by the fame falts, only acting on oils more rarified. For the oil of thyme, of a purple violet colour, diluted with rectified fpi- rit of wine, being united with oil of tartar, becomes green. Mem. Acad. Par. 1707.
Eoccone is of opinion, that in many plants the colour of the flower is wholly owing to the colour of the juices of the root. This he inftances in the greater celandine, whofe roots and Jiowcrs are of the lame yellow colour. The barberry in like
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manner he obferves, has both its roots and its flowers yellow. The dentillaria has its roots and flowers both of a pale red and the acacia indica Aldini, and many other plants, he fays are inftances of this.
The reafon that he affigns for this is, that the more fixed parts wherein this colour confifts, prelerve the fame tin£ture, with- out being at all alter'd by fo long a circulation as that from the root to the flower ; and he adds another very remarkable obfervation, which is, that in all thefe plants and trees whofe roots and flowers are of the fame colour, the juices are more fixed ; and therefore, that thefe are more fit for dyin^ than any other coloured woods or plants. Vid. Boeeone MuC de Piant. Prefervation of Flowers. The method of preferving^ftiitwr in their beauty thro' the whole year, has been diligently fought after by many people ; (bme have attempted it, by gathering them when dry, and not too much opened, and burying them in dry fand ; but this tho' it preferves their figure well, yet takes off from the livelinefs of their colour. Muntingius gives a method which he fays is preferable to all others ; this is as- follows : gather rofes or other flowers when they are not yet thoroughly open, in the middle of a dry day; put them into a good earthen veffel glazed within ; fill the veiled up to the top with them ; and when full, fprinkle them over with fome good French wine with a little lalt in it; then fet them by in a cellar, tying the mouth of the pot carefully down. After this, they may be taken out at pleafure, and on fettinf them in the fun, or within the reach of the fire, they will open as if on the tree, and not only the colour, but the fmell will be preferved.
The flowers of plants are by much the moft difficult part of them to preferve in any tolerable degree of perfection ; of this we have inftances in all the collections of drjed plants or hortijicci. In thefe the leaves and ftalks and the roots and feeds of the plants appear very well preferved, the ftrong tex- ture of thefe parts making them always retain their natural form, and the colours in many fpecies naturally remainine ; but where thofe fade, the plant is little the worfe for ufe, "as to the knowing the fpecies by it. But it is very much other- wife in regard to flowers : thefe are naturally by much the moft beautiful part of the plant to which they belong ; but they are fo injured in the common way of drying, that they not only lofe, but change their colours one into another, by which means they give a handle to many errors ; and they ufu- ally alfo wither up, fo as to loofe their very form and natural fhape. The primrofe and cowllip kind are very eminent in- ftances of the change of colours in the flowers of dried fpeci- mens; for thofe of this clafs of plants eafily dry in their natu- ral fhape, but they not only lofe their yellow, which might be expected naturally enough, but they acquire a fine deep green, much fuperior to that of the leaves in their moft per- fect ftate. The flowers of all the violet kind, lofe their no- ble blue, and become of a dead white, fo that in dried fpeci- mens, there is no difference between the blue flowered vio- let and the white flowered kinds.
Sir Robert Southwell has communicated to the world a method of doing the bufinefs of drying plants, by which this inconve- nience is propofed to be in a great meafure remedied, and all flowers to be preferved in their natural fhape, and many in their proper colours. To this purpofe two plates of iron are to be prepared of the fize of a large half fheet of paper or larg- er for particular occafions ; thefe plates muft be made fo thick as not to have any power of bending, and there muft be a hole made near every corner for the receiving a fcrew to faftea them clofe together.
When thele plates are prepared, lay in readinefs feveral flieets of paper, and then gather the plants with their flowers, when they are quite perfea ; let this always be done in the middle of a dry day, and then lay the plant and its flower on one of the fheets of paper doubled in half, fpreading out all the leaves and petals as nicely as can be. If the ftalk be thick, it muft be pared or cut in half, fo that it may lie flat, and if it be woody, it may be peel'd and only the bark left ; when the plant is thus expanded, lay round about it, fome loofe leaves and petals of the flower, which may ferve to compleat any part that may prove deficient ; when all is thus prepared lay feveral fheets of paper over the plant, and as many under it ; then put the whole into the iron plates, laying the papers fmoothly on one, and laying the other evenly over them ; then fcrew them clofe and put them into an oven after the bread is drawn, and let them lie there two hours ; after this make a mixture of equal parts of aqua fortis and common brandy ; make thefe well together, and when the flowers are taken out of the preflure of the plates, rub them lightly over with a camel's hair pencil dipped in this liquor ; then lay them upon frefti brown paper,and covering them with fome other fheets, prels them between this and other papers with a handkerchief, till the wet of thele liquors is dried wholly away. When the plant is thus far prepared, take the quantity of a nutmeg of gum dugon, put this into a pint of fair water cold, and let it Hand four and twenty-hours; it will in this time be wholly
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