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satisfactorily proved, that the tubular vessels of both plants and animals are mere absorbents and propellants, whilst the interstices of both flesh and bark convey the chyle or crude sap to the external surface of these tubes, and likewise retain that portion of it which is rejected by the main tubes.

There is this difference between the tubular system of animals and plants. In the former, having but one spongelet, called the lungs, both for the admission and expulsion of the gases, necessary to the tubular action, the whole circulation is effected by two impulses the filling and emptying of the lungs. The reason of this is obvious; in this case there is but one individual system to be nourished by the process. In plants, each bud is an individual; and each bud, therefore, receives its own sustenance from its own vascular action: the circulation of elaborated sap is effected by that section of tubes which lies in the vicinity of the bud to be nourished, whilst the crude sap, admitted by the many spongelets, at the roots, rises through a porous medium, unconnected, but by a glutinous ligament, and dispenses the elementary particles to the whole range of tubes.

But, although that portion of the crude sap which the main tubes reject, is retained by the porous medium which elevated it, yet it is retained only till it can be absorbed by other vessels which convey these rejected, unnecessary particles to the cuticle of the leaves and bark. The whole system-the support of vitality—is strictly analogous to that of animals; the same beautiful system of absorption and rejection by differently constructed organs.

Gases are so evanescent and intractable, that they could not be directed to any fixed point, were it not that they are capable of being transmitted through tubes, porous substances, and the interstices of a fluid. Water is a medium for the transmission of gases, used by nature and art. The gases, charged with nutritive and other matter, move with ease through all fluids; at the same time, water, when thus impelled by gases, is not available to us unless its motion can be controlled. It must itself have a conductor through which it can traverse. The particles of a fluid cannot be sustained or held together, unless in individual drops; nor can a fluid be elevated in an upright column, without it has a tremendous gaseous power to propel it. If gases, by a fixed law, are compelled to expand and reach the highest point in as short a time as possible, all matter must be subordinate to their action. In consequence of this, fluids are obliged to present as wide a surface as their globules will allow, that gases may elevate themselves, and the particles with which they are charged, with greater ease.

Unless, therefore, water is conveyed through tubes or a porous medium, we cannot avail ourselves of its power; con

sequently, the united energies of gases and fluids are best obtained when their motions are directed through tubes and porous bodies. It is in this way that all the great work of nature is effected; but how many centuries it was before man could comprehend it.

It is capillary attraction,-as it is miscalled,-which elevates a fluid through sponges, sugar, soils, pith, and all porous substances, and it is in proportion as the particles of water are connected that they are capable of elevating themselves. There is a peculiar principle in water which we do not recollect ever to have seen noticed, as applied to the rise of fluids in capillary tubes. This principle admits of an easier flow of water when its particles are connected. A greater quantity will flow from an upper to a lower reservoir, in a given time, when the tube through which it runs extends, uninterruptedly, from the bottom of the upper reservoir, to the water in the lower one, than if the tube did not reach the water. Water, likewise, will not flow from the narrow mouth of a large phial when it is turned upside down, unless in single drops at certain intervals of time, but if a piece of wet rag, thread, or other wet porous substance, comes in contact with the drop which hangs suspended from the mouth of the phial, the water will run out immediately in a connected stream. Even a piece of wet sponge or rag, of size sufficient to fill the neck of the phial, will enable the water from the inverted phial to flow out readily.

Whilst the leaves, buds, and roots-or even the leaves alone for a time-are attached to a plant, fluids will rise to the extremities. But when these conducting media are separated from the tree, capillary action is discontinued. As long as there is vitality in the trunk of a tree, the sap will ascend, but if there be no outlet for the sap thus raised, there is an end of all vascular action.

If we break off the stem of a dead plant, or a capillary tube, below the point whence water rises by what is called capillary attraction, the water does not overflow,-and why? Because there is no longer a conducting medium. But, as in the case of the inverted phial, if a wet thread be laid on the broken tube, so that it touches the water in the bore of the tube, the water will elevate itself by means of its own particles in the wet thread. If a single filament of flax, or any fine thread, is introduced through one of these tubes, the water from the basin, which was only elevated one inch above the level, will rise to the very top of the tube, even if it is twelve inches in height.

This phenomenon cannot be explained on the principle of capillary attraction as taught in the schools; for let the bore of the tube be of what size it may, whether only capable of admitting a fine hair, or of a foot diameter, the effect is the same,

water will rise if it have a porous or other conducting medium. It is well known that if a napkin be suspended over a basin of water, so that the lower part of it is kept wet, the water will soon rise to the top of the napkin, but it will rise in the interstices of the napkin much sooner if it is dipped in water and then wrung out, before it is suspended over the basin. A napkin thrown over the side of a basin, one end touching the water, will act like a syphon, and in a short time will empty the basin. At some future time we may enter more at large on the subject of what is called capillary attraction, and endeavour to account for the limited action of a fluid in capillary tubes, and the unlimited ascent of a fluid in the interstices of porous bodies. Our present object is to speak of the manner in which we apprehend sap may rise to the extremities of a plant.

Neither the roots nor the leaves of a plant can exist independently of the branches and trunk; but the twigs or terminal shoots, can live when separated from the tree. The conserve, or concentrated cambium, which is deposited at the articulations, serves the cutting as a pabulum for its nourishment, until leaves and roots are formed. Nature is provident and careful of all organised matter, and leaves but little to chance; where reason does not direct, she substitutes instinct, and where instinct is limited, she takes the matter more immediately in her own hands. In a cutting, the means of life are amply afforded until the roots are formed; and when a swarm of bees leave the parent hive to form another colony, they, by some instinctive regulation, carry with them honey and farina sufficient to sustain themselves until their cells are made.

The rapidity with which the sap circulates, in some plants, would very soon destroy vegetable life, were it not that a kind Providence, in all cases, has allowed them a respite from this powerful excitement. This is accomplished by withdrawing the exciting cause for a stated time. In the American climate, particularly, the life of a plant would be short, but for the length of its repose in winter; and in all climates either night or winter comes to its relief.

This rest, or sleep, so perceptible in many plants, is supposed by some philosophers to be occasioned by the loss they sustain of part of the vivifying gases. They imagine that light disperses this gas. That cannot, however, be called a loss, which renews and refreshes instead of exhausts; yet it is no doubt owing to the action of gases that leaves and flowers expand or open in the morning. The relief that a plant obtains by this repose, arises from the slowness of circulation; when the exciting cause, solar light and heat,-is withdrawn, the fluids rise slowly and are retained longer in the interstices. If the leaves perspired at night, as copiously as they do by day, the

circulation would be just as rapid as in the day;-far more water flows over an inclined plane at night, when evaporation ceases, than when the surface is exposed to the heated rays of the sun. The fluidity thus restored at night, enables the plant to meet a renewed excitement during the succeeding day; animals require repose likewise, for in addition to the same excitement which brings on indirect debility in the plant, such as is caused by atmospheric pressure and internal gaseous repulsion, they are enervated by the fatigue of labour and of recreation, such as their wants and their pleasures require.

In those climates where leaves drop off early in November, a slight circulation is still perceptible; the surface of the bark, as may be known by the presence of the green tint, is sufficiently stimulated by light and by the vital principle, so that if a tree does not actually grow, the organs do not collapse. A great quantity of crude sap remains in the interstices; were it not for this circumstance, severe frosts could not burst the trees asunder; this very fact proves that a slow circulation is going on during the winter, for if gases did not find an outlet in winter, capillary action would cease, and fluids would be compelled to gravitate: none would remain in the tree.

It is to the appearance of these gaseous movements, that a new theory has been formed in France, and a regular pulsation attributed to the rise of sap. But there is nothing regular in the movements of those gaseous particles which depend on the impulse they receive on entering the spongelets, for according to the quantity of fermentation going on near the extremities, will the force of the gaseous particles be.

Gases, charged with the fluid and minute particles of elementary matter for the use of the plant; or, in more appropriate terms, gases that are forcing up this matter,-for the whole is a compulsatory and not an attractive effort,-do not move in a continued stream, but interruptedly and in distinct separate globules of irregular size. Let any force whatever be applied to extricate gas from a solid or fluid mass-withdraw it by suction, or force it out by pressure, quickly or slowly, the globules will be of different diameters, scarcely two being of the same

size.

In objection to this, it may be urged that the matter thus. extricated cannot be deemed gas-that it is nothing more than a thin distension of the globules of water which we see, and that the gas, or rather the particles of gas, are never visible,that the principle itself can never be known to us but by the motion it produces amongst disjointed or solid masses of matter. All this is true, but it should be recollected that the effect of a first principle is all by which it can be judged. We cannot see the principle of decay nor the principle of life, yet we speak of

life and death merely from being familiar with the effects of these two great first principles; so in like manner we speak of gases, from a conviction that the power exists within the bubble of water. If through the interstices of a fermenting mass the extricated air is traversing, and it encounters no obstacle, the fluid particles which surround it are distended, and the diameter of the globule, thus formed, is in proportion to the quantity of air that forces itself in this globule, and the energy of the gas is in proportion to the quantity of elementary matter with which the globule of water is charged.

Let any one examine the fluids of his own mouth; he will perceive that the pores of the salival glands are filled with air bubbles of different diameters, and he will find that all the secretions are mere congeries of fluid bubbles of a larger or smaller size, the veins and arteries being likewise filled with these gaseous secretions.

As it respects the rise of fluids in vegetable pores, when it is freely acknowledged that one of the laws of matter compels gases to extricate themselves from restraint, it follows, that as soon as the pressure of the first air bubble is removed the next will rise to fill the vacuum. Gases, whether free from elementary matter, or charged with it, effect the purposes of organized life by moving through tubes and pores. They overcome the gravitating propensity of other bodies and force them in the same direction with themselves, and when it is considered that fluids are subject to their power, the ascent of water in capillary ducts and pores can be accounted for on the soundest principles of philosophy, water is compelled to follow the pressure of gas, when the latter is in quantity sufficient to overcome the downward propensity common to all fluids, and it is in this universal solvent-water-that all matter is elaborated, whether it is to build up or to destroy, whether it be to aid the principle of life or of death.

Every one of the fixed principles, or laws of nature, has a power over matter in its different forms, accommodating its force to the size and weight of the body presented to it. Gravity acts on solids and fluids according to their compactness and distance from the surface of the earth. Levity impels matter from the surface to the limits of the atmosphere, according to the lightness and the number of porous interstices a body contains. If there were a column of sand extending from the centre of the earth to the surface, and there were water enough at the base to reach the top of this column, the water would be impelled to the very top. Where, therefore, is the mystery of the rise of sap in the capillary pores of a plant, so suited to the admission of gaseous fluids? Added to this is the impulse

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