NORTH WINDS consist, first, of air flowing slowly from the north, so that they acquire the velocity of the earth's surface as they approach, are fair or frosty, seldom occur. 2. They consist of retrograde south winds; these continue but a day or two, are preceded by south-west winds; and are generally succeeded by north-east winds, cloudy or rainy, barometer rising.
SOUTH WINDS consist, first, of air flowing slowly from the south, loosing their previous western velocity by the friction of the earth's surface as they approach, moist, seldom occur, 2. They consist of retrograde north winds; these continue but a day or two, are preceded by north-east winds, and generally succeeded by south-west winds, colder, barometer sinking.
EAST WINDS consist of air brought hastily from the north, and not impelled farther southward, owing to a sudden beginning absorption of air in the northern regions, very cold, barometer high, generally succeeded by south-west wind.
WEST WINDS consist of air brought hastily from the south, and checked from proceeding further to the north by a beginning production of air in the northern regions, warm and moist, generally succeeded by north-east wind. 2. They consist of air bent down from the higher regions of the atmosphere, if this air be from the south, and brought hastily it becomes a wind of great velocity, moving perhaps 60 miles an hour, is warm and rainy; if it consists of northern air bent down it is of less velocity and colder.
Application of the preceding Theory to Some Extracts from a Journal of the Weather.
Dec. 1, 1790. The barometer sunk suddenly, and the wind, which had been some days north-east with frost, changed to south-east with an incessant though moderate fall of snow. A part of the northern air, which had passed by us I suppose, now became retrograde before it had acquired the velocity of the earth's surface to the south of us, and being attended by some of the southern air in its journey, the moisture of the latter became condensed and frozen by its mixture mith the former.
Dec. 2, 3. The wind changed to north-west and thawed the snow. A part of the southern air, which had passed by us or over us, with the retrograde northern air above described, was now in its turn driven back, before it had lost the velocity of the surface of the earth to the south of us, and consequently became a north-west wind; and not having lost the warmth it brought from the south produced a thaw.
Dec. 4, 5. Wind changed to north-east with frost and a rising barometer. The air from the north continuing to blow, after it had driven back the southern air as above described, became a north-east wind, having less velocity than the surface of the earth in this climate, and produced frost from its coldness.
Dec. 6, 7. Wind now changed to the south-west with incessant rain and a sinking barometer. From unknown causes I suppose the quantity of air to be diminished in the polar regions, and the southern air cooled by the earth's surface, which was previously frozen, deposits its moisture for a day or two; afterwards the wind continued south-west without rain, as the surface of the earth became warmer.
March 18, 1785. There has been a long frost; a few days ago the barometer sunk to 291/2, and the frost became more severe. Because the air being expanded by a part of the pressure being taken off became colder. This day the mercury rose to 30, and the frost ceased, the wind continuing as before between north and east. March 19. Mercury above 30, weather still milder, no frost, wind north-east. March 20. The same, for the mercury rising shews that the air becomes more compressed by the weight above, and in consequence gives out warmth.
April 4, 5. Frost, wind north-east, the wind changed in the middle of the day to the north-west without rain, and has done so for three or four days, becoming again north-east at night. For the sun now giving greater degrees of heat, the air ascends as the sun passes the zenith, and is supplied below by the air on the western side as well as on the eastern side of the zenith during the hot part of the day; whence for a few hours, on the approach of the hot part of the day, the air acquires a westerly direction in this longitude. If the north-west wind had been caused by a retrograde motion of some southern air, which had passed over us, it would have been attended with rain or clouds.
April 10. It rained all day yesterday, the wind north-west, this morning there was a sharp frost. The evaporation of the moisture, (which fell yesterday) occasioned by the continuance of the wind, produced so much cold as to freeze the dew.
May 12. Frequent showers with a current of colder wind preceding every shower. The sinking of the rain or cloud pressed away the air from beneath it in its descent, which having been for a time shaded from the sun by the floating cloud, became cooled in some degree.
June 20. The barometer sunk, the wind became south-west, and the whole heaven was instantly covered with clouds. A part of the incumbent atmosphere having vanished, as appeared by the sinking of the barometer, the remainder became expanded by its elasticity, and thence attracted some of the matter of heat from the vapour intermixed with it, and thus in a few minutes a total devaporation took place, as in exhausting the receiver of an air-pump. See note XXV. At the place where the air is destroyed, currents both from the north and south flow in to supply the deficiency, (for it has been shewn that there are no other proper winds but these two) and the mixture of these winds produces so sudden condensation of the moisture, both by the coldness of the northern air and the expansion of both of them, that lightning is given out, and an incipient tornado takes place; whence thunder is said frequently to approach against the wind.
August 28, 1732. Barometer was at 31, and Dec. 30, in the same year, it was at 28 2-tenths. Medical Essays, Edinburgh, Vol. II. p. 7. It appears from these journals that the mercury at Edinburgh varies sometimes nearly three inches, or one tenth of the whole atmosphere. From the journals kept by the Royal Society at London it appears seldom to vary more than two inches, or one-fifteenth of the whole atmosphere. The quantity of the variation is said still to decrease nearer the line, and to increase in the more northern latitudes; which much confirms the idea that there exists at certain times a great destruction or production of air within the polar circle.
July 2, 1732. The westerly winds in the journal in the Medical Essays, Vol. II. above referred to, are frequently marked with the number three to shew their greater velocity, whereas the easterly winds seldom approach to the number two. The greater velocity of the westerly winds than the easterly ones is well known I believe in every climate of the world; which may be thus explained from the theory above delivered. 1. When the air is still, the higher parts of the atmosphere move quicker than those parts which touch the earth, because they are at a greater distance from the axis of motion. 2. The part of the atmosphere where the north or south wind comes from is higher than the part of it where it comes to, hence the more elevated parts of the atmosphere continue to descend towards the earth as either of those winds approach. 3. When southern air is brought to us it possesses a westerly direction also, owing to the velocity it had previously acquired from the earth's surface; and if it consists of air from the higher parts of the atmosphere descending nearer the earth, this westerly velocity becomes increased. But when northern air is brought to us, it possesses an apparent easterly direction also, owing to the velocity which it had previously acquired from the earth's surface being less than that of the earth's surface in this latitude; now if the north-east wind consists of air descending from higher parts of the atmosphere, this deficiency of velocity will be less, in consequence of the same cause, viz. The higher parts of the atmosphere descending, as the wind approaches, increases the real velocity of the western winds, and decreases the apparent velocity of the eastern ones.
October 22. Wind changed from south-east to south-west. There is a popular prognostication that if the wind changes from the north towards the south passing through the east, it is more likely to continue in the south, than if it passes through the west, which may be thus accounted for. If the north-east wind changes to a north-west wind, it shews either that a part of the northern air descends upon us in a spiral eddy, or that a superior current of southern air is driven back; but if a north-east wind be changed into a south-east wind it shews that the northern air is become retrograde, and that in a day or two, as soon as that part of it has passed, which has not gained the velocity of the earth's surface in this latitude, it will become a south wind for a few hours, and then a south-west wind.
The writer of this imperfect sketch of anemology wishes it may incite some person of greater leizure and ability to attend to this subject, and by comparing the various meteorological journals and observations already published, to construct a more accurate and methodical treatise on this interesting branch of philosophy.
NOTE XXXIV.—VEGETABLE PERSPIRATION.
And wed the enamoured Oxygene to Light.
CANTO IV. l. 34.
When points or hairs are put into spring-water, as in the experiments of Sir B. Thompson, (Philos. Trans. Vol. LXXVII.) and exposed to the light of the sun, much air, which loosely adhered to the water, rises in bubbles, as explained in note on Fucus, Vol. II. A still greater quantity of air, and of a purer kind, is emitted by Dr. Priestley's green matter, and by vegetable leaves growing in water in the sun-shine, according to Mr. Ingenhouze's experiments; both which I suspect to be owing to a decomposition of the water perspired by the plant, for the edge of a capillary tube of great tenuity may be considered as a circle of points, and as the oxygene, or principle of vital air, may be expanded into a gas by the sun's light; the hydrogene or inflammable air may be detained in the pores of the vegetable.
Hence plants growing in the shade are white, and become green by being exposed to the sun's light; for their natural colour being blue, the addition of hydrogene adds yellow to this blue, and tans them green. I suppose a similar circumstance takes place in animal bodies; their perspirable matter as it escapes in the sun-shine becomes decomposed by the edges of their pores as in vegetables, though in less quantity, as their perspiration is less, and by the hydrogene being retained the skin becomes tanned yellow. In proof of this it must be observed that both vegetable and animal substances become bleached white by the sun-beams when they are dead, as cabbage-stalks, bones, ivory, tallow, bees-wax, linen and cotton cloth; and hence I suppose the copper-coloured natives of sunny countries might become etiolated or blanched by being kept from their infancy in the dark, or removed for a few generations to more northerly climates.
It is probable that on a sunny morning much pure air becomes separated from the dew by means of the points of vegetables on which it adheres, and much inflammable air imbibed by the vegetable, or combined with it; and by the sun's light thus decomposing water the effects of it in bleaching linen seems to depend (as described in Note X.): the water is decomposed by the light at the ends or points of the cotton or thread, and the vital air unites with the phlogistic or colouring matters of the cloth, and produces a new acid, which is either itself colourless or washes out, at the same time the inflammable part of the water escapes. Hence there seems a reason why cotton bleaches so much sooner than linen, viz. because its fibres are three or four times shorter, and therefore protrude so many more points, which seem to facilitate the liberation of the vital air from the inflammable part of the water.
Bee's wax becomes bleached by exposure to the sun and dews in a similar manner as metals become calcined or rusty, viz. by the water on their surface being decomposed; and hence the inflammable material which caused the colour becomes united with vital air forming a new acid, and is washed away.
Oil close stopped in a phial not full, and exposed long to the sun's light, becomes bleached, as I suppose, by the decomposition of the water it contains; the inflammable air rising above the surface, and the vital air uniting with the colouring matter of the oil. For it is remarkable, that by shutting up a phial of bleached oil in a dark drawer, it in a little time becomes coloured again.
The following experiment shews the power of light in separating vital air from another basis, viz. from azote. Mr. Scheel inverted a glass vessel filled with colourless nitrous acid into another glass containing the same acid, and on exposing them to the sun's light, the inverted glass became partly filled with pure air, and the acid at the same time became coloured. Scheel in Crell's Annal. 1786. But if the vessel of colourless nitrous acid be quite full and stopped, so that no space is left for the air produced to expand itself into, no change of colour takes place. Priestley's Exp. VI. p. 344. See Keir's very excellent Chemical Dictionary, p. 99. new edition.
A sun-flower three feet and half high according to the experiment of Dr. Hales, perspired two pints in one day (Vegetable Statics.) which is many times as much in proportion to its surface, as is perspired from the surface and lungs of animal bodies; it follows that the vital air liberated from the surfaces of plants by the sunshine must much exceed the quantity of it absorbed by their respiration, and that hence they improve the air in which they live during the light part of the day, and thus blanched vegetables will sooner become tanned into green by the sun's light, than etiolated animal bodies will become tanned yellow by the same means.
It is hence evident, that the curious discovery of Dr. Priestley, that his green vegetable matter and other aquatic plants gave out vital air when the sun shone upon them, and the leaves of other plants did the same when immersed in water, as observed by Mr. Ingenhouze, refer to the perspiration of vegetables not to their respiration. Because Dr. Priestley observed the pure air to come from both sides of the leaves and even from the stalks of a water-flag, whereas one side of the leaf only serves the office of lungs, and certainly not the stalks. Exper. on Air, Vol. III. And thus in respect to the circumstance in which plants and animals seemed the furtherest removed from each other, I mean in their supposed mode of respiration, by which one was believed to purify the air which the other had injured, they seem to differ only in degree, and the analogy between them remains unbroken.
Plants are said by many writers to grow much faster in the night than in the day; as is particularly observable in seedlings at their rising out of the ground. This probably is a consequence of their sleep rather than of the absence of light; and in this I suppose they also resemble animal bodies.
NOTE XXXV.—VEGETABLE PLACENTATION.
_While in bright veins the silvery sap ascends.
CANTO IV. l. 419.
As buds are the viviparous offspring of vegetables, it becomes necessary that they should be furnished with placental vessels for their nourishment, till they acquire lungs or leaves for the purpose of elaborating the common juices of the earth into nutriment. These vessels exist in bulbs and in seeds, and supply the young plant with a sweet juice till it acquires leaves, as is seen in converting barley into malt, and appears from the sweet taste of onions and potatoes, when they begin to grow.
The placental vessels belonging to the buds of trees are placed about the roots of most, as the vine; so many roots are furnished with sweet or mealy matter as fern-root, bryony, carrot, turnip, potatoe, or in the alburnum or sap-wood as in those trees which produce manna, which is deposited about the month of August, or in the joints of sugar cane, and grasses; early in the spring the absorbent mouths of these vessels drink up moisture from the earth, with a saccharine matter lodged for that purpose during the preceding autumn, and push this nutritive fluid up the vessels of the alburnum to every individual bud, as is evinced by the experiments of Dr. Hales, and of Mr. Walker in the Edinburgh Philosophical Transact. The former observed that the sap from the stump of a vine, which he had cut off in the beginning of April, arose twenty- one feet high in tubes affixed to it for that purpose, but in a few weeks it ceased to bleed at all, and Dr. Walker marked the progress of the ascending sap, and found likewise that as soon as the leaves became expanded the sap ceased to rise; the ascending juice of some trees is so copious and so sweet during the sap-season that it is used to make wine, as the birch, betula, and sycamore, acer pseudo-platinus, and particularly the palm.
During this ascent of the sap-juice each individual leaf-bud expands its new leaves, and shoots down new roots, covering by their intertexture the old bark with a new one; and as soon as these new roots (or bark) are capable of absorbing sufficient juices from the earth for the support of each bud, and the new leaves are capable of performing their office of exposing these juices to the influence of the air; the placental vessels cease to act, coalesce, and are transformed from sap- wood, or alburnum, into inert wood; serving only for the support of the new tree, which grows over them.
Thus from the pith of the new bud of the horse-chesnut five vessels pass out through the circle of the placental vessels above described, and carry with them a minuter circle of those vessels; these five bundles of vessels unite after their exit, and form the footstalk or petiole of the new five-fingered leaf, to be spoken of hereafter. This structure is well seen by cutting off a leaf of the horse-chesnut (Aesculus Hippocastanum) in September before it falls, as the buds of this tree are so large that the flower may be seen in them with the naked eye.
After a time, perhaps about midsummer, another bundle of vessels passes from the pith through the alburnum or sap-vessels in the bosom of each leaf, and unites by the new bark with the leaf, which becomes either a flower-bud or a leaf-bud to be expanded in the ensuing spring, for which purpose an apparatus of placental vessels are produced with proper nutriment during the progress of the summer and autumn, and thus the vegetable becomes annually increased, ten thousand buds often existing on one tree, according to the estimate of Linneus. Phil. Bot.
The vascular connection of vegetable buds with the leaves in whose bosoms they are formed is confirmed by the following experiment, (Oct. 20, 1781.) On the extremity of a young bud of the Mimosa (sensitive plant) a small drop of acid of vitriol was put by means of a pen, and, after a few seconds, the leaf in whose axilla it dwelt closed and opened no more, though the drop of vitriolic acid was so small as apparently only to injure the summit of the bud. Does not this seem to shew that the leaf and its bud have connecting vessels though they arise at different times and from different parts of the medulla or pith? And, as it exists previously to it, that the leaf is the parent of the bud?
This placentation of vegetable buds is clearly evinced from the sweetness of the rising sap, and from its ceasing to rise as soon as the leaves are expanded, and thus compleats the analogy between buds and bulbs. Nor need we wonder at the length of the umbilical cords of buds since that must correspond with their situation on the tree, in the same manner as their lymphatics and arteries are proportionally elongated.
It does not appear probable that any umbilical artery attends these placental absorbents, since, as there seems to be no system of veins in vegetables to bring back the blood from the extremities of their arteries, (except their pulmonary veins,) there could not be any vegetable fluids to be returned to their placenta, which in vegetables seems to be simply an organ for nutrition, whereas the placenta of the animal foetus seems likewise to serve as a respiratory organ like the gills of fishes.
NOTE XXXVI—VEGETABLE CIRCULATION.
And refluent blood in milky eddies bends.
CANTO IV. l. 420.
The individuality of vegetable buds was spoken of before, and is confirmed by the method of raising all kinds of trees by Mr. Barnes. (Method of propagating Fruit Trees. 1759. Lond. Baldwin.) He cut a branch into as many pieces as there were buds or leaves upon it, and wiping the two wounded ends dry he quickly applied to each a cement, previously warmed a little, which consisted principally of pitch, and planted them in the earth. The use of this cement I suppose to consist in its preventing the bud from bleeding to death, though the author ascribes it to its antisceptic quality.
These buds of plants, which are thus each an individual vegetable, in many circumstances resemble individual animals, but as animal bodies are detached from the earth, and move from place to place in search of food, and take that food at considerable intervals of time, and prepare it for their nourishiment within their own bodies after it is taken, it is evident they must require many organs and powers which are not necessary to a stationary bud. As vegetables are immoveably fixed to the soil from whence they draw their nourishment ready prepared, and this uniformly not at returning intervals, it follows that in examining their anatome we are not to look for muscles of locomotion, as arms and legs; nor for organs to receive and prepare their nourishment, as a stomach and bowels; nor for a reservoir for it after it is prepared, as a general system of veins, which in locomotive animals contains and returns the superfluous blood which is left after the various organs of secretion have been supplied, by which contrivance they are enabled to live a long time without new supplies of food.
The parts which we may expert to find in the anatome of vegetables correspondent to those in the animal economy are, 1. A system of absorbent vessels to imbibe the moisture of the earth similar to the lacteal vessels, as in the roots of plants; and another system of absorbents similar to the lymphatics of animal bodies, opening its mouths on the internal cells and external surfaces of vegetables; and a third system of absorbent vessels correspondent with those of the placentation of the animal foetus. 2. A pulmonary system correspondent to the lungs or gills of quadrupeds and fish, by which the fluid absorbed by the lacteals and lymphatics may be exposed to the influence of the air, this is done by the green leaves of plants, those in the air resembling lungs, and those in the water resembling gills; and by the petals of flowers. 3. Arterial systems to convey the fluid thus elaborated to the various glands of the vegetable for the purposes of its growth, nutrition, and various secretions. 4. The various glands which separate from the vegetable blood the honey, wax, gum, resin, starch, sugar, essential oil, &c. 5. The organs adapted for their propagation or reproduction. 6. Muscles to perform several motions of their parts.
I. The existence of that branch of the absorbent vessels of vegetables which resembles the lacteals of animal bodies, and imbibes their nutriment from the moist earth, is evinced by their growth so long as moisture is applied to their roots, and their quickly withering when it is withdrawn.
Besides these absorbents in the roots of plants there are others which open their mouths on the external surfaces of the bark and leaves, and on the internal surfaces of all the cells, and between the bark and the alburnum or sap-wood; the existence of these is shewn, because a leaf plucked off and laid with its under side on water will not wither so soon as if left in the dry air,—the same if the bark alone of a branch which is separated from a tree be kept moist with water,—and lastly, by moistening the alburnum or sap-wood alone of a branch detached from a tree it will not so soon wither as if left in the dry air. By the following experiment these vessels were agreeably visible by a common magnifying glass, I placed in the summer of 1781 the footstalks of some large fig-leaves about an inch deep in a decoction of madder, (rubia tinctorum,) and others in a decoction of logwood, (haematoxylum campechense,) along with some sprigs cut off from a plant of picris, these plants were chosen because their blood is white, after some hours, and on the next day, on taking out either of these and cutting off from its bottom about a quarter of an inch of the stalk an internal circle of red points appeared, which were the ends of absorbent vessels coloured red with the decoction, while an external ring of arteries was seen to bleed out hastily a milky juice, and at once evinced both the absorbent and arterial system. These absorbent vessels have been called by Grew, and Malphigi, and some other philosophers, bronchi, and erroneously supposed to be air-vessels. It is probable that these vessels, when cut through, may effuse their fluids, and receive air, their sides being too stiff to collapse; since dry wood emits air-bubles in the exhausted receiver in the same manner as moist wood.
The structure of these vegetable absorbents consists of a spiral line, and not of a vessel interrupted with valves like the animal lymphatics, since on breaking almost any tender leaf and drawing out some of the fibres which adhere longest this spiral structure becomes visible even to the naked eye, and distinctly so by the use of a common lens. See Grew, Plate 51.
In such a structure it is easy to conceive how a vermicular or peristaltic motion of the vessel beginning at the lowest part of it, each spiral ring successively contracting itself till it fills up the tube, must forcibly push forwards its contents, as from the roots of vines in the bleeding season; and if this vermicular motion should begin at the upper end of the vessel it is as easy to see how it must carry its contained fluid in a contrary direction. The retrograde motion of the vegetable absorbent vessels is shewn by cutting a forked branch from a tree, and immersing a part of one of the forks in water, which will for many days prevent the other from withering; or it is shewn by planting a willow branch with the wrong end upwards. This structure in some degree obtains in the esophagus or throat of cows, who by similar means convey their food first downwards and afterward upwards by a retrograde motion of the annular muscles or cartilages for the purpose of a second mastication of it.
II. The fluids thus drank up by the vegetable absorbent vessels from the earth, or from the atmosphere, or from their own cells and interfaces, are carried to the foot-stalk of every leaf, where the absorbents belonging to each leaf unite into branches, forming so many pulmonary arteries, and are thence dispersed to the extremities of the leaf, as may be seen in cutting away slice after slice the footstalk of a horse- chesnut in September before the leaf falls. There is then a compleat circulation in the leaf; a pulmonary vein receiving the blood from the extremities of each artery on the upper side of the leaf, and joining again in the footstalk of the leaf these veins produce so many arteries, or aortas, which disperse the new blood over the new bark, elongating its vessels, or producing its secretions; but as a reservoir of blood could not be wanted by a vegetable bud which takes in its nutriment at all times, I imagine there is no venous system, no veins properly so called, which receive the blood which was to spare, and return it into the pulmonary or arterial system.
The want of a system of veins was countenanced by the following experiment; I cut off several stems of tall spurge, (Euphorbia helioscopia) in autumn, about the centre of the plant, and observed tenfold the quantity of milky juice ooze from the upper than from the lower extremity, which could hardly have happened if there had been a venous system of vessels to return the blood from the roots to the leaves.
Thus the vegetable circulation, complete in the lungs, but probably in the other part of the system deficient in respect to a system of returning veins, is carried forwards without a heart, like the circulation through the livers of animals where the blood brought from the intestines and mesentery by one vein is dispersed through the liver by the vena portarum, which assumes the office of an artery. See Note XXXVII.
At the same time so minute are the vessels in the intertexture of the barks of plants, which belong to each individual bud, that a general circulation may possibly exist, though we have not yet been able to discover the venous part of it.
There is however another part of the circulation of vegetable juices visible to the naked eye, and that is in the corol or petals of flowers, in which a part of the blood of the plant is exposed to the influence of the air and light in the same manner as in the foliage, as will be mentioned more at large in Notes XXXVII and XXXIX.
These circulations of their respective fluids seem to be carried on in the vessels of plants precisely as in animal bodies by their irritability to the stimulus of their adapted fluids, and not by any mechanical or chemical attraction, for their absorbent vessels propel the juice upwards, which they drink up from the earth, with great violence; I suppose with much greater than is exerted by the lacteals of animals, probably owing to the greater minuteness of these vessels in vegetables and the greater rigidity of their coats. Dr. Hales in the spring season cut off a vine near the ground, and by fixing tubes on the remaining stump of it, found the sap to rise twenty-one feet in the tube by the propulsive power of these absorbents of the roots of it. Veget. Stat. p. 102. Such a power can not be produced by capillary attraction, as that could only raise a fluid nearly to the upper edge of the attracting cylinder, but not enable it to flow over that edge, and much less to rise 21 feet above it. What then can this power be owing to? Doubtless to the living activity of the absorbent vessels, and to their increased vivacity from the influence of the warmth of the spring succeeding the winter's cold, and their thence greater susceptibility to irritation from the juices which they absorb, resembling in all circumstances the action of the living vessels of animals.
NOTE XXXVII—VEGETABLE RESPIRATION.
While spread in air the leaves respiring play.
CANTO IV. l. 421.
I. There have been various opinions concerning the use of the leaves of plants in the vegetable oeconomy. Some have contended that they are perspiratory organs; this does not seem probable from an experiment of Dr. Hales, Veg. Stat. p. 30. He found by cutting off branches of trees with apples on them, and taking off the leaves, that an apple exhaled about as much as two leaves, the surfaces of which were nearly equal to the apple; whence it would appear that apples have as good a claim to be termed perspiratory organs as leaves. Others have believed them excretory organs of excrementious juices; but as the vapour exhaled from vegetables has no taste, this idea is no more probable than the other; add to this that in moist weather, they do not appear to perspire or exhale at all.
The internal surface of the lungs or air-vessels in men, are said to be equal to the external surface of the whole body, or about fifteen square feet; on this surface the blood is exposed to the influence of the respired air through the medium however of a thin pellicle; by this exposure to the air it has its colour changed from deep red to bright scarlet, and acquires something so necessary to the existence of life, that we can live scarcely a minute without this wonderful process.
The analogy between the leaves of plants and the lungs or gills of animals seems to embrace so many circumstances, that we can scarcely withhold our assent to their performing similar offices.
I. The great surface of the leaves compared to that of the trunk and branches of trees is such, that it would seem to be an organ well adapted for the purpose of exposing the vegetable juices to the influence of the air; this however we shall see afterwards is probably performed only by their upper surfaces, yet even in this case the surface of the leaves in general bear a greater proportion to the surface of the tree, than the lungs of animals to their external surfaces.
2. In the lungs of animal, the blood after having been exposed to the air in the extremities of pulmonary artery, is changed in colour from deep red to bright scarlet, and certainly in some of its essential properties; it is then collected by the pulmonary vein and returned to the heart. To shew a similarity of circumstance in the leaves of plants the following experiment was made, June 24, 1781: A stalk with leaves and seed-vessels of large spurge (Euphorbia helioscopia) had been several days placed in a decoction of madder (Rubia tinctorum) so that the lower part of the stem, and two of the undermost leaves were immersed in it. After having washed the immersed leaves in clear water, I could readily discern the colour of the madder passing along the middle rib of each leaf. This red artery was beautifully visible both on the under and upper surface of the leaf; but on the upper side many red branches were seen going from it to the extremities of the leaf, which on the other side were not visible except by looking through it against the light. On this under side a system of branching vessels carrying a pale milky fluid were seen coming from the extremities of the leaf, and covering the whole underside of it, and joining into two large veins, one on each side of the red artery in the middle rib of the leaf, and along with it descending to the footstalk or petiole. On slitting one of these leaves with scissars, and having a common magnifying lens ready, the milky blood was seen oozing out of the returning veins on each side of the red artery in the middle rib, but none of the red fluid from the artery.
All these appearances were more easily seen in a leaf of Picris treated in the same manner; for in this milky plant the stems and middle rib of the leaves are sometimes naturally coloured reddish, and hence the colour of the madder seemed to pass further into the ramifications of their leaf-arteries, and was there beautifully visible with the returning branches of milky veins on each side.
3. From these experiments the upper surface of the leaf appeared to be the immediate organ of respiration, because the coloured fluid was carried to the extremities of the leaf by vessels most conspicuous on the upper surface, and there changed into a milky fluid, which is the blood of the plant, and then returned by concomitant veins on the under surface, which were seen to ooze when divided with scissars, and which in Picris, particularly render the under surface of the leaves greatly whiter than the upper one.
4. As the upper surface of leaves constitutes the organ of respiration, on which the sap is exposed in the terminations of arteries beneath a thin pellicle to the action of the atmosphere, these surfaces in many plants strongly repel moisture, as cabbage-leaves, whence the particles of rain lying over their surfaces without touching them, as observed by Mr. Melville (Essays Literary and Philosop. Edinburgh) have the appearance of globules of quicksilver. And hence leaves laid with the upper surfaces on water, wither as soon as in the dry air, but continue green many days, if placed with the under surfaces on water, as appears in the experiments of Mons. Bonnet (Usage des Fevilles.) Hence some aquatic plants, as the Water-lily (Nymphoea) have the lower sides of their leaves floating on the water, while the upper surfaces remain dry in the air.
5. As those insects, which have many spiracula, or breathing apertures, as wasps and flies, are immediately suffocated by pouring oil upon them, I carefully covered with oil the surfaces of several leaves of Phlomis, of Portugal Laurel, and Balsams, and though it would not regularly adhere, I found them all die in a day or two.
Of aquatic leaves, see Note on Trapa and on Fucus, in Vol. II. to which must be added that many leaves are furnished with muscles about their footstalks, to turn their upper surfaces to the air or light, as Mimosa and Hedysarum gyrans. From all these analogies I think there can be no doubt but that leaves of trees are their lungs, giving out a phlogistic material to the atmosphere, and absorbing oxygene or vital air.
6. The great use of light to vegetation would appear from this theory to be by disengaging vital air from the water which they perspire, and thence to facilitate its union with their blood exposed beneath the thin surface of their leaves; since when pure air is thus applied, it is probable, that it can be more readily absorbed. Hence in the curious experiments of Dr. Priestley and Mr. Ingenhouze, some plants purified air less than others, that is, they perspired less in the sunshine; and Mr. Scheele found that by putting peas into water, which about half- covered them, that they converted the vital air into fixed air, or carbonic acid gas, in the same manner as in animal respiration. See Note XXXIV.
7. The circulation in the lungs or leaves of plants is very similar to that of fish. In fish the blood after having passed through their gills does not return to the heart as from the lungs of air-breathing animals, but the pulmonary vein taking the structure of an artery after having received the blood from the gills, which there gains a more florrid colour, distributes it to the other parts of their bodies. The same structure occurs in the livers of fish, whence we see in those animals two circulations independent of the power of the heart, viz. that beginning at the termination of the veins of the gills, and branching through the muscles; and that which passes through the liver; both which are carried on by the action of those respective arteries and veins. Monro's Physiology of Fish, p. 19.
The course of the fluids in the roots, leaves, and buds of vegetables seems to be performed in a manner similar to both these. First the absorbent vessels of the roots and surfaces unite at the footstalk of the leaf; and then, like the Vena Portarum, an artery commences without the intervention of a heart, and spreads the sap in its numerous ramifications on the upper surface of the leaf; here it changes its colour and properties, and becomes vegetable blood; and is again collected by a pulmonary vein on the under surface of the leaf. This vein, like that which receives the blood from the gills of fish, assumes the office and name of an artery, and branching again disperses the blood upward to the bud from the footstalk of the leaf, and downward to the roots; where it is all expended in the various secretions, the nourishment and growth of the plant, as fast as it is prepared.
II. The organ of respiration already spoken of belongs particularly to the shoots or buds, but there is another pulmonary system, perhaps totally independent of the green foliage, which belongs to the fructification only, I mean the corol or petals. In this there is an artery belonging to each petal, which conveys the vegetable blood to its extremities, exposing it to the light and air under a delicate membrane covering the internal surface of the petal, where it often changes its colour, as is beautifully seen in some party-coloured poppies; though it is probable some of the iridescent colours of flowers may be owing to the different degrees of tenuity of the exterior membrane of the leaf refracting the light like soap-bubbles, the vegetable blood is then returned by correspondent vegetable veins, exactly as in the green foliage; for the purposes of the important secretions of honey, wax, the finer essential oil, and the prolific dust of the anthers.
1. The vascular structure of the corol as above described, and which is visible to the naked eye, and its exposing the vegetable juices to the air and light during the day, evinces that it is a pulmonary organ.
2. As the glands which produce the prolific dust of the anthers, the honey, wax, and frequently some odoriferous essential oil, are generally attached to the corol, and always fall off and perish with it, it is evident that the blood is elaborated or oxygenated in this pulmonary system for the purpose of these important secretions.
3. Many flowers, as the Colchicum, and Hamamelis arise naked in autumn, no green leaves appearing till the ensuing spring; and many others put forth their flowers and complete their impregnation early in the spring before the green foliage appears, as Mezereon, cherries, pears, which shews that these corols are the lungs belonging to the fructification.
4. This organ does not seem to have been necessary for the defence of the stamens and pistils, since the calyx of many flowers, as Tragopogon, performs this office; and in many flowers these petals themselves are so tender as to require being shut up in the calyx during the night, for what other use then can such an apparatus of vessels be designed?
5. In the Helleborus-niger, Christmas-rose, after the seeds are grown to a certain size, the nectaries and stamens drop off, and the beautiful large white petals change their colour to a deep green, and gradually thus become a calyx inclosing and defending the ripening seeds, hence it would seem that the white vessels of the corol served the office of exposing the blood to the action of the air, for the purposes of separating or producing the honey, wax, and prolific dust, and when these were no longer wanted, that these vessels coalesced like the placental vessels of animals after their birth, and thus ceased to perform that office and lost at the same time their white colour. Why should they loose their white colour, unless they at the same time lost some other property besides that of defending the seed-vessel, which they still continue to defend?
6. From these observations I am led to doubt whether green leaves be absolutely necessary to the progress of the fruit-bud after the last year's leaves are fallen off. The green leaves serve as lungs to the shoots and foster the new buds in their bosoms, whether these buds be leaf-buds or fruit-buds; but in the early spring the fruit-buds expand their corols, which are their lungs, and seem no longer to require green leaves; hence the vine bears fruit at one joint without leaves, and puts out a leaf-bud at another joint without fruit. And I suppose the green leaves which rise out of the earth in the spring from the Colchicum are for the purpose of producing the new bulb, and its placenta, and not for the giving maturity to the seed. When currant or goosberry trees lose their leaves by the depredation of insects the fruit continues to be formed, though less sweet and less in size.
7. From these facts it appears that the flower-bud after the corol falls off, (which is its lungs,) and the stamens and nectary along with it, becomes simply an uterus for the purpose of supplying the growing embryon with nourishment, together with a system of absorbent vessels which bring the juices of the earth to the footstalk of the fruit, and which there changes into an artery for the purpose of distributing the sap for the secretion of the saccharine or farinaceous or acescent materials for the use of the embryon. At the same time as all the vessels of the different buds of trees inosculate or communicate with each other, the fruit becomes sweeter and larger when the green leaves continue on the tree, but the mature flowers themselves, (the succeeding fruit not considered) perhaps suffer little injury from the green leaves being taken off, as some florists have observed.
8. That the vessels of different vegetable buds inosculate in various parts of their circulation is rendered probable by the increased growth of one bud, when others in its vicinity are cut away; as it thus seems to receive the nourishment which was before divided amongst many.
NOTE XXXVIII.—VEGETABLE IMPREGNATION.
Love out their hour and leave their lives in air.
CANTO IV. l. 456.
From the accurate experiments and observations of Spallanzani it appears that in the Spartium Junceum, rush-broom, the very minute seeds were discerned in the pod at least twenty days before the flower is in full bloom, that is twenty days before fecundation. At this time also the powder of the anthers was visible, but glued fast to their summits. The seeds however at this time, and for ten days after the blossom had fallen off, appeared to consist of a gelatinous substance. On the eleventh day after the falling of the blossom the seeds became heart- shape, with the basis attached by an appendage to the pod, and a white point at the apex; this white point was on pressure found to be a cavity including a drop of liquor.
On the 25th day the cavity which at first appeared at the apex was much enlarged and still full of liquor, it also contained a very small semi- transparent body, of a yellowish colour, gelatinous, and fixed by its two opposite ends to the sides of the cavity.
In a month the seed was much enlarged and its shape changed from a heart to a kidney, the little body contained in the cavity was increased in bulk and was less transparent, and gelatinous, but there yet appeared no organization.
On the 40th day the cavity now grown larger was quite filled with the body, which was covered with a thin membrane; after this membrane was removed the body appeared of a bright green, and was easily divided by the point of a needle into two portions, which manifestly formed the two lobes, and within these attached to the lower part the exceedingly small plantule was easily perceived.
The foregoing observations evince, 1. That the seeds exist in the ovarium many days before fecundation. 2. That they remain for some time solid, and then a cavity containing a liquid is formed in them. 3. That after fecundation a body begins to appear within the cavity fixed by two points to the sides, which in process of time proves to be two lobes containing a plantule. 4. That the ripe seed consists of two lobes adhering to a plantule, and surrounded by a thin membrane which is itself covered with a husk or cuticle. Spalanzani's Dissertations, Vol. II. p. 253.
The analogy between seeds and eggs has long been observed, and is confirmed by the mode of their production. The egg is known to be formed within the hen long before its impregnation; C.F. Wolf asserts that the yolk of the egg is nourished by the vessels of the mother, and that it has from those its arterial and venous branches, but that after impregnation these vessels gradually become impervious and obliterated, and that new ones are produced from the fetus and dispersed into the yolk. Haller's Physiolog. Tom. VIII. p. 94. The young seed after fecundation, I suppose, is nourished in a similar manner from the gelatinous liquor, which is previously deposited for that purpose; the uterus of the plant producing or secreting it into a reservoir or amnios in which the embryon is lodged, and that the young embryon is furnished with vessels to absorb a part of it, as in the very early embryon in the animal uterus.
The spawn of frogs and of fish is delivered from the female before its impregnation. M. Bonnet says that the male salamander darts his semen into the water, where it forms a little whitish cloud which is afterwards received by the swoln anus of the female, and she is fecundated.—He adds that marine plants approach near to these animals, as the male does not project a fine powder but a liquor which in like manner forms a little cloud in the water.—And further adds, who knows but the powder of the stamina of certain plants may not make some impression on certain germs belonging to the animal kingdom! Letter XLIII. to Spalanzani, Oevres Philos.
Spalanzani found that the seminal fluid of frogs and dogs even when diluted with much water retained its prolific quality. Whether this quality be simply a stimulus exciting the egg into animal action, which may be called a vivifying principle, or whether part of it be actually conjoined with the egg is not yet determined, though the latter seems more probable from the frequent resemblance of the fetus to the male parent. A conjunction however of both the male and female influence seems necessary for the purpose of reproduction throughout all organized nature, as well in hermaphrodite insects, microscopic animals, and polypi, and exists as well in the formation of the buds of vegetables as in the production of their seeds, which is ingeniously conceived and explained by Linneus. After having compared the flower to the larva of a butterfly, confining of petals instead of wings, calyxes instead of wing-sheaths, with the organs of reproduction, and having shewn the use of the farina in fecundating the egg or seed, he proceeds to explain the production of the bud. The calyx of a flower, he says, is an expansion of the outer bark, the petals proceed from the inner bark or rind, the stamens from the alburnum or woody circle, and the style from the pith. In the production and impregnation of the seed a commixture of the secretions of the stamens and style are necessary; and for the production of a bud he thinks the medulla or pith bursts its integuments and mixes with the woody part or alburnum, and these forcing their passage through the rind and bark constitute the bud or viviparous progeny of the vegetable. System of Vegetables translated from Linneus, p. 8.
It has been supposed that the embryon vegetable after fecundation, by its living activity or stimulus exerted on the vessels of the parent plant, may produce the fruit or seed-lobes, as the animal fetus produces its placenta, and as vegetable buds may be supposed to produce their umbilical vessels or roots down the bark of the tree. This in respect to the production of the fruit surrounding the seeds of trees has been assimilated to the gall-nuts on oak-leaves, and to the bedeguar on briars, but there is a powerful objection to this doctrine, viz. that the fruit of figs, all which are female in this country, grow nearly as large without fecundation, and therefore the embryon has in them no self-living principle.
NOTE XXXIX.—VEGETABLE GLANDULATION.
Seeks, where fine pores their dulcet balm distil.
CANTO IV. l. 503.
The glands of vegetables which separate from their blood the mucilage, starch, or sugar for the placentation or support of their seeds, bulbs, and buds; or those which deposit their bitter, acrid, or narcotic juices for their defence from depredations of insects or larger animals; or those which secrete resins or wax for their protection from moisture or frosts, consist of vessels too fine for the injection or absorption of coloured fluids, and have not therefore yet been exhibited to the inspection even of our glasses, and can therefore only be known by their effects, but one of the most curious and important of all vegetable secretions, that of honey, is apparent to our naked eyes, though before the discoveries of Linneus the nectary or honey-gland had not even acquired a name.
The odoriferous essential oils of several flowers seem to have been designed for their defence against the depredations of insects, while their beautiful colours were a necessary consequence of the size of the particles of their blood, or of the tenuity of the exterior membrane of the petal. The use of the prolific dust is now well ascertained, the wax which covers the anthers prevents this dust from receiving moisture, which would make it burst prematurely and thence prevent its application to the stigma, as sometimes happens in moist years and is the cause of deficient fecundation both of our fields and orchards.
The universality of the production of honey in the vegetable world, and the very complicated apparatus which nature has constructed in many flowers, as well as the acrid or deleterious juices she has furnished those flowers with (as in the Aconite) to protect this honey from rain and from the depredations of insects, seem to imply that this fluid is of very great importance in the vegetable economy; and also that it was necessary to expose it to the open air previous to its reabsorption into the vegetable vessels.
In the animal system the lachrymal gland separates its fluid into the open air for the purpose of moistening the eye, of this fluid the part which does not exhale it absorbed by the puncta lachrymalia and carried into the nostrils; but as this is not a nutritive fluid the analogy goes no further than its secretion into the open air and its reabsorption into the system; every other secreted fluid in the animal body is in part absorbed again into the system, even those which are esteemed excrementitious, as the urine and perspirable matter, of which the latter is secreted, like the honey, into the external air. That the honey is a nutritious fluid, perhaps the most so of any vegetable production, appears from its great similarity to sugar, and from its affording sustenance to such numbers of insects, which live upon it solely during summer, and lay it up for their winter provision. These proofs of its nutritive nature evince the necessity of its reabsorption into the vegetable system for some useful purpose.
This purpose however has as yet escaped the researches of philosophical botanists. M. Pontedera believes it designed to lubricate the vegetable uterus, and compares the horn-like nectaries of some flowers to the appendicle of the caecum intestinum of animals. (Antholog. p. 49.) Others have supposed that the honey, when reabsorbed, might serve the purpose of the liquor amnii, or white of the egg, as a nutriment for the young embryon or fecundated seed in its early state of existence. But as the nectary is found equally general in male flowers as in female ones; and as the young embryon or seed grows before the petals and nectary are expanded, and after they fall off; and, thirdly, as the nectary so soon falls off after the fecundation of the pistillum; these seem to be insurmountable objections to both the above-mentioned opinions.
In this state of uncertainty conjectures may be of use so far as they lead to further experiment and investigation. In many tribes of insects, as the silk-worm, and perhaps in all the moths and butterflies, the male and female parents die as soon as the eggs are impregnated and excluded; the eggs remaining to be perfected and hatched at some future time. The same thing happens in regard to the male and female parts of flowers; the anthers and filaments, which constitute the male parts of the flower, and the stigma and style, which constitute the female part of the flower, fall off and die as soon as the seeds are impregnated, and along with these the petals and nectary. Now the moths and butterflies above-mentioned, as soon as they acquire the passion and the apparatus for the reproduction of their species, loose the power of feeding upon leaves as they did before, and become nourished by what?—by honey alone.
Hence we acquire a strong analogy for the use of the nectary or secretion of honey in the vegetable economy, which is, that the male parts of flowers, and the female parts, as soon as they leave their fetus-state, expanding their petals, (which constitute their lungs,) become sensible to the passion, and gain the apparatus for the reproduction of their species, and are fed and nourished with honey like the insects above described; and that hence the nectary begins its office of producing honey, and dies or ceases to produce honey at the same time with the birth and death of the stamens and the pistils; which, whether existing in the same or in different flowers, are separate and distinct animated beings.
Previous to this time the anthers with their filaments, and the stigmas with their styles, are in their fetus-state sustained by their placental vessels, like the unexpanded leaf-bud; with the seeds existing in the vegetable womb yet unimpregnated, and the dust yet unripe in the cells of the anthers. After this period they expand their petals, which have been shewn above to constitute the lungs of the flower; the placental vessels, which before nourished the anthers and the stigmas, coalesce or cease to nourish them; and they now acquire blood more oxygenated by the air, obtain the passion and power of reproduction, are sensible to heat, and cold, and moisture, and to mechanic stimulus, and become in reality insects fed with honey, similar in every respect except their being attached to the tree on which they were produced.
Some experiments I have made this summer by cutting out the nectaries of several flowers of the aconites before the petals were open, or had become much coloured, some of these flowers near the summit of the plants produced no seeds, others lower down produced seeds; but they were not sufficiently guarded from the farina of the flowers in their vicinity; nor have I had opportunity to try if these seeds would vegetate.
I am acquainted with a philosopher, who contemplating this subject thinks it not impossible, that the first insects were the anthers or stigmas of flowers; which had by some means loosed themselves from their parent plant, like the male flowers of Vallisneria; and that many other insects have gradually in long process of time been formed from these; some acquiring wings, others fins, and others claws, from their ceaseless efforts to procure their food, or to secure themselves from injury. He contends, that none of these changes are more incomprehensible than the transformation of tadpoles into frogs, and caterpillars into butterflies.
There are parts of animal bodies, which do not require oxygenated blood for the purpose of their secretions, as the liver; which for the production of bile takes its blood from the mesenteric veins, after it must have lost the whole or a great part of its oxygenation, which it had acquired in its passage through the lungs. In like manner the pericarpium, or womb of the flower, continues to secrete its proper juices for the present nourishment of the newly animated embryon-seed; and the saccharine, acescent, or starchy matter of the fruit or seed- lobes for its future growth; in the same manner as these things went on before fecundation; that is, without any circulation of juices in the petals, or production of honey in the nectary; these having perished and fallen off with the male and female apparatus for impregnation.
It is probable that the depredations of insects on this nutritious fluid must be injurious to the products of vegetation, and would be much more so, but that the plants have either acquired means to defend their honey in part, or have learned to make more than is absolutely necessary for their own economy. In the same manner the honey-dew on trees is very injurious to them; in which disease the nutritive fluid, the vegetable- sap-juice, seems to be exsuded by a retrograde motion of the cutaneous lymphatics, as in the sweating sickness of the last century. To prevent the depredation of insects on honey a wealthy man in Italy is said to have poisoned his neighbour's bees perhaps by mixing arsnic with honey, against which there is a most flowery declamation in Quintilian. No. XIII. As the use of the wax is to preserve the dust of the anthers from moisture, which would prematurely burst them, the bees which collect this for the construction of the combs or cells, must on this account also injure the vegetation of a country where they too much abound.
It is not easy to conjecture why it was necessary that this secretion of honey should be exposed to the open air in the nectary or honey-cup, for which purpose so great an apparatus for its defence from insects and from showers became necessary. This difficulty increases when we recollect that the sugar in the joints of grass, in the sugar-cane, and in the roots of beets, and in ripe fruits is produced without the exposure to the air. On supposition of its serving for nutriment to the anthers and stigmas it may thus acquire greater oxygenation for the purpose of producing greater powers of sensibility, according to a doctrine lately advanced by a French philosopher, who has endeavoured to shew that the oxygene, or base of vital air, is the constituent principle of our power of sensibility.
From this provision of honey for the male and female parts of flowers, and from the provision of sugar, starch, oil, and mucilage, in the fruits, seed-cotyledons, roots, and buds of plants laid up for the nutriment of the expanding fetus, not only a very numerous class of insects, but a great part of the larger animals procure their food; and thus enjoy life and pleasure without producing pain to others, for these seeds or eggs with the nutriment laid up in them are not yet endued with sensitive life.
The secretions from various vegetable glands hardened in the air produce gums, resins, and various kinds of saccharine, saponaceous, and wax-like substances, as the gum of cherry or plumb-trees, gum tragacanth from the astragalus tragacantha, camphor from the laurus camphora, elemi from amyris elemifera, aneme from hymenoea courbaril, turpentine from pistacia terebinthus, balsam of Mecca from the buds of amyris opobalsamum, branches of which are placed in the temples of the East on account of their fragrance, the wood is called xylobalsamum, and the fruit carpobalsamum; aloe from a plant of the same name; myrrh from a plant not yet described; the remarkably elastic resin is brought into Europe principally in the form of flasks, which look like black leather, and are wonderfully elastic, and not penetrable by water, rectified ether dissolves it; its flexibility is encreased by warmth and destroyed by cold; the tree which yields this juice is the jatropha elastica, it grows in Guaiana and the neighbouring tracts of America; its juice is said to resemble wax in becoming soft by heat, but that it acquires no elasticity till that property is communicated to it by a secret art, after which it is poured into moulds and well dried and can no longer be rendered fluid by heat. Mr. de la Borde physician at Cayenne has given this account. Manna is obtained at Naples from the fraxinus ornus, or manna-ash, it partly issues spontaneously, which is preferred, and partly exsudes from wounds made purposely in the month of August, many other plants yield manna more sparingly; sugar is properly made from the saccharum officinale, or sugar-cane, but is found in the roots of beet and many other plants; American wax is obtained from the myrica cerifera, candle-berry myrtle, the berries are boiled in water and a green wax separates, with luke-warm water the wax is yellow: the seed of croton sebiferum are lodged in tallow; there are many other vegetable exsudations used in the various arts of dyeing, varnishing, tanning, lacquering, and which supply the shop of the druggist with medicines and with poisons.
There is another analogy, which would seem to associate plants with animals, and which perhaps belongs to this Note on Glandulation, I mean the similarity of their digestive powers. In the roots of growing vegetables, as in the process of making malt, the farinaceous part of the seed is converted into sugar by the vegetable power of digestion in the same manner as the farinaceous matter of seeds are converted into sweet chyle by the animal digestion. The sap-juice which rises in the vernal months from the roots of trees through the alburnum or sap-wood, owes its sweetness I suppose to a similar digestive power of the absorbent system of the young buds. This exists in many vegetables in great abundance as in vines, sycamore, birch, and most abundantly in the palm-tree, (Isert's Voyage to Guinea,) and seems to be a similar fluid in all plants, as chyle is similar in all animals.
Hence as the digested food of vegetables consists principally of sugar, and from that is produced again their mucilage, starch, and oil, and since animals are sustained by these vegetable productions, it would seem that the sugar-making process carried on in vegetable vessels was the great source of life to all organized beings. And that if our improved chemistry should ever discover the art of making sugar from fossile or aerial matter without the assistance of vegetation, food for animals would then become as plentiful as water, and mankind might live upon the earth as thick as blades of grass, with no restraint to their numbers but the want of local room.
It would seem that roots fixed in the earth, and leaves innumerable waving in the air were necessary for the decomposition of water, and the conversion of it into saccharine matter, which would have been not only cumberous but totally incompatible with the locomotion of animal bodies. For how could a man or quadruped have carried on his head or back a forest of leaves, or have had long branching lacteal or absorbent vessels terminating in the earth? Animals therefore subsist on vegetables; that is, they take the matter so far prepared, and have organs to prepare it further for the purposes of higher animation, and greater sensibility. In the same manner the apparatus of green leaves and long roots were found inconvenient for the more animated and sensitive parts of vegetable-flowers, I mean the anthers and stigmas, which are therefore separate beings, endued with the passion and power of reproduction, with lungs of their own, and fed with honey, a food ready prepared by the long roots and green leaves of the plant, and presented to their absorbent mouths.
From this outline a philosopher may catch a glimpse of the general economy of nature; and like the mariner cast upon an unknown shore, who rejoiced when he saw the print of a human foot upon the sand, he may cry out with rapture, "A GOD DWELLS HERE."