« ՆախորդըՇարունակել »
I concur with these elegant writers in admitting the beautiful and harmonious relation so obviously established between minerals, plants, and animals; but it is at the same time impossible to allow of the distinction between vegetable and animal life here laid down; because, first, vegetables are by no means nourished exclusively, as, indeed, M. Mirbel himself frankly allows, from terrene elements; and, secondly, because animals are as little nourished exclusively from vegetable materials. Among insects, worms, and even fishes, there are many tribes that derive by far the greater portion of their increase from the mineral kingdom alone ; while even in man himself, air, water, common salt, and lime, which last is almost always an ingredient of common salt, are substances indispensable to his growth, and are derived immediately from the mineral kingdom.
In laying down, therefore, a distinctive character for animals and plants, we are compelled to derive it from the more perfect of each kind; and to leave the extreme cases to be determined by the chemical components eliminated on their decomposition. And under this broadview of the subject I now proceed to observe, that while they agree in an origin by generation, a growth by nutrition, and a termination by death; in an organized structure, and an internal living principle; they differ in the powers with which the living principle is endowed, and the effects it is capable of exerting. In the plant it is limited, so far as we are capable of tracing it, to the properties of irritability, contractility, and simple instincts; in the animal it superadds to these properties those of muscularity, sensation, and voluntary motion.
There have been, indeed, and there still are, physiologists who,-not ad. verting to the extraordinary effects which the power of irritability is capable of producing when roused by different stimulants, and under the influence of an internal and all-pervading principle of life, operating by instinctive laws and instinctive actions, or those, as we shall show hereafter, which are specially directed to the growth, preservation, or reproduction of a living frame, or any particular part of it-have conceived plants as well as animals to be possessed of sensation and muscular fibres; and as sensation is the result of a particular organ, and the organ producing it is connected with various others, have at the same time liberally endowed them with a brain, a heart, and a stomach; and have very obligingly permitted them to possess ideas, and the means of communicating ideas; to fall in love and to marry, and thus far to exercise the distinctive faculty of volition. The whole of which, however, is mere fancy, grounded altogether upon an erroneous and contracted view of the effects of the principle of irritability when powerfully excited by the influence of light, heat, air, moisture, and other causes.
In reality, such kinds of loves and intermarriages are not peculiar to plants, but are common to all nature: they exist between atom and atom, and the philosopher calls them attractions; they exist between congeries and congeries, and the chemist calls them affinities; they exist between the iron and the loadstone, and every one denominates them magnetism. Nor let it be said that in these cases of mutual union we have nothing more than a mere aggregation of body; for we have often a third substance produced, and actually generated, as the result of such union, far more discrepant from the parent substances both in quality and feature than are ever to be met with in vegetable or animal life. Thus, if an acid be married to an alkali, the progeny brought forth will be a neutral salt, possessing not the remotest resem. blance to the virtues of either of its parents. In like manner, is alkohol be married to any of the more powerful acids, and the banns be solemnized over an altar of fire, but not otherwise, the offspring engendered will be a substance called ether, equally unlike both its parents in its disposition. But the form or features are as frequently changed as the temper. Thus, if we unite olive oil, which is a liquid, with some of the oxides of lead, which are pow. ders, the result is neither a liquid nor a powder, nor a medium of the two, which would be a paste, but the hard adhesive plaster usually called diachylon. So, again, if muriatic acid, which is a liquid, sport in dalliance with the
volatile nymph ammonia, which is an invisible gas, the fruit of their enibraces will be still more extraordinary in point of form, for the gas and the liquid will engender that solid substance commonly known by the name of sal ammoniac, or, in the new nomenclature, muriate of ammonia. In like manner, our common smelling salts, or carbonate of ammonia, though a hard, concrete crystallization, are the mere result of the union of two invisible gases, ammonia and carbonic acid gas, or fixed air; and which, having duly paid their court to each other, give birth to this solid substance.
But in all this it may be said that we have no instance of a multiplication of species; nor in reality of any thing more than the production of a third substance, issuing, like the fabled phenix of antiquity, out of the ashes or decomposition of the parent stock; yet in many cases we have instances of multiplication also-and instances far more extraordinary and far more prolific than are ever to be found in the multiplication of either animals or vegetables. Such especially are those wonderful increases that occur in the case of ferments and of contagions. A few particles of yest lying dormant in a dessert-spoon are introduced into a barrel of beer, or of any other fermentable fluid, and in a few hours propagate their kind through the largest vessel that was ever manufactured; so that at length every particle of the fluid is converted into a substance of their own nature. A few pestilential miasms are thrown forth from a stagnant marsh or a foul prison, and give birth instantaneously to myriads and myriads of the same species of particles, till the atmosphere becomes impregnated with them through a range of many miles in diameter. Two or three particles of the matter of plague are packed up in a bag of cotton at Aleppo, and are many months afterward set at liberty in Great Britain. Aided by the stimulus of the air, they instantly set to work, and procreate so rapidly, that the whole country in less than a week is laid prostrate by the enormity of their increase.
Now the terms loves and marriages will just as well apply to all these as to the vegetable creation. The cause of the respective unions, and of the changes that take place in consequence of such unions, are in both cases nothing more than elective attractions : in the mineral and gaseous kingdoms produced by what chemists have denominated the principle of affinity, and in the vegetable by what physiologists have called the principle of irritability; a principle far nicer and nobler and more delicate than that of affinity, and under the influence of an internal, an all-pervading, and identifying vital power, capable, as differently excited by different stimulants, of producing far nicer and nobler, more delicate and more complicated effects ; but which in itself is not more different from the principle of affinity than it is from that of sensation.
No experiment or observation has hitherto proved vegetables to be possessed of any higher powers than those of irritability, contractility, and those instinctive energies which we shall hereafter show are dependent upon the principle of life.
It is almost superfluous to observe, in this place, that there are also powers and faculties of a much higher character than any I have yet noticed, appertaining to the nobler ranks of animals; for at present I am only pointing out the leading characters by which animals in general may be distinguished from vegetables in general, and shall have sufficient opportunities, as we proceed, of adverting to these additional faculties, and of investigating their respective excellencies.
Our immediate concern, then, is with vegeTABLE LIFE; its general laws, structure, and phenomena. And upon this subject I shall touch as briefly as possible, intending it as a mere vestibule or introduction to the more imporiant study of animal philosophy.
Plants, then, like animals, as I have already observed, are produced by generation, and through the medium of ova, or eggs. The exceptions to this common rule are few, and they occur equally in both kingdoms. The egg of the plant is its seed; a doctrine not of modern origin, but taught and understood quite as clearly, and with as close a reference to the rise of animal
life, by the ancients, as in the present day. The seed is sometimes naked, but more generally covered with a pericarp, whence plants become naturally divided into the two grand arrangements of gymnospermous and angiospermous. The pericarp is of various forms and structures; and of these the more common are the legume, silique, or silicle, being merely varieties of what, among ourselves, is denominated in popular language cod or pod; the loment which is a kind of pod not so frequent as either of the former, but of which we have an instance in the mimosas and the cassia fistula; the pome or core-apple, of which we have instances in the common apple and the pear; the drupe, or stone-apple, instances of which occur to us in the plum, cherry, and almond; the glume or chaff; the berry; the acinus or conglomerate berry, as in the rasp; the nut; and the capsule.†
Stripping off this outer covering, we find the seed to consist internally of a corculum, or heartlet, and externally of a fleshy or parenchymatous substance, surrounded with a double integument, sometimes single, sometimes bifid, and sometimes more than bifid; and hence denominated monocotyledonous, dicotyledonous, polycotyledonous. In popular language these are called seed-lobes, or seed-leaves: and in the phaseolous vulgaris, or common kidney-bean, we have as striking an instance as in any plant, and which every one must have noticed, just peeping in two distinct segments above the ground, as soon as the seed has begun to germinate. It was very generally supposed formerly, and is still supposed by some botanists, that the seeds of various orders of plants, as the mosses, fungi, and algæ, are acotyledonous, or totally destitute of a cotyledon of any kind. But as many, perhaps most, plants of this kind have of late been found to possess some such parenchyma, we have great reason for believing that this organ is universal, and that there is no such thing as an acotyledonous seed in the whole vegetable kingdom. In reality, the cotyledon appears absolutely necessary for the germination and future growth of the seed, and may hence be denominated its lungs or placentule. Like the perfect plant, it possesses lymphatics and air-vessels. Through the former of these it absorbs the moisture of the soil into which it is plunged, decomposes a part of it into its elementary principles, and conducts those principles, together with the undecomposed water, to the corcle or heartlet, which becomes stimulated to the process of germination by the oxygen thus set at liberty.
Mrs. Ibbetson has attempted to prove that the cotyledon is of no use whatever for the purpose of nourishment; which, according to her observations, is only conveyed to the corcle by what she calls a system of nourishing vessels, altogether distinct from the cotyledon. It is not very clear, however, what is here meant by nourishing vessels; nor can we for a moment admit that so large an organ as the cotyledon, and apparently so important, can be designed for no other office than merely, as this lady conjectures, to screen the primordial leaves from the light and air on their first formation."
According to Mr. Mirbel's experiments, as detailed in the Memoirs of the National Institute, the soil.and the albumen in the cotyledon are both concerned in the developement of the germ; and both continue to contribute conjointly till the albumen is entirely absorbed at which time the plant has strength enough to derive from the soil or the atmosphere the nourishment it requires from this period. In this respect the albumen of the cotyledon corresponds with the vitellus of the hen's egg.
In marine plants that are destitute of a radicle, as the water caltrop (trapa
* Οὕτω δ' ὠοτοκεῖ μικρὰ δένδρεα πρῶτον ἐλαίας,
So plants, like animals, uprise to air,
And upon this beautiful verse, which he has preserved as a fragment, Aristotle remarks, 76 Te yàp ủồ κύημά ἐστι, καὶ ἔκ τινος αὐτοῦ γίγνεται τὸ ζῶον, "For the egg is the conception, and after the same manner the animal is created."-De Generat. Animal. i. 23.
Compare Knight's General Theory of Vegetable Physiology, Horticultural Transactions, vol. i. p. 217, with Nicholson's Journal, vol. xxxii. p. 350.
Nicholson's Journal, vol. xxvii. 9,
natans), the germ must necessarily be supported in the first instance by means of the cotyledon.
It is the corcle which is the true punctum saliens of vegetable life, and to this the cotyledon is subservient. The corcle consists of two parts, an ascending and a descending; the former called its plumule, which gives birth to the trunk and branches; the latter named its rostel, which gives birth to the root and radicles. The position of the corcle in the seed is always in the vicinity of the hilum or eye, which is a cicatrix or umbilicus remaining after the separation of the funis or umbilical cord from the pericarp, to which the seed has hereby been attached. The first radicle or germinating branch of the rostel uniformly elongates, and pushes into the earth, before the plumule evinces any change. Like the cotyledon, the radicles consist chiefly of lymphatics and air-vessels, which serve to separate the water from the soil, in order that the oxygen may be separated from the water.
Hence originates the root, unquestionably the most important part of the plant, and which in some sense may be regarded as the plant itself: for if every other part of the plant be destroyed, and the root remain uninjured, this organ will regerminate and the whole plant be renewed; but if the root perish, the plant becomes lost irrecoverably. Yet there are various phenomena in vegetable life that manifest a smaller difference in the nature of the root and the trunk, than we should at first be induced to suppose; for Willoughby observed, more than a century and a half ago,* that in several species, and especially those of the prunus and salix, cherry and willow tribes, if the stem branches be bent down to the earth, plunged into it, and continued in this situation for a few months, these branches will throw forth radicles; and if, after this, the original root be dug up, and suffered to ascend into the air, so that the whole plant become completely inverted, the original root will throw forth stem-branches and bear the wild fruit peculiar to its tribe. The rhizophora Mangle, or mangrove-tree, grows naturally in this manner; for its stem-branches, having reached a certain perpendicular height, bend downwards of their own accord, and throw forth root-branches into the soil, from which new trunks arise, so that it is not uncommon, in some parts of Asia and Africa, to meet with a single tree of this species covering the oozy waters in which it grows with a forest of half a mile in length. The ficus Indica, or banyan, grows in the same manner, and often with enormous trunks, equally derived from a primary root. The largest tree of this kind known to Europeans, is on an island in the river Nerbedda in the Guzzerat, distinguished in honour of a Bramin, of high reputation, by the name of Cubbeer Bur. High floods have destroyed many of its incurved stems, yet its principal stems measure two thousand feet in circumference, the number of its larger trunks, each exceeding the bulk of our noblest oaks, amount to three hundred and fifty, while that of its smaller are more than three thousand; so that seven thousand persons may find ample room to repose under its enormous shade, and may at the same time be richly supplied from the vast abundance of fruit which it yields in its season.
The solid parts of the trunk of the plant consist of CORTEX, cuticle, or outer bark; LIBER, CUTIS, or inner bark; ALBURNUM, or soft wood; LIGNUM, or hard wood; and MEDULLA, or pith. Linnæus gave the name of medulla to the pith of plants, upon a supposition that it had a near resemblance to the medulla spinalis of quadrupeds. A closer investigation, however, has since proved that this resemblance is very faint, and that the pith or medulla of
Phil. Trans. year 1669, iv. p. 963,-1670, v. p. 1165. 1168. 1199,-1671, vi. p. 2119.
†There is a curious paper of Count Rumford's, mentioned among the labours of the French Imperial Institute for 1812, upon the chemical properties of the different parts entering into the composition of the trunk of trees, for an account of which see also Thomson's Annals of Philos. vol. i. p. 386. By a variety of experiments Count Rumford was led to this singular conclusion, that the specific gravity of the solid matter which constitutes the timber of wood is almost the same in all trees. By the same means he determined that the woody part of oak in full vegetation is only four-tenths of the whole. Air constitutes onefourth of it, and the rest consists in sap. Light woods have still a much less quantity of solid matter: but the season of the year and the age of the tree occasion considerable variations. Ordinary dry wood contains about one-fourth of its weight of water. Even the oldest wood, though in the state of timber for ages, never contains less than one-sixth of its weight of water. All absolutely dry woods give from 42 to 43 per cent. of charcoal: whence he concludes, that the ligneous matter is identic in all woods.
vegetables consists of nothing more than a mere spongy cellular substance, forming, indeed, an admirable reservoir for moisture; and hence of the utmost importance to young plants, which, in consequence of their want of leaves and branches, whose surfaces are covered with the bibulous mouths of innumerable lymphatics, would otherwise be frequently in danger of perishing through absolute drought; but gradually of less use as the plant advances in age, and becomes possessed of these ornamental appendages; and hence, except in a few instances, annually encroached upon, and at length totally obliterated by the surrounding lignum.
All these lie in concentric circles; and the trunk enlarges, by the formation of a new liber or inner bark every year; the whole of the liber of one year, excepting indeed its outermost layer, which is transformed into cortex, becoming the alburnum of the next, and the alburnum becoming the lignum. Such, at least, is the common theory, and which seems to be well supported by the experiments of Malpighi and Grew: but it has lately been controverted hy Mr. Knight, who contends, that the liber has no concern in the formation of new wood, which proceeds from the alburnum alone, a new layer of alburnum being formed for this purpose annually. I cannot discuss the argument at present: nor is it of any great importance; since, under either system, it is obvious that a mark of any kind, which has penetrated through the outer into the inner bark, must in a long process of years be comparatively transferred to the central parts of the trunk. On which account we often find, in felling trees of great longevity, as an oak, for example, the date of very remote national eras, and the initials of monarchs, who flourished in very early periods of our national history, stamped in the very heart of the timber on its being subdivided.
Some of these memorials are very curious, and M. Klein, the well-known Secretary of Dantzic, has given various examples in his letter to Sir Hans Sloane, bart., the President of the Royal Society.* One of these consists of a long series of letters discovered, in 1727, in the trunk of a full-grown beech, near Dantzic, in land belonging to the family of Daniel Berckholtz. The letters D. B. were chiefly conspicuous in the solid wood; the wood towards the bark, and that towards the heart, that is, in each extremity, “bearing not the least trace of letters.” M. Klein relates another example from the Ephemerides of Natural Curiosities, recorded by Joannes Myerus. It consists of a thief hanging from a gibbet, apparently drawn by nature's own pencil in the timber of a beech-tree: as also the figure of a crucified man, found in a tree of the same kind; and that of a chalice with a sword, perpendicularly erect, sustaining a crown on its point; which was preserved at the Hague, and had been seen by himself.
Such marks were formerly attributed to miraculous intervention, or regarded as marvellous sports of nature : but the hints now offered will easily explain their origin.
Foreign substances have often been found imbedded in the same way, having at one time been sunk into the inner bark, or penetrated it by a wound or other excavation, and afterward covered over with new annual growths of liber and alburnum. Thus Sir John Clerk gives an account of a horn of a large deer which was found in the heart of an oak in Winfield Park, Cumberland, fixed in the timber with large iron cramps, with which, of course, it had been fastened on. And we are hence able to account for the occasional detection of a capricorn beetle,ọ or other insect which has been found in the centre of a trunk, the animal having crept into an accidental cleft, and either died there naturally, or been arrested and imprisoned by the secretion of the matter of new inner bark while in the torpitude of its aurelian state. And hence, indeed, the cause of the very wonderful phenomena of toads or frogs Deing at times found in a like situation ; having in the same way been impacted in the hole or crack into which they had crept, by the glutinous fluid of the inner bark, during sickness or a protracted winter sleep. Some Phil. Trans. for 1739, vol. xli. p. 231.
† Ephem. Nat. Cur. decad. iii. an. v. obs. 29. † Phil. Trans. for 1740, vol. xli. p. 448.
Ib. 1741, vol. xli. p. 861.