which life gives to all the particles of matter of which an organised body is composed.

Having said thus much of the rise of sap-and, we trust, without presumption-we should proceed to another part of the physiology of plants, which is quite as interesting: the limits of the connection between the tree and the layers and cuttings or grafts taken from it.

A tree and an oyster carry their progeny on the back, both united to the parent stock by means of a glutinous ligament, and adhering with equal tenacity. The smallest excrescence on the oyster is capable of becoming an animated being as soon as it is detached from the back of its parent; and one of the terminal shoots of the tree can become a tree, likewise, when cut off and planted. The same aliment which sustained the tree, is forced up in the slip to nourish that likewise, but every organ and part of a plant requires different aliment. As there is no central reservoir, no stomach in which all the crude sap could be elaborated, and as there are so many individual parts to be sustained-considering each articulation as a separately organised plant-it follows that each section or joint must elaborate the proper juices for itself; and when the matter is suitably prepared by the different processes which take place, in the spiral, clostral, and other tubes, the next course is to deposit the portion necessary to each leaf and bud, at the base of this leaf and bud. The twig on which this leaf and bud exist--if it be one of a year's growth--can easily be separated, for the ligature which connects it to the lower joint is of a frail texture. This ligature is composed of a continuation of tubular and porous vessels, the mere rupture of which does not injure the general circulation of fluids, for they are themselves jointed, as it were, at short intervals, if we may except the spiral vessels, the true office of which is not yet known. As to the porous part of the limb, where the twig is cut off, it is well known that fluids do not rise when there is no longer a connecting medium.

The slip, therefore, that is broken from the tree or plant, becomes an independent body, with the habits and character of the parent stock, and is entitled to the same privileges as well as subject to the same evils. But the sustenance designed for the roots is not of the same nature as that which is prepared for the fruit-buds and leaves, neither is the nutriment which is elaborated in the stomach of an animal circulated indiscriminately. Those vessels that build up bones absorb such portions from the blood as are requisite, whilst those that supply the flesh abstract that which is wanted for the purpose. Perhaps the interstitial medium receives that in its pores which is to enlarge and repair the vessels themselves. The nutriment required to sustain a plant, when it grows to a large tree, VOL. XXI.-NO. 41. 18

is immense; and if there were returning vessels, or a regular flow of sap or cambium from top to bottom, then surely the sucker buds at the upper part of the roots would receive the saine nourishment as the buds of the graft. That this is not the case, a moment's reflection will teach us.

It may be suggested that the suckers from trees not inoculated all produce fruit like the main stock; this is true only with particular trees-but it is one of the strongest proofs of the limited action of the tubular vessels; for we have observed, throughout, that the tubes furnish the proper juices only to those buds in their immediate section. If no buds grow under ground, then the elaborating vessels only absorb such portions of the crude sap as is requisite to sustain the tubular and porous organs of the section to which the absorbent vessels are attached.

The decay of trees has been the subject of much curious speculation, and it has settled down into an opinion that a tree, which has grown from a scion or graft taken from another tree, is merely the extension of the parent tree. It is interred that, in consequence of the identity, the young tree must partake of the destiny, as well as the character, of the original. How physiologists could have fallen into this error, is inconceivable; for, according to this doctrine, if the parent tree died of age, then a tree grafted from it the year before must die at the same time.

Each slip or terminal shoot is as much a distinct and independent individual, when the roots are formed, as one of the Siamese twins would be if the membrane which united them could be severed. No one supposes for an instant that, if these young men were separated, one must necessarily die when the other did. We do not allude to death in consequence of cutting asunder the strong ligature which unites them, but to death from old age: one might live to the age of a hundred, and the other die of exhaustion at seventy-five. If the duration of the life of an apple tree was a century, a slip taken from this tree in its ninetieth year has the same chance of living out the term as the parent tree had. When the pores and tubes are divided at the junction of the articulation, which is effected by snapping asunder the slip and the section attached to it, there is an end of all connection between the parent and the slip. The organs of the new plant, being of the same form and capacity as those of the tree whence the graft was taken, go on to enlarge the different parts-build up and repair-until the term allotted to its race has expired. As long as an animal or tree is permitted to grow as long as extension is possible-so long is there an enlargement, both in height and diameter, of each pore and organ. When the gravitating principle will not admit of fur

ther increase of size, the whole energies of the plant are in requisition to repair the waste and injuries to which it is subject, and to keep off the approach of death as long as possible. This is the instinctive property of organized matter-it belongs to the constitution of a plant as well as to that of an animal, to prevent decay when it can no longer increase in size,

The vital principle, therefore, is not the exclusive property of the whole tree, as one body, like that possessed by an animal, but belongs to every articulated section. The abstraction of life from one part does not affect the health of the rest. Vegetable life is a principle that can exist, or rather animate, a thousand parts at once, and yet connect itself with the whole. When the terminal shoot is cut off, vital energy still remains in it; and if the slip be so planted as that the embryo organs can protrude, and thus obtain nourishment for the upper part, life remains and animates the plant. If the slip is not planted, then the vital principle slowly leaves it and the slip dies. Even life can be stimulated to remain some time longer in a plant divided from the roots, by placing the stem-when the leaves, flowers, and bark, are in a state of collapse-in boiling water, showing of how much power gaseous action is in the economy of the vital principle. With a knowledge of this one important fact, why may not the trial be made of the introduction of certain gaseous fluids through the vascular tubes of an animal exhausted by hunger or disease? Oxygen gas, when inhaled, and thus forced by the lungs through the porous interstices, shows how speedily the system may be stimulated. It appears, therefore, that if the alimentary principles which nourish the body were forced either through the pores or tubular vessels by means of gases, the system might be sustained until the stomach and other digestive organs should recover their tone. We hope the trial may be made.

Trees, whether large or small, are not in the least indebted to high winds, or even to the ordinary winds of summer, for this enlargement or health. Many at the present day imagine that winds promote a healthy circulation, and that nature has endowed them with this invigorating power. But how could any one accustomed to the care and observation of plants fall into such an error? To be sure, we see the body and limbs of a tree bend to the blast, and toss to and fro when agitated by fitful gusts of wind, and we perceive that they apparently recover from these shocks, and give signs of health and fruitfulness; it is therefore concluded that this excitement is as necessary to the prolongation of their vigour and life as exercise is to an animal. The truth forced upon us by long experience is, that so far from being necessary, the action of winds is positively injurious.

It might as well be urged that gales of wind are of service to

a ship at sea, because she weathers the storm and comes sailing quietly into the harbour, looking as beautiful and as sound as when she left the port. But experienced seamen know that she has received many a strain, that her timbers have been wrung, her masts weakened, her sails rent, and that the foundation of decay sprung from those very gales.

A breeze just strong enough to give a gentle motion to the leaves, is, in reality, all the motion required from external causes. The experiment can be made at any time, by planting two trees of the same kind, of equal size and health, in different positions. If one be trained closely to the wall of a house, and confined by ligatures at every joint, continuing this restraint from year to year, and if the other be planted in an open field as a standard, the tree which is unable to move a single joint will grow rapidly under all the disadvantages of confinement. When all the twigs and limbs that were cut away from the tree which was trained, are taken into consideration, as well as the height and breadth of it as it stands, it will be perceived that it has grown to more than twice the size of the standard tree.

Winds undoubtedly retard the growth of a tree, and to one that is tall, the injury is very great; the bark and delicate vessels are not all that suffer, the petioles of the leaves also are tortured and twisted, until life is almost driven out. Every one must have witnessed this deplorable state of exhaustion which a tree is in after it has been thus violently blown about. The leaves droop, the tender limbs hang listlessly for several days, and many of a delicate nature wither and die.

Although trees are deprived of the power of locomotion, yet they are endowed with a capacity to resist or counteract many of the evils incident to their confined fixed position. One remarkable instance of this is the equilibrium to which they have the power of returning when accident or continued pressures have destroyed it. No sooner is a plant injured, than ramifications of equal extent to the wounds or amputations shoot out immediately and supply the waste. Another mode which a tree has of preserving a balance, when suffering under the harsh influence of regularly recurring northwest winds, is to strengthen the under or curved side of the limb or trunk that is bent out of its upright position. This is done by detaining a greater quantity of the proper juices, or assimilatory matter, in this curved spot.

If a transverse cut be made in the curved branch of a tree, it will be seen that the curved or concave part is thicker from the centre to the circumference than that of the upper or convex part. The concentric layers are equal in number, but the porous interstices are larger, and more of the elementary particles are deposited there. This same phenomenon occurs when trees are

placed in a cold northern exposure, even when they are not bent out of the perpendicular by strong winds. When cut cross, the layers on the south side will be found thicker and fuller than on the north side. This proceeds from some obstruction to the lateral pressure or direction of the secretions by the tubular and other vessels, for if external cold prevents the exit from within of rejected secretions, if the bark has not sufficient energy to slough off the fungus which is constantly deposited on unresisting substances, then the circulation on the north side must be weaker than that on the south.

It may not be irrelative to observe in this place, that it is to the presence of fungus or moss on the north side of trees, that travellers and Indians direct their course through unfrequented forests. In forests of pine, to which no moss adheres, travellers are guided by the enlargement of limbs and the fuller luxuriance which the south side exhibits. The particular qualities of the sap of resinous trees is not the sole cause that prevents the adhesion of atmospheric depositions, for in consequence of the enlargement of the porous and membranous organs, gaseous fluids are more abundantly present. Consequently the rejected secretions are forced off to the surface, and this lubrication of the bark or cuticle prevents the dust and other atmospheric particles from clogging up. the pores. We perceive that the quickest growing limbs have the smoothest bark-neither canker, rust, nor fungi rest upon it.

But of all the mysteries connected with the rise of sap, and, in fact, connected with the circulation of the blood, there is none so extraordinary and inexplicable as the vital principle itself. Many physiologists have adopted the notion that this principle is transmitted to the different parts of a plant and animal through the medium of the sap and blood. We do not believe in the exclusive vivification of the sap and blood; the principle called life does not adhere to or traverse through any particular section or organ. It is an impulse which is diffused throughout the whole organic system of both plants and animals. It is a primary essence existing independently throughout space, traversing unrestrained, and attaching itself to all organized

As long as the organized body is sustained by the two great powers-centripetal and centrifugal pressures-as long as the one power can prevent the undue pressure of the other-or, in other words, as long as an equilibrium is kept up, the action of the vital principle is unimpaired. But if the centrifugal power, or levity, forces up alimentary particles in too great a quantity, so as to overcome that portion of centripetal, or gravitating power which is opposed to it-which two powers operate on organic as well as inorganic matter-then the action of