V. composita, ovato-truncata, pedunculo reflexili ramosissimo.Plate XXVII.Fig. 61. Compound vorticella, oval, truncated, with a bending branching stalk.
When viewed with a small magnifier, they appear like so many little trees; the upper part or heads are egg-shaped, the top truncated, the lower part filled with intestines; the branches are thick set with little knobs.a, the trunk;b b b, the branches;c c, the head when extended;d, the small knobs on the branches.
V. composita, pedunculo rigido, pedicellis ramosissimis longis. Compound, rigid pedicle, with small branched long feet.
To the naked eye it appears like the vorticella socialis, described inpage 395, but is distinguished from it by always adhering to the sides of the vessel in which it is placed. With the microscope, a long very slender pedicle is discovered sticking to the sides of the vessels, from which proceed an innumerable quantity of crystalline pellucid pearls, which, together with the stalk, are variously agitated in the water. They sometimes move separately, at other times together, are sometimes drawn down to the root, and in a moment expanded again.
Vermis contractilis, testa tectus, ciliis rotatoriis. A worm capable of contracting, covered with a shell, and furnished with rotatory cilia.
B. univalvis, testa ovata striata, apice sexdentata, basi integra, cauda nulla.Plate XXVII.Fig. 64 and 65. Univalved brachionus, the shell oval and striated, six notches or teeth round the upper edge, the base whole or even, without a tail.
The shell is oblong, pellucid, and capable of altering its figure. The apex,a, is truncated, with six small teeth on the edge of it, twelve longitudinal streaks down the back, the base obtuse and smooth. The teeth are occasionally either protruded or retracted; on the other side of the shell, towards the tail, there are two little spines or horns,c.
The animalculum itself is muscular, pellucid, and crystalline, often of a yellow colour; from the apex it now and then puts forth three little bundles of playing hairs, the two lateral ones shorter than the middle one; a forked deglutatory muscle,e, is perceptible; and on the under side, when the apex is drawn in, two rigid points may be discovered. It is found in sea water.
B. univalvis, testa orbicularis, apice truncata quadridentata, basi integra, cauda nulla. Univalved brachionus, with an orbicular shell; the apex truncated, and having four teeth, the base smooth, no tail.
B. univalvis, testa oblonga excavata, apice quadridentata, basi integra, cauda nulla. Univalved brachionus, with an oblong excavated shell, four long teeth at the apex, the base smooth, no tail. It is of a yellow colour.
B. univalvis, testa oblonga inflexa, apice decemdentata, basi integra, cauda spuria. Univalvedbrachionus, the shell oblong and inflected, ten teeth at the apex, the base smooth, and a spurious tail.
B. univalvis, testa orbiculari integra, cauda mutica. Univalved brachionus, with an orbicular shell, the edges regular, and having a long beardless tail.
The patina is extremely bright and splendid; it has a large body, a crystalline and nearly circular shell, without either incision or teeth, though towards the apex it falls in so as to form a smooth notch; the body is affixed to the middle of the shell; a double glittering organ, with ciliated edges, is projected from the apex; both these organs are of a conical figure, appearing to stand on a pellucid substance, which is divided into two lobes; between these and the rotatory organ there is a silver-coloured crenulated membrane; two small claws may be discovered near the mouth. It is reckoned as one of the rarer species of vorticella, and is found in stagnant waters in the month of May.
B. univalvis, testa oblonga, apice emarginata, basi integra, cauda mutica. Univalved brachionus, the shell oblong, the apex notched, the base smooth, and the tail naked.
B. univalvis, testa producta, apice integra, basi tricorni, cauda bipili. Univalved brachionus, the shell extending considerably beyond the body; the base divided into three small horns, with two hairs at the end of the tail.
B. univalvis, testa ovata, apice bidentata, basi emarginata, cauda biseta. Brachionus with a univalveoval shell, two teeth at the apex, the base notched; two bristles at the tail.
The shell plain, oval, orbicular, crystalline, with the anterior part terminating in two acute points on both sides, though the intervening space is commonly filled up with the head of the animal. The head, the tail, and the trunk are very distinct; the bottom of the trunk is terminated in a semicircle, the fore-part marked with two transverse lines; it occupies the disc of the shell. The intestines are indistinct, and the tail affixed to the trunk; it is short, annulated, flexible, the middle projecting beyond the shell, the apex diverging into two very fine bristles; it fastens itself by these, and whirls about with the body erect; the rotatory cilia are not perceptible without great difficulty. It is found in marshy water all the winter.
B. univalvis, testa suborbiculari, apice lunata, basi integra, cauda spina duplici. Univalved brachionus, the shell rather orbicular, lunated apex, smooth base, and the tail furnished with two spines.
B. univalvis, testa oblonga, apice crenulata, basi emarginata. Univalved brachionus, with an oblong shell, the apex hairy, and the base notched.
B. bivalvis, testa depressa, apice emarginata, basi incisa, cauda cirro duplici. Bivalved brachionus, with a flattened shell, the apex notched, a hollow part at the base, the tail formed of two tufts of hair.
B. bivalvis, testa apice mutica, basi tricorni, cauda duplici.Plate XXVII.Fig. 59. Bivalved, theapex of the shell beardless, three horns at the base, and double tail.
The body is pellucid, nearly triangular, bivalved, and open on the back of the animalculum; from the orifice proceed two little laminæ larger than the rotatory cilia; at the bottom are three or four rigid points,e f e, and a moveable tail,g, between them, divided into two filaments, which the little creature opens and shuts at pleasure; by these it fixes itself to objects.a a, the lateral cilia;b, two small laminæ;c, a deglutatory muscle;d, an opake mass.
B. bivalvis, testa arcuata, apice et basi utrinque dentata, cauda spina duplici. Bivalved brachionus, with an arched shell; the apex and the base are both toothed, and the tail formed of two spines.
B. bivalvis, subquadrata, apice et basi utrinque mucronata, cauda spina duplici. Bivalved, somewhat of a square form; the base and apex pointed; the tail consisting of two spines.
B. bivalvis, testa ovali, apice integra, basi mucronata, cauda rugosa biseta.Plate XXVII.Fig. 55. Bivalved brachionus, with an oval shell, the apex even, the base pointed, two thick bristles for the tail.
This is one of the smallest bivalved animalcula, muscular, the apex and anterior part round, the hinder part straight, terminating in a point, furnished with a hook on the fore-part, a small rotatory organ, a long tail composed of joints, and divided at the end into two bristles. It can open its shell both at the fore and hind-part.a, the shell when close;c, the posterior point;d, the animalculum;h, the tail;i, the bristles.
B. capsularis, testa apice producta, basi curti bicorni, cauda biseta. Larger than the preceding, ventricose, somewhat pellucid, the head conical, with a bundle of hairs on both sides; it has likewise a rotatory organ.
B. capsularis, testa cylindracea, frontis cirris binis pendulis, setaque caudali unica. Capsular brachionus, in a cylindric shell, with two long pendulous locks of hair proceeding from the front; the tail consists of a single bristle.
B. capsularis, testa quadrangula, apice bidentata, basi bicorni, cauda nulla. Capsular brachionus, in a quadrangular shell, with two small teeth at the apex, two horns proceeding from the base, and no tail.
B. capsularis, testa quadrangula, apice integra, basi obtusi emarginata, cauda flexuosa. Capsular brachionus, the shell quadrangular, a smooth undivided apex; obtuse base; notched margin, and a flexuous tail.
For a full description of this animalculum, being the same as the vorticella urceolaris, the reader will please to refer topage 408. Views of the animal in its different positions will be found inPlate XXII.Fig. 36, 37, 38, and inPlate XXVII.Fig. 56 and 57. Fig. 56,a a, are the two fibrillæ;b, the head;f, the intestines;i, the aperture from which the tail is protruded;i k, the tail; at the end,k, is a cleft, enabling the animal to affix itself more firmly to any substance.Fig. 57, ata c a, are seen the fibrillæ;dshews the moveable intestine, supposed to be the heart or lungs;f, the intestines;h i k, the tail.
B. capsularis, testa ventricosa, apice quadridentata, basi bicorni, cauda longa bicuspi.Plate XXVII.Fig. 58. Capsular brachionus, the shell ventricose, four teeth at the apex, two horns at the base, and a long tail terminating in two short points.
This differs considerably from the foregoing in the shape of the shell, from each side of which there is a curved projection,f f, inclining towards the tail, nearly of the same length with it, and terminating in a point,h h. The upper part also of the shell is of a different form, having in general four longer spiculæ, and two shorter ones. From the head two arms or branches,e e, are frequently extended; the circular end of each is furnished with a tuft of little hairs, which sometimes move in a vibratory manner, at other times have a rotatory motion. The eggs are either affixed to the tail, or the curved part of the shell; they have from one to five hanging from them. Müller has likewise discovered in this animalculum two small feelers, and a kind of tongue.a a, the rotatory organs;b, the tongue;c c, the feelers;d d, a ciliated part on the side of the shell;g, the heart or lungs;m k, the tail; at the extremity,k, two sharp points.
B. capsularis, testa ventrosa, apice octodentata, basi lunata quadricorni, cauda brevi bicuspi. Capsular brachionus, the shell ventricose, eight teeth at the apex, the base lunated or hollowed into the form of a crescent, and furnished with four horns; the tail short, with two small points at the end.
378. Fig.A A A. An animalculum found in ditch water in the month of September, represented in three different forms which it assumed.
379. Fig.B B B. A species of testaceous wheel-animal;a, its appearance when protruded;b, when in the shell;c, another appearance of the same.
380. Fig.C, shews one of the same species; and
381. Fig.D, exhibits another of the same kind; they both appear as protruded from the shell. The above are all drawn as they were found adhering to a vegetable substance.
382. Fig.E E E. Several appearances of an animalculum found in stagnant water in September, about the one-hundredth part of an inch in length; it moved slowly, and there appeared a wheel-like motion in certain fibrillæ in the head. The double-forked part of the tail had a similar motion to the tail of the pulex aquaticus; the intestines appeared of different colours, as brown, yellow, and reddish, and had a quick irregular motion; the external parts were very transparent.
383. Fig.F F F F. Several animalcula in a drop of water from a leaden cistern; of different sizes, but apparently of the same species. They moved either end foremost, without any undulating motion, but very uniform and slow; each end appeared alike, and very transparent; the middle clear, brown, with a blackishlist nearly the whole length of the animal. The large one,a, lay sometime bent, as in the drawing, the others, both when in motion and at rest continuing quite straight. Some of the very small ones were transparent; others appeared as atbandc.[128]
[128]In the former edition of this work, owing to an error in the numeration, it appeared that 379 of these animalcula were described, though in reality it contained only 377, or the number which has already been given.Previous to the publication of Mr. Adams’s edition, a friend communicated to him drawings and descriptions of several of these minute beings which had fallen under his observation; but they were received too late for insertion. Mr. A. having at that time favoured me with a copy of the drawings and manuscript, they are now added, with the hope that they will not prove unacceptable to the curious reader.Edit.
[128]In the former edition of this work, owing to an error in the numeration, it appeared that 379 of these animalcula were described, though in reality it contained only 377, or the number which has already been given.
Previous to the publication of Mr. Adams’s edition, a friend communicated to him drawings and descriptions of several of these minute beings which had fallen under his observation; but they were received too late for insertion. Mr. A. having at that time favoured me with a copy of the drawings and manuscript, they are now added, with the hope that they will not prove unacceptable to the curious reader.Edit.
Having in this and the preceding chapter described an extensive variety of those minute and wonderful productions of nature, the hydræ, vorticellæ, and animalcula infusoria, I shall take my leave of the subject with remarking, that though by the assistance of the microscope myriads of animated beings, roving in the smallest drop of water as if it were a sea, have been exhibited to the astonished eyes of attentive observers, it surely cannot be deemed an unreasonable supposition, that theAdorable Creator, who has filled the immensity of extent with suns and worlds, has also peopled every particle of fluid with beings far more minute than any apparatus of ours can perceive; and however insignificant many of the smaller parts of the creation may appear to the uninformed bulk of mankind, there cannot exist a doubt, but that they were all, collectively and individually, formed for the wisest purposes; and, though in many instances these designations are to us incomprehensible, let us not on that account rashly withhold our admiration. These sentiments are beautifully enforced in the following expressive lines of Thomson:
Gradual from these what num’rous kinds descend,Evading ev’n the microscopic eye!Full nature swarms with life; one wond’rous massOf animals, or atoms organized,Waiting the vital breath, when parent heavenShall bid his spirit blow. The hoary fen,In putrid streams, emits the living cloudOf pestilence. Thro’ subterranean cells,Where searching sun-beams scarce can find a way,Earth animated heaves. The flowery leafWants not its soft inhabitants. Secure,Within its winding citadel, the stoneHolds multitudes. But chief the forest boughs,That dance unnumber’d to the playful breeze,The downy orchard, and the melting pulpOf mellow fruit, the nameless nations feedOf evanescent insects. Where the poolStands mantled o’er with green, invisible,Amid the floating verdure, millions stray.Each liquid too, whether it pierces, soothes,Inflames, refreshes, or exalts the taste,With various forms abounds. Nor is the streamOf purest crystal, nor the lucid air,Tho’ one transparent vacancy it seems,Void of their unseen people. These, conceal’dBy the kind art of forming heaven, escapeThe grosser eye of man:————Let no presuming impious railer taxCreative Wisdom, as if aught was form’dIn vain, or not for admirable ends.Shall little haughty Ignorance pronounceHis works unwise, of which the smallest partExceeds the narrow vision of her mind?As if upon a full-proportion’d dome,On swelling columns heav’d, the pride of art!A critic fly, whose feeble ray scarce spreadsAn inch around, with blind presumption bold,Should dare to tax the structure of the whole.And lives the man, whose universal eyeHas swept at once th’ unbounded scheme of things;Mark’d their dependance so, and firm accord,As with unfaultering accent to concludeThat this availeth nought? Has any seenThe mighty chain of beings lessening downFrom infinite perfection to the brinkOf dreary nothing, desolate abyss!From which astonish’d thought, recoiling, turns?Till then alone let zealous praise ascend,And hymns of holy wonder, to that Power,Whose wisdom shines as lovely on our minds,As on our smiling eyes his servant sun.
Gradual from these what num’rous kinds descend,Evading ev’n the microscopic eye!Full nature swarms with life; one wond’rous massOf animals, or atoms organized,Waiting the vital breath, when parent heavenShall bid his spirit blow. The hoary fen,In putrid streams, emits the living cloudOf pestilence. Thro’ subterranean cells,Where searching sun-beams scarce can find a way,Earth animated heaves. The flowery leafWants not its soft inhabitants. Secure,Within its winding citadel, the stoneHolds multitudes. But chief the forest boughs,That dance unnumber’d to the playful breeze,The downy orchard, and the melting pulpOf mellow fruit, the nameless nations feedOf evanescent insects. Where the poolStands mantled o’er with green, invisible,Amid the floating verdure, millions stray.Each liquid too, whether it pierces, soothes,Inflames, refreshes, or exalts the taste,With various forms abounds. Nor is the streamOf purest crystal, nor the lucid air,Tho’ one transparent vacancy it seems,Void of their unseen people. These, conceal’dBy the kind art of forming heaven, escapeThe grosser eye of man:————Let no presuming impious railer taxCreative Wisdom, as if aught was form’dIn vain, or not for admirable ends.Shall little haughty Ignorance pronounceHis works unwise, of which the smallest partExceeds the narrow vision of her mind?As if upon a full-proportion’d dome,On swelling columns heav’d, the pride of art!A critic fly, whose feeble ray scarce spreadsAn inch around, with blind presumption bold,Should dare to tax the structure of the whole.And lives the man, whose universal eyeHas swept at once th’ unbounded scheme of things;Mark’d their dependance so, and firm accord,As with unfaultering accent to concludeThat this availeth nought? Has any seenThe mighty chain of beings lessening downFrom infinite perfection to the brinkOf dreary nothing, desolate abyss!From which astonish’d thought, recoiling, turns?Till then alone let zealous praise ascend,And hymns of holy wonder, to that Power,Whose wisdom shines as lovely on our minds,As on our smiling eyes his servant sun.
Gradual from these what num’rous kinds descend,Evading ev’n the microscopic eye!Full nature swarms with life; one wond’rous massOf animals, or atoms organized,Waiting the vital breath, when parent heavenShall bid his spirit blow. The hoary fen,In putrid streams, emits the living cloudOf pestilence. Thro’ subterranean cells,Where searching sun-beams scarce can find a way,Earth animated heaves. The flowery leafWants not its soft inhabitants. Secure,Within its winding citadel, the stoneHolds multitudes. But chief the forest boughs,That dance unnumber’d to the playful breeze,The downy orchard, and the melting pulpOf mellow fruit, the nameless nations feedOf evanescent insects. Where the poolStands mantled o’er with green, invisible,Amid the floating verdure, millions stray.Each liquid too, whether it pierces, soothes,Inflames, refreshes, or exalts the taste,With various forms abounds. Nor is the streamOf purest crystal, nor the lucid air,Tho’ one transparent vacancy it seems,Void of their unseen people. These, conceal’dBy the kind art of forming heaven, escapeThe grosser eye of man:————Let no presuming impious railer taxCreative Wisdom, as if aught was form’dIn vain, or not for admirable ends.Shall little haughty Ignorance pronounceHis works unwise, of which the smallest partExceeds the narrow vision of her mind?As if upon a full-proportion’d dome,On swelling columns heav’d, the pride of art!A critic fly, whose feeble ray scarce spreadsAn inch around, with blind presumption bold,Should dare to tax the structure of the whole.And lives the man, whose universal eyeHas swept at once th’ unbounded scheme of things;Mark’d their dependance so, and firm accord,As with unfaultering accent to concludeThat this availeth nought? Has any seenThe mighty chain of beings lessening downFrom infinite perfection to the brinkOf dreary nothing, desolate abyss!From which astonish’d thought, recoiling, turns?Till then alone let zealous praise ascend,And hymns of holy wonder, to that Power,Whose wisdom shines as lovely on our minds,As on our smiling eyes his servant sun.
The subject of the following chapter opens an extensive field for observation to the naturalist, in which the labour of a life may be well employed: it is a branch where the observer will find the microscope of continual use, and without which he will scarce be able to form any just idea of the organization of trees and plants, or of the variations in the disposition, the number, nature, and offices of their several parts.
Vegetables are beautiful and perfect in their kind, wonderful in their growth, beneficial in their uses. “Herbs and flowers may be regarded by some persons as objects of inferior consideration in philosophy; but every thing must be great which has God for its author. To him all the parts of nature are equally related: the flowers of the earth can raise our thoughts up to the Creator of the world as effectually as the stars of heaven; and, till we make this use of both, we cannot be said to think properly of either. All trees and herbs in their place and seasons speak the same language from the climates of the north to the torrid regions of the south, and from the winter to the spring and the harvest, they join their voices in the universal chorus of all createdbeings, and to the ear of reason celebrate the wisdom of the Almighty Creator.”
Malpighi, Grew, Duhamel, Hill, Bonnet, and De Saussure, are almost the only writers who have treated on the interior structure of vegetables; and, if we consider the imperfection of the instruments used by some of them in these anatomical researches, and the little attention paid by the rest to the advantages their favourite pursuits might have derived from the use of the microscope, as well as the dissecting knife, we find greater cause to wonder at what has been done, than at what remains to be performed. To the general inattention to the structure of plants, we may, amongst other causes, also ascribe the instability and fluctuation of the different theories on the principles of vegetation. We are, however, so little acquainted with the steps which Providence takes to lead intellectual, but free agents, to the knowledge of truth, and the various difficulties, errors, and prejudices, necessary to be removed, before it can shine in its native colours, that it is our duty to encourage every humble effort towards the advancement of science, that thus we may co-operate with our Creator and Redeemer in promoting that vast plan to which all things are now converging, the bringing all his creatures to a state of truth, goodness, and consequent happiness, an end worthy of the best and wisest of beings.[129]
[129]See the Bishop of Exeter’s Sermon before the Society for the Propagation of the Gospel.
[129]See the Bishop of Exeter’s Sermon before the Society for the Propagation of the Gospel.
As Dr. Hill is the first writer who has treated this part of natural history in an orderly and scientific manner, I shall use the names he has adopted for characterizing the different parts of trees, &c. which are, 1. the rind; 2. the bark; 3. the blea; 4. the wood; 5. the corona or circle of propagation; 6. the pith. These are placed immediately within or under one another; they are the essential parts upon which the strength of the tree depends: in,among, and between these, the various vessels are placed, which nourish the whole, and maintain and carry on the vegetation of the tree, and from which it obtains its peculiar qualities and virtues. These vessels are of five kinds:
Of these, the first are placed between the rind and bark; the second, in the substance of the bark; the third, in the substance of the blea; the fourth, in the substance of the wood; the fifth, in the corona.
More accurate instruments, or a more minute investigation of the parts, may probably discover new vessels in a system which appears to be entirely vascular, and brings us more thoroughly acquainted with the nature of vegetation.
The exterior covering of all trees is a thin, dry, parched substance, which has been compared by many writers to the skin of animals, and called by names analogous thereto; thus it is called the epidermis by Duhamel, the skin by Grew, the rind by Hill.
When a tree is full of sap, this membrane may be easily detached from the part it covers; it may be separated from green branches which are not in sap, by boiling them in water; large pieces of it may also be obtained from rotten branches; the rind of the leaves of many trees is detached with singular dexterity from the other parts, by some of the mining caterpillars; artificialmethods for effecting this purpose have been described inpage 160of this work. Though the rind may at first sight be thought to be of little use, it will be found to be a principal organ in the process of vegetation. The part which covers the root has the most important offices assigned to it.
Many are of opinion that the rind is formed of dried vesiculæ; and Malpighi says, that we may see in the vascular texture of the bark of the cherry and plumb-trees an arrangement of the parts proper to form the rind, and this arrangement is occasioned by the endeavour of the vascular part to extend itself to the circumference, and the resistance it meets with from the rind; and that hence the vessels are flattened, and assume a membranaceous form.
The rind is a general covering to the young trunks of trees, to the branches, the roots, the leaves, the fruit, the flowers, &c. Upon the trunks of large trees some pieces only of the rind are to be found, having probably been broken by the increased size of the tree. The rind of some species of trees will bear being stretched much further than those of others, and remain for a considerable time uniformly spread over the bark. Du Hamel asserts, that the rind of vigorous healthy, trees remains longer whole than on those that are more languid, notwithstanding that the growth of the last is slower, and therefore makes less efforts against the rind. This circumstance is much in favour of the distinct organization of the rind, and against the opinion of those who only suppose it to consist of dried bladders.
Thin as the rind is, it is formed of many coats, adhering closely to each other, which in some species may be separated with ease, in others, with difficulty. Du Hamel says, that he has divided the rind of the birch into six distinct coats, and that he had no doubtbut what the division might have been carried much further. Dr. Hill says, that unless some of these coats be obtained in a state of separation from the rest, the true construction of the rind cannot be discovered, for the connection and form of the parts are lost by the confusion in which they appear while they lie one upon another.
The following experiments may throw a little light upon this obscure subject.[130]All the rind was taken from the trunk of a cherry-tree, and the tree thus skinned exposed to the air; a part of the bark which was next to the rind dried up and exfoliated; the part next to this did the same; after two or three exfoliations, a farinaceous substance covered the superfice of the trunk, soon after which a new rind appeared. Some pieces of rind were taken from a few young branches, and the wounds were covered with a cloth that had been soaked in wax and turpentine; on these the rind appeared in a very little time, without any apparent exfoliation. From some other branches, not only the rind, but a part of the bark was also taken away, and the wounds covered as before; a slight exfoliation was observed here, which was soon followed with a new rind. The bark was taken entirely off from a vigorous cherry-tree, while it was in full sap, so that the wood appeared the whole extent of the trunk. This was protected from the rays of the sun, and from the air. A new bark and rind formed themselves upon the trunk, but they did not originate from the bark that was left on the branches and the root, but extended from different spots, which were first formed at considerable distances from each other. After a lapse of fifteen years, this new rind did not appear like the natural rind of the cherry-tree. From these experiments we learn, that the rind regenerates more readily in some cases than in others, and that it preservesand prevents in a degree the bark from becoming dry too soon, and in consequence thereof exfoliating.
[130]Du Hamel Physique des Arbres, tom. 1, p. 12.
[130]Du Hamel Physique des Arbres, tom. 1, p. 12.
Aided by the microscope, a number of luminous points may be discovered in the rind;[131]these are so many minute holes for other purposes of transpiration. In the cane these holes are visible to the naked eye. A few oval holes may also be perceived in it; these are, however, no more than a separation of the parts, occasioned by the extension of the vasa interiora.
[131]Du Hamel Physique des Arbres, tom. 1, p. 9.
[131]Du Hamel Physique des Arbres, tom. 1, p. 9.
Dr. Grew supposed the rind to be formed of small vesicles, or bladders, clustered together, and intermixed with ligneous fibres or vessels, which run through the length of the rind; these are conjoined by other transverse ones, but that as the rind dries, the bladders or blebs shrink up and disappear. This account does not differ much from that of Dr. Hill, who says, that the rind is formed of a series of longitudinal vessels, and a filmy substance, between them, which, when viewed in a transverse section, form small circles, the sides of which are supported and made up of these longitudinal fibres; that the transverse vessels are only a deception, occasioned by the spaces between them and part of the film. The mode of obtaining an accurate view of the organization of this part, by conveying coloured liquors into the several vessels thereof, has been already described inpage 160of these Essays; by these means, together with the microscope, we find that the vessels are everywhere pierced with small dots or openings: of the use of these, the following conjectures have been formed.[132]
[132]Hill’s Construction of Timber, &c. p. 37.
[132]Hill’s Construction of Timber, &c. p. 37.
The root, which is equal in surface to a third part of the tree above ground, is covered with a pierced rind. The cold ofwinter contracts the whole of this, the parts are drawn closer together, and the mouths of these innumerable vessels are shut or nearly so, by this contraction; a very little of the half-congealed moisture of the ground gets into them, but this suffices for the service of the tree, when there is little heat to cause any perspiration, and at a time when in the deciduous trees, the very organs of the greatest perspiration, the leaves, do not exist.
The warmth of the spring arrives, the fluids of the earth grow thinner, every part of the root expands; this opens the mouths of the vessels, and the torrent of nutrition rushes in. By these means, every coat of the rind, and the interstitial spaces thereof, are rendered supple, and may be easily separated from the under coverings.
In roots, the colour of the rind varies very much, being white in some, brown in others, &c. Every root, according to Grew, after it has arrived at a certain age, has a double skin, the one coeval with the other parts, and exists in the seed; a ring is afterwards sent off from the bark, which forms the second skin; thus in the root of dandelion, towards the end of May, the original or outer skin appears shrivelled, and is easily separated from the new one, which is fresher, and adheres more firmly to the bark. Perennial plants are supplied in this manner with a new skin every year; the outer one always falls off in the autumn and winter, and a new one is formed from the bark in the succeeding spring.
These are called by Du Hamel the cellular coat, enveloppe cellulaire; by Hill, the exterior vessels, and the vasa propria exteriora.
It has been already observed, that in trees the juice vessels, or vasa propria, do not form those constituent parts of the wood of which the timber consists, but that it is from the nature of these recipient vessels that it derives its virtues, qualities, and specific properties.[133]A tree may grow, live, and give shade without them; but on those its peculiar character and decided virtues depend; these are greatest where the vasa propria are largest or most numerous; and where we do not find these, we scarce find any thing that will affect the taste or the smell. There are different ranges of these vessels between the several parts, each of which has its allotted place, its peculiar form, its different structure, and its separate use. Many trees have them in all their parts, others only in some of them, while others do not exhibit any.
[133]Hill’s Construction of Timber, p. 73.
[133]Hill’s Construction of Timber, p. 73.
On taking off the rind, we find a substance of a deep green colour, succulent and herbaceous, formed of a prodigious number of filaments interwoven together in various directions; it is more abundant in some trees than in others, particularly in the elder, and more succulent in summer than in winter; it is then also less adherent to the rind. Dr. Hill thinks the best time of separating the rind, in order to view this part, is in a living branch, at the time of its swelling for the spring, or for the midsummer shoot, but much easier by the means of maceration.[134]
[134]Hill’s Construction of Timber, p. 75.
[134]Hill’s Construction of Timber, p. 75.
When the rind is perfectly separated, it leaves the vasa propria of this class behind it; they scarce adhere to the inner bark, and but little to the rind; they are disposed in packets, and do not run straight down the branch, but interweaving with each other, form a kind of net. These packets may be separated easily from the bark; when a thin transverse section of one of them is examined,it is found to be composed of twelve or fifteen distinct vessels with hard rinds. Dr. Hill says, that with a great deal of patience, a vast number of objects, and a good microscope, we may see by what means these vessels adhere to the bark; for we shall find upon the sides small oval depressions which fit thereto, and that are probably a kind of glands, that separate from the general store of sap, with which the bark is filled, the juices peculiar to these vessels.
The bark lies next within the rind, and differs but little from it in construction, though it holds a more important office in the scale of vegetation, the growth and qualities of the tree being in a great measure connected with it. It is, therefore, found to differ considerably in substance, quantity, and quality, in various kinds.
It is originally the outer membrane, covering the lobes of the seed. Even there, as in the branch of a tree, it appears in the form of a kind of spunge, or like a crust of bread, composed of flatted bladders.
Its spunge-like nature may be further inferred from the contraction of its pores when dry, and the ease with which they dilate when in water. Grew has called it a most curious and exquisitely fine, wrought spunge. In the course of its growth, the outer ranges of these bladders drying, it becomes what we call the rind; for the rind was once bark, and has only suffered a slight change in separating from it.
By the bark the tree is fed with a continual supply of moisture, protected from external injuries, and defended from the excessesof heat and cold; for these purposes it is variously disposed in different trees. In the hardy and slow growing, as the oak and chesnut, it is thin; in the quick growing, as willow, poplar, and the like, it is thick. And what is more particularly to be attended to is, that in some its inner verge is radiated. There are some trees, and a great many herbaceous plants, in which this part is continued inward, in form of rays, through the blea into the wood, and seems to form so many green wedges, that split as it were the substance of both those parts;[135]a circumstance which accounts for the vegetation of some particular trees, which are known to live when deprived of the bark; because they have rays of the same substance within which answer the purpose, and this in a degree answering to the nature of their life.
[135]Hill’s Construction of Timber, p. 118. Ibid. p. 120,
[135]Hill’s Construction of Timber, p. 118. Ibid. p. 120,
The bark appears to be formed, first, of longitudinal fibres, which Du Hamel considers as so many lymphatic vessels; secondly, by a sort of a filmy cellular tissue, which has been considered as a kind of bladders by some, or as parenchymatous by others; thirdly, of the vasa propria interiora, or interior juice vessels.
The longitudinal fibres are disposed in strata, which lie one over the other. In that stratum which is next the rind, or rather the cellular coat, we perceive a net of longitudinal fibres, the meshes of which are large and easily distinguished, particularly when the cellular tissue that fills up the interstices is removed. To do this, the branches should be macerated for a considerable time; some require to be kept in this state for years. It will then be easy to separate first the rind, then the cellular coating, and afterwards this pulpy matter. It may sometimes be easily removed after the branches have been boiled.
The most exterior stratum, when examined by the naked eye, seems to be formed of simple fibres, which graft, solder, or inosculate one with the other; but when examined by a microscope, each of these fibres will be found to be a bundle of filaments, which may be easily separated from each other.
Grew says, that each filament, like the nerves in animals, consists of twenty or thirty small contiguous tubes, which run uniformly from the extremity of the root, without sending off any branches, or suffering any change in their size and shape. Hence the bark may be torn or divided lengthwise, with greater ease than in an horizontal direction; when macerated, they are capable of a very great degree of subdivision.
The filaments of a cortical vessel are to be looked on, agreeable to what we have already observed, as so many little bundles placed near together, and at first growing parallel to each other; but soon quitting this direction, the filaments of one fascicle parting from that to which they originally belonged, and inclining more or less obliquely towards another, sometimes uniting with it, at others, bending backwards, and uniting again with that from which it proceeded, or with some one that it meets with. In this manner new fascicles are often formed, while other parcels are increased or diminished by the additions of new filaments; by these means, a kind of irregular net is formed, and the fibres proceed in a serpentine line from the top to the bottom of the tree.
The thickness of the bark is entirely formed of strata of these longitudinal fibres, which lie one over the other; each of these strata is similar to the exterior one, only the meshes are smaller, and the fibres finer, in proportion as they are more interior,insomuch that at last the meshes are almost annihilated, and the fibres seem to lie quite parallel to each other.
There are some trees, however, where the meshes are not visible, and in which the fibres lie quite in a straight direction. There are many other circumstances in which they vary in different trees; in some the meshes of each stratum correspond with each other, diminishing gradually in size as they are more interior, and forming as it were so many conical cells.
We may, I think, conclude from what has been said, that the bark is composed of several thin membranes, which extend over the whole exterior surface of the tree. The most exterior membrane is the rind; under this is what Du Hamel calls the cellular coat; next to this the cortical stratum or true bark of the tree, which is formed of lymphatic vessels ranged more or less in a reticular form, and of the vasa propria interiora. The meshes are so constituted as to form large cavities next the rind, and small ones near the wood. These cavities are filled with a parenchymatous substance or the cellular tissue, which being continued from the wood to the rind, joins and unites the cortical stratum, and afterwards spreading on the outside thereof, forms what has been termed the cellular coat.
We now proceed to give some account of the substance which fills up the vacant spaces that are left between the longitudinal fibres. It is called by Grew the parenchyma or pulp, by Malpighi, the vesicular tissue or web; both of them consider it as formed of small bladders or reticles, that are in contact with each other, lying in an horizontal position, or at right angles to the longitudinal fibres: they do not suppose them to be all of thesame size, or even of the same figure: Grew compares it to the froth of beer or eggs. The flesh of fruits consists for the most part of this substance, very much filled with juice, though with considerable difference in its organization. Be this as it may, the nature of this substance, its form and structure, are at present but very little known. It is floccose, and varies in colour in different species.
Besides the lymphatic vessels and the cellular substance, we find the juice vessels, or vasa propria, in the bark. In those trees which are famous for medicinal virtues, they are usually very large; they carry the milky juices of the sumach, and in them is lodged the finest and highest-flavoured turpentine in all the kinds of pine. Dr. Hill thinks that a tree of that genus exhibits them best, and the more, as the turpentine which fills them may be perfectly dissolved in spirit of wine. The pinus orientalis is the species in which these vessels are most distinctly seen.
This is that part of the tree which is formed into wood, and therefore lies between it and the bark, and may be separated from them by maceration.
A longitudinal piece of the blea, when examined by the microscope, exhibits a number of vessels running parallel to each other, the interstitial spaces being filled with a floccose, white, formless substance, of which Dr. Hill suspects even the vessels themselves to be formed. Innumerable small openings or mouths may be discovered in these vessels, suited to imbibe the moisture which is so essential to the life and health of plants. Thesemouths cannot be well discerned, except when they are opened by the season of the year, either before the first leaves of spring, or in the midsummer shooting time; though a small quantity of moisture will keep them open at that time, yet no quantity would be sufficient at an improper season.[136]