out having been connected with any

current.

It is very fingular that the Ifland of Lipari and that of Vulcano, fhould be the only volcanoes in Europe that produce the pumice-ftone in great quantity. Etna yields none, Vefuvius very little, and that in detached pieces. It is not found in the extinguished volcanoes of Sicily, of Italy, of France, of Spain, or of Portugal. I acknowledge, however, that I am not well enough acquainted with the productions of Hecla in Iceland, to deter mine whether our stone is found there. The production of this fubftance muft be attributed to a particular foffil which volcanoes feldom meet with, and which must be fituated near the fires of these two iflands: we must look for this foffil among the rocks that are deftitute of iron, and confequently we muft exclude argillaceous fchiftus, horn-ftone, porphyrics, &c. Chalks and white calcareous stones, we may fuppofe, have furnished it in paffing to the ftate of quick lime ftrongly calcined; but the fire could never give them the fibrous texture of the pumice-ftones; and, befides, it is not probable that these abforbent fubftances are found in the heart of the primary mountains in which the feat of the fire of thefe volcanoes must be placed.

Being convinced that, in natural history and in natural philofophy, reafoning and conjecture are never to be put in competition with experiment and obfervation, for the want of which they feldom make amends, I applied myself to study with the greatest at tention, and to examine the nature of pumice-ftones on the spot. I attended chiefly to thofe that are heavy, which, as they feem lefs altered by the fire, may be prefumed to preferve fome characters of their primitive bafis. I could trace in fome of them the grain, the fhining fcales, and fiffile appearance of the whitish, micaceous fchiftus which is found interpofed in immenfe quantity in the midst of the

beds of granite that compofe the mountains of the Val-Demona. I could perceive in others the remains of granite, in which were still distinguishable the three conftituent parts, quartz, feldtfpat, and mica; and I obferved that thefe three fubftances, which mutually ferve as fluxes to each other, acquire by the action of fire, a fpecies of vitrification between that of enamel and porcelaine, and which may be compared to a fcoria pretty full of air bubbles (frite une peu bourfoufflée.) I faw them acquire by degrees the loose and fibrous texture with the confiftence of pumice, and I could no longer doubt that the laminated granitical and micaceous rock, and even the granite itself were the principal materials to which, when altered by fire, the formation of pumice-stones ought to be attributed.

Thefe materials which, I fuppofe, have ferved as the bafis of pumiceftones, are not peculiar to the mountains of the Val-Demona, they are found abundantly in thofe mountains that are called Primary. M. d'Arcet, in his Memoirs on the action of a continued fire, informs us, that the tales and micas are easily fufible; he tried a granite of Burgundy, which melted while it fwelled a good deal in the crucible: this fufion, fays he, is beyond the state of fcoria. He found, that a great number of heavy fpars melted eafily, and accelerated the fufion of other matters. The kaolin, which is made ufe of at Alençon in the making of earthen ware, is a kind of granite of three component parts, the scoria of which comes very near the state of the heavy pumice-ftones. The granites of the Pyrenean mountains, and that which compofes the famous pedestal of the ftatue of Peter the Great, undergo a demi-fufion, and form a grey opake, and fometimes a kind of bloated body according to the force of the fire applied. The granites of the Limofin and la Marche are very fufible, and more or lefs refemble the Petunzé of

of

of Saint Irie, which is made ufe of at the manufactory of Seve, where the feldufpat, which ferves as a flux, contains a portion of clay fuperabundant to its nature. The fcoria of all these granites is white, because they contain no iron; and if they were all expofed to a fire, equal to that of volcanoes, they would produce punice-ftones of different kinds.

To this an objection may be urged, which it becomes me to obviate: Since the materials proper for forming pumice are fo frequent in nature, how comes it that the Lipari iflands are the only volcanoes that furnish in any quantity this fingular production? It may be farther objected to me, that there is a contradiction in faying that pumiceftone exifts almoft in a fingle volcano only, while the greater part of the ancient mountains contain fubftances capable of acquiring this particular state of porous and bloated fcoria which conftitutes them, I answer, that it is very feldom that the furnace of a volcano is placed in the midst of granite; it is almost always fituated in rocks of argillaceous fchift, containing porphyrics, petro-filex, flate, fchorl, &c. matters which, when operated upon by fire, and much lefs altered than is generally fuppofed, ferve as the bafis of the ferruginous black and red lavas which are met with in all volcanoes. It would appear that thefe argillaceous rocks contain in abundance, and pers haps exclufively, the combuftible fubftances which maintain the inflammation of the fubterraneous fires; the vitriolic acid, and the inflammable principle with which they abound, are perhaps the means made ufe of by nature

to produce thefe fires, the existence of which is perhaps a phenomenon as difficult to be accounted for as any other in Nature. I imagine it is owing to accidental circumftances that the vol canoes of Lipari have found near the feat of their fires confiderable strata, or beds of granite, placed amidst the rocks that fupply them with fuel, in the fame manner as many beds of gra nite in the Pyrenees are included in fchift and petro-filex. It is certain, that the volcanic fires of Lipari muft be fituated in the very point of contact between thefe different substances, the schifts and the granites, as their productions are fo diflimilar that fome of them contain iron, while others are deftitute of it. For the production of pumice, it is neceffary that the granite be of a nature exceedingly fusible, and that the fire of the volcano be more intenfe and more active than it genes rally is. The lava that iffued from the fides of Etna in the year 1669, and that deluged Catagna, has for its bafis a granite which has not been changed, and none of its constituent parts have been altered. This lava, expofed again to the heat of a fire fufficient to fufe to it, vitrifies, and af fumes the appearence of an opake fcoria fomewhat porous, which resembles pumice; a certain proof that a more intenfe fire in the volcano would have changed that immenfe torrent of lava into pumice-ftones fimilar to thofe of Lipari. The vitreous character of the black lavas of Lipari, the quantity of lapis obfidianus which they contain, evidently fhew that the inflammation in those islands is more intense than in the Sicilian volcano,

at Paris.

T

ing, is not an attribute peculiar to them. A great number of plants exhibit figns of irritability more or lefs apparent in proportion to their age, their ftrength, or the part to which the irritating caufe is applied. Several authors have obferved this in the leaves and flowers of many plants. M. Duhamel has accurately defcribed the curious motion of the fenfitive plant. M. Bonnet has proved that leaves poffefs the power of voluntary motion, that they always prefent their upper furface to the air, and that whenever a branch is turned out of its natural pofition, the leaves of it immediately affume a new direction. Linnæus has carried his inquiries on this fubject ftill farther, and, in a differtation, intitled Somnus Plantarum, has demonftrated the daily motion of the leaves in a very confiderable number of plants, and has proved that the phenomenon does not depend on the fate of the atmofphere. After having obferved that many flowers open pretty conftantly at ftated hours of the day, he very ingenioufly conceived the idea of making thefe flowers anfwer the purpofe of a clock, under the title of horologium flora. It is known that the extremity of the leaves in the dionæa mufcipula open with two valves, like a trap, and fuddenly close upon the leaft irritation. The leaves of the hedyfarum gyrans *, or moving plant, likewife exhibit the moft evident and wonderful motions.

Thefe different movements of the leaves and of the petals, as well as thofe of the stamina and piftilla, which we are about to describe, seem to us to depend effentially on the particular organization of the plants, and on their

vegetable life. They can no more be accounted for by mechanical laws than the mufcular action of animals; for both undoubtedly depend on the fame caufes, which we fhall never be able to difcover.

The motions that take place in the ftamina and piftilla have hitherto been obferved but in few plants, fuch as the barberry (berberis vulgaris,) the Indian fig (cactus opuntia), the dwarf ciftus (cifus helianthemum), and some others, which are enumerated in one of the differtations of the Amanitates Academica, intitled Sponfalia Plantarum. Thefe organs, however, difplay an irritability more univerfal and more manifeft than is to be found in any other part of the plant. We fhall prefently establish this fact by a detail of obfervations made on the fexual or gans of a great number of plants.

Motions of the stamina t.

The antheræ of feveral fpecies of lilies before the capfules open are fix"ed lengthways on the filaments, and parallel to the ftyle, from which they are diftant about five or fix lines. When the pollen begins to iffue from its cells, the antheræ become moveable on the extremity of the filaments that fuftain them, they approach the ftigma one after another, and retire again as foon as they have shed their duft on that organ. Thefe motions are very evident in the Canadian martagon (lilium fuperbum.)

The ftamina of the Jacobea lilly (amaryllis formofiffima), thofe of the fea-daffodils (pancratium maritimum & illyricum), exhibit a very curious phenomenon, and fomewhat different from that just mentioned. The anthere

there of thefe plants before fecundation are like thofe of the lilies fixed along their filaments parallel to the style. When the cells begin to open, they affume a horizontal pofition, and fometimes turn on the extremity of the filament, as on a pivot, that they may apply to the ftigma the particular part by which the pollen is escaping.

If we obferve with attention the ftamina of the Perfian fritillary (fritillaria perfica), we will difcover an irritability ftill more obvious. The fix ftamina of this plant are four or five lines diftant from the ftyle before fecundation; but almoft immediately after the flower expands they fucceffively approach the ftyle, and apply their antheræ close to the ftigma. Af ter the pollen is difcharged, they recede generally in the fame order as they advanced, and take their former diftant ftation. Thefe motions are fometimes performed within the fpace of four-and-twenty hours. Similar phenomena are observeable in the stamina of the flowering rufh (butomus umbellatus), and even in thofe cf many species of allium, ornithogalum and afparagus, but in thefe indeed they are not fo apparent.

I have never obferved any motion in the stamina of the crown imperial (fritillaria imperialis), or in the fritillaria meleagris; but thefe two plants at their fecundation prefent a phenomenon of another kind not lefs interefting. Their ftamina stand naturally clofe to the style, and the ftigmata furpass them in length. Any particular motion, therefore, beflowed on the ftamina of these plants, could have anfwered no purpofe, and accordingly nature has made ufe of another means to affift the procefs of fecundation. Their flowers are made to hang down while the pollen is discharged from its cells, that it may the more eafily fall upon the stigma and fertilife it. What renders this explanation probable is, that as foon as the fecundation is performed, the footstalk of the flower be

comes erect, and the germen is fuftained in a vertical pofition. The fame circumftances take place in the colum bines (aquilegia), in the different fpecies of campanula, and in many others which are mentioned by Linnæus.

But the plants of this particular clafs (the liliacea), are not the only ones that fhew signs of irritability; fuch are observeable in many others of very different natural families. The rues (ruta) prefent us at once with a very ftriking and obvious example of this faculty. All the plants of the genus have from eight to ten ftamina, of which one ftamen is oppofite to each petal, and one ftands in the interftice between every two petals. If the ftamina are obferved before the dif charge of the pollen takes place, they are found at right angles with the piftillum, one ftamen lying in the cavity of each petal. When the moment of fruc tification arrives, they raise themselves up two and two, or three and three together, lay their antheræ upon the ftigma, and, after having fertilized it, they retite and fall back again into the cavity of the petals. I have likewise remarked very evident motion in the ftamina of the zygophyllum fabago. Thefe proceed, one after another, out of the corolla, and prefent their anthere to the ftigma. The ftamina of the fraxinella (dictamnus albus), a genus approaching very nearly to that of the rue, affords a very curious fpectacle which is favourable to our opinion. Before fecundation the filaments are inclined downwards, fo that they almoft touch the lower petals. As foon as the capfules are ready to open, and the action of the piftillum irritates the ftamina, their filaments, one after another, bend themfelves in the form of an arch towards the style; by which means the antheræ are placed immediately above the ftigma, fo that the pollen must fall on that organ and fertilize it.

If we obferve the ftamina of the Indian crefs (tropaolum), when the cells

are

are about to burst, we will easily perceive that the extremity of each fila ment forms a curve, and bears its anthera towards the ftyle. This approach indeed is much lefs quick and lefs fenfible than in the fraxinella. Laftly, the geranium fufcum, g. alpinum, and g. reflexum, afford fimilar obfervations. Their ftamina, before the antheræ open, are all bent fo that their top is turned to the centre of the corolla. When the capfules begin to open, the filaments rife towards the style, and each of them generally touches its correfponding ftigma. Thofe of the columbines raife themfelves nearly in the fame manner a little after the unfolding of the flower.

To what cause are these motions to be attributed but to the action of the piftillum, which irritates in each ftamen a peculiar organ fomewhat fimilar to that of animals? Indeed, if thefe motions do not depend on irritability, why should the ftamina approach the ftyle only at the inftant when the anthere are about to open; and why fhould they recede from it immediate ly after they have fhed their pollen on the ftigma? I fhall here bring a few other facts to prove that the motions of the fexual parts of plants do not depend on a mechanical caufe. Let us begin with the faxifrages. Imme diately upon the opening of the corolla, the ten ftamina of the greater part of these plants are fome lines diftant from the ftyle: they approach it af terwards generally by pairs, and recede in the fame order after the pollen is difcharged. The ftamina in many plants of the natural order of caryophyllei, and, among others, thofe of the ftellaria, of the chickweed (alfine media), and of the moerrhingia mufcofa, betray a very evident motion towards the piftillum. Thofe of the plygonum tataricum, p. penfylvanicum, and the greater part of that numerous genus, exhibit motions very fimilar to thofe of the faxifrages: differing only

in this, that the ftamina of the polygonums generally approach the ftyle by turns. I have obferved the fame contraction in thofe of the fertia pe rennis. The ftamina of the grafs of Parnaffus (parnassia_paluftris), raise themfelves very quickly, their filaments are fo bent that each anthera is laid immediately over the stigmata, and after having performed the office of fecundation, they retire and hang down towards the ground.

If we attend to the flower of the little field-madder (herardia arvenfis), immediately after it is expanded, we will likewife perceive that its four ftamina go by turns to difperfe their pollen upon the ftigma, and that they not only recede after a few days, but that they fink down while they defcribe the femi-circumference of a circle. Thofe of feveral fpecies of veronica evidently approach the centre of the corolla immediately above the. style, fo that the pollen may fall perpendicularly upon the ftigma. This may be easily obferved in the veronica arvenfts and v. agreftis. The filaments of the feveral species of valeriana stand erect and close to the ftyle during the difcharge of the pollen as foon as it proceeds from the capfules, and then bend backwards, as in the fherardia. Thofe of the rhamnus palyurus alfo bend back in the fame manner, after the fecundation.

Let us next attend to the ftamina! of the kalnia. Thefe are ten in each flower, which are kept in a horizontal fituation by means of an equal number of cavities round the middle of the corolla, in which the top of each anthera is lodged. When the capfules are about to open, the filaments make a curve that the antheræ may overcome the obftacle which confines them. and may be at liberty to scatter their pollen on the figma.

The ftamina of all thofe plants, which we have hitherto mentioned, approach the ftyle by turns, fometimes by twos or by threes; thofe of the to

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